CA2277657A1 - Apparatus and method for treating drill cuttings - Google Patents

Abstract

An apparatus and method for treating drill cuttings is taught. The drill cuttings are compressed under high pressures to remove most of the residual drilling fluid therefrom. The drilling fluid removed from the drill cuttings can be recycled to the drilling operation while the drill cuttings can be disposed of without environmental risk.

Description

APPARATUS AND METHOD FOR TREATING DRILL CUTTINGS
FIELD OF THE INVENTION
The present invention is directed to an apparatus and a method for processing drill cuttings from a wellbore drilling operation and, in particular, to an apparatus and method for processing the drill cuttings collected from the drilling fluid returning from the wellbore.
BACKGROUND OF THE INVENTION
In the process of drilling a wellbore, for example in the petroleum industry, a drill bit is used to form the wellbore. During operation of the drill bit, drilling fluid is circulated through the drill string, past the drill bit and back up the wellbore to surface. The drilling fluid carries with it formation drill cuttings created by the progressing drill bit.
The preferred type of drilling fluid in terms of hole stability and rate of drilling is an oil-based liquid including oil, for example diesel oil, and additives such as, for example, polymers and viscosifyers. The drilling fluid is very expensive. In addition, the fluid is considered to represent an environmental risk and, therefore, can only be disposed of in a controlled. Because of the costs of the fluid and their environmental risk, it is desirable to recycle the drilling fluid whenever possible.
At surface, therefore, the drilling fluid is processed to remove contaminants, such as the drill cuttings, so that it can be recycled. These drill cuttings are removed by use of sieve devices commonly called "shale shakers". In these devices, the drilling fluid is applied to a sieve screen which retains the drill cuttings which are too large to pass through the sieve and permits the drilling fluid to pass. The drilling fluid can then be passed through more processors such as centrifuges for removal of fine drill cuttings which are capable of passing through the shale shakers.

The drill cuttings which are removed from the drilling fluid include a mixture of materials ranging from gravel-sized rocks to rock fines. The drill cuttings retain a large amount of drilling fluid between the rock particles and, accordingly, the drill cuttings which are recovered are in the form of a slurry containing cuttings and drilling fluid.
In some instances, the slurry can contain more than 20%, by volume, drilling fluid. As a result, the slurry also represents an environmental risk and must be contained and handled according to regulations.
The handling of the slurry, which is a waste product of wellbore drilling, previously included mixing the slurry with an absorptive material such as, for example, sawdust, hauling the mixture to a landfarm and treating the mixture there for more than a year in order to bring it to a level of less than 2.0% drilling fluid by volume so that it can be returned to the environment, for example, by spreading on a field. Costs for the containment, shipping and treatment of the slurry are very high and represent a large portion of the costs of wellbore formation. These costs are increased greatly where the drilling operation is offshore.
Because of the need for addition of the absorptive material to the slurry, the end volumes of contaminated material which must be landfarmed is increased. In addition, much expensive drilling fluid is lost.
A method and apparatus are needed for effectively and safely processing the drill cuttings separated from a drilling fluid stream to facilitate handling thereof.
SUMMARY OF THE INVENTION
An apparatus and method have been invented for processing the drill cuttings from drilling fluid. The apparatus and method according to the present invention remove at least a portion of the drilling fluid from the interstices of the cuttings so that the processed drill cuttings create less or, essentially, no environmental risk and can be handled in a less controlled way and over a shorter period of time. In addition, the apparatus and method provide for the recycling of the drilling fluid which is recovered from the drill cuttings. The apparatus is transportable to permit onsite treatment of the drill cuttings to reduce transportation costs.
According to a broad aspect of the present invention, there is provided a method for processing a slurry obtained from the drilling of a wellbore, the slurry containing a solid component and a liquid component, the method comprising: compressing the slurry to remove at least a portion of the fluid component from the solid component.
The liquid component includes drilling fluid for use in the drilling of the wellbore. The solid component of the slurry includes drill cuttings such as, for example, those removed from "spent" drilling fluid returning to the surface after passing a progressing drill bit. The drill cuttings can be removed from the "spent" drilling fluid by use of shale shakers, centrifuges and/or other drilling fluid processors.
In one preferred embodiment, the step of compressing the slurry is carried out in a filter chamber and, in particular, the method comprises providing a filter chamber including walls, at least some of the walls having apertures therethrough; introducing the slurry to the chamber, compressing the slurry in the chamber such that at least a portion of the fluid component is forced through the apertures of the chamber walls and at least a portion of the solid components is retained within the chamber.
Preferably, the fluid component which is removed from the solid component is recycled, for example, to a drilling operation.
The step of compressing preferably applies pressure of at least about 500 psi to the slurry. In one preferred embodiment, the slurry is compressed at at least 800 psi.
Where the slurry contains a larger proportions of rocks relative to fines, higher compressive pressures are required to be used to effect preferred fluid component removal.
In one embodiment, the method results in the production of a solid component which contains less than 10% fluid component by volume. To reduce the environmental risk of the solid component to a more acceptable level, however, preferably the solid component after the compressing step contains less than 8% fluid component by volume and more preferably less than 6% by volume. Preferably, the solid component is compressed to bind to form a solid which is easy to handle.
In a preferred embodiment the compression step takes place over an extended time and substantially without mixing the slurry. In order for the method to be ecorromically useful, at least 0.2 cube of slurry can be processed per hour (1 cube = 6.25 barrels).
In a preferred method, at least 0.5 cube of slurry is processed per hour while more preferably slurry is compressed at at least 1.0 cube/hour. In a most preferred embodiment, the method is selected to keep pace with the generation of drill cuttings during the drilling of the wellbore.
According to a broad aspect of the present invention, there is provided an apparatus for treating a slurry including a solid component and a liquid component to remove the liquid component from the solid component, the apparatus comprising: a chamber formed to accept the slurry therein and including an end and side walls, at least some of the end and side walls including apertures extending therethrough between the chamber's interior and the chamber's exterior; a piston disposed to move into the chamber and toward and away from the end wall in substantial sealing engagement with the side walls; and a drive means for driving the piston into the chamber, the piston 2o being moveable in the chamber to apply pressure to slurry contained in the chamber such that at least some of the fluid component in the slurry is forced from the solid component and passes through the apertures.
The chamber can be any desired shape suitable for accepting a piston therein for example, cylindrical or cubic.
2s In one embodiment, the drive means is selected to be capable of exerting at least 1.5 million Ibs force on the piston. In preferred embodiments, the drive means is selected to be capable of exerting at least 2 million Ibs force on the piston. The chamber is selected to withstand such forces.

