Drill Cuttings Transfer System and Related Methods

Abstract

A system for handling drill cuttings conveys cuttings into bulk tanks via a conduit. The bulk tanks have a lower portion that converges to an elongated opening. A conveyance member positioned at the elongated opening forces the cuttings out of a discharge port at the bottom of the bulk tank. Once suitable conveyance member is a screw-type conveyor coupled to a motor that applies a motive force to the cuttings. The bulk tank lower portion can be formed as a wedge or trough that generally conforms to the configuration of the conveyance member. The bulk tanks hold the cuttings until it can be discharged via the discharge port to a transport vessel for processing or disposal. For offshore operations, the system includes a separation unit on the rig that forms the cuttings from fluid returning from the wellbore and a cuttings flow unit that conveys the cuttings from the separation unit to the bulk tanks.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application takes priority from U.S. Provisional Patent Application Ser. No. 60/789,395, filed Apr. 5, 2006.

BACKGROUND OF THE DISCLOSURE

1. Field of the Disclosure

This disclosure relates generally to handling of waste materials, especially particulate drill solids.

2. Description of the Related Art

In the drilling of oil and gas wells, drilling fluids or “muds” are used to provide well bore lubrication, to cool the drill bit, to protect against corrosion and to provide a pressure head to maintain formation integrity. There are two main types of drilling muds: water-based and oil-based. Generally, surface pumps circulate drilling mud down the tubular drill string. The mud exits at the drill bit and flows up the annulus between the drill string and the bore. The returning fluid (or return fluid) carries the drill cuttings away from the bit and out of the wellbore. Oil-based drilling muds are stable oil external-water internal emulsions including wetting agents to hold solids such as drill cuttings in the oil phase. The drill cuttings thus tend to become oil wet, trapping large quantities of oil-based mud in their intergranular spaces and creating environmental concerns regarding disposal of the oil-contaminated drill cuttings.

In the prior art, drill cuttings contaminated with oil-based drilling muds were often collected in settling tanks where re-usable drilling mud was drawn off the top of the tank and contaminated drill cuttings, as bottoms, were transported to appropriate disposal sites. Such storage and transportation operations are costly and environmentally undesirable especially in offshore drilling operations. Typically, oil-contaminated cuttings contain about fifty percent (50%) by volume of oil-based liquid. The value of this large volume of entrained oily liquids is considerable, and there is a strong incentive to recover the oil-based drilling mud both for economic as well as environmental reasons.

Accordingly, the cuttings are commonly separated from the drilling fluid by devices such as shale shakers, which remove cuttings and large solids from the drilling fluid during the circulation thereof. Basically, such a device has a sloping, close mesh screen over which fluid returning from the hole being drilled passes. The solids captured on the screen travel down the sloping surface to be collected in the shaker ditch or cuttings trough. It is also desirable to recover as much of the expensive drilling fluids as possible. Therefore, other devices, which play a role in the separation of solids from drilling fluids, include cyclone separators and centrifuges. The cuttings discharged from the shakers, cyclones and centrifuges that are collected in the shaker ditch or cuttings trough are still highly contaminated with the drilling fluids and therefore form a slurry or heavy sludge. Typically the slurry is conveyed into containers or skips, which are then periodically moved by crane from the rig onto a vessel.

This process is disadvantageous for a number of reasons. First, the skips take up considerable valuable space on the rig floor. Moreover, the handling of the skips requires the use of the rig crane, which may divert the crane from other important duties. One prior art device uses a pneumatic conveyance arrangement to convey materials out of a bulk tank that has a conical hopper section. It is believed that one drawback of such an arrangement is that using pressurized air as a sole means for discharging cuttings may not adequately evacuate the bulk tank of cuttings. It is believed that another drawback is that the circular opening of the conical hopper section could get plugged with cuttings.

The present disclosure addresses these and other drawbacks of the prior art.

SUMMARY OF THE DISCLOSURE

In aspects, the present disclosure provides efficient systems and methods for processing, storing and transporting drill cuttings that are generated while drilling hydrocarbon-producing wellbores. These cuttings as noted earlier are entrained in a drilling fluid returning from the wellbore (return fluid). After the return fluid is separated to form a slurry of cuttings, the cuttings are conveyed into one or more bulk tanks via conduits such as hoses, pipes or tubing. The bulk tank has a lower portion that converges to an elongated opening at which a cuttings conveyance member is positioned. To discharge cuttings, the cuttings conveyance member, when energized, applies a motive force that causes the cuttings to flow out of a bulk tank discharge port to a transfer line. As the cuttings flow out of the bottom of the tank, gravity pulls more cuttings into the cuttings conveyance member. The cuttings conveyance member may be operated in a first mode to flow cuttings and a second mode to mix cuttings. One suitable cuttings conveyance member includes a rotating screw-type conveyor or auger coupled to a motor.

In one embodiment, the lower portion of the bulk tank has a wedge or trough shape that feeds cuttings to the cuttings conveyance member. In contrast to a conical shaped lower portion that is defined by a single inclined wall that converges to a circular exit opening, the wedge shaped lower portion is defined by at least two walls that converge to an elongated slot-like exit opening. Advantageously, due to its relatively large size, the elongated slot-like exit opening is less susceptible to plugging during discharge operations. Additionally, the elongated slot-like exit opening can be configured to conform with a horizontally aligned cuttings conveyance member such that cuttings are evenly fed into the cuttings conveyance member.

To further assist the discharge of cuttings out of the bulk tank, pressurized air can be fed into one or more locations in the bulk tank. One function for this pressurized air is to balance the pressure between the bulk tank and devices connected to the bulk tank. In some arrangements, the cuttings conveyance member feeds cuttings into a transfer line in communication with a pneumatic flow device. The pneumatic flow device uses high pressure air to propel cuttings along the transfer line. To prevent back flow of cuttings into the tank, it may be desirable to balance the pressure inside the tank with the pressure at the pneumatic flow device. Thus, in one aspect, pressurized air is fed into the bulk tank at a pressure value that compensates for increased pressures generated by the pneumatic flow device. In another aspect, pressurized air can be used to fluidize the cuttings in the bulk tank. For example, when the cuttings have been kept in the bulk tank for an extended time, the weight of the cuttings can force liquids to flow out of the cuttings at the bottom of the tank. Thus, a form of stratification occurs wherein a relatively dense cuttings layer forms along the interior surfaces of the lower portion of the bulk tank. This dense cuttings layer can slow or even choke off the flow of cuttings out of the bulk tank. To break up or reduce the viscosity of this relatively dense cuttings layer, pressurized gas such as air can be introduced at one or more points near the lower portion of the bulk tank. The inflowing gas penetrates this relatively dense cuttings layer and reduces its density and/or physically displaces this layer. In one arrangement, a first pressurized gas line at a top of the tank pressure balances the tank and a second pressurized gas line fluidizes the relatively dense cuttings layer. In another arrangement, the pressurized gas line for fluidizing the relatively dense cuttings layer provides gas at a pressure value that also pressure balances the bulk tank.

In one arrangement suited for offshore operations, the system includes a separation unit on the rig that forms the slurry of cuttings. The separation unit can include one or more shakers, centrifuge-type separators and/or other suitable devices. A cuttings flow unit conveys the cuttings from the separation unit to the bulk tanks or other selected location. The cuttings flow unit can include, for example, an auger type conveyor and pump or blower device to flow the cuttings and one or more diverter valves that can direct the cuttings flow as needed. In one arrangement, a controller controls the flow of cuttings into the plurality of bulk tanks. Sensors positioned on each of the bulk tanks produce signals indicative of the volume of cuttings in an associated bulk tank. The controller controls the flow of cuttings in response to the sensor signals. The bulk tanks can be filled simultaneously, sequentially or by any other scheme. The bulk tanks can hold the cuttings until it can be discharged to a transport vessel or vehicle for processing and/or disposal. The transport vessel or vehicle can have a bank of containers adapted to receive the cuttings from the bulk tanks.

