Cavity positioning tool and method

Information

  • Patent Grant
  • 6412556
  • Patent Number
    6,412,556
  • Date Filed
    Thursday, August 3, 2000
    24 years ago
  • Date Issued
    Tuesday, July 2, 2002
    22 years ago
Abstract
A cavity positioning tool is provided that includes a head piece adapted to receive a downhole string having a longitudinal axis. A plurality of blunt arms are coupled to the head piece. The blunt arms are operable to be radially extended outward from a first position of substantial alignment with the longitudinal axis to a second extended position.
Description




TECHNICAL FIELD OF INVENTION




This invention relates generally to the field of downhole cavity tools and more particularly to a cavity positioning tool and method.




BACKGROUND OF THE INVENTION




Subsurface resources such as oil, gas, and water are typically recovered by drilling a bore hole from the surface to a subterranean reservoir or zone that contains the resources. The bore hole allows oil, gas, and water to flow to the surface under its own pressure. For low pressure or depleted zones, rod pumps are often used to lift the fluids to the surface.




To facilitate drilling and production operations, cavities are often formed in the production zone. The cavity allows the well bore to be more readily intersected during drilling operations and collects fluids during production operations. The collection of fluids allows pumps to be operated intermittently when the cavity is full, which reduces wear on the pump.




Short extensions called a “rat hole” are often formed at the bottom of the cavity to collect cuttings and other drilling debris. As the subsurface liquids collect in the well bore, the heavier debris falls to the bottom of the rat hole and is thereby both centralized and collected out of the cavity. To avoid being clogged with debris, inlets for rod and other downhole pumps should be positioned within the cavity above the rat hole. In addition, the pump inlet should be positioned fairly low in the cavity to avoid vapor lock (i.e., below the fluid waterline). Traditional methods of positioning the pump inlets, however, are often inaccurate and inefficient, leading to clogging or vapor lock and increased maintenance and operation costs for the well.




SUMMARY OF THE INVENTION




In accordance with the teachings of the present invention, a cavity positioning tool and method are provided that substantially eliminate and reduce disadvantages and problems with prior systems and methods. In particular, a cavity positioning tool efficiently and accurately positions pump inlets and other downhole devices within or relative to a cavity.




In accordance with one embodiment of the present invention, a cavity positioning tool is provided that includes a head piece adapted to receive a downhole string having a longitudinal axis. A plurality of blunt arms are coupled to the head piece. In operation, the arms are operable to be radially extended outward from a first position of substantial alignment with the longitudinal axis to a second extended position.




More specifically, in accordance with a particular embodiment of the present invention, the arms are pivotally connected to the head piece. In this and other embodiments, the arms extend in response to rotation of the tool. In the absence of rotation, the arms automatically retract by force of gravity.




In accordance with another aspect of the present invention, a device is positioned relative to a subsurface cavity by coupling the device to a plurality of blunt arms. The blunt arms are lowered in a substantially retracted position into the subsurface cavity through a restricted passageway. In the cavity, the blunt arms are radially extended outward from the retracted position to an extended position. The blunt arms are then rested on the floor of the cavity, in the extended position.




In accordance with still another aspect of the present invention, a method is provided for degasifying a coal seam by lowering an inlet of a pump through a well bore into a cavity formed in a coal seam. The cavity extends radially from the well bore. A plurality of arms are coupled to the pump inlet. When the pump inlet is disposed within the cavity, the arms are radially extended. The pump inlet is then lowered until the arms rest on a floor of the cavity, such that the inlet is in a lower part of the cavity and above a rat hole extending below the cavity. Fluids are collected in the cavity and removed with the pump. Gas is recovered through the well bore.




In accordance with yet another aspect of the present invention, a method is provided for degasifying a coal seam by lowering an inlet of a pump through a well bore into a cavity formed in a coal seam. The cavity extends radially from the well bore. A plurality of arms are coupled to the pump inlet. When the pump inlet is disposed within the cavity, the arms are radially extended. The pump inlet is then lowered until the arms rest on a floor of the cavity, such that the inlet is in a lower part of the cavity and above a rat hole extending below the cavity. The pump inlet and arms are rotated, while the pump inlets maintain the same relative position within the cavity. Fluids are collected in the cavity and removed with the pump. Gas is recovered through the well bore.




Important technical advantages of the invention include providing an improved cavity positioning tool and method. In particular, the tool includes arms that are retractable for lowering through a well bore to a cavity and extendable in the cavity to position a device within or at a set relation to the cavity. In one embodiment, the arms are extended by centrifugal force and automatically retract in the absence of centrifugal force. As a result, the tool has a minimum of parts and is highly durable.