Any or all of the end and side walls can be apertured. In a preferred embodiment, all of the end and side walls are apertured and the piston is provided with apertures therethrough.
The apertures are sized with consideration as to the nature of the solid component s being of the slurry to permit fluid to pass therethrough, while excluding the passage of at least some of the solid components. It being understood, that it may not be necessary to exclude passage of all of the solid components, for example, fines.
In a preferred embodiment to provide for collection and containment of the fluids passing through the apertures, the apparatus further comprises a housing on the exterior of the chamber mounted about any apertured areas of the end and side walls, the housing selected to prevent the passage of liquids therethrough.
BRIEF DESCRIPTION OF THE DRAWINGS
A further, detailed, description of the invention, briefly described above, will follow by reference to the following drawings of specific embodiments of the invention.
These drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. In the drawings:
Figure 1 is a perspective view of an apparatus according to the present invention;
Figure 2 is a sectional view along line 2-2 of Figure 1;
Figure 3 is a sectional view along line 3-3 of Figure 1;
2o Figure 4 is an enlarged view of an end of an apparatus according to one embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of clarity, in the Figures only reference numerals of the main components are indicated and like reference numerals relate to like components.
The figures show an apparatus for treating a slurry containing a solid component and a liquid component. The slurry can be, for example, a slurry of drill cuttings containing residual drilling fluid. As will be described in more detail hereinafter, the apparatus can be operated to treat the slurry of drill cuttings and drilling fluid obtained from a drilling operation to remove the drilling fluid from the drilling cuttings by compression. Thus, preferably the chamber is sized to accept an amount of slurry which would make it useful for operation to treat the drill cuttings generated during a normal drilling operation. Since the slung of drill cuttings is environmentally unfriendly and difficult to store, preferably the apparatus is sized to keep pace with the generation of drill cuttings.
The apparatus includes a chamber 10 defined by a bottom end 11 and by side walls 12, 13, 14, 15. The chamber is open at its upper end such that a slurry of drill cuttings and drilling fluid can be introduced thereto, as by dumping. Preferably, a funnel-shaped wall ~5 17 is provided to direct the slurry into the chamber.
A piston 18 is disposed above and aligned with chamber 10. Piston 18 is driven by six, or any number as desired, hydraulic cylinders 20 to move into chamber 10 and toward and away from end 11 in substantial sealing engagement with side walls 12,13, 14, 15.
The piston can be fully removed from chamber 10, as shown, to permit introduction of 2o the slurry into the chamber. Where desired, a seal (not shown), such as, for example, a neoprene wiper seal, is mounted about the piston to enhance sealing engagement with the walls.
Hydraulic cylinders 20 are securely attached to an upper frame 22 by bolts 23.
Cylinders 20 act between piston 18 and frame 22 to drive piston into and out of 25 chamber 10. The hydraulic cylinders are controlled by a hydraulic system (not shown).
A cover 24 is disposed over the motor, valves and control elements of the hydraulic system to provide protection therefor. To facilitate operation thereof, preferably, the hydraulic system is controlled by a wireless remote system.

The number and sizes of the hydraulic cylinders are selected to be capable of exerting at least about 1.5 million Ibs and, preferably, at least about 2.0 million Ibs of force to the piston such that, when a slurry is contained in the chamber, at least about 500 psi and preferably at least 800 psi pressure can be applied to the slurry. Chamber and frame 22 are formed to withstand such pressure without failing. As an example, 1.5 to 2.0 inch thick steel is used throughout with reinforcements, as required.
End 11 and walls 13, 14, 15 have apertures 25 formed therethrough. The apertures are sized to permit drilling fluid to pass therethrough but to block passage of a majority of drill cuttings. Generally, the apertures are 1/8 to 1/4 inches in diameter, with a preferred diameter of 3/16 inch. Referring to Figure 4, to reduce the plugging of the apertures, preferably, they are formed with an increased diameter d2 adjacent their outer ends.
As an example, in a preferred aperture 25a the inner opening to the chamber has a diameter d1 of 3/16 inch and a diameter d2 of 1/4 inch at its outer end.
The apertures are spaced apart over at least portions of end 11 and walls 13, 14, 15.
~5 The apertures are spaced apart such that they do not overly weaken the structure of the wall but so that there are sufficient apertures to effectively treat the drill cuttings.
In the preferred embodiment, the aperatures are regularly spaced at 2 inch intervals.
The apertures are preferably spaced apart uniformly to facilitate construction of the apparatus. To enhance removal of the liquid component by reducing the migration 2o path length, apertures are formed through as much of the surface area of end 11 and walls 13, 14, 15 as possible and as will be in contact with the slurry, with consideration as to the fill level of the chamber.
In a preferred embodiment, as shown, piston 18 also has formed therethrough apertures 25c. The aperatures are as described above. Any liquid passing through the 25 aperatures onto the top of the piston drains through apertures in wall 13, 14, 15.
Preferably, end 11 has disposed thereover a finer filtration medium such as, for example, wire screen 26. Wire screen 26 is attached over the surface of end 11 for example by use of bolted clamps. In a particularly preferred embodiment, where piston 18 is apertured, a screen 27 is fixed over its face. It has been found that providing mesh over end 11 and face of piston 18 reduces fines migration from the chamber, resulting in a drilling fluid with fewer fines therein. In one embodiment, 100 mesh wire screen is used.
s Housing panels 30 are spaced outwardly of walls 13, 14, 15 and form cavities 31 a, 31 b, 31c about the apertured areas of the chamber. Panels 30 contain and divert drilling fluid passing, sometimes at great pressures, through the apertures in the walls.
Housing panels 30 are formed to prevent passage of fluid therethrough.
Drilling fluid passing though the walls moves through the cavities and through openings into the interior chamber 32 formed within a transportable skid 34. Thus, skid 34 serves dual purposes of a holding tank for separated drilling fluids and to permit transport of the chamber.
Reinforcing beams 36 within skid 34 serve also as baffles within the chamber enhancing separation of any fines carried with the drilling fluid. A port 37 is provided 15 for access to tank 32 for holding the drilling fluid. Openings 38 in beams 36 permit the drilling fluid to flow to fill the chamber within the skid.
To provide for cleaning and inspection of the cavities 31 a, 31 c and of the chamber within skid 34, doors 39a, 39b are provided.
In other embodiments, a holding tank is not required and the drilling fluid is diverted, as 20 by pumping, through a tubing system away from the chamber.
To facilitate removal of the drill cuttings from the chamber after treatment thereof, preferably, removal system is provided. In particular, wall 12 is formed to be removable. While other removal arrangements are possible, in the illustrated embodiment, wall 12 is mounted in guides 40 and is slidable upwardly in guides away 2s from its closed position against end 11. Wall 12 is driven to slide in guides 40 by a hydraulic drive system including a hydraulic cylinder 42 mounted between a beam 44 on frame 22 and a bracket 46 attached to wall 12. Guides 40 are formed to urge wall 12 tightly against walls 13,15 and end 11 so that a seal is effected therebeteen. In a preferred embodiment a bar 47 is mounted in a channel 48 below wall 12. Bar 47 is biased upwardly in channel by springs 49 mounted under the bar and acting against end wall of channel 48. The arrangement of bar 47, channel 48 and springs 49 is selected such that when bar 47 is biased by springs upwardly in channel 48, the bar is remains positioned in channel and, preferably, is positioned such that that the upper surface of the bar rests flush with the channel opening. When wall 12 is moved down, the wall drives bar 47 down into channel 48 and wall enters channel on top of bar.
Thus, wall 12 at its lower end is supported by and sealed against channel 48.
To provide for cleaning of the channel to, thereby, enhance the seal with the wall, when wall 12 is raised, bar is biased upwardly in channel 48 to push any materials which have fallen onto the bar out of the channel. These materials will be pushed away from the channel opening by the movement of wall 14, as will be discussed hereinbelow.
Wall 14 is formed to be moveable into chamber 10 to apply force against the drill ~5 cuttings in the chamber to move them out of the chamber through the opening formed by sliding wall 12 upwardly. Wall 14 is preferably moved by a hydraulic cylinder 50.
Wall 14 engages and rides along rails 52 which extend out from walls 13 and 15. Wall 14 has mounted about its edges a seal 54 formed for example of heavy neoprene rubber. Seal 54 substantially prevents leakage of fluids about the wall and enhances 2o removal of drill cuttings from the chamber.
By use of wall 14, the drill cuttings, which after compression are generally in the form of a solid block, are pushed out onto platform 60. Platform includes an upstanding wall 62 against which the drill cuttings can be abutted to facilitate removal by, for example, a bulldozer or the like.
25 As noted previously, in operation, the apparatus is useful for compressing a slurry including a liquid component and a solid component to remove at least a portion of the liquid component from the solid component. While the apparatus is particularly useful for compressing a slurry of drill cuttings and drilling fluid, it is to be understood that the apparatus can also be used for other slurries such as from pulp and paper operations or contaminated soils from spill sites.
Thus, a preferred method according to the present invention includes placing the slurry in chamber 10 and compressing the slurry under to force the drilling fluid out of the drill cuttings. The drilling fluid is then collected and returned to a drilling operation. The drill 5 cuttings, which as a result of the compression, contain less than 10% and preferably less than about 8% drilling fluid, are treated such as by land farming. In one test the apparatus was used to reduce the levels of drilling fluid in a amount of drill cuttings to about 5.2%. At this level landfarming to bring the level to 2% may take less than a year and probably less than six months. In addition, the drill cuttings after compression are consolidated and can be stored, handled and transported without mixing with inert materials or binding agents such as sawdust.
The characteristics of the slurry will determine what pressures are required to be applied in order to suitably compress the slurry. As an example, variables including the viscosity of the drilling fluid, the rock which forms the drill cuttings (ie.
Shale, sandstone, ~5 etc.) and the size of the drill cuttings will all effect the pressures which are required to be applied. Generally, it has been found that suitable compression has been achieved by treating the slurry at pressures of at least 800 psi and preferably 800 to 1200 psi.
In a normal drilling operation on land, generally 1 to 2 cubes of drill cuttings slurry will be recovered every hour from spent drilling fluid. In offshore operations, the amounts of drill cuttings slurry produced are much higher, for example, generally 6 to cubes/hour. The drill cuttings will be collected from the shale shakers, centrifuges and other drilling fluid processing equipment. The apparatus is preferably capable of processing the slurry of drill cuttings generally as they are produced and without creating a back log as this would require storage of the drill cuttings slurry prior to processing by the apparatus. In a preferred embodiment, the chamber is sized to accept up to 2.5 cubes of slurry.
Preferably, the piston is moved slowly such that very little mixing occurs in the slurry during compression. Reducing mixing facilitates removal of the drilling fluid from the drill cuttings. In a preferred embodiment, the slurry is compressed for at least 5 minutes and, in particular, in one preferred embodiment, the slurry is compressed for about 5 to 20 minutes until a maximum preferred pressure is reached. The maximum preferred pressure is then maintained for at least 2 minutes and preferably for about 7 to 10 minutes.
It will be apparent that many other changes may be made to the illustrative embodiments, while falling within the scope of the invention and it is intended that all such changes be covered by the claims appended hereto.

Claims (15)

1. A method for processing a slurry obtained from the drilling of a wellbore, the slurry containing a solid component including drill cuttings and a liquid component including drilling fluid, the method comprising: compressing the slurry in a filter to remove at least a portion of the liquid component from the solid component.

2. The method of claim 1 wherein the drilling fluid is oil-based.

3. The method of claim 1 wherein the slurry is obtained from drilling fluid returning to the surface after passing a progressing drill bit.

4. The method of claim 1 wherein the slurry is obtained as waste product from a shale shaker or a centrifuge.

5. The method of claim 1 the method further comprising: collecting the liquid component removed from the solid component and recycling the liquid component.

6. The method of claim 1 wherein the step of compressing preferably applies a pressure of at least about 500 psi to the slurry.

7. The method of claim 1 wherein after the compression step the solid component contains less than 10% fluid component by volume.

8. The method of claim 1 wherein at least 0.2 cube of slurry is compressed per hour.

9. An apparatus for treating a slurry including a solid component and a liquid component to remove the liquid component from the solid component, the apparatus comprising: a chamber formed to accept the slurry therein and including an end and side walls, at least some of the end and side walls including apertures extending therethrough between the chamber's interior and the chamber's exterior; a piston disposed to move into the chamber and toward and away from the end wall in substantial sealing engagement with the side walls; and a drive means for driving the piston into the chamber, the piston being moveable in the chamber to apply pressure to slurry contained in the chamber such that at least some of the fluid component in the slurry is forced from the solid component and passes through the apertures.

10. The apparatus of claim 9 wherein the drive means is selected to be capable of exerting at least 1.5 million lbs force on the piston.

11. The apparatus of claim 9 wherein the piston is provided with apertures therethrough.

12. The apparatus of claim 9 wherein the apparatus further comprises a housing on the exterior of the chamber mounted about any apertured areas of the end and side walls, the housing selected to prevent the passage of liquids therethrough.

13. The apparatus of claim 9 wherein a mesh material is applied over the apertures of the end wall.

14. The apparatus of claim 11 wherein a mesh material is applied over the apertures of the piston.

15. The apparatus of claim 9 wherein one of the side walls is removable and an ejection means is provided for moving materials through an opening in the chamber left by the one side wall when it is removed.