Examples of the more important features of the disclosure have been summarized (albeit rather broadly) in order that the detailed description thereof that follows may be better understood and in order that the contributions they represent to the art may be appreciated. There are, of course, additional features of the disclosure that will be described hereinafter and which will form the subject of the claims appended hereto.

BRIEF DESCRIPTION OF THE FIGURES

For detailed understanding of the present disclosure, reference should be made to the following detailed description of the preferred embodiment, taken in conjunction with the accompanying drawing:

FIG. 1 schematically illustrates a system for processing, storing and offloading drill cuttings made in accordance with one embodiment of the present disclosure;

FIG. 2A schematically illustrates a side view of a bulk tank in accordance with one embodiment of the present disclosure;

FIG. 2b schematically illustrates an end view of a bulk tank in accordance with one embodiment of the present disclosure;

FIG. 3 schematically illustrates an wedge shaped lower section of a bulk tank made in accordance with one embodiment of the present disclosure;

FIG. 4 schematically illustrates a bulk tank and pressurized air supply system in accordance with one embodiment of the present disclosure; and

FIG. 5 schematically illustrates a bulk tank in accordance with one embodiment of the present disclosure used in an offshore drilling environment.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure relates to devices and methods for processing, storing and transporting a slurry of drill cuttings. The present disclosure is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the present disclosure with the understanding that the present disclosure is to be considered an exemplification of the principles of the disclosure, and is not intended to limit the disclosure to that illustrated and described herein. Further, none of the described elements or combination of elements should be considered essential features of the present teachings unless the description expressly describes the element or combination of elements as essential.

As shown in FIG. 1, in one embodiment particularly suited for use on an offshore drilling rig, a cuttings handling system 10 may include a separation unit 12, cuttings flow units 14, 15, and one or more bulk tanks 16. The system offloads the cuttings to one or more suitable containers 18 on a transport vessel (not shown). In one mode of operation, the system receives return fluid, which has entrained cuttings, from a wellbore being drilled. The separations unit 12 separates some of the drilling fluid from the return fluid for re-use in further drilling and also forms a slurry of cuttings. The cuttings flow unit 14 conveys the cuttings via a conduit 20 to the bank of bulk tanks 16. After the bulk tanks 16 are filled with cuttings, a mechanically driven and gravity assisted conveyance member discharges the cuttings from the bulk tanks 16. The cuttings flow unit 15 propels the discharged cuttings via a transfer line 22 to the container(s) 18 or bulk tanks of the transport vessel (not shown). Thus, in contrast to conventional cuttings handling arrangements, less human intervention is needed to collect, store and move drill cuttings on a rig. The elements making up the FIG. 1 embodiment are discussed in further detail below.

The separations unit 12 extracts the relatively expensive drilling fluid from the return fluid. In one arrangement, the separations unit 12 can include one or more shale shakers 21. Within the shale shaker 21, the return fluid and entrained solids are discharged over a vibratory separator that has one or a series of tiered screens. The screens catch and remove solids from the return fluid flowing therethrough. The separations unit 12 can also include other separation devices, such as a centrifugal separator 22, that are also configured to extract drilling fluid from the cuttings. Such separation devices and techniques are known in the art and will not be discussed in further detail. The effluent or output of the separations unit 12 is a relatively viscous slurry made up of oil or additive-covered rock, earth and debris. The terms cuttings and slurry will be used interchangeably.

The cuttings flow unit 14 transports the cuttings from the separations unit 12 to other devices such as the bulk tanks 16 or another location such as the vessel storage tanks 18. In one embodiment, the cuttings flow unit 14 includes an auger-type device that continually conveys the cuttings to a dense phase blower 24 that impels the cuttings through a conduit 20 such as piping or hoses. Suitable valves such as a diverter valve can be used in the conduit 20 to selectively direct flow of the cuttings.

Referring now to FIGS. 1 and 2A-B, the bulk tanks 16 receive and store the flow of cuttings from the conduit 20. The tanks 16 have an upper cylindrical portion 26 and a lower portion 28 that converges to an elongated opening 29. In a manner described in further detail below, the lower portion 28 promotes mass flow of cuttings through the tank 16. Positioned at a bottom end of the lower portion 28 is a conveyance member 32 that applies a motive force that impels the cuttings out of the bulk tanks 16. Pressurized gas, such as air, from a source 34 is fed into one or more locations in the bulk tank 16 to maintain a pressure balance in the system 10 and/or to fluidize the cuttings in the bulk tank 16.