Another technical advantage of the present invention includes providing a method and system for positioning a pump inlet in a cavity. In particular, the pump inlet is positioned in a lower portion of the cavity by extending arms that rest on the cavity floor above a rat hole. This position of the pump inlet significantly reduces clogging of the pump inlets and prevents the pump from inadvertently entering the rat hole. Additionally, this position minimizes vapor lock.




Still another technical advantage of the present invention includes providing an improved method for supporting a pump string extended from the surface to a subterranean zone. In particular, a pump string is supported from the floor of the cavity. This allows well head maintenance and other surface operations to be performed without pulling out or otherwise supporting the string from the surface.




Still another technical advantage of the present invention includes providing an improved method for removing solid-laden fluids from a coal seam or other subterranean zone. In particular, a pump inlet is coupled to a cavity positioning device with extending arms that rest on a cavity floor above a rat hole. The arms are rotated slowly to agitate the liquid in the cavity, thereby suspending debris to allow removal within the liquid and lowering the tendency of particulate matter to coalesce. Thus, the debris and particulate matter is less likely to form clumps of larger particles, which reduces clogging of the pump inlets.




Other advantages are readily apparent to one skilled in the art from the following figures, descriptions, and claims.











BRIEF DESCRIPTION OF THE DRAWINGS




For a more complete understanding of the present invention and its advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which:





FIGS. 1A-B

are diagrams illustrating side views of a cavity positioning tool in accordance with one embodiment of the present invention;





FIGS. 2A-C

are a series of diagrams illustrating operation of the tool of

FIG. 1

in accordance with one embodiment of the present invention; and,





FIGS. 3A-B

are a series of diagrams illustrating operation of the tool of

FIG. 1

, in accordance with another embodiment of the present invention.











DETAILED DESCRIPTION OF THE INVENTION





FIGS. 1A-B

illustrate a cavity positioning tool


10


in accordance with one embodiment of the present invention. In this embodiment, tool


10


is adapted to position a pump inlet in a subsurface cavity. It will be understood that tool


10


may be adapted to position other suitable devices within or in relation to a cavity. For example, motors, controllers, and valves may be positioned in or relative to a cavity with the tool


10


. Tool


10


is constructed of steel or other suitable metals or materials, such that are resistant to damage in the downhole environment.




Referring to

FIG. 1A

, the tool


10


comprises a head piece


12


and a plurality of blunt arms


14


. As described in more detail below, the arms are coupled to the head piece


12


and operable to be radially extended outward from a first position of substantial alignment with a longitudinal axis associated with the head piece


12


to a second extended position. In the illustrated embodiment, the blunt arms


14


are coupled to head piece


12


by pivot assembly


16


. It will be understood that blunt arms


14


may by slidably or otherwise suitably coupled to head piece


12


.




The head piece


12


is configured at one end to receive a downhole string


20


. Head piece


12


may be threaded to receive a downhole string, or may include clamps, interlocking pieces, or be otherwise suitably configured to attach to, engage, or mate with downhole string


20


. Head piece


12


may be an integrated piece or a combination of components. For example, head piece


12


may include a downhole motor for rotating the head piece


12


, such as a bottom part of the head piece


12


, relative to the downhole string.




The downhole string


20


is a drill string, pump string, pipe, wireline, or other suitable downhole device that can be used to dispose the tool


10


within a cavity and extend the blunt arms


14


. In the illustrated embodiment, the downhole string


20


is a pump string


22


with an inlet


24


coupled directly to the tool


10


. The pump string


22


may be a sucker or other rod or multistage pump, a downhole pump with piping to the surface, or other suitable pumping system.




The blunt arms


14


are rounded, dull, or otherwise shaped so as to prevent substantial cutting of or damage to the cavity. In the illustrated embodiment, blunt arms


14


are cylindrical in shape with an elongated body and having a circular cross-section.




The blunt arms


14


may be end-weighted by adding weight to the ends distal to the head piece


12


, or may comprise a hollow portion proximate to the head pin such that the ends of the blunt arms


14


are thereby made heavier than the rest of the blunt arms


14


. The blunt arms


14


are sized to fit within a cavity when in an extended position and to exceed a diameter of a rat hole, bore hole, or other extensions, if any, below the cavity.




The pivot assembly


16


rotatably connects the blunt arms


14


to the head piece


12


. In one embodiment, the pivot assembly


16


allows the blunt arms


14


to radially extend and retract in response to rotational energy applied to the tool


10


. In this embodiment, pivot assembly


16


may be a clovis-and-pin type assembly.




As illustrated, blunt arms


14


hang freely down, in substantial alignment with the longitudinal axis of head piece


12


. Blunt arms


14


are in substantial alignment when the blunt arms


14


hang freely down, within a few degrees of the longitudinal axis and/or fit down and through a well bore. As described in more detail below, in response to rotation of head piece


12


, blunt arms


14


are radially extended towards a perpendicular position relative to head piece


12


. The blunt arms


14


are automatically retracted when head piece


12


ceases to rotate by force of gravity or other suitable mechanism. It will be understood that the blunt arms


14


may be slidably or otherwise suitably connected to the head piece


12


.




