Apparatus for separating solids from liquids

Abstract

In a drilling operation, where used drilling fluid is screened into a substantially solid portion and a substantially liquid drilling fluid and the drilling fluid is thereafter stored in a storage tank. A method and apparatus for of separating solids from liquids. The apparatus comprises a recirculation tank having a second liquid for receiving the solid portion, and a first rotational particle separator for separating the solid portion from the second liquid. The apparatus further includes a pump for pumping the solid portion and the second liquid from the recirculation tank to the first rotational particle separator and a bin region to receive and retain the separated solids from the first rotational particle separator, wherein the separated second liquid is returned to the recirculation tank.

Description

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a method and apparatus for separating solids from liquids in general and in particular to a method and apparatus for separating solids from liquids in an oil well drilling operation.

2. Description of Related Art

Wells for recovering oil, gas and the like are typically created by drilling into an underground source using a hollow drill string supported by a drilling rig. The drill string includes a drill bit at the lower end that is rotated into the ground to create a well bore. As the drill bit is rotated, drilling fluid is pumped down through the interior of the drill string to pass through the bit and return to the surface in the well bore external to the drill string. The drilling fluid acts to lubricate the drill bit and carries the loose solids or cuttings created by the drill bit to the surface. At the surface, the used drilling fluid is collected and recycled by removing some or all of the cuttings. The composition of the cuttings content in the drilling fluid can be varied depending on the state of the drilling process and the location of the drill bit below the surface.

Presently, a mud storage tank to hold drilling fluid and a shale shaker to perform screening of larger cuttings tend to be standard equipment for a drilling rig. In normal well site operation, drilling fluid is circulated out of the borehole and passed over a shale shaker which is a screen to separate large solid particles from the drilling fluid. The shale shaker is generally positioned directly above the mud storage tank and the large particles are collected in a shale bin. The resulting collected large particles typically still have at least some drilling fluid on them after being deposited in the shale bin and are typically in the form of a slurry. A rotational particle separator such as for example a centrifuge or cyclonic separator is typically used to remove the smaller particles remaining in the drilling fluid in the storage tank.

Drilling fluids are typically either water based or oil based. Regulations in many countries require that when an oil based drilling fluid is used, the cuttings in the shale bin be hauled away for disposal or blended with sawdust and canola for land spreading. This is because the remaining drilling fluid on the cuttings discussed above would contaminate any site at which the cuttings were disposed unless the drilling fluid was removed beforehand. Blending of the cuttings prior to land spreading increases the cost to dispose of cuttings as compared to the cost of disposal of dry cuttings alone. In addition, the resulting wet cuttings composition is greater in volume and weight than dry cuttings alone. This increased weight and volume of the wet cuttings further increases transportation and disposal costs.

While the smaller particles in the drilling fluid are typically separated from the drilling fluid by a centrifuge, the larger particles removed by the shale shaker are not. The wet cuttings resulting from not centrifuging the larger particles results in the aforementioned problems with disposal of such wet cuttings. Previous attempts to pass all of the cuttings through a centrifuge have not been successful.

Heretofore, it has been impractical to pass all of the solid materials removed by the shale shaker through a centrifuge to further remove any drilling fluid from the solid material. The larger particles removed by the shale shaker would constitute too dry of a composition to properly pass through a centrifuge or cyclonic separator without plugging the same.

In addition, it has not been practical to pass all of the used drilling fluid through a centrifuge without first separating the drilling fluid from the larger particles with a shale shaker. Because of the relatively large volume of the mud storage tank, the velocity and agitation of the drilling fluid in this tank is relatively low. The lack of agitation of the mud storage tank allows the small and large particles to accumulate on the bottom of the tank. Because of the settling of the particles on the bottom of the tank, the larger particles would accumulate in the tank and thereby would not be removed quickly enough from the mud storage tank by the centrifuge. This allows for solids carry over between chambers of the mud storage tank and eventually allows for recirculation of the solids in the mud storage tank down the drill string which is undesirable.

What is desirable is a solid separation system that produces a drier solid product that does not require blending prior to disposal. Specifically, a method and apparatus that enables all of the solid material to be passed through a centrifuge or cyclonic separator so as to produce a drier solid is desirable.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus that enables all of the solid material in a drilling fluid to be passed through a centrifuge or cyclonic separator to remove all excess drilling fluid from the solid material. Specifically, the present invention permits the solid material removed from the drilling fluid by a shale shaker or screen to be passed through a centrifuge or cyclonic separator to further remove any drilling fluid from the solid material.

According to a first embodiment of the present invention, there is provided an apparatus for separating solids from liquids in a drilling operation. In the drilling operation, used drilling fluid is screened into a substantially solid portion and a substantially liquid drilling fluid whereby the drilling fluid is stored in a storage tank. The apparatus comprises a recirculation tank having a second liquid for receiving the solid portion, and a first rotational particle separator for separating the solid portion from the second liquid. The apparatus further includes a pump for pumping the solid portion and the second liquid from the recirculation tank to the first rotational particle separator and a bin region to receive and retain the separated solids from the first rotational particle separator, wherein the separated second liquid is returned to the recirculation tank.

The rotational particle separator may comprise a centrifuge. The rotational particle separator may comprise a cyclonic separator. The apparatus may be further mounted on a field transportable skid. The skid may include a raised platform for mounting the rotational particle separator. The apparatus may further comprise a second rotational particle separator for removing particles from the drilling fluid supplied from the storage tank wherein the particles are deposited in the bin region wherein the drilling fluid is returned to the storage tank.

The recirculation tank may include an angled bottom having a high end and a low end relative to each other. The pump may draw the solid portion and the second liquid proximate to the low end. The recirculation tank may further include a closable top. The second liquid may comprise drilling fluid. The apparatus may further include at least one tank for supplying a particle separation assisting agent to the input of the second rotational particle separator when said drilling fluid is a water based drilling fluid.

According to a further embodiment of the present invention, there is provided a method for separating solids from liquids in a drilling operation. In the drilling operation, used drilling fluid is screened into a substantially solid portion and a substantially liquid drilling fluid, wherein the drilling fluid is stored in a storage tank. The method comprises depositing the solid portion in a recirculation tank having a second liquid and drawing off the solid portion and the second liquid from the recirculation tank for delivery to a first rotational particle separator. The method further comprises separating the solid portion from the second liquid in a first rotational particle separator and collecting the separated solids in a bin region and deposing the second liquid back in the recirculation tank. The method may further include removing solid particles from a portion of the screened drilling fluid in a second rotational particle separator and returning the liquid portion to a collection tank, wherein the solids are deposited in a bin region.

Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

In drawings which illustrate embodiments of the invention,

FIG. 1 is a schematic view of a drilling system incorporating the drilling fluid cleaning system of the present invention.

FIG. 2 is a perspective view of a preferred embodiment of the drilling fluid cleaning system according to the present invention.

FIG. 3 is a top plan view of the drilling fluid cleaning system of FIG. 2.

FIG. 4 is cross sectional view of the recirculation tank of FIG. 2 taken along the line 4-4 of FIG. 3.

FIG. 5 is cross sectional view of the shale bin and two polymer tanks of FIG. 2 as taken along the line 5-5 of FIG. 3.

FIG. 6 is cross sectional view of the shale bin of FIG. 2 as taken along the line 6-6 of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, there is shown a schematic view of a well drilling system 10, which includes a drill rig 12, and a transportable drilling fluid cleaning system 40. The drilling rig includes a drill derrick 14 supporting a drill string 16, which is rotated to drill a well bore into the ground. A mud storage tank 20 is associated with the drilling rig and stores drilling fluid 18. The composition of the drilling fluid 18 can be adjusted depending on the stage to which the well bore is drilled. The apparatus of the present invention can be used to remove undesirable solids from the drilling mud and to recycle the drilling fluid to the tank 20 at a desired viscosity.

The drilling fluid is pumped in a conventional manner from the tank 20 through a conduit 22 into drill string 16. Drilling fluid 18 flows downwardly through the drill string to exit from the lower end of the string at bit 17. The drilling fluid 18 acts to lubricate the drill bit and collect cuttings created by the drilling action of the bit. The drilling fluid with additional solids flows upwardly in the well bore externally to the drill string to be collected near the surface. The collected drilling fluids/solids mixture passes through conduit 24 to be delivered to a shale shaker 26. Shale shaker is a vibrating screen positioned above the tank 20 that removes larger solids from the drilling fluid and delivers cleaned drilling fluid back to the tank 20. The larger solids are delivered to the apparatus for further removal of drilling fluid for collection. Drilling fluid from the tank 20 may also be pumped by conventional means to the cleaning system 40 for further removal of smaller particles via conduit 28 wherein cleaned drilling fluid is returned to the tank 20 via conduit 30.

FIG. 2 shows a side elevation view of a preferred embodiment of the drilling fluid cleaning system 40. The system includes a recirculation tank 50, a shale bin 70, a first centrifuge 92 and a pump house 100. The system may also include a second centrifuge 94 and a plurality of strip tanks and polymer tanks 102 and 104 respectively. The above components may be arranged on a platform, preferably in the form of a skid 42, to permit loading of the system onto a trailer towable by a truck for transport of all of the components as a unit in a single trip by roads between drilling sites. In the province of Alberta, Canada, where the inventors are based, skid 42 can be dimensioned to a maximum size of 63 feet long, 12.5 feet wide and 17.5 feet high in order to be transportable on roads and highways as a non-divisible load. A skid of this size requires a special permit for oil field hauling, however, a pilot vehicle to lead the truck is not required. Skids of different sizes may be permitted in other jurisdictions.

The centrifuges 92 and 94 may be located on a secondary platform 96 above the shale bin and recirculation tank. The secondary platform 96 may also be moveable between a stored position during transportation and an operating position. The secondary be located above the shale bin 70 and recirculation tank 50 by means of telescoping arms 98 wherein the telescoping arms facilitate movement between the stored and operating positions. It will be appreciated that other means of moving the secondary platform between the stored and operating positions, such as, for example, by means of supporting the secondary platform on rotatable arms, will also be acceptable.

FIG. 3 shows a plan view of the fluid cleaning system 40 with the centrifuges removed showing details primarily of recirculation tank 50, shale bin 70 and strip tanks and polymer tanks 102 and 104, respectively. The recirculation tank and shale bin are located at a first end 44 of the skid 42. The pump house 100 is located at a second end 46 of the skid 42 and includes various pumps and ancillary equipment for use in the fluid cleaning operation including pump 48. The strip tanks and polymer tanks 102 and 104, respectively, are located intermediate the pump house 100 and the shale bin 70 and recirculation tank 50.

In the preferred embodiment shown in FIG. 3, the recirculation tank 50 is located longitudinally along the skid 42 adjacent to the first end 44 of the skid. The shale bin 70 is located adjacent to the recirculation tank 50 and is substantially coterminous along the longitudinal length of the skid 42. The recirculation tank 50 comprises a substantially rectangular container region defined by first and second longitudinal walls 52 and 54 respectively, first and second end walls 56 and 58, respectively, and a bottom 60.

Turning now to FIG. 4, a cross sectional view of the recirculation tank is shown along the line 4-4 from FIG. 3. As shown in FIG. 4, the recirculation tank includes an opening 62 which may be connected to a conduit 47 as shown in FIG. 5. The conduit connected to the opening 62 may be further connected to a pump 48 of conventional means which serves to supply a flow of the solid particles and drilling fluid in the recirculation tank to the first centrifuge 92. In a preferred embodiment as shown in FIG. 4, the bottom 60 may be angled so as to direct any particles settling on the bottom to the opening 62 for pickup and processing by the centrifuges. The recirculation tank 50 may also include a cover 64 that is positionable over the recirculation tank as shown in FIG. 6. Cover 64 may be connected to the recirculation tank by a hinge or other suitable pivot 66 so that the cover may be opened to permit depositing of solid material in the recirculation bin or closed so as to aid in depositing of solid material directly into the shale bin 70. In a preferred emobidment as shown in FIG. 6, the cover 64 opens inwardly into the recirculation tank 50. The cover 64 may be retained in a closed position over the recirculation tank 50 by any suitable means, such as, for example, by a chain (not shown) suspended from the secondary platform 96 connected to the free end 67 of the cover 64 at an appropriate position to substantially cover the recirculation tank. It will be appreciated by those of skill in the art that other methods of retaining the cover in a closed position may also be applied to the present apparatus.

The recirculation tank 50 is sized such that the addition of solid particles and cleaned drilling fluid at the top and the removal of the same from the bottom produces a sufficient agitation as to prevent the settling of a large quantity of particles before being drawn into the opening 62. In practice, the applicant has found that a distance of approximately about 18 inches or less between the first and second longitudinal walls 52 and 54, respectively, is sufficient to prevent excessive settling of any solid particles in the recirculation tank with a distance of 12 inches being preferred.

Referring back to FIG. 1, drilling fluid pumped out of the recirculation tank 50 is directed to the first centrifuge 92 for further solids separation. The first centrifuge separates the solids from the drilling fluid/solid particles mixture and deposits the solid particles in the shale bin 70. The cleaned drilling fluid is then returned to the recirculation tank 50. Furthermore, in a preferred embodiment, the system also includes a second centrifuge for separating the solids from the drilling fluid in the mud storage tank 20 of the drilling rig. The solid/drilling fluid in the mud storage tank 20 is pumped by a conventional pump to the centrifuge. The centrifuge separates the solids from the liquids and deposits the solids in the shale bin 70. The cleaned drilling fluid is then returned to the mud storage tank 20.

Solids removed from the drilling fluid by centrifuges 92 and 94 as well as solids not requiring centrifuging are preferably stored in a shale bin 70 adjacent to the first end 44 of the skid 42. Bin 70 is defined by four walls and floor 80 at a region of the skid adjacent to the recirculation tank 50. The first and second walls 72 and 74 respectively of the bin 70 are transverse to the longitudinal length of the skid 42 while the third and fourth walls 76 and 78 are substantially parallel the longitudinal length of the skid. Preferably, as shown in FIGS. 5 and 6, the bottom of each of the walls of the bin 70 may be offset towards the center of the bin so as to angled the wall. Alternatively, the walls of the bin 70 may be substantially vertical or the fourth wall 78 may alternatively include a hinged bottom to facilitate access for removing solid particles from the bin 70.

In certain circumstances during drilling, for example when the drilling fluid is being changed from a water based drilling fluid to an oil based drilling fluid, it may be desirable to use a flocculating agent to promote the removal of solids from the drilling fluid. To address this need, the system of the present invention may include a flocculent source for adding a flocculating agent to the drilling fluid. Preferably, the flocculent source comprises at least one compartment for holding and mixing a flocculating agent and a delivery system to deliver flocculating agent to the centrifuges. Preferably, flocculating agent is added to the drilling fluid at the inlets of pumps supplying the centrifuges so the agent is mixed with the drilling fluid prior to centrifuging. Flocculating agents are conventional and may include a calcium water solution or a polymer based flocculating agent. According to a preferred embodiment, the fluid cleaning system 40 of the present invention includes two strip tanks 102 for holding a calcium water solution and two polymer tanks 104 for holding a polymer flocculating agent.

Operation

In use, the drilling fluid cleaning system 40 of the present invention is operated according to different schemes depending on the drilling stage.

During drilling of the “surface hole” (the first portion of the borehole), water based drilling fluid is commonly used to protect groundwater aquifers. During drilling of the surface hole, larger particles may be deposited directly into the shale bin 70 and the cover 64 of the recirculation tank positioned over the recirculation tank. The large particles may thereby slide over the cover 64 and into the shale bin 70. The second centrifuge 94 may also be used to remove smaller particles from the drilling fluid 18 from the mud storage tank 20 whereby the particles are deposited in the shale bin 70 and the cleaned drilling fluid returned to the mud storage tank 20.

During changeover of the drilling fluid from a water based drilling fluid to an oil based drilling fluid, the recirculation tank 50 may remain covered by cover 64. The drilling fluid 18 in the mud storage tank 20 may be pumped into the second centrifuge 94 to remove any particles in the drilling fluid. In addition, calcium water from the strip tanks 102 or a polymer flocculating agent from the polymer tanks 104 may be added to the inlet of the centrifuge 94 along with the drilling fluid to enhance the separation of the solid particles from the drilling fluid. Thereafter the solid particles may be deposited in the shale bin 70 while the drilling fluid is returned to one or more of the strip tank 102, polymer tank 104 or mud storage tank 20. When the water based drilling fluid is sufficiently cleaned of particles it may be disposed of in a sump on or off site.