The filling of the bulk tanks 16 can be controlled manually, automatically or a combination thereof. In one arrangement, a controller 35 receives signals from sensors 36 positioned on the bulk tanks 16. The sensor signals indicate the amount of cuttings in the bulk tanks 16. Thus, in one arrangement, a controller 35 can have a programmable logic circuit (PLC) that directs flow into a bulk tank 16 until the associated sensor 36 indicates that the bulk tank 16 is full. Thereafter, the PLC stops flow to the bulk tank 16 by actuating appropriate valves and initiates flow into the next bulk tank 16. This process can continue until all of the bulk tanks 16 are filled. While a sequential filling process has been described, it should be appreciated that two or more bulk tanks 16 can be filled at the same time. While in some embodiments, the tank can be constructed to hold 100 BBL of drill cuttings having a specific gravity of 2.34, other sizes and configurations can also be used.

As explained earlier, the slurry of cuttings can be relatively viscous and not flow effectively under the effect of only gravity. Therefore, the conveyance member 32 forcibly impels the cuttings out of the bulk tanks 16. In one embodiment, the conveyance member 32 is a rotating screw conveyor driven by a motor drive 33. A screw flight portion extends horizontally along a long axis of the wedge shaped portion 28. Rotation of the screw propels the cuttings to the transfer line 22 and the cuttings flow unit 15. In some arrangements, the conveyance member 32 is right and left hand reversible. In the right hand rotation mode, the cuttings flow downward to a port 36. In the left hand rotation mode, the cuttings are mixed to maintain material consistency. This is advantageous when the cuttings are stored for long periods of time, since heavier material will settle to the tank bottom and lighter fluids will flow to the top. This stratification of materials can make it difficult to empty the tank of the cuttings. In such circumstances, the left hand rotation will mix the cuttings and enable the cuttings to flow out of the tank. In still other embodiments, two or more conveyance members can cooperate to expel the cuttings out of the bulk tank 16. A screw or auger is merely one illustrative member suitable for applying a motive force throughout the body of the cuttings. It should be appreciated that the conveyance member 32 positioned within the bulk tank is susceptible to numerous variations that can adequately apply a motive force to expel the cuttings out of the bulk tank 16. For example, suitable conveyance mechanisms include pneumatic systems, progressive cavity pumps, and vacuum pumping systems.

Referring now to FIGS. 2A-B and 3, the lower portion 28 cooperates with the conveyance member 32 to discharge flow out of the tank 16. In one embodiment, the lower portion 28 has a wedge, chisel or trough shape that is generally defined by two sets of walls 40 and 42. For convenience, such a shape will be referred to as a wedge shape. Each set of walls 40 and 42 has an associated angle 46 and 48 from horizontal, respectively. The angles 46 and 48 are selected such that the first drill cuttings that enter into the tank are the first drill cuttings to exit the tank, i.e., mass flow. The walls 40 and 42 converge to the opening 29 that is longitudinally aligned with the conveyance member 32. As should be appreciated, in contrast to a conical shaped section that converges to a circular opening, the opening 29 presents a relatively large elongated slot-like cross-sectional flow area through which the cuttings can flow. Thus, there is a reduced risk that cuttings can occlude or plug the opening 29. Furthermore, it should also be appreciated that the wedge shaped portion 28 and elongated opening 29 can evenly distribute cuttings across a relatively large portion of the conveyance member 32. Other elongated or non-conical shapes can also be used in certain applications.

In an exemplary operating mode for discharging cuttings, gravity pulls the cuttings into the conveyance member 32, which then conveys the cuttings out of the tank 16. As the cuttings exit the tank 16, additional cuttings fall into the conveyance member 32. Advantageously, the wedge shaped portion 28 cause a mass flow of cuttings that substantially uniformly loads the conveyance member 32 during this process. Thus, in one aspect, the system 10 discharges cuttings out of the tank 16 using a mechanically driven and gravity assisted arrangement.

To support the cutting discharge operation, there is shown in FIG. 4 a source 60 that provides pressurized gas such as air for pressure balancing the tank 16 and/or fluidizing the cuttings in the tank 16. In one embodiment, ports 62a and 62b that are coupled to the source 60 via suitable conduits 64 introduce pressurized gas at one or more points along the bulk tank 16. One or more of the ports 62a can be positioned to break up or reduce the viscosity of settled cuttings that layer the interior surfaces of the lower wedge shaped portion 28. The gas flowing through such ports 62a penetrates this relatively dense cuttings layer and reduces its overall density. That is, the gas intermixes with or “fluffs” the cuttings layer. The inflowing gas can also physically displace or dislodge portions of this layer from the interior surfaces of the tank 16. One or more ports 62b can also be positioned at or near a top of the tank 16 to provide pressure balancing gas. In the FIG. 4 embodiment, the source 60 operates as the cuttings flow unit 15 (FIG. 1) by supplying high pressure gas to propel cuttings through the transfer line 22. For example, the source 60 can supply a continuous flow of high pressure air into the transfer line 22 at the same time the conveyance member 32 (FIG. 2A) feeds cuttings into the transfer line 22. Because the source 60 and the bulk tanks 16 are in fluid communication via the transfer line 22, the high pressure gas in the transfer line 22 can apply a back pressure at the tank 16. This applied back pressure can restrict the flow of cuttings out of the tank 16. To compensate for the operating pressure generated by the source 60, pressurized gas fed through the ports 62b increases the pressure in the tank 16 to at least partially offset this applied back pressure. Of course, in certain embodiments, the pressurized gas flowing through ports 62a can both fluidize the relatively dense cuttings layer and provide gas at a pressure value that also pressure balances the bulk tank.

A number of instruments and device can be utilized to control the flow of pressurized gas. For example, valves 70 for selectively feeding gas into the ports 62a and 62b can be controlled by solenoid controls 72. A solenoid 64 control unit can also be used to control a valve 74 feeding pressurized air into the transfer line 22. Additionally, suitable gauges 76 such as pressure gauges and level gages can be positioned as desired on the tank 16. In many applications, the pressurized gas can be air, but other gases such as nitrogen can be used.

Referring now to FIG. 5, there is shown an embodiment of the present disclosure that is suited for offshore drilling applications. As is known, platform, floater, jack up or work over drilling operations utilize a surface facility such as an offshore rig 70 from which a drilling riser 72 or other device conveys a drill string 74 into a subsurface well (not shown). Positioned on the offshore rig 70 is cuttings handling system 71 that processes the return fluid from the subsurface wellbore (not shown) using equipment previously discussed and conveys the cuttings to a bank of bulk tanks 76. During drilling, the return fluid is processed and the cuttings continuously conveyed and stored in the bulk tanks 76. A controller fills the bulk tanks 76 using preprogrammed instructions and signals from suitably positioned sensors. Periodically, a transport vessel 78 such as a barge is moored adjacent to the rig 70 and storage tanks 80 in the barge 78 are connected to the cuttings handling system 71. Thereafter, high pressure gas is fed into the bulk tanks 76 to fluidize the cuttings and balance the pressure in the bulk tanks 76. Once the conveyance device 32 (FIG. 2A) is energized, cuttings flow out of the bulk tanks 76 and to the barge 78.

It should be appreciated that the cuttings handling systems described above offer enhanced safety due to the reduced number of handling operations such as interventions by personnel to hook up containers to the crane, manual shoveling of cuttings into containers, transfers of containers around the rig floor, use of the crane rig, etc. Furthermore, the transport vessel to which the cuttings is offloaded is only temporarily moored adjacent the rig. A continuously moored transport vessel could pose a hazard to the rig and itself during rough seas. Thus, reducing the time the transport vessel is moored to the rig also reduces the risk that inclement weather will interfere with drilling operations.

While the foregoing disclosure is directed to the preferred embodiments of the disclosure, various modifications will be apparent to those skilled in the art. It is intended that all variations within the scope of the appended claims be embraced by the foregoing disclosure.

Claims

1. A system for handling a return fluid formed of drilling fluid and entrained cuttings recovered while drilling a wellbore in an earthen formation, comprising:

(a) a separation unit at least partially separating the drilling fluid from the return fluid, a slurry of cuttings thereby being formed;

(b) a cuttings flow unit receiving the cuttings from the separation unit, the cutting flow unit conveying the cuttings through a conduit coupled thereto;

(c) at least one tank coupled to the conduit, the tank having a lower portion converging to an elongated opening; and

(d) a conveyance member positioned adjacent to the elongated opening receiving the cuttings from the lower portion and flowing the cuttings out of the at least one bulk tank.

2. The system of claim 1, further comprising a flow device receiving the flow of cuttings from the conveyance member and conveying the cuttings to a selected location.

3. The system of claim 2, further comprising a gas source providing a pressurized gas to the at least one tank to at least partially offset a pressure increase associated with operation of the cuttings flow device.

4. The system of claim 1, further comprising a gas source providing a gas to the at least one tank to fluidize at least a portion of the cuttings in the at least one tank.

5. The system of claim 1, wherein the lower portion is wedge shaped and wherein the conveyance member includes an auger longitudinally aligned with the elongated opening.

6. The system of claim 1, wherein the at least one tank includes a cylindrical upper portion, the cuttings flowing from the upper portion to the lower portion.

7. The system of claim 1 wherein the conveyance member operates in a first mode to flow the cuttings and a second mode to mix the cuttings.

8. A method for handling a return fluid formed of drilling fluid and entrained cuttings recovered while drilling a wellbore in an earthen formation, comprising:

(a) separating the drilling fluid from the return fluid to form a slurry of cuttings with a separation unit;

(b) conveying the cuttings through a conduit coupled to the separation unit using a cuttings flow unit;

(c) receiving the cuttings into at least one tank coupled to the conduit, the bulk tank having a lower portion converging to an elongated opening; and

(d) flowing the cuttings out of the at least one tank using a conveyance member positioned adjacent to the elongated opening.

9. The method of claim 8, further comprising conveying the cuttings to a selected location using a flow device that receives the flow of cuttings from the conveyance member.

10. The method of claim 9, further at least partially offsetting a pressure increase associated with operation of the flow device using a gas source that provides a pressurized gas to the at least one tank.

11. The method of claim 8, further comprising fluidizing at least a portion of the cuttings in the at least one tank using a gas source that provides a gas to the at least one tank.

12. The method of claim 8, wherein the lower portion is wedge shaped and wherein the conveyance member includes an auger longitudinally aligned with the elongated opening.

13. The method of claim 8, wherein the at least one tank includes a cylindrical upper portion, the cuttings flowing from the cylindrical upper portion to the lower portion.

14. The method of claim 8 further comprising operating the conveyance member in a first mode to flow the cuttings and a second mode to mix the cuttings.

15. A system for handling cuttings separated from a return fluid formed of drilling fluid and entrained cuttings, comprising:

(a) a tank for receiving the cuttings, the tank having a cylindrical upper portion and a wedge shaped lower portion converging to an elongated opening; and

(b) a conveyance member positioned adjacent to the elongated opening receiving the cuttings from the wedge shaped lower portion and flowing the cuttings out of the tank.

16. The system of claim 15, further comprising a flow device receiving the flow of cuttings from the conveyance member and conveying the cuttings to a selected location.

17. The system of claim 16, further comprising a gas source providing a pressurized gas to the tank to at least partially offset a pressure increase associated with operation of the cuttings flow device.

18. The system of claim 15, further comprising a gas source providing a gas to the tank to fluidize at least a portion of the cuttings in the tank.

19. The system of claim 15 wherein the conveyance member operates in a first mode to flow the cuttings and a second mode to mix the cuttings.

20. The system of claim 15 wherein the lower portion is defined by a first set of walls and a second set of walls, each of the walls of the first and second set of walls having an angle selected to cause mass flow of the cuttings.