The pivot assembly


16


may include stops


18


to control extension of blunt arms


14


. Stops


18


may be configured to allow blunt arms


14


to extend ninety degrees to a perpendicular position, may limit the extension of blunt arms


14


to a lesser range, or permit a range greater than ninety degrees. Stops


18


may be integral or adjustable. Controlling the stops


18


, and the extension of blunt arms


14


thereby, controls the resting place of the pump string


22


relative to the floor of the cavity.





FIGS. 2A-C

are a series of drawings illustrating the operation of tool


10


. Referring to

FIG. 2A

, a pump string is positioned in a cavity for a degasification operation in connection with a coal seam prior to mining operations. In this embodiment, a well bore


30


is drilled from the surface


35


into a coal seam


40


. A cavity


32


is formed within the coal seam


40


. A rat hole


34


is drilled at the bottom of cavity


32


. The rat hole


34


has a diameter


37


. In a preferred embodiment, the blunt arms


14


have a length such that when extended, the distance from the distal end of one blunt arm


14


to the distal end of another blunt arm


14


exceeds the diameter


37


. It will be noted that in this instance, as well as throughout this description, use of the word “each” includes all of any particular subset. A drainage pattern


45


is drilled from a radiused bore


46


and extends into the coal seam


40


and connects to cavity


32


. The well bore


30


may have a diameter between seven and ten inches, the cavity a diameter between seven and nine feet, and the rat hole a diameter between seven and ten inches. Further information regarding the dual wells and drainage pattern is described in co-owned U.S. patent application Ser. No. 09/444,029, entitled “Method and System for Accessing Subterranean Deposits from the Surface,” which is hereby incorporated by reference.




The pump string


20


is positioned by coupling an inlet to the coupling means


12


of the positioning tool


10


. Next, the tool


10


on the pump string


20


is lowered through the well bore


30


. While tool


10


is lowered through well bore


30


, the blunt arms


14


remain in the retracted position with the blunt arms


14


hanging down in substantial alignment with the longitudinal axis of pump string


20


. Blunt arms


14


are lowered until proximate to the cavity


32


. Estimating the position of the cavity may be accomplished by comparing the known approximate depth of the cavity


32


to the length of pump string


20


in hand or deployed, or other suitable methods.




Referring to

FIG. 2B

, after the tool is positioned proximate to the cavity


32


, blunt arms


14


are extended by rotating the head piece


12


. In the illustrated embodiment, head piece


12


, is rotated by rotating the pump string


20


, for example, in the direction of arrow


38


. As pump string


20


is rotated, the blunt arms


14


are extended radially outward from pump string


20


in opposite directions, traveling generally as indicated by arrow


50


. One skilled in the art will recognize that other methods are available to extend blunt arms


14


radially outward from pump string


20


. For example, mechanical means such as a wire connected to blunt arms


14


might be used to extend blunt arms


14


radially outward from pump string


20


. The blunt arms


14


are extended until they contact the stops


18


.




Referring to

FIG. 2C

, once the blunt arms


14


are extended, or while being extended, the pump string


20


is lowered further into well bore


30


. Pump string


20


is lowered until blunt arms


14


make contact with the floor


33


of cavity


32


. When resting on the cavity floor


33


, pump inlets


24


are at a known position within the cavity


32


. By adjusting the spacing between the pump inlets


24


and the blunt arms


14


of the tool


10


, the distance between the pump inlets


24


and the cavity floor


33


can be modified. This adjustment may be made in a variety of ways, including adding spacers to the head piece


12


. Additionally, by changing the maximum angle of the blunt arms


14


, the distance between the pump inlets


24


and the cavity floor


33


can be modified. Adjusting the maximum angle of the blunt arms


14


can be accomplished in a variety of ways, including adjusting the stops


18


to restrict the radial extension of the blunt arms


14


. Therefore, the present invention provides for more definite location of the pump inlets


24


within cavity


32


, by use of positioning tool


10


.




Once the pump


22


is positioned within cavity


32


by tool


10


, fluids that drain from the drainage pattern


45


into the cavity


32


are pumped to the surface with the pump string


20


. Fluids may be continuously or intermittently pumped as needed to remove the fluids from the cavity


32


. Additionally, gas is diffused from the coal seam


40


and is continuously connected at the surface


35


as it passes through well bore


30


.




When fluid and gas removal operations are complete, the tool


10


may be removed from its position within cavity


32


. In reverse operation, pump string


20


is raised until blunt arms


14


are no longer in contact with the floor


33


of cavity


32


. Blunt arms


14


are moved from an extended position to one of substantial alignment with pump string


20


. If the blunt arms


14


were extended by centrifugal force, