CA2200524A1

CA2200524A1 - Separator for removing solids from drilling fluid

Info

Publication number: CA2200524A1
Application number: CA002200524A
Authority: CA
Inventors: Phil Stevens
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-03-20
Filing date: 1997-03-20
Publication date: 1998-09-20

Abstract

A method and apparatus for separating solids from drilling fluid returning from a drilling operation wherein the apparatus comprises a separation tank divided into first and second compartments each of downwardly diminishing cross-sectional areas. There are continuous solid removal means at the bottom of each compartment. The drilling fluid is passed through a shale shaker and deposited in the first compartment where a portion of the solids settle and are removed by a clean out auger. The drilling fluid is skimmed from the first compartment and transferred to the second compartment where more solids settle and are removed. The drilling fluid then is passed through a plate separator comprising a plurality of horizontally stacked and spaced bidirectionally corrugated plates. Solids removed by the plate separator is returned to the second compartment while the remaining drilling fluid is collected and returned to the drilling operation. Flow of the drilling fluid through the apparatus is gravity-driven.

Description

2~n52 4 SEPARATOR FOR REMOVING SOLIDS FROM DRILLING FLUID

FIELD OF THE INVENTION

This invention relates to a separator for removing particulate solids from drilling fluid returning from a well.

BACKGROUND OF THE INVENTION
Wells have long been drilled using drilling fluid as the circulating medium.
Drilling fluid may be fresh water or, if finely divided clay has been added, drilling mud. One purpose of drilling fluid is to provide a column of fluid that exerts hydrostatic pressure at the bottom of the wellbore which prevents the entry of pressurized LylL~lI,a~ into the wellbore from the formation being drilled. It also serves to carry solid cuttings up and out of the wellbore. A primary dl~al~allla~ associated with the use of drilling fluid is the expense associated with using large volumes of fluid. In view of the high cost of drilling fluid, it is desirable to develop methods of recovering and reusing the drilling fluid.

The most common technique has been to use mud pits or settlement tanks where the drilling fluid is stored and particulate matter allowed to settle out with the passage of time. This technique has a major drawback in the length of time required and in many instances, complete separation of solids from the fluid cannot be achieved in a reasonable length of time. This is especially true with very fine solids.
A more recently developed techmique involves the use of centrifuge separators to remove the solids. For example, a centrifugal separation system is described in U.S. Patent 5,344,570 issued to ~ h~ et.al. Although centrifugal separation accelerates the speed of separation, there are drawbacks inherent in such techniques related primarily to the expense and complexity of such systems.

It is also possible to physically filter drilling fluid to separate solids usingscreens or other filter means. In U.S. Patent 4,243,527 issued to Leonard, there is described ~ 2 0 ~ ~ 2 4 an apparatus which treats drilling fluids by means of a screen and conveyor mounted screen cleaning means which physically scrapes the screen and removes solids from the apparatus.
However, this system is unable to remove finer solids which pass through the screen. Also, the screen may still clog despite the screen cleaning m~ nicm The prior art also discloses the use of plate separators to remove solids that are suspended in a liquid. In U.S. Patent 4,897,206 issued to Castelli discloses a bidirectionally corrugated plate separator for fluid mixtures. The plate separator comprises a horizontal stack of b;Ji~ ally corrugated plates with bleed holes in the crests and valleys to allow passage 10 of solids downward through the stack and the fluid upward through the stack.

Therefore, it is known to provide settlement as a method of separating solids from drilling fluid. It is also known to use plate separators to remove solids in ~ p.~n~ion These concepts are hlc~ nJI ' into the present invention which improves on the prior art by 15 providing a mobile, compact, self-contained solids separator for drilling fluid which quickly and effectively removes virtually all solids.

