Downhole Circulation Apparatus

Abstract

A downhole circulation apparatus comprises at least one tubular body portion defining a first through-flow passage through which drilling fluid can pass along the drill string. A first sleeve is slidably mounted in the tubular body portion and is biased into a position in which the first port means is closed by a biasing means such as a spring. Second port means is formed through the tubular body portion at a location below the first port means in the drill string. The second port means may comprise a plurality of second nozzles, wherein each of the second nozzles has a diameter greater than the diameter of each of the first nozzles of the first port means. Larger nozzles enable large particle size drilling fluid to be bypassed. A second sleeve is slidably mounted inside the tubular body portion.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date of British Patent Application GB 0920109.6 filed Nov. 18, 2009, the disclosure of which is hereby incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a downhole circulation apparatus arranged to be disposed in a drill string, and relates particularly, but not exclusively, to a downhole circulation apparatus which enables a drill string operator to both split the flow of drilling fluid to increase flow rates and also enable the operator to bypass large particle size drilling fluid to plug a formation and prevent drilling fluid loss the formation.

BACKGROUND

In order to meet demand for energy the drilling of oil and gas wells is becoming more and more complex in order to open up new reserves. Wells can be drilled from land directionally and wells are also being drilled in deeper and deeper formations.

A significant difficulty in extreme and complicated drilling operations is the cleaning of the drilled hole. Drilled strata can accumulate in the drilled well bore which can lead to a drill string becoming stuck. Debris in the well bore can cause additional torque on the drill string which can lead to drill string failure.

There are already concepts for bore hole cleaning in the prior art.

WO 01/06086 discloses a fluid flow actuated downhole tool which is configurable in at least a first tool configuration and a second tool configuration. The tool comprises a tubular housing and an activating sleeve, the housing being adapted to catch the sleeve when the sleeve is dropped from surface and the engagement of the sleeve with the housing permitting actuation of the tool between the first and second tool configurations. A flow restriction is provided for permitting fluid flow actuation of the tool when the activating sleeve has been caught in the body.

US 2004/0035586 discloses a method and an apparatus for obstructing the passage of fluid within a fluid flow conduit and subsequently reconfiguring the tool to allow substantially full-bore passage therethrough. Pressure developed upstream of the obstruction can be utilized to operate pressure actuated tools such as liner hangers. Equipment used in subsequent well bore operations such as drill pipe darts can pass undamaged through the opened port. In an embodiment, the flow through a tubular is obstructed by placing a ball on an expandable ball seat, developing a pressure differential across the ball seat, equalizing the pressure after the hydraulically actuated tool completes its function, and mechanically manipulating the drill string to open the expandable ball seat and allow the ball to pass through.

US 2009/0084555 discloses an activating mechanism for controlling the operation of a downhole tool in a drill string and which is intended to be housed in a portion of the drill string upstream of the downhole tool, in which the activating mechanism has a first mode in which it allows through-flow of drilling fluid to the downhole tool and a second mode in which through-flow of fluid is blocked. The activating mechanism has a number of through-flow ports permitting through-flow of drilling fluid in said first mode of the mechanism and which are capable of being blocked by launching a number of flow blocking activator balls down the drill string and which each are of such size and shape that they can block access to said through-flow ports in order to activate the mechanism to the second mode and thereby adjust the downhole tool from one mode of operation to another.

WO 04/022907 discloses a by-pass tool for incorporation in a drillstring, and which is adjustable between an inactive mode in which it allows fluid flow lengthwise of the drillstring during normal drilling operation, and an active by-pass mode when drilling is to be interrupted. The tool comprises an outer casing; a sleeve displaceable axially within the casing, a valve seat associated with the sleeve and arrange to receive an activating ball, when the latter is launched from the surface and down the drillstring, said valve seat being operative to displace the sleeve axially and thereby initiate adjustment of the tool from the inactive mode to the active by-pass mode, and by-pass port means in the casing and arranged to be closed by the sleeve when the tool is in its inactive mode and to be opened to communicate with the interior of the drillstring when the tool is in its active mode, said by-pass port means being arranged above the valve seat so as to allow a locking ball (when launched from the surface after the valve seat has received the activating ball) to partially block the port means and thereby initiate flushing-out of any drillstring fluid debris above the valve seat via the port means.

However, an increased performance of downhole tools would still be desirable.

SUMMARY

It is therefore desirable to increase drilling fluid flow rates circulating in the borehole to help clean the borehole. However, some drill string element such as directional drilling tools, standard drilling motors, rotary steerable tools, measurement while drilling tools and log while drilling tools are highly sensitive to increased flow rates and can even be damaged by high fluid flow rates.

Consequently, newer sophisticated drill strings have restrictions on the amount of volume that can be pumped through the drill string. Pumping fluid at high rates to clean a well bore and reduce effective circulating densities (ECDs) can damage sophisticated and expensive drill strings beyond repair. On the other hand, pumping at lower rates through such tools can cause the drill strings to become stuck.

A second problem associated with drilling extreme wells is lost circulation of drilling fluid. Lost circulation of drilling fluid can occur when drilling under pressured formations. These formations are common in areas that have previously been drilled many years ago. Often, when drilling in such formations drilling fluid pumped down the drill string might migrate into low pressure areas of formation. One way of counteracting this effect is to pump large particle size drilling fluid, know as lost circulation material (LCM) into the drill string. LCM has particles of large size which can plug the formation and prevent loss of drilling fluid.

It is an object of the invention to provide a downhole tool having an increased performance.

In order to achieve the object defined above, the subject-matter according to the independent claims is provided.

According to an exemplary embodiment, a downhole circulation apparatus arranged to be mounted in a drill string is provided, the apparatus comprising:

at least one tubular body portion for mounting in a drill string, at least one said tubular body portion defining a first through-flow passage for receiving a flow of drilling fluid through the drill string;

first port means formed through at least one said tubular body portion;

a first sleeve slidably mounted inside at least one said tubular body portion, the first sleeve moveable between a closed position in which said first port means is closed by the first sleeve and an open position in which said first port means is open to allow drilling fluid to circulate out of the apparatus;

first biasing means biasing the first sleeve into the closed position;

second port means formed through at least one said tubular body portion at a location below the first port means when the apparatus is in use;

a second sleeve slidably mounted inside at least one said tubular body portion, the second sleeve moveable between a closed position in which said second port means is closed by the second sleeve and an open position in which said second port means is open to allow drilling fluid to circulate out of the apparatus; and

second biasing means biasing the second sleeve into the closed position.

According to another exemplary embodiment, a downhole circulation system is provided which comprises:

a downhole circulation apparatus having the above-mentioned features;

a first restriction device; and

a second restriction device adapted to cooperate with said first restriction device.

According to still another exemplary embodiment, a method of operating a downhole circulation apparatus having the above-mentioned features is provided, the method comprising:

a) causing an increase in fluid pressure in the apparatus to move the first sleeve from the closed to the open position;

b) causing the first biasing means to move the first sleeve back to the closed position; and

c) causing a fluid pressure increase in the apparatus to move the second sleeve from the closed to the open position.

According to an exemplary embodiment of the invention, two or more serially coupled downhole tools are provided each of which being activatable separately from the other one, and each of which being selectively bringable in a bypass mode in which a drilling fluid can be pumped from an interior of the tubular body portion to an exterior thereof. By serially coupling multiple of such downhole tools along a drill string, it is possible to selectively introduce drilling fluid at various defined positions along the bore hole. Not only the position at which the drilling fluid is introduced in the bore hole can be selected by activating a respective one of the normally closed bypass valves, but it is also possible to adjust the kind of drilling fluid (a bore hole cleaning liquid or loss of circulation material, for instance) in accordance with specific requirements at different depths of the drill string.

Next, further exemplary embodiments of the downhole circulation apparatus will be explained. However, these embodiments also apply to the method.

In an embodiment, the first sleeve and/or the second sleeve comprises a flow responsive portion responsive to a flow (or fluid actuation pressure) of drilling fluid through the first through-flow passage to be thereby movable between the closed position and the open position depending on the flow of drilling fluid (i.e. the amount of pressure or flow rate adjustable by an operator via a fluid pump can be used to switch the respective sleeve open or closed). The term “flow responsive portion” may particularly denote a specific component of the sleeve which is configured so that a fluid flow exceeding a certain threshold value will actuate the flow responsive portion to thereby move the respective sleeve from the closed position to the open position triggered by the fluid flow. Hence, such an embodiment will not necessarily require balls or other activation structures to be engaged by a seat of the sleeve or the like, in contrast to this the fluid pressure of the pumped drilling fluid will be used for activating the respective downhole tool. For instance, such a flow responsive portion may be a narrowing section of the respective sleeve designed to be actuated by a certain fluid flow. However, the flow responsive portion may alternatively be a portion or part of the sleeve which is not directly, but only indirectly influenced by the actual value of the flow. In such an embodiment, application of fluid actuation pressure to the interior of the tubular component may act directly on any appropriate internal member such as a mandrel or the like. Hence, it is also possible that a mandrel or the like is arranged in the drill string which is movable along the tool under the influence of fluid pressure. The internal member may be coupled to the respective sleeve to axially (optionally also rotatably) displace the respective sleeve when the internal member is actuated by the fluid. By providing a flow responsive portion, opening or closing the respective port means may be triggered by a corresponding adjustment of the pressure conditions or the flow rate conditions (flowing fluid volume or mass per time interval). Hence, opening and closing of ports may be performed using pressure action, particularly increasing and equalizing pump pressure or pump differential.

Still referring to the previously described embodiment, the apparatus may comprise a first clutch member secured to the at least one said tubular body portion and a second clutch member axially spaced from the first clutch member and secured to the at least one said tubular body portion. The respective sleeve may be axially arranged between the first clutch member and the second clutch member and may be movable between cooperative engagement with the first clutch member or the second clutch member by an indexable latch mechanism. Such a configuration may be denoted as a clutch mechanism. In such an embodiment, the sleeve is axially, i.e. in flow direction of the drilling fluid, arranged between the fixed clutch members which serve as an upper stop element and a lower stop element for restricting the moving range of the sleeve. Moreover, also in this embodiment the sleeve may be biased to the closed position, i.e. abut or be in cooperative engagement with the upper clutch member in the absence of external forces. However, triggered by fluid flow (or alternatively triggered by an activation means such as a ball) the sleeve may be moved from the cooperative engagement with the upper clutch member to cooperative engagement with the lower clutch member, or vice versa. For this purpose, an indexable latch mechanism may be implemented. Such an index mechanism is disclosed as such for instance in U.S. Pat. No. 6,041,874 which is therefore incorporated by reference.

It should further be mentioned here that, although the clutch mechanism is operable in one embodiment without activation balls or the like (for instance in a manner as disclosed in U.S. Pat. No. 6,041,874), it is also possible to provide a corresponding clutch mechanism additionally using activation or deactivation balls (for instance in a way as disclosed as such in U.S. Pat. No. 7,673,708 which is therefore incorporated by reference).

In an embodiment, the first sleeve and/or the second sleeve may comprise engagement means configured for being engaged by or for receiving a first restriction device. The apparatus may comprise the first restriction device which comprises a second through-flow passage (which may be smaller than the first through-flow passage) and which may be configured so that dropping the first restriction device into the apparatus causes the first restriction device to engage the engagement means to cause an increase in fluid pressure in the apparatus above the first restriction device which moves the respective sleeve from the closed to the open position. The apparatus may further comprise a second restriction device configured so that dropping the second restriction device into the apparatus causes the second restriction device to engage the first restriction device and block the second through-flow passage to cause a fluid pressure increase in the apparatus above the first and second restriction devices which moves the first and second restriction devices past the respective sleeve to cause the respective biasing means to move the respective sleeve back to the closed position. Such a configuration may be denoted as a split flow mechanism. The first restriction device in the described embodiment may be a separate body which can be dropped into the drill string from outside of a bore hole. The first restriction device can for instance be a dart or any other appropriately shaped physical structure having an internal fluid conduit denoted as the second throughflow passage. The first restriction device may be configured so that, upon travelling downwards the drill string, it will rest on the engagement means of the apparatus due to corresponding shapes, particularly in a manner that the second through-flow passage is arranged in parallel to the first through-flow passage. Therefore, when the first restriction device engages the engagement means, the fluid flow along the axial direction of the downhole tool will continue, since the drilling fluid will partially pass through the second through-flow passage but will at the same time close the first through-flow passage partially. Thus, while the flow of drilling fluid continues towards the deepest position of the bore hole (for instance for operating a downhole motor, or for lubricating or cooling purposes), the pressure above the first restriction device will at the same time be increased to open the upper bypass valve so as to enable, simultaneously to the axial flow, flow of drilling fluid through the first port means. However, upon dropping the second restriction device into the bore hole following the first restriction device, the second restriction device will engage the first restriction device and will entirely close both through-flow passages, thereby preventing further flow of drilling fluid towards the deepest portion of the bore hole and increasing the pressure above the restriction devices in the engagement means or seat of the respective sleeve. A result a certain pressure, the restriction devices will together pass through the engagement means. In one embodiment, the restriction devices are simply sheared or pressed through the engagement means. It is also possible that the first restriction device and/or the engagement means of the sleeve comprises a deformable material which allows to perform an elastic deformation so as to enable the respective restriction devices to pass the engagement means without any deterioration.

Still referring to the previously described embodiment, the apparatus may comprise deactivation means (such as one or more deactivation balls) which may be configured so that dropping the deactivation means into the apparatus closes the respective port means to cause a further fluid pressure increase in the apparatus above the first and second restriction devices which moves the first and second restriction devices and the deactivation means past the respective sleeve to cause the respective biasing means to move the respective sleeve back to the closed position. Hence, to avoid large pressure values in the drill string (which may be advantageous for sensitive components in the drill string), one or more ports of the respective port means may be closed by the deactivation means prior to forcing the restriction devices through the engagement means. Optionally, such deactivation means may be used in conjunction with the above-mentioned restriction devices. Such deactivation means may, prior to initiating travel of the restriction devices through the engagement means, close the respective ports to further increase the pressure on the restriction devices without an external increase of pump pressure. The number of deactivation balls of the deactivation means may correspond to the number of ports of the port means being controlled by the restriction devices and the deactivation means (one deactivation ball per port).

Still referring to the previously described embodiment, the second restriction device and/or the deactivation means may be connected to a respective wireline so as to be retrievable from the apparatus after use to be removed out of the bore hole. When the described split flow tool relates to the upper sleeve and when the lower sleeve also works based on activation means and/or deactivation means dropped into the bore hole, it may be advantageous to prevent the second restriction device and/or the deactivation means from travelling downwards. Hence, the second restriction device and/or the deactivation means may be connected to a wireline so that it can be pulled out of the bore hole after having done its job to close the second through-flow passage or the port means in the upper one of the serial downhole tools. Optionally, it is also possible that the first restriction device is connected to a wireline so that also the first restriction device can be pulled out of the bore hole after use in the upper downhole valve.

In an embodiment, the first sleeve and/or the second sleeve may comprise engagement means configured for receiving activation means. The apparatus may comprise these activation means which may be configured so that dropping the activation means into the apparatus causes the activation means to engage the engagement means to cause an increase in fluid pressure in the apparatus above the activation means which moves the respective sleeve from the closed to the open position. The activation means may further be configured so that dropping the activation means into the apparatus causes the first through-flow passage to be closed by the activation means. The apparatus may comprise deactivation means configured so that dropping the deactivation means into the apparatus closes the respective port means to cause a further fluid pressure increase in the apparatus above the activation means which moves the activation means and the deactivation means past the respective sleeve to cause the respective biasing means to move the respective sleeve back to the closed position. In such an embodiment, the activation means may be free of a through-hole passage and will therefore completely close the fluid path towards the deepest position of the bore hole when the activation means are engaged by the engagement means. In case of this engagement, the pressure above the respective sleeve and activation means will increase, thereby opening the respective port means, since the biasing force of the respective biasing means will then be overcome by the fluid pressure increase. Then, the drilling fluid may pass through the respective ports. In order to deactivate the device, the activation means (for instance smaller balls in a number corresponding to the number of ports of the respective port means) may be dropped into the bore hole so that they will close the respective ports. Consequently, the pressure will be further increased above engagement means and activation means, thereby forcing the activation means and consequently the deactivation means to pass through the engagement means. This can be performed by shearing the respective structures (for instance balls) through the engagement means, or by providing the structures and/or engagement means of an elastically deformable material which deforms upon exceeding a certain pressure, thereby forcing the activation means and the deactivation means through the engagement means.

Still referring to the above described embodiment, the apparatus may optionally comprise locking means configured so that dropping the locking means into the apparatus (prior to dropping the deactivation means into the apparatus) locks the respective port means open until the deactivation means force the locking means to move out of the port means to an exterior of the tubular body portion. Such an embodiment may also be denoted as an automatic locking tool or autolock tool. In this embodiment, the ports will be locked open by dropping the locking means (for instance a locking ball of a certain size and of a certain material) into the drill string. Thus, by clamping the locking means into the open ports between sleeve and tubular section, the ports will remain open. Upon dropping the deactivation means into the bore hole, the locking means will be pressed laterally outwardly of the drill string so that the locking means will travel in an annulus between drill string and surrounding bore hole wall.

In an embodiment, at least one of the first sleeve and the second sleeve comprises engagement means configured for receiving frangible activation means. The apparatus may further comprise the frangible activation means which may be configured so that dropping the frangible activation means into the apparatus causes the frangible activation means to engage the engagement means to cause an increase in fluid pressure in the apparatus above the frangible activation means which moves the respective sleeve from the closed to the open position. The frangible activation means can be configured so that a further fluid pressure increase in the apparatus above the frangible activation means destroys (e.g. breaks) the frangible activation means which (e.g. decomposed into smaller particles or pieces) thereby moves through the engagement means to cause a decrease in fluid pressure in the apparatus above the engagement means which in turn moves the respective sleeve from the closed to the open position. In certain embodiments of the apparatus with serially arranged downhole tools, there is the challenge that the provision of multiple serially coupled downhole tools located above one another can cause problems with activation or deactivation means which have been used for an upper downhole tool and which will later on travel downwardly. Also bringing activation or deactivation means to a lower downhole tool requires the means to pass an upper downhole tool first which may be a mechanical obstacle. In some embodiments, this challenge can be tackled by an appropriate adjustment of the dimensions of the various sleeves, engagement means, and activation/deactivation/restriction means. However, the here described embodiment provides an alternative solution. In this embodiment, the activation means are made of a frangible material, i.e. material which breaks or is destroyed in another way in a defined manner when certain mechanical load is exceeded. For instance, when a threshold pressure is exceeded, this will cause the frangible activation means to be destroyed, for instance to break into multiple small pieces which can then simply travel downwardly along the bore hole. For example, such a frangible activation means may be provided with a predetermined breaking point. For instance, it may be a hollow structure with a certain mechanical weakness at one or more predefined positions, so as to allow to predict the way the frangible activation means will break upon exceeding of a certain mechanical load, particularly fluid pressure. Such an embodiment has the advantage over the prior art of providing means for actuating a downhole tool with an actuating ball which does not form an undesirable obstruction once the tool has been actuated.

In an embodiment, the first sleeve or the second sleeve is configured with a clutch mechanism as described above, and the other one of the first sleeve and the second sleeve is configured with an autolock mechanism as described above. The flow responsive portion should be dimensioned to be passed by the activation means. It is possible to arrange the clutch mechanism above or below the autolock mechanism.

In an embodiment, the first sleeve or the second sleeve is configured with a clutch mechanism as described above, and the other one of the first sleeve and the second sleeve is configured with a split flow mechanism as described above. The flow responsive portion shall be dimensioned so that it can be passed by the first restriction device upon dropping the first restriction device into the apparatus. The split-flow mechanism may be arranged above or below the clutch mechanism.

In order to allow the at least two downhole tools of the apparatus to be operated and activated separately, the flow responsive portion may be designed (particularly sized) so that the restriction device used for activating the split flow tool will simply pass the clutch mechanism without any interaction. Therefore, it can be ensured that any of the two downhole tools can be operated independently from one another, depending on which port shall be opened (either by adjusting a flow for actuating the flow responsive portion of the clutch mechanism or by dropping corresponding activation means into the drill string for operating the split flow tool).

In an embodiment, the first sleeve and the second sleeve are both configured with an autolock mechanism as described above. The first port means may have one or more ports having a smaller dimension than one or more ports of the second port means. The deactivation means for the first sleeve may be dimensioned to pass through the second port means (or may alternatively be connected to a wireline or rope in a wireline embodiment so that it can be retrieved after having operated the upper autolock tool). Also in this embodiment, independent operability of the two autolock tools is advantageous. For this purpose, one and the same first restriction device may be used for both autolock mechanisms (alternatively, two different and differently sized first restriction devices may be used for the two autolock mechanisms which may be connected to a wireline or rope in a wireline embodiment). After passing (for instance shearing through) the upper engagement means, the single first restriction device will simply travel to the lower engagement means and will be engaged here. As an alternative to passing by shearing, it is also possible to realize the engagement means and/or the first restriction device from a deformable material so that the first restriction device is not in the danger of being deteriorated by the shearing through the upper engagement means. Moreover, the dimensioning of the second port means to be larger than the first port means has several advantages. Firstly, relatively large lower ports may simplify the supply of lost circulation material to the lower downhole valve. Secondly, the larger lower ports may be used for removing the deactivation means of the upper downhole valve out of the drill string, since they can pass the lower ports due to their larger size when travelling downwardly. Hence, different deactivation means (and if required, different locking means), can be used for the two or more autolock tools arranged above one another.

In an embodiment, the first sleeve and the second sleeve are both configured with a frangible body mechanism as described above. The frangible activation means for the second sleeve may be dimensioned to pass through the engagement means of the first sleeve. Even when using frangible activation means, it shall be ensured that the two mechanisms are adjusted to one another so as to allow independent operation of the two downhole tools. If the frangible activation means and the corresponding engagement means of the upper sleeve have a larger dimension than that the respective components of the lower sleeve, the upper sleeve can be activated by the larger frangible activation means. Subsequently, the frangible activation means is broken into small pieces which can then also pass the lower engagement means without undesired activation. Subsequently, dropping a smaller frangible activation means into the drill string will allow this smaller frangible activation means to pass the upper engagement means and seat in the lower, smaller engagement means of the lower sleeve.

In another embodiment, the first sleeve and the second sleeve are both configured with a split flow mechanism as described above. In this embodiment, the first restriction device for the first sleeve may be the same physical structure as the first restriction device for the second sleeve. In such a combination of two above-mentioned split-flow tools, one and the same first restriction device may be used for both tools, i.e. the two engagement means may be configured in a similar or identical way. Also the second restriction device may be the same used for the upper and the lower split-flow tool. Alternatively, it may be advantageous to remove the second restriction device from the drill string after having operated the upper sleeve. Otherwise, the second restriction device could travel downwards together with the first restriction device and could continue to block the second through-flow passage in the lower downhole tool. This can be for instance prevented by providing the second restriction device with a wireline to pull it out from the drill string before the first restriction device travels from the upper engagement means to the lower one. As an alternative to a wireline, it is possible to provide the first and second restriction devices with significantly different densities so that upon travelling downwards in the drill string, the buoyancy force acting on both restriction devices will be significantly different so that they will be separated from one another while travelling downwardly, thereby enabling the split flow mode in the lower downhole valve as well.

In an embodiment of the invention, the apparatus comprises at least one restriction device (or activation device) configured so that dropping the at least one restriction device into the apparatus causes the at least one restriction device to engage first engagement means of the first sleeve to cause an increase in fluid pressure in the apparatus above the at least one restriction device which moves the first sleeve from the closed to the open position, and subsequently releasing the at least one restriction device from the first engagement means of the first sleeve moves the at least one restriction device down the apparatus to engage second engagement means of the second sleeve to cause a fluid pressure increase in the apparatus above the at least one restriction device to move the second sleeve from the closed to the open position. Hence, it is possible to use the same restriction device for activating both the upper and the lower sleeve. The releasing may further force the first sleeve to move back from the open to the closed position.

As an alternative, an apparatus according to another preferred embodiment is a combination of a clutch mechanism as defined above and being operated by fluid flow rather than by one or more drop devices (such as balls or darts) dropped into the apparatus, and a drop device operated mechanism (such as a split flow tool or an autolock tool) operated by one or more devices dropped into the apparatus. Due to the completely different activation/deactivation characteristics of such a combination, independent operation of both mechanisms is ensured increasing flexibility for a user.

In an embodiment, the apparatus comprises third port means formed through at least one said tubular body portion at a location below the second port means when the apparatus is in use, a third sleeve slidably mounted inside at least one said tubular body portion, the third sleeve moveable between a closed position in which said third port means is closed by the third sleeve and an open position in which said third port means is open to allow drilling fluid to circulate out of the apparatus, and third biasing means biasing the third sleeve into the closed position. Accordingly, it is possible to also combine three or more downhole tools serially above one another. The various combined downhole tools may be of the same type (for instance all of them may be autolock tools or all of them may be clutch mechanisms, or different types can be combined, for instance autolock tools and/or split-flow tools and/or clutch mechanisms).

In an embodiment, the first sleeve and the second sleeve of the apparatus may be operable independently from one another, i.e. each of the bypass paths formed by the drill string and the port means may be operated (opened or closed) independently from the other one.

A preferred embodiment of the present invention seeks to overcome the above disadvantages of the prior art, partially or entirely.

According to an aspect of the present invention, there is provided a downhole circulation apparatus arranged to be mounted in a drill string, the apparatus comprising:

at least one tubular body portion for mounting in a drill string, at least one said tubular body portion defining a first through-flow passage for receiving a flow of drilling fluid through the drill string;

first port means formed through at least one said tubular body portion;

a first sleeve slidably mounted inside at least one said tubular body portion, the first sleeve moveable between a closed position in which said first port means is closed by the first sleeve and an open position in which said first port means is open to allow drilling fluid to circulate out of the apparatus;

first biasing means biasing the first sleeve into the closed position;

second port means formed through at least one said tubular body portion at a location below the first port means when the apparatus is in use;

a second sleeve slidably mounted inside at least one said tubular body portion, the second sleeve moveable between a closed position in which said second port means is closed by the second sleeve and an open position in which said second port means is open to allow drilling fluid to circulate out of the apparatus; and

second biasing means biasing the second sleeve into the closed position;

wherein the apparatus is arranged such that:

a) dropping a first restriction device comprising a second through-flow passage into the apparatus causes the first restriction device to engage first engagement means of said first sleeve to cause an increase in fluid pressure in the apparatus above the first restriction device which moves the first sleeve from the closed to the open position;

b) dropping a second restriction device into the apparatus after the first restriction device has been dropped causes the second restriction device to engage the first restriction device and block the second through-flow passage to cause a fluid pressure increase in the apparatus above the first and second restriction devices which moves the first and second restriction devices past the first sleeve to cause the first biasing means to move the first sleeve back to the closed position; and

c) wherein the first and second restriction devices move down the apparatus to engage second engagement means of said second sleeve to cause a fluid pressure increase in the apparatus above the first and second restriction devices to move the second sleeve from the closed to the open position.

By providing a downhole circulation tool comprising first and second port means and sleeves that are operable in response to the dropping of first and second restriction devices as defined above, this provides the advantage of a downhole circulation apparatus that can be used to both increase flow rates of drilling fluid in the tool for use in cleaning well bores and also can be used to bypass large particle size drilling fluid (LCM) in order to plug formations and prevent lost circulation.

Dropping a first restriction device comprising a second through-flow passage into the apparatus enables a split flow of drilling fluid to be achieved. Some of the flow continues through the second through-flow passage of the dart and some of the drilling fluid is bypassed out of the first port means to travel back up the well bore and clean the bore. This enables operators on the surface to increase fluid flow without damaging the drill string below the split at the first port means because the additional flow will exit the first port means.

Alternatively, if large particle size drilling fluid is required to be used during the same drilling operation to plug under-pressured formations and prevent lost circulation, the second restriction device can be dropped. The second restriction device is adapted to block the second through-flow passage of the first restriction device to prevent flow of drilling fluid in the drill string below the combination of the first and second restriction devices. This protects sensitive components of the drill string and opens the second port means such that LCM can be circulated. Consequently, the apparatus enables two important functions to be achieved by the same drill string.

This also provides the advantage that the apparatus can be used to control the speed of standard drilling motors. Standard drilling motors function by means of a positive displacement rotor and stator in which the speed (RPM) is directly controlled by the volume of fluid pumped through the motor. Splitting the fluid flow in the apparatus therefore could be used to change the flow rate through the motor.

Such an arrangement allows to combine split flow systems for hole cleaning applications with circulating systems to pump high concentrations of lost circulation material (LCM). These challenges are unique and are unrelated to each other. It is believed to be impossible or at least very difficult to provide one circulating tool to deal with both problems as split flow/flow booster systems may require small tungsten carbide nozzles in the tool for certain applications. These smaller nozzles will control the bypassed flow out of the tool and need to maintain high pressure drops through the nozzles to maintain high operating pressures in the drill string. Conversely, a multiple function autolock bypass system may utilize ports with a TFA (total flow area) as large as possible to allow for any pumpable size or concentration of LCM to be easily pumped through the ports in the tool. These large ports also help with the filling of the pipe and draining of the pipe during drill string removal from the well or tripping. These large ports will also help when reverse circulating is required. Embodiments for such a tandem device as disclosed herein are designed to deal with these two common problems with a system that implements two or more systems and optionally one ball catcher system run below. With a split flow dart system/ball cluster run above and a multiple activation autolock bypass system run below, operators will finally have the ability to deal with both these problems with tools that work in tandem in the same drill string. The split flow tool may be run above the autolock tool. To activate the split flow a split flow dart is pumped into the split flow tool when it lands it activates the split flow. With this system activated, drill and hole cleaning can be enhanced. If lost circulation is encountered then the following procedure will be performed. Drop one of the split flow deactivation balls. When this deactivation ball reaches the split flow dart it will plug the dart. This will cause a significant reduction in the TFA and allow the system to pressure up to the point at which the split flow dart will shear through the seat in the split flow tool. When the dart leaves the split flow tool, the sleeve in the split flow tool will close. The split flow dart and deactivation ball will land in the autolock tool below opening the autolock tool. With the split flow dart and deactivation ball landed on the autolock tool the ports on the autolock tool will open. With the ports on the autolock tool open, the displacement of LCM can start. Because the dart has the split flow deactivation ball in place plugging the internal diameter of the dart, all the LCM will be displaced out of the ports into the open hole. Because the TFA on the ports in the tool is so large this dart and ball will stay in place as long as it is required. To pressure up and close the system the other two split flow deactivation balls are dropped and when they reach the autolock tool they will plug the circulating ports allowing the system to pressure up and deactivate the autolock tool. The dart and balls will be retained in the ball catcher. Both of these tools will work in the same drill string and can be activated independently.

In a preferred embodiment, the second sleeve is moveable back to the closed position by said second biasing means in response to dropping deactivation means into the apparatus to block said second port means and cause a fluid pressure increase in the apparatus to move the first and second restriction devices past the second sleeve.

This provides the advantage that dropping deactivation means into the apparatus closes the second port means and cycles the apparatus back to the starting condition. The cycle can be started again by dropping first restriction means.

The deactivation means may comprise at least one deactivation ball.

The apparatus of any of the embodiments disclosed herein which includes at least one activation means/deactivation means/restriction device (such as balls, darts or the like) may further comprise a restriction device catcher located below said second sleeve when the apparatus is in use.

In a preferred embodiment, said first port means comprises a plurality of first nozzles arranged to direct drilling fluid into a drilled borehole in a direction opposite to the direction of advancement of the apparatus.

This provides the advantage of minimising hole erosion and increasing the cleaning effect of the bypassed fluid.

Said plurality of first nozzles may be formed from tungsten carbide.

This provides the advantage of hard wearing nozzles which consistently pass a predetermined volume of fluid.

In a preferred embodiment, the second port means comprises a plurality of second nozzles, wherein each said second nozzle has a diameter greater than the diameter of each of said first nozzles.

This provides the advantage of nozzles that are suited to bypassing large particle size drilling fluid (LCM).

The first restriction device may be arranged to allow approximately 70% of the fluid flow in the apparatus to pass through the second through-flow passage when engaged with the first engagement means, such that approximately 30% of the fluid flow in the apparatus is directed through said first port means.

The apparatus may be formed from an assembly of a plurality of drill string elements comprising:

a first tool element comprising a first tubular body portion, first port means formed through said first tubular body portion and a first sleeve slidably mounted inside said first tubular body portion;

a second tool element arranged below said first tool element when the apparatus is in use, the second tool element comprising a second tubular body portion, second port means formed through said second tubular body portion and a second sleeve slidably mounted inside said second tubular body portion; and at least one drill pipe element disposed between and interconnecting said first tool element with said second tool element.

The apparatus may further comprise a plurality of drill pipe elements disposed between and interconnecting said first tool element with said second tool element.

This provides the advantage of preventing the first and second restriction devices from blowing past the second engagement means of the second sleeve which would cause the second sleeve not to activate. When the first and second restriction devices blow past the first sleeve, they have a considerable velocity and inertia which is reduced by having several lengths of drill pipe (extending to 60 feet for example) above the second sleeve.

In a preferred embodiment, said first restriction device is a dart comprising:

a hollow body portion defining said second through-flow passage;

at least one deformable portion arranged to engage the first and second engagement means of the respective first and second sleeves; and

a ball seat disposed in the second through-flow passage, the ball seat arranged to receive a ball to block said second through-flow passage.

Said dart may further comprise retention means disposed adjacent said ball seat, the retention means arranged to prevent a ball located in the ball seat from moving out of the ball seat in a first direction, but permit a ball located in the ball seat to move past the ball seat in a second direction.

This provides the advantage of preventing a ball located in the ball seat from moving back up the drill string, i.e. towards the surface. If this happened, the ball could become lodged in one of the circulation ports which could cause a drill string failure.

Said retention means may comprise a plurality of teeth disposed on the hollow body portion.

According to another aspect of the present invention, there is provided a downhole circulation system comprising:

a downhole circulation apparatus as defined above;

a first restriction device comprising a second through-flow passage; and

a second restriction device adapted to engage said first restriction device and block the second through-flow passage.

According to a further aspect of the present invention, there is provided a method of operating a downhole circulation apparatus as defined above, the method comprising the steps of:

a) dropping a first restriction device comprising a second through-flow passage into the apparatus to cause the first restriction device to engage first engagement means of said first sleeve and cause an increase in fluid pressure in the apparatus above the first restriction device to move the first sleeve from the closed to the open position;

b) dropping a second restriction device into the apparatus after the first restriction device has been dropped to cause the second restriction device to engage the first restriction device and block the second through-flow passage to cause a fluid pressure increase in the apparatus above the first and second restriction devices which moves the first and second restriction devices past the first sleeve and causes the first biasing means to move the first sleeve back to the closed position; and

c) wherein the first and second restriction devices move down the apparatus to engage second engagement means of said second sleeve to cause a fluid pressure increase in the apparatus above the first and second restriction devices to move the second sleeve from the closed to the open position.

This provides the advantage of a method of operating a downhole circulation apparatus that can be used to both increase flow rates of drilling fluid in the tool for use in cleaning well bores and can also be used to bypass large particle size drilling fluid (LCM) in order to plug formations and prevent lost circulation.

Dropping a first restriction device comprising a second through-flow passage into the apparatus enables a split flow of drilling fluid to be achieved. Some of the flow continues through the second through-flow passage of the dart and some of the drilling fluid is bypassed out of the first port means to travel back up the well bore and clean the bore. This enables operators on the surface to increase fluid flow without damaging the drill string below the split at the first port means because the additional flow will exit the first port means.

Alternatively, if large particle size drilling fluid is required to be used during the same drilling operation to plug under-pressured formations and prevent lost circulation, the second restriction device can be dropped. The second restriction device is adapted to block the second through-flow passage of the first restriction device to prevent flow of drilling fluid in the drill string below the combination of the first and second restriction devices. This protects sensitive components of the drill string and opens the second port means such that LCM can be circulated. Consequently, the apparatus enables two important functions to be achieved by the same drill string.

The method may further comprise dropping at least one deactivation means into the apparatus to block said second port means and cause a fluid pressure increase in the apparatus to move the first and second restriction devices past the second sleeve and cause the second biasing means to move the second sleeve back to the closed position.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will now be described, by way of example only, and not in any limitative sense, with reference to the accompanying drawings in which:

FIGS. 1 to 11 are a series of cross-sectional drawings of a downhole circulation apparatus embodying the present invention showing progressive steps from dropping a first restriction device in FIG. 1 to the end of the cycling of the tool in FIG. 11;

FIG. 12 is a cross-sectional close up view of the first and second restriction devices;

FIG. 13a is a cross sectional view of a second embodiment of the first restriction device comprising retention means;

FIG. 13b is a close up of the retention means of FIG. 13a engaging a second restriction device;

FIG. 14 is a cross-sectional drawing of a downhole circulation apparatus embodying the present invention showing a combination of a clutch mechanism downhole tool above and an autolock mechanism downhole tool below;

FIG. 15 is a cross-sectional drawing of a downhole circulation apparatus embodying the present invention showing a combination of an autolock mechanism downhole tool above and a clutch mechanism downhole tool below;

FIG. 16 is a cross-sectional drawing of a downhole circulation apparatus embodying the present invention showing a combination of a split flow mechanism downhole tool above and a clutch mechanism downhole tool below;

FIG. 17 is a cross-sectional drawing of a downhole circulation apparatus embodying the present invention showing a combination of an autolock mechanism downhole tool above and another autolock mechanism downhole tool below;

FIG. 18 is a cross-sectional drawing of a downhole circulation apparatus embodying the present invention showing a combination of a frangible activation mechanism downhole tool above and another frangible activation mechanism downhole tool below;

FIG. 19 is a cross-sectional drawing of a downhole circulation apparatus embodying the present invention showing a combination of a split flow mechanism downhole tool above and another split flow mechanism downhole tool below;

FIG. 20 is a cross-sectional drawing of a downhole circulation apparatus embodying the present invention showing a combination of three serially arranged autolock downhole tools;

FIG. 21 to FIG. 26 show cross-sectional drawings of a downhole circulation apparatus embodying the present invention showing a combination of a ball operated downhole tool above and a clutch mechanism downhole tool below.

The illustration in the drawings is schematic. In different drawings, similar or identical elements are provided with the same reference numerals.

DETAILED DESCRIPTION

Referring to FIG. 1, a downhole circulation apparatus 2 is arranged to be mounted in a drill string as shown in FIG. 1. The downhole circulation apparatus 2 comprises at least one tubular body portion 4 defining a first through-flow passage 6 through which drilling fluid can pass along the drill string.

First port means 8 is formed through the tubular body 4. The first port means is a bypass port and may comprise a plurality of nozzles formed from tungsten carbide. A first sleeve 10 is slidably mounted in the tubular body portion 4 and is biased into a position in which the first port means 8 is closed by a biasing means such as a spring 12. The first sleeve 10 is disposed in a first drill string element which is connected to several joints of drill pipe 16 at a lower end 14. The interconnection of drill string elements will be familiar to person skilled in the art.

Second port means 18 is formed through the tubular body portion 4 at a location below the first port means 8 in the drill string. The second port means 18 may comprise a plurality of second nozzles, wherein each of the second nozzles has a diameter greater than the diameter of each of the first nozzles of the first port means 8. Larger nozzles enable large particle size drilling fluid such as LCM to be bypassed. A second sleeve 20 is slidably mounted inside the tubular body portion 4 and is arranged to close second port means 18 in the condition shown in FIG. 1. Second sleeve 20 comprises second engagement means 21 such as a ball or dart seat. A restriction device catcher, such as a ball and dart catcher assembly 24 is provided below the first and second sleeves.

Although the embodiment shown shows the first and second sleeves located in different drill string elements, they could alternatively be mounted in a single drill string element. Also all further embodiments shown below can have the different sleeves in different drill strings, or may be mounted in a single drill string element.

Referring to FIG. 12, a first restriction device 30 comprises a second through flow passage 32. The first restriction device 30 may be a dart formed from steel. Second through flow passage 32 is narrower than first flow through passage 6 and therefore will cause a fluid pressure increase above dart 30. A restricted through-flow passage member 34 may also be mounted in the deformable dart 30, although the restricted through-flow passage 34 could be integrally formed in the deformable dart 30. By providing interchangeable restricted through-flow passage members 34, the dart can be changed to be used with different tools and applications.

A deformable portion 36 forms a widened portion of the deformable dart 34. The deformable portion 36 is arranged to abut against first engagement means 11 or second engagement means 21 of the downhole circulation apparatus 2. When the portion 36 contacts seat 11, the increased pressure resulting from fluid passing through restriction 34 pushes on the dart causing the first sleeve 10 to move downwardly against spring 12.

A second restriction device 38 may comprise a ball or other member suitable for blocking second through flow passage 32. Ball 38 may be formed from steel or plastics material and is arranged to seat in an opening seat 40 of the dart 30. The ball blocks the second through-flow passage 32 preventing drilling fluid from passing through dart 30 and therefore to the part of the drill string below the dart and ball combination 30, 38. If sufficient force is applied to the dart and ball combination 30 and 38, deformable portion 36 deforms enabling flushing of the dart and ball past the second engagement means 21.

Referring to FIGS. 13a and 13b, a second embodiment of first restriction device 30 comprises retention means for retaining the ball in seat 40. The retention means may comprise for example a plurality of teeth 41 that grip the ball 38 and prevent it from moving back along the drill string towards the surface, but permit the ball 38 to move downwardly in the drill string. Another example of a retention means that could be used is a split ring having a taper.

The operation of the downhole circulation tool 2 will now be described by referring to FIGS. 1 to 11 in sequence describing the steps that comprise a full cycle of the apparatus 2.

Referring to FIG. 1, dart 30 (FIG. 12) is dropped into the drill string containing the apparatus 2. It will be appreciated by persons skilled in the art that dart 30 is dropped from the surface and there may be several lengths of drill string above the portion shown in FIG. 1 such that the dart 30 travels along with drilling fluid down to the location of the portion shown in Figure.

Referring to FIG. 2, dart 30 engages first seat 11 and as a result of a fluid pressure increase in the drill string caused by fluid passing through second through-flow passage 32 (FIGS. 12 and 13), the first sleeve 10 is pushed downwardly against first spring 12 opening the first bypass port means 8. Consequently, drilling fluid 50 can pass through first port means 8 and out of the tool. In the embodiment shown in FIG. 2, the nozzles forming first port means 8 are arranged to direct fluid upwardly away from the direction of advancement of the drill string to minimise hole erosion and help with hole cleaning. In this example, the dart is arranged to pass 70% of the fluid down the drill string such that 30% of the fluid 50 is bypassed.

When first port means 8 opens, the drill string operator at the surface may see a decrease in pump pressure. The operator can then increase the volume of fluid pumped without damaging the drill string.

Referring to FIG. 3, in order to close first port means 8 a second restriction device such as ball 38 is dropped into the drill string.

Referring to FIG. 4, the ball 38 seats in dart 30 as shown in FIG. 12. Ball 30 may also be retained by teeth 41 (FIG. 13). This causes a blockage in the drill string and prevents drilling fluid from passing the dart and ball 30, 38. This causes a large pressure increase above the ball 38.

Referring to FIG. 5, this large pressure increase causes the first and second restriction devices to move past the first sleeve. For example, the deformable portion 36 of dart 30 deforms and the ball and dart 30, 38 blow past the first seat 11. The dart and ball 30, 38 are therefore pushed down the drill string along with drilling fluid.

Referring to FIG. 6, the ball and dart 30, 38 come into engagement with second seat 21. Second sleeve 20 is therefore moved downwardly against spring 22 to cause the second port means 18 to be opened. Large particle size drilling fluid 60 can be circulated from second port means 18, which may comprise a plurality of large nozzles, in order to plug a formation and prevent fluid circulation loss.

Referring to FIG. 7, the apparatus comprises an auto-lock feature which can be used to clean the interior of the drill string and allow the drill string to be drained and filled as required. A plastic auto-lock ball 42 having a diameter greater than the diameter of one of the nozzles of the second port means 18 is dropped into the string and seats in one of the nozzles. This blocks the nozzle and only enables drilling fluid 60 to be circulated out of the other nozzle. In the embodiment shown in the drawings, there are two nozzles forming second port means 18, although it will be apparent to person skilled in the art that one or more nozzles can be employed.

Referring to FIG. 8, in order to deactivate the apparatus, deactivation means such as at least one steel deactivation ball 44 is dropped. If only one nozzle is present in second port means 18, only a single deactivation ball 44 is required. However, in the embodiment shown in the drawings there are two ports forming second port means 18 and therefore two deactivation balls 44 are required to be dropped into the drill string.

Referring to FIG. 9, if the plastic auto-lock ball 42 is present, deactivation balls 44 seat in the nozzles 18. Also, the drill string is blocked by the ball and dart combination 30, 38. This causes a large increase in pressure and blows auto-lock ball 42 out of the nozzle. The large increase in pressure also causes deformable portion 36 of dart 30 to shear and be blown past second seat 21.

Referring to FIG. 10, the ball and dart 30, 38 and the two steel deactivation balls 44 fall through the drill string and are caught in ball catcher 24 as shown in FIG. 11. This completes a cycle of the apparatus. The cycle can be started again from the step of FIG. 1 and the cycle can be repeated until the ball and dart catcher 24 is full.

Furthermore, several alternatives to the described embodiments of FIG. 1 to FIG. 13 are possible. For example, it is possible to omit the plastic auto-lock ball 42. In such an embodiment, the tool will function without a locking feature which reduces the amount of required balls to be dropped into the drill string.

In a further alternative, it is possible to provide two additional balls for the upper split flow mechanism, in addition to the restriction devices 30, 38. These two additional balls can have a similar function as steel deactivation balls 44 used for operating the lower mechanism. When such additional balls are used for the upper split-flow mechanism, it is possible to close the upper ports 8 in an operation mode between FIG. 4 and FIG. 5, thereby allowing to further increase the pressure above the restriction devices 38, 30 before forcing them through the engagement means 11 of the upper sleeve 10.

FIG. 14 shows a downhole circulation apparatus 1400 according to another exemplary embodiment of the invention.

As in the embodiment of FIG. 1 to FIG. 11, also the downhole circulation apparatus 1400 is arranged to be mounted in a drill string. A tubular body portion 4 is foreseen for mounting in a drill string. A through-flow passage 6 is defined as a lumen within the tubular body portion 4 for receiving a flow of drilling fluid through the drill string. First ports 8 in the form of nozzles are formed through the tubular body portion 4. A first sleeve 10 is mounted inside the tubular body portion 4 to be movable between a closed position (shown in FIG. 14) in which the port means 8 is closed due to intended misalignment with ports 74 of the first sleeve 10 and an open position in which the port means 8 is open due to alignment with ports 74 (not shown) to allow drilling fluid being conducted from an upper end 70 of the through-flow passage 6 to circulate out of the apparatus via the ports 74 and the port means 8. An annulus 76 is formed between an outer surface of the tubular body portion 4 and a wall 72 of the bore hole which is surrounded by formation material. In other words, in the configuration shown in FIG. 14, the port means 8 of the tubular body portion 4 is not in alignment with the ports 74 of the sleeve 10, thereby preventing fluid communication between an interior of the tubular body 4, the ports 74, the ports means 8 and annulus 76. However, upon a certain downward movement of the sleeve 10, it is possible to bring the ports 8, 74 in alignment, thereby selectively enabling fluid communication between through-flow passage 70, ports 74, 8 and the annulus 76.

Biasing means (not shown in FIG. 14) such as a spring (compare reference numeral 80) or the like is provided which biases the sleeve 10 in the closed position as shown in FIG. 14. Such biasing means can be configured for instance in a similar manner as reference numeral 18 in FIG. 1A of WO 01/06086.

Additionally, a second port means 18 is formed through the tubular body 4 at a location below the first port means 8. Correspondingly, a second sleeve 20 is slidably mounted inside the tubular body portion 4, being movable between a closed position (shown in FIG. 14) in which the second port means 18 are closed by the second sleeve 20 (more precisely due to intended misalignment with ports 78 of the second sleeve 20) and an open position (not shown) in which the second port means 18 is open due to alignment with ports 78 to allow drilling fluid to circulate out of the apparatus 1400 via the lower port means 18 and ports 78. As can be taken from FIG. 14, the lower port means 18 is not in alignment with ports 78 of the second sleeve 20. However, if the second sleeve 20 is moved downwardly, the ports 18, 78 can be brought in alignment, thereby allowing for fluid communication between the first through-flow passage 6, the ports 78, 18 and the annulus 76. Second biasing means in the form of a spring 80 is provided which biases the second sleeve 20 towards the closed position.

In the embodiment of FIG. 14, the upper downhole tool of apparatus 1400 is realized as a clutch mechanism, as will be described in the following in more detail. The first sleeve 10 comprises a flow responsive portion 82 in the form of a narrowing section of an annular shape. The flow responsive portion 82 is arranged to interact with drilling fluid conducted by a pump (not shown) along an axial direction 84 of the apparatus 1400. When a fluid pressure of the drilling fluid which is conducted along the axial direction 84 (for instance in order to drive a downhole motor (not shown), lubricate downhole components, etc.) exceeds a predefined threshold value, the force acting on the flow responsive portion 82 will be larger than the biasing force of the first biasing means (not shown). Hence, this force will move sleeve 10 downwardly to bring the ports 8, 74 in alignment, thereby enabling bypassing of fluid from the flow through-passage 6 towards the annulus 76. For example, drilling fluid for bore hole cleaning can be conducted into the annulus 76. Hence, by adjusting the flow rate or the liquid pressure, it is possible to operate the upper clutch mechanism.

In addition to the already described features, the clutch mechanism furthermore comprises a first clutch member 86 secured to the tubular body 4 in a fixed manner. Moreover, a second clutch member 88 is axially spaced with regard to the first clutch member 86 but is also rigidly fixed or secured to the tubular body portion 4. The sleeve 10 is axially arranged or sandwiched between the first clutch member 86 and the second clutch member 88 and can be mounted for axial and/or rotational displacement between the upper abutment position shown in FIG. 14 and the lower abutment position in which the lower end of the sleeve 10 abuts against the second clutch member 88. Furthermore, when the sleeve 10 abuts against one of the clutch members 86, 88, a cooperative engagement between the sleeve 10 and the respective one of the clutch members 86, 88 occurs which can be realized by an indexable latch mechanism (not shown in detail). Therefore, the sleeve 10 will interlock with the corresponding latching mechanism, thereby locking the sleeve 10 selectively in the upper or the lower position. The biasing means will always have the tendency to drive back the sleeve 10 into the upper position in the absence of external forces. The skilled person is aware of corresponding latching mechanisms for latching a clutch mechanism in the upper or lower position, compare for instance U.S. Pat. No. 6,041,874 or WO 01/06086.

While the clutch mechanism in the upper portion of FIG. 14 will be operated by fluid pressure, the autolock mechanism located in the lower portion of the apparatus 1400 will be operated by dropping a number of balls, as will be described in the following in more detail.

For this purpose, the second lower sleeve 20 comprises the engagement means 21 in the form of a seat which is shaped so as to receive a spherical activation ball 90. This activation ball 90 which may be made of steel can be dropped into the tubular body 4 from a top of the bore hole. Since a lateral extension of the activation ball 90 is smaller than a lateral extension of the narrowest portion of the flow responsive portion 82, the activation ball 90 will travel downwardly along the axial direction 84 and will be seated in the seat of the engagement means 21 in a position indicated with 1. This will increase the fluid pressure above the activation means 90 in the engagement means 21 which moves the second sleeve 20 from the closed position (FIG. 14) to the open position (not shown) in which the ports 78, 18 are in alignment. In this position, it is possible to bypass a bore hole fluid such as a cleaning fluid or loss circulation material through the ports 78, 18 into the annulus 76.

In order to lock the apparatus 1400 in the open state of ports 18, 78, a plastic locking ball 42 is dropped into the bore hole and will clamp between the ports 18, 78, as indicated schematically with II in FIG. 14. In other words, locking ball 42 will clamp between ports 18, 78 and will therefore lock the lower bypass valve in the open state.

In order to subsequently close the locked lower bypassing mechanism, steel balls 44 are dropped into the apparatus 1400. They will accommodate in the ports 78, as indicated with III and IV. Furthermore, the deactivation ball 44 placed at the position IV will also press locking ball 42 outwardly so that the latter will move into the annulus 76. Closing the ports 78 by the deactivation balls 44 will further increase the pressure above engagement means 21 which is already in engagement with activation means 90, thereby pressing activation means 90 and deactivation means 44 through the seat of engagement means 21. Hence, the balls 90, 44 will be stored in a ball catcher assembly (compare reference numeral 24 in FIG. 1 to FIG. 11) not shown in FIG. 14 and the following figures.

FIG. 15 shows an apparatus 1500 according to another exemplary embodiment of the invention. Apparatus 1500 differs from the apparatus 1400 only in that the upper downhole tool is an autolock mechanism and the lower downhole tool is a clutch mechanism, so that the downhole tools of FIG. 14 are interexchanged.

Apparatus 1600 according to another exemplary embodiment and shown in FIG. 16 differs from the apparatus 1500 in that the upper downhole tool is not realized as an autolock tool (as in FIG. 15), but as a split-flow tool (as in FIG. 1). In other words, the upper downhole tool of FIG. 16 can be realized in a similar manner as the upper downhole tool described above referring to FIG. 1 to FIG. 13.

In FIG. 16, the upper sleeve 10 comprises engagement means 11 configured for receiving a first restriction device 30. The first restriction device 30 has a second through-flow passage 32 and is configured so that dropping the first restriction device 30 into the apparatus 1600 causes the first restriction device 30 to engage the engagement means 11 to cause an increase in fluid pressure above the first restriction device 30 which moves the first sleeve 10 from the closed position (compare FIG. 16) to the open position (not shown). In the open position, ports 74, 8 are in alignment, whereas they are not in alignment in the operation mode shown in FIG. 16. When the first restriction device 30 (which can be realized as a dart or in the way shown in FIG. 12 or FIG. 13) engages engagement means 11 to bring ports 74, 8 in alignment, there is simultaneously a fluid flow along first through-flow passage 70 as well as a bypass flow through aligned ports 74, 8. Dropping subsequently a second restriction device 38, realized as a ball in FIG. 16, into the apparatus 1600 causes the second restriction device 38 to engage the first restriction device 30, thereby blocking the second through-flow passage 32. This causes a fluid pressure increase in the apparatus 1600 above the restriction devices 30, 38. This moves both restriction devices 30, 38 past the upper sleeve 10 to cause biasing means 80 of the split flow mechanism to move the first sleeve 10 back to the closed position of FIG. 16. This can be performed in a similar manner as described above referring to FIG. 1 to FIG. 5.

However, it is optionally possible to use deactivation means 44 in a similar manner as described above referring to FIG. 14 and FIG. 15 for an

autolock mechanism: The fluid pressure above the restriction devices 30, 38 in engagement means 11 can be further increased by dropping deactivation means 44 into the apparatus 1600 so that they will block ports 74, thereby forcing members 30, 38, 44, 44 to pass through engagement means 11 as well as through the below clutch mechanism in a downward direction to be caught in a ball catching device 24 (not shown in FIG. 16).

Since the diameter of the flow responsive portion 82 below is, even at the narrowest position, wider than a lateral extension of first restriction device 30, downward travel of members 30, 38, 44, 44 will not influence the lower downhole tool in FIG. 16.

The lower downhole tool in FIG. 16, a clutch mechanism, can again be operated in a similar way as described referring to FIG. 14 and FIG. 15.

It should also be said that the clutch mechanism and the split-flow mechanism of FIG. 16 can be arranged vice versa, i.e. the clutch mechanism above the split-flow mechanism.

In the following, referring to FIG. 17, an apparatus 1700 according to another exemplary embodiment of the invention will be described which is basically a combination of two autolock tools of the type shown in the upper portion of FIG. 15. In the shown embodiment, both autolock devices are configured identically with the exception that the lower autolock tool has larger ports 74′ of the sleeve 10 as compared to the ports 74 of the upper sleeve 10. Upper port means have smaller ports 8 than ports 18 of lower port means of the tube 4. For operation, steel ball 90 functioning as an actuating means is dropped into the drill string to thereby be engaged in the engagement means 11 of the upper downhole tool. This increases the fluid pressure above the arrangement 11, 90, thereby opening the above bypass valve so that ports 74, 8 are aligned and drilling fluid can be bypassed from through-flow passage 70 via ports 74, 8 into the surrounding annulus. For locking the upper bypass valve open, optional but advantageous locking ball 42 may be dropped into the drill string which will clamp between ports 8, 74. Subsequently, deactivating means in the form of two smaller (as compared to ball 90) balls 44 are dropped into the drill string and will close the ports 74. This will increase the pressure above arrangement 90, 11 thereby forcing activating ball 90 together with deactivating balls 44 in a downward direction. Locking ball 42 will move out of the drill string under the influence of one of the deactivating balls 44.

When arriving at the lower autolock tool of FIG. 17, activation ball 90 will be engaged by engagement means 11 of the lower downhole valve. Since the ports 74′, 18 are larger than the corresponding ports 74, 8, deactivating balls 44 may leave the apparatus 1700 towards the annulus or may remain on engagement means 11. Hence, the system is then in an operation mode in which the lower bypass valve is open due to the increased pressure resulting from the activating means 90 being engaged in the engagement means 11 of the lower downhole valve. This allows to bypass fluid via the fluid communication path 70, 74′, 18. In order to lock the lower bypass valve open, an optional locking ball 42′ having a larger dimension as compared to locking ball 42 is dropped into the bore hole which locks the path 18, 74′ open. Deactivating balls 44′ having a larger size as compared to deactivation balls 44 due to the larger size of the ports 74′ as compared to the ports 74 are then dropped into the drill string to close the ports 74′. At the end of the procedure, the deactivation ball 90 together with balls 44′ will move through the engagement means 11 of the lower bypass valve and will be collected by a ball catch assembly 24.

FIG. 18 shows an apparatus 1800 according to another exemplary embodiment of the invention. As in FIG. 17, also the apparatus 1800 comprises two engagement means 11, 11′ which however have a different diameter or size for engaging balls of different sizes. However, in FIG. 18 the ports 18, 74 of the lower downhole tool need not be larger than those of the upper one, although this may be preferred for LCM purposes.

The apparatus 1800 comprises a first frangible activation ball 92 designed as a hollow sphere which is configured so that it breaks upon exertion of a predefined mechanical load. Such a frangible hollow sphere can be manufactured from boro-silicate (Pyrex) to form a toughened glass. In a similar fashion as activation ball 90 in FIG. 17, the frangible activation ball 92 can be dropped into the drill string to be engaged by the engagement means 11 of the upper downhole tool. This will open, in accordance with the above description, the fluidic path 70, 74, 8 since the ports 74, 8 are then in alignment. Hence, bypassing of fluid is then possible via the fluidic path 70, 74, 8. Upon further increasing the pressure above the arrangement of engagement means 11 and frangible activation means 92, the frangible activation means 92 will break and small pieces thereof will move downwardly through engagement means 11 as well as through engagement means 11′ of the lower downhole valve. This will again close the upper valve without influencing the operation mode of the lower valve.

Subsequently, a second frangible activation ball 94 may be dropped into the drill string which has a size small enough to pass the engagement means 11 of the upper downhole tool without interaction. However, since the inner diameter of the engagement means 11′ of the lower downhole tool is smaller than that of the upper downhole tool 11, the second frangible activation means 92 will be engaged by the engagement means 11′ to thereby open the lower valve. Opening the lower valve in this respect means that the ports 74, 18 are brought in alignment with one another, since the increased pressure above the arrangement 11′, 94 is larger than the biasing force of the spring 80. A further increase of the pressure will then also break the frangible activation means 94 into pieces which are pumped away so as to again close the lower valve.

FIG. 19 shows an apparatus 1900 according to another exemplary embodiment of the invention. In this embodiment, two split-flow downhole tools are combined, each of which functioning in a similar way as described referring to the apparatus 1600.

In this embodiment, the second restriction device 38 is provided with a wire line 98 so that the second restriction device 38 can be pulled out of the bore hole after having closed the second through-flow passage 32.

The operation of the apparatus 1900 is as follows: The first restriction device 30 is dropped in the drill string and engages with the engagement means 11 of the upper downhole tool of FIG. 19. In the same way as described above referring to FIG. 16, this splits the flow into an axial component and a lateral bypass component. In order to again close the upper valve, the second restriction device 38 is dropped into the bore hole which engages the engagement portion 40 of the first restriction device 30. This closes the upper downhole valve by forcing the first restriction device 30 through the first engagement means 11 to travel downwards towards the engagement means 11 of the lower downhole valve of FIG. 19. Since the second restriction device 38 is connected to the wireline 98, it cannot travel downwards, but can be pulled upwards out of the bore hole.

The skilled person will understand that any desired ball or dart disclosed in any of the embodiments may also be equipped with a wireline so as to be retrievable from the bore hole. By taking such a measure, if desired or required, it may be prevented that a drop device used for operating the upper downhole tool could have an undesired impact on the lower downhole tool.

Coming back to FIG. 19, a similar split flow procedure as performed with the upper downhole valve can be repeated with the lower engagement means 11. Its through flow path can either also be closed again by the second restriction device 38 having the wireline 98 or alternatively by a third restriction device 38′ which does not necessarily need a wireline.

After use, the restriction devices 30, 38′ can be collected in a catch assembly 24.

FIG. 20 shows an apparatus 2000 according to still a further exemplary embodiment of the invention, in which three downhole valves are serially connected in a single drill string. In the shown embodiment, three autolock devices, as compared to two autolock devices shown in FIG. 17, are connected in series. Correspondingly, a third downhole valve has third port means 100, and third sleeve means 10 are also provided. The third sleeve means 10 are provided with ports 74″. A single activation ball 90 can be used for all three downhole valves, each having an engagement means 11 for engaging activation ball 90. However, the locking is performed with separate locking balls 42, 42′, 42″ of plastic material which can be locked between the respective sleeve 10 and ports 8, 18, 100. Deactivation means 44, 44′ and 44″, respectively, can be used as well. In the shown embodiment, the size of the locking means and deactivation means is the larger the lower the corresponding downhole valve is located.

FIG. 21 to FIG. 26 show cross-sectional drawings of a downhole circulation apparatus 2100 embodying the present invention showing a combination of a ball operated downhole tool 2102 above and a clutch mechanism downhole tool 2104 below.

In the tandem device shown in FIG. 21 to FIG. 26, the two downhole tools 2102, 2104 for bypassing drilling fluid are serially coupled, one of which (2104) being a clutch mechanism. There is a first biasing means 12 (such as a spring) biasing the clutch mechanism to the closed state and a separate second biasing means 12 (such as another spring) biasing the other downhole tool (2102) to the closed state.

FIG. 21 shows the complete tandem device having the ball-operated downhole tool 2102 on top (FIG. 22 and FIG. 23 show details) and clutch mechanism downhole tool 2104 (pressure-operated) below (FIG. 24 to FIG. 26 show details).

In addition to the explicitly described combinations of downhole tools, many other combinations of different downhole tools are possible, i.e. any desired combination of autolock tools and/or split-flow tools and/or frangible activation means tools and/or clutch mechanisms.

It will be appreciated by person skilled in the art that the above embodiment has been described by way of example only and not in any limitative sense, and that the various alternations and modifications are possible without departure from the scope of the invention as defined by the appended claims.

Claims

1. A downhole circulation apparatus arranged to be mounted in a drill string, the apparatus comprising:

at least one tubular body portion for mounting in a drill string, at least one said tubular body portion defining a first through-flow passage for receiving a flow of drilling fluid through the drill string;

first port means formed through at least one said tubular body portion;

a first sleeve slidably mounted inside at least one said tubular body portion, the first sleeve moveable between a closed position in which said first port means is closed by the first sleeve and an open position in which said first port means is open to allow drilling fluid in to circulate out of the apparatus;

first biasing means biasing the first sleeve into the closed position;

second port means formed through at least one said tubular body portion at a location below the first port means when the apparatus is in use;

a second sleeve slidably mounted inside at least one said tubular body portion, the second sleeve moveable between a closed position in which said second port means is closed by the second sleeve and an open position in which said second port means is open to allow drilling fluid to circulate out of the apparatus; and

second biasing means biasing the second sleeve into the closed position.

2. An apparatus according to claim 1, wherein at least one of the first sleeve and the second sleeve comprises a flow responsive portion responsive to a flow or a pressure of drilling fluid through the first through-flow passage to be thereby movable between the closed position and the open position depending on the flow of drilling fluid.

3. An apparatus according to claim 2, comprising a first clutch member secured to the at least one said tubular body portion and a second clutch member axially spaced from the first clutch member and secured to the at least one said tubular body portion, the respective sleeve being axially arranged between the first clutch member and the second clutch member and being movable between cooperative engagement with the first clutch member or the second clutch member, the cooperative engagement being controlled by an indexable latch mechanism.

4. An apparatus according to claim 1,

wherein at least one of the first sleeve and the second sleeve comprises engagement means configured for receiving a first restriction device;

wherein the apparatus comprises the first restriction device comprising a second through-flow passage and configured so that dropping the first restriction device into the apparatus causes the first restriction device to engage the engagement means to cause an increase in fluid pressure in the apparatus above the first restriction device which moves the respective sleeve from the closed to the open position;

wherein the apparatus comprises a second restriction device configured so that dropping the second restriction device into the apparatus causes the second restriction device to engage the first restriction device and block the second through-flow passage to cause a fluid pressure increase in the apparatus above the first and second restriction devices which moves the first and second restriction devices past the respective sleeve to cause the respective biasing means to move the respective sleeve back to the closed position.

5. An apparatus according to claim 4,

wherein the apparatus comprises deactivation means configured so that dropping the deactivation means into the apparatus closes the respective port means to cause a further fluid pressure increase in the apparatus above the first and second restriction devices which moves the first and second restriction devices and the deactivation means past the respective sleeve to cause the respective biasing means to move the respective sleeve back to the closed position.

6. An apparatus according to claim 4, wherein the second restriction device and/or the deactivation means is connected to a wireline.

7. An apparatus according to claim 1,

wherein at least one of the first sleeve and the second sleeve comprises engagement means configured for receiving activation means;

wherein the apparatus comprises the activation means configured so that dropping the activation means into the apparatus causes the activation means to engage the engagement means to cause an increase in fluid pressure in the apparatus above the activation means which moves the respective sleeve from the closed to the open position;

wherein the apparatus comprises deactivation means configured so that dropping the deactivation means into the apparatus closes the respective port means to cause a further fluid pressure increase in the apparatus above the activation means which moves the activation means and the deactivation means past the respective sleeve to cause the respective biasing means to move the respective sleeve back to the closed position.

8. An apparatus according to claim 7,

wherein the apparatus comprises locking means configured so that dropping the locking means into the apparatus locks the respective port means open until the deactivation means force the locking means to move out of the port means towards an exterior of the tubular body portion.

9. An apparatus according to claim 1,

wherein at least one of the first sleeve and the second sleeve comprises engagement means configured for receiving frangible activation means;

wherein the apparatus comprises the frangible activation means configured so that dropping the frangible activation means into the apparatus causes the frangible activation means to engage the engagement means to cause an increase in fluid pressure in the apparatus above the frangible activation means which moves the respective sleeve from the closed to the open position;

wherein the frangible activation means is configured so that a further fluid pressure increase in the apparatus above the frangible activation means breaks the frangible activation means which thereby moves through the engagement means to cause a decrease in fluid pressure in the apparatus above the engagement means which moves the respective sleeve from the closed to the open position.

10. An apparatus according to claim 1,

wherein one of the first sleeve and the second sleeve is configured according to claim 2, and the other one of the first sleeve and the second sleeve is configured according to claim 7;

wherein the flow responsive portion is dimensioned to be passable by the activation means.

11. An apparatus according to claim 1,

wherein one of the first sleeve and the second sleeve is configured according to claim 2, and the other one of the first sleeve and the second sleeve is configured according to claim 4;

wherein the flow responsive portion is dimensioned to be passable by the first restriction device.

12. An apparatus according to claim 1,

wherein the first sleeve and the second sleeve are both configured according to claim 7;

wherein one or more ports of the first port means have a smaller dimension than one or more ports of the second port means;

wherein the deactivation means for the first sleeve is dimensioned to pass through the second port means.

13. An apparatus according to claim 1,

wherein the first sleeve and the second sleeve are both configured according to claim 9;

wherein the frangible activation means for the second sleeve is dimensioned to pass through the engagement means of the first sleeve.

14. An apparatus according to claim 1,

wherein the first sleeve and the second sleeve are both configured according to claim 4;

wherein the first restriction device for the first sleeve is the first restriction device for the second sleeve.

15. An apparatus according to claim 1, wherein the apparatus comprises at least one restriction device configured so that

dropping the at least one restriction device into the apparatus causes the at least one restriction device to engage first engagement means of the first sleeve to cause an increase in fluid pressure in the apparatus above the at least one restriction device which moves the first sleeve from the closed to the open position; and

releasing the at least one restriction device from the first engagement means of the first sleeve moves the at least one restriction device down the apparatus to engage second engagement means of the second sleeve to cause a fluid pressure increase in the apparatus above the at least one restriction device to move the second sleeve from the closed to the open position.

16. An apparatus according to claim 1, wherein the apparatus comprises:

third port means formed through at least one said tubular body portion at a location below the second port means when the apparatus is in use;

a third sleeve slidably mounted inside at least one said tubular body portion, the third sleeve moveable between a closed position in which said third port means is closed by the third sleeve and an open position in which said third port means is open to allow drilling fluid to circulate out of the apparatus; and

third biasing means biasing the third sleeve into the closed position.

17. An apparatus according to claim 1, wherein the apparatus is arranged such that:

a) dropping a first restriction device comprising a second through-flow passage into the apparatus causes the first restriction device to engage first engagement means of said first sleeve to cause an increase in fluid pressure in the apparatus above the first restriction device which moves the first sleeve from the closed to the open position;

b) dropping a second restriction device into the apparatus after the first restriction device has been dropped causes the second restriction device to engage the first restriction device and block the second through-flow passage to cause a fluid pressure increase in the apparatus above the first and second restriction devices which moves the first and second restriction devices past the first sleeve to cause the first biasing means to move the first sleeve back to the closed position; and

c) wherein the first and second restriction devices move down the apparatus to engage second engagement means of said second sleeve to cause a fluid pressure increase in the apparatus above the first and second restriction devices to move the second sleeve from the closed to the open position.

18. An apparatus according to claim 17, wherein the second sleeve is moveable back to the closed position by said second biasing means in response to dropping deactivation means into the apparatus to block said second port means and cause a fluid pressure increase in the apparatus to move the first and second restriction devices past the second sleeve.

19. An apparatus according to claim 18, wherein the deactivation means comprises at least one deactivation ball.

20. An apparatus according to claim 1, further comprising a restriction device catcher located below said second sleeve when the apparatus is in use.

21. An apparatus according to claim 1, wherein said first port means comprises a plurality of first nozzles arranged to direct drilling fluid into a drilled borehole in a direction opposite to the direction of advancement of the apparatus.

22. An apparatus according to claim 21, wherein said plurality of first nozzles is formed from tungsten carbide.

23. An apparatus according to claim 6, wherein the second port means comprises a plurality of second nozzles, wherein each said second nozzle has a diameter greater than the diameter of each of said first nozzles.

24. An apparatus according to claim 17, wherein the first restriction device is arranged to allow approximately 70% of the fluid flow in the apparatus to pass through the second through-flow passage when engaged with the first engagement means, such that approximately 30% of the fluid flow in the apparatus is directed through said first port means.

25. An apparatus according to claim 1, wherein the apparatus is formed from an assembly of a plurality of drill string elements comprising:

a first tool element comprising a first tubular body portion, first port means formed through said first tubular body portion and a first sleeve slidably mounted inside said first tubular body portion;

a second tool element arranged below said first tool element when the apparatus is in use, the second tool element comprising a second tubular body portion, second port means formed through said second tubular body portion and a second sleeve slidably mounted inside said second tubular body portion; and

at least one drill pipe element disposed between and interconnecting said first tool element with said second tool element.

26. An apparatus according to claim 25, further comprising a plurality of drill pipe elements disposed between and interconnecting said first tool element with said second tool element.

27. An apparatus according to claim 17, wherein said first restriction device is a dart comprising:

a hollow body portion defining said second through-flow passage;

at least one deformable portion arranged to engage the first and second engagement means of the respective first and second sleeves; and

a ball seat disposed in the second through-flow passage, the ball seat arranged to receive a ball to block said second through-flow passage.

28. An apparatus according to claim 27, wherein said dart further comprises retention means disposed adjacent said ball seat, the retention means arranged to prevent a ball located in the ball seat from moving out of the ball seat in a first direction, but permit a ball located in the ball seat to move past the ball seat in a second direction.

29. An apparatus according to claim 28, wherein said retention means comprises a plurality of teeth disposed on the hollow body portion.

30. An apparatus according to claim 17, wherein said second restriction device comprises a ball.

31. (canceled)

32. A downhole circulation system arranged such that

a) dropping a first restriction device comprising a second through-flow passage into the apparatus causes the first restriction device to engage first engagement means of said first sleeve to cause an increase in fluid pressure in the apparatus above the first restriction device which moves the first sleeve from the closed to the open position,

b) dropping a second restriction device into the apparatus after the first restriction device has been dropped causes the second restriction device to engage the first restriction device and block the second through-flow passage to cause a fluid pressure increase in the apparatus above the first and second restriction devices which moves the first and second restriction devices past the first sleeve to cause the first biasing means to move the first sleeve back to the closed position, and

c) wherein the first and second restriction devices move down the apparatus to engage second engagement means of said second sleeve to cause a fluid pressure increase in the apparatus above the first and second restriction devices to move the second sleeve from the closed to the open position, the downhole circulation system, comprising:

a first restriction device comprising a second through-flow passage; and

a second restriction device adapted to engage said first restriction device and block the second through-flow passage.

33. (canceled)

34. A method of operating a downhole circulation apparatus having at least one tubular body portion for mounting in a drill string, the at least one said tubular body portion defining a first through-flow passage for receiving a flow of drilling fluid through the drill string, first port means formed through at least one said tubular body portion, a first sleeve slidably mounted inside at least one said tubular body portion, the first sleeve moveable between a closed position in which said first port means is closed by the first sleeve and an open position in which said first port means is open to allow drilling fluid to circulate out of the apparatus, first biasing means biasing the first sleeve into the closed position, second port means formed through at least one said tubular body portion at a location below the first port means when the apparatus is in use, a second sleeve slidably mounted inside at least one said tubular body portion, the second sleeve moveable between a closed position in which said second port means is closed by the second sleeve and an open position in which said second port means is open to allow drilling fluid to circulate out of the apparatus and second biasing means biasing the second sleeve into the closed position, the method comprising:

a) causing an increase in fluid pressure in the apparatus to move the first sleeve from the closed to the open position;

b) causing the first biasing means to move the first sleeve back to the closed position; and

c) causing a fluid pressure increase in the apparatus to move the second sleeve from the closed to the open position.

35. A method of claim 34, the method comprising:

a) dropping a first restriction device comprising a second through-flow passage into the apparatus to cause the first restriction device to engage first engagement means of said first sleeve and cause an increase in fluid pressure in the apparatus above the first restriction device to move the first sleeve from the closed to the open position;

b) dropping a second restriction device into the apparatus after the first restriction device has been dropped to cause the second restriction device to engage the first restriction device and block the second through-flow passage to cause a fluid pressure increase in the apparatus above the first and second restriction devices which moves the first and second restriction devices past the first sleeve and causes the first biasing means to move the first sleeve back to the closed position; and

c) wherein the first and second restriction devices move down the apparatus to engage second engagement means of said second sleeve to cause a fluid pressure increase in the apparatus above the first and second restriction devices to move the second sleeve from the closed to the open position.

36. A method according to claim 35, further comprising:

dropping at least one deactivation means into the apparatus to block said second port means and cause a fluid pressure increase in the apparatus to move the first and second restriction devices past the second sleeve and cause the second biasing means to move the second sleeve back to the closed position.

37. (canceled)