During drilling with oil based drilling fluid, the cover 64 to the recirculation tank 50 may be positioned off of the recirculation tank and the larger particles from the shale shaker 26 may be deposited in the recirculation tank. As previously indicated, the recirculation tank 50 contains a second fluid, which may be a drilling fluid similar to the drilling fluid as is used to drill the well. The drilling fluid and solid particles are drawn out of the recirculation tank 50 at opening 62 and passed through the first centrifuge 92. The centrifuge removes the solids and deposit them into shale bin 70 and returns the drilling fluid to the recirculation tank 50. The second centrifuge 94 draws the drilling fluid 18 from the mud storage tank 20, removes the solids from the drilling fluid and returns the drilling fluid to the tank 20. The solids are thereafter deposited in the shale bin 70. The solids in the shale bin may thereafter be removed for land spreading or disposal by other means.

It will be appreciated that as the foregoing equipment is located on a field transportable skid, transportation to and from a drilling site is greatly simplified as compared to the transportation of various equipment separate from each other. In addition, the close proximity of all of the equipment set out above will greatly facilitate the switch over between different types of drilling fluid as well as switching over from removing solids from the drilling fluid to removing the water based drilling fluid from the drilling system.

While specific embodiments of the invention have been described and illustrated, such embodiments should be considered illustrative of the invention only and not as limiting the invention as construed in accordance with the accompanying claims.

Claims

1. An apparatus for separating solids from liquids in a drilling operation wherein used drilling fluid is screened into a substantially solid portion and a substantially liquid drilling fluid, the drilling fluid being stored in a storage tank, the apparatus comprising:

a recirculation tank having a second liquid for receiving said solid portion;

a first rotational particle separator for separating said solid portion from said second liquid;

a pump for pumping said solid portion and said second liquid from said recirculation tank to said first rotational particle separator; and

a bin region to receive and retain said separated solids from said first rotational particle separator,

wherein said separated second liquid is returned to said recirculation tank.

2. The apparatus of claim 1 wherein said rotational particle separator comprises a centrifuge.

3. The apparatus of claim 1 wherein said rotational particle separator comprises a cyclonic separator.

4. The apparatus of claim 1 wherein said apparatus is mounted on a field transportable skid.

5. The apparatus of claim 4 wherein said skid includes a raised platform for mounting said rotational particle separator.

6. The apparatus of claim 1 further comprising a second rotational particle separator for removing particles from the drilling fluid supplied from the storage tank, said particles being deposited in said bin region wherein said drilling fluid is returned to the storage tank.

7. The apparatus of claim 1 wherein said recirculation tank includes an angled bottom having a high end and a low end relative to each other.

8. The apparatus of claim 7 wherein said pump draws said solid portion and said second liquid proximate to said low end.

9. The apparatus of claim 8 wherein said recirculation tank includes a closable top

10. The apparatus of claim 9 wherein when said drilling fluid is a water based drilling fluid, said top may be closed such that said solid portion slide across said top to be deposited into said bin and when said drilling fluid is an oil based drilling fluid, said top may be opened such that said solid portion is deposited in said recirculation tank.

11. The apparatus of claim 1 wherein said second liquid is drilling fluid.

12. The apparatus of claim 1 further comprising at least one tank for supplying a particle separation assisting agent to the input of said second rotational particle separator when said drilling fluid is a water based drilling fluid.

13. The apparatus of claim 12 wherein said particle separation assisting agent is a calcium water solution.

14. The apparatus of claim 13 wherein said calcium water solution is stored in a stripping tank.

15. The apparatus of claim 14 wherein said apparatus includes two stripping tanks.

16. The apparatus of claim 12 wherein said particle separation assisting agent is a polymer flocculating agent.

17. The apparatus of claim 16 wherein said flocculating agent is stored in at least one polymer tank.

18. The apparatus of claim 17 wherein said apparatus includes two polymer tanks.

19. A method for separating solids from liquids in a drilling operation wherein used drilling fluid is screened into a substantially solid portion and a substantially liquid drilling fluid, the drilling fluid being stored in a storage tank, the method comprising:

depositing said solid portion in a recirculation tank having a second liquid;

drawing off said solid portion and said second liquid from said recirculation tank for delivery to a first rotational particle separator;

separating said solid portion from said second liquid in a first rotational particle separator; and

collecting said separated solids in a bin region and deposing said second liquid back in said recirculation tank.

20. The method of claim 19 further comprising removing solid particles from a portion of screened drilling fluid in a second rotational particle separator and returning the liquid portion to a collection tank, wherein said solids are deposited in said bin region.