SUMMARY OF THE INVENTION~0 In general terms, the invention provides a self contained apparatus for separating solids from drilling fluid received from a drilling operation ~

(a) a separation tank having an internal wall which divides the separation tank into first and second .;.~IlllJalllll.. ~ the first ~ulll~ ll being operative to receive the drilling fluid from a drilling operation;

(b) first means to ~o .~ remove solids from the first l,OIll~ ll located at the bottom of the first ._olll~Jalllll~....~0 5 ~ 4 (c) means for skimming drilling fluid from the first ~Ulll,Uall~ and ll~l~f~,.flllg the drilling fluid to the second culll,ua~

(d) second means to ~ y remove solids from the second ~,UIII,Ual ~11.~,.11 S located at the bottom of the second ~;UIll~

(e) means for separating the remaining solids from the drilling fluid from the second ~ ,.l1, said separation means positioned above the second ~,ulll,u~llll~.ll such that solids removed by the separation means fall back into the second ~,U.. I,Ual~ ,lll, and (f) meams for collecting separated drilling fluid from the separation means.

Preferably, the skimming means is above the horizontal level of the separation 15 means such that the flow of drilling fluid from the first ~;ulll~ lll to the collection means is driven by gravity alone.

In accordance with another feature of the invention, there may also be screening meams associated with the separation tank for removing larger solid particles from 20 the drilling fluid prior to the drilling fluid entering the first CUIll~

It is a preferred feature of the invention that the first and second ~;UIIIIJa~llll..lll:i have downwardly ,' ' ~ cross-sectional areas which ~,u~ u~ settling solids towards the first and second solid removal means 1~ ,livt;ly. This may be ~cornrlieh~d by sloping 25 the lateral walls of the separation tank and the dividing wall such that each of the first and second COIll~llll~,llb have a "V" shape in cross-section.

The separation means may comprise a plurality of horizontally stacked and spaced corrugated plate separators having bleed holes in the crests and valleys of the plates.
30 Preferably, the plate separators are bidirectionally corrugated.

~ ~ a ~ 5 2 4 - In another aspect of the invention, there is provided a method of removing sllh~tS~ ly all of the solids from drilling fluid returning from a drilling operation, said drilling fluid comprising a liquid, coarse solids, fine solids, finer solids and finest solids, the method ~
s (a) screening the drilling fluid to separate the coarse solids;

(b) providing a separation tank divided into first and second ~;u~ ,llL~ and having fluid skimming and transfer means to skim and transfer drilling fluid from the first ~U~IIAU~ to the second ~,olll~JalLIll~,lll, (c) introducing the drilling fluid into the first ~;ulll~u~~ t and allowing fine solids to settle downwardly and removing the fine solids collected at the bottom of the first ~,UIIII)alLlll.,ll~, (d) ~ .l,f~,llhlg the drilling fluid from the first ~ulll~JalLlllclll to a second 1~ and allowing the finer solids to settle duwllwaldly and removing the finer solids collected at the bottom of the second ~,UIII~/alLIII.,Il~, (e) filtering the drilling fluid from the second ~,UIIIIJalllll~,lll to remove the finest solids, retaining the finest solids in the second CUIIIIJOILIII~.IIL, and (f) removing and collecting the drilling fluid and returning the drilling fluid to the drilling operation.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred emh-)~l of the invention will now be described in reference 30 to the accul~ illg drawings in which:

2 ~

Figure I is a schematic flow sheet of separation system.

Figure 2 is a partial cut-away view of the separator.

Figure 3 is a side cut-away view of the separator showing some internal Figure 4 is a top cut-away view of the separator.

Figure 5 is view is an individual plate separator used in the plate separator array.

Figure 6 is a schematic diagram of the electrical control system.

Figure 7 is a schematic diagram of the hydraulic motor and pump system.

Figure 8 is a view of a flow control valve and motor group.

Figure 9 is a view of the hydraulic tank pump and drive motor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention in its apparatus form is a separator (10) for treating drilling fluid 25 being returned from a well to remove substantially all of the solids suspended in the drilling fluid so that the drilling fluid may be returned to the well to be reused.

The apparatus comprises a separation tank (12) which is divided into first (14) and second (16) . . l~ lt~ by a dividing wall (18), a clean-out auger (20) in the first 30 ~ J~llllC;lll (14), a skimming trough (22) to transfer drilling fluid from the first 2 ~ 2 4 ~;u.~ ,llL (14) to the second CUIII~ lllClll (16), a clean-out conveyor (24) in the second ~;UIll,ualllll~,lll (16) and an array of plate separators (26).

The dimensions of the separator (10) are not essential to the invention.
S However, the preferred cilllb(nlilll~,lll of the separator (10) is small enough that it may be cul~ tly transported from site to site on a flat bed truck or trailer. It is large enough to handle the flow from most drilling operations. It is a,u,ul~ 'y 38 feet long, 8 feet wide and 12 high. and has a total capacity of ~ JIU ' ' 1~/ 150 barrels: the first ~_Ulll,Uall (14) has a capacity of ~llJ,UIU ' ' Iy 50 barrels while the second ~_UllI,Ual~ lll (16) has a 10 capacity of a~ 'y 100 barrels.

The separation tank (12) is generally rectangular when viewed from above and is supported by a frame (28) of steel beams. The bottom portion (30) of the separation tank (12) is formed by inclined first (32) and second (34) lateral walls which meet to form a "V".
15 The dividing wall (18) is also inclined generally parallel to the first lateral wall (32) and attaches to the second lateral wall (34) to form the first UUIIIIJalllll~,.ll (14). Thus, both the first amd second ~,UIII~JolLlll~,.lt:~ (14, 16) have a "V" shaped bottom portion when viewed in cross-section (See Figure 2). The bottom of the first ~ulll,~ (14) is ~U~ y midway down the separation tank (12).
The separator (10) does not require pumps to flow drilling fluid through the separator (10). Because the first ~_Ulll,Ualllll~ (14) is higher than the second UUlll,Ualllll~,lll (16), the plate separators (26) and the clean water tank (64) and skimmers (60), the force of gravity causes the flow of drilling fluid through the separator (10). The rate of flow may be 25 controlled by the rate of addition of drilling fluid to the first CU..IIJalllll~,.ll (14).

A skimming trough (22) is provided at the top and to the side of the first UUIIIIJalllll~.llt (14). The trough (22) has openings (23) in the trough bottom which connect to transfer pipes (36) which lead to the second, , ~ ll1 (16). If the first CUIII~ (14) 30 is full, drilling fluid will spill into the trough (22) and the transfer pipes (36).

A screw type auger (20) for cleaning out solids is positioned in the "V" of the bottom portion of the first ~,u~ Jal~ (14). The clean-out auger (20) extends the length of the first ~;wll,ualLlllwll (14). A first transfer auger (38) is placed at the output end (40) of the clean-out auger (20) to lift the solids out of the first ~ullllJall~ ll (14). In turn, the first 5 transfer auger (38) leads to a drying auger (42) where the remaining drilling fluid is drained from the solids. The solids are then deposited by the drying auger (42) into the mud tank (not shown) while the fluid is returned to the first l,ullllJalllll~,lll (14) of the separation tank (12).

A clean-out conveyor (44) is positioned in the "V" of the bottom portion (30) of the second CUIII~ ;III (16). In the preferred nlllhO.~ l. .,1 the conveyor (44) is a belt (46) with transverse members (48) to physically move solids which have settled to the bottom of the second UUIII~ (16). The conveyor (44) leads to a second transfer auger (50) which lifts solids out the second ~,Olll~alllll~lll (16) and into the drying auger (42) where the solids mix with solids from the first transfer auger (38) and are eventually deposited into the mud tank.

Rotary shale shakers (52) which are well known in the art are positioned above the first l,Ulll~ ll. In the preferred rlllhO.I:.ll. .,l two shakers (52) are provided which are elongated rotating drums. The drums include screening and flighting to separate larger particles from the drilling fluid.

In operation, drilling fluid is taken directly from the flow nipple of the drilling rig (not shown) and is pumped to the shale shakers (52). In the shale shakers, the screens (53) separate solid particles about 500 microns in diameter or larger, which are then removed by the flighting and deposited into the mud tank. Drilling fluid and smaller solids fall through the screens and are deposited in the first ~;ulll~ (14) of the separation tank (12).

Upon entering the first ~,ulll,uall~ lll (14), the fluid and solids are allowed to settle. Settlement is aided by a vibrating bar (54) which is suspended in the first ~ulllAua~

5 2 ~

(14). Settlement is further aided by the slope of the second lateral wall (34) and the dividing wall (18) which form the first uullluall~ lt (14). The sloping walls (34, 18) direct solids which l.;UII~ ' in the bottom of the first ~ (14). The clean-out auger (20) ly rotates to transfer the settled solids to one end of the ~,ulll,ualllll~,lll (14) and 5 deposits the solids into the first transfer auger (38) which removes the solids from the first IUlC~ (14). A chemical floculant may be added to the drilling fluid in the first~,ulll,ualL~ (14) which causes à~ ;al;on of the solids to speed up the settlement process.

Drilling fluid at the top of the first ~,wll~ualllll~,lll (14) is skimmed by the trough (22) and transferred to the second UUIII~Jalllll~,.ll (16) via the transfer pipes (36). There is no need for a baffle or weir in the first ~;ulll,uall~ ,lll (14) to separate the incoming stream of drilling fluid from the trough (22) as long as the incoming stream is diffuse amd is directed away from the trough (22). The fluid is allowed to further settle in the second ~,UIII~Ual~lll~,lll (16) and for a longer length of time than in the first culllualllll~,llt (14) due to the larger capacity of the second ~ . 11.. ~.. 1(16). There is a second vibrating bar (56) suspended in the second uullluali (16) which aids in the settling process. Settled solids arelr. ..l~ i by the sloping walls (32, 34) of the second cUlll,Ual~ ;lll (16). Solids which settle out in the second l,Olll~alllll.,lll (16) accumulate at the bottom of the "V" and are removed by the continuous conveyor (44) which leads to the second transfer auger (50).
Drilling fluid in the second ~,UllI,Ualilll~,lll (16) is pushed up through the plate separators (26). The plate separators (26) are a plurality of horizontally stacked plate separators (26) that cause the fluid to flow in a sinusoidal and laminar manner. In the preferred rllll,o.l;~"r.,l bidirectionally corrugated plates of the type lllallll~al,lul~;l by Facet 25 Quantek, Inc. of Tulsa, Oklahoma are used. The drilling fluid is pushed upward into channel A in between the two arrays of plate separators (26). The fluid then passes horizontally and laterally in the direction of arrows B and C. The plate separatûrs (26) cause the drilling fluid to migrate upwards through bleed holes in the crests while solids migrate downwards through bleed holes in the valleys of the plates. Solids which are retained in the separator (10) by the 30 plate separators (26) fall back into the second uulll,ualL~ (16). Clean drilling fluid is collected by the clean water skimmers which are elongated troughs (60) located lateral to the ) 5 ~ ~

upper portion of the plate separators (26). Clean drilling fluid may then flow over the clean water weir (62) and into the clean water ~,I~IIIIJol~IIICll~ (64). The drilling fluid in the clean water ~ J~ i (64) may then be pumped back to the drilling rig for reuse.

S The separator (10) is electrically controlled and has an integral power supply.
A hydraulic pump is electrically driven to pressurize hydraulic fluid and operate an array of hydraulic motors. The hydraulic motors drive the clean-out auger (20), the first transfer auger (38), the drying auger (42), the clean-out conveyor (44), the second transfer auger (50) and the shale shakers (52). The electrical and hydraulic systems of the preferred embodiment are shown in Figures 6 to 9.

Variations and mo(lifil~ti~ns of the disclosed preferred rllllloll;lllrlll will be apparent to skilled pr~titionPrs. All such variations and mn~lifi-~ti~ns are intended to be rll~ d by the claims set forth herein.

Claims

1. A self-contained apparatus for separating solids from drilling fluid received from a drilling operation comprising:

(a) a separation tank having an internal wall which divides the separation tank into first and second compartments, the first compartment being operative to receive the drilling fluid from a drilling operation;

(b) first means to continuously remove solids from the first compartment located at the bottom of the first compartment;

(c) means for skimming drilling fluid from the first compartment and transferring the drilling fluid to the second compartment;

(d) second means to continuously remove solids from the second compartment located at the bottom of the second compartment;

(e) means for separating the remaining solids from the drilling fluid from the second compartment, said separation means positioned above the second compartment such that solids removed by the separation means fall back into the second compartment; and (f) means for collecting separated drilling fluid from the separation means.

2. The apparatus of claim 1 wherein the skimming means is above thehorizontal level of the separation means such that the flow of drilling fluid from the first compartment to the collection means is driven by gravity alone.

3. The apparatus of claim 1 or 2 further comprising screening means associated with the separation tank for removing large solid particles from drilling fluid received from a drilling operation, prior to the drilling fluid entering the first compartment of the separation tank.

4. The apparatus of claim 2 further comprising means for inducing vibration in the drilling fluid to assist settlement of solids, said vibration means being located within the first compartment and/or the second compartment.

5. The apparatus of claim 4 wherein the vibration means comprises a vibration member suspended within the first compartment and/or the second compartment.

6. The apparatus of claim 1 or 2 wherein a lower portion of the first compartment is of downwardly diminishing cross-sectional area, said first compartment shaped to direct settling solids to the first solids removal means.

7. The apparatus of claim 6 wherein the second compartment is of downwardly diminishing cross-sectional area, said second compartment shaped to direct settling solids to the second solids removal means.

8. The apparatus of claim 6 or 7 wherein the first solids removal means comprises an auger having a first end and a second end which, when rotated, continuously displaces solids toward the second end thereof.

9. The apparatus of claim 8 wherein the second solids removal means comprises an elongated conveyor having a first end, a second end and a plurality of scraper elements which continuously displaces solids towards the second end thereof.

10. The apparatus of one of claims 1, 2, 7 or 9 wherein the separation means comprises a plurality of horizontally stacked and spaced corrugated plate separators.

11 11. The apparatus of claim 6 wherein the separation means comprises a plurality of horizontally stacked and spaced corrugated plate separators.

12. A method of removing substantially all of the solids from drilling fluid returning from a drilling operation, said drilling fluid comprising a liquid, coarse solids, fine solids, finer solids and finest solids, the method comprising.

(a) screening the drilling fluid to separate the coarse solids;

(b) providing a separation tank divided into first and second compartments and having fluid skimming and transfer means to skim and transfer drilling fluid from the first compartment to the second compartment;

(c) introducing the drilling fluid into the first compartment and allowing fine solids to settle downwardly and removing the fine solids collected at the bottom of the first compartment;

(d) transferring the drilling fluid from the first compartment to a second compartment and allowing the finer solids to settle downwardly and removing the finer solids collected at the bottom of the second compartment;

(e) filtering the drilling fluid from the second compartment to remove the finest solids, retaining the finest solids in the second compartment; and (f) removing and collecting the drilling fluid and returning the drilling fluid to the drilling operation.

13. The method of claim 12 wherein the movement of the drilling fluid through the separation tank and driven by gravity alone.

14. The method of claim 12 wherein the removal of solids from the first and second compartments is continuous while drilling fluid moves through the separation tank.

15. The method of 12, 13 and 14 wherein the drilling fluid is filtered by a plurality of horizontally stacked and spaced bidirectionally corrugated plate separators.

16. The method of claim 13 or 14 further comprising the step of adding flocculant to the drilling fluid before it enters or while it is in the first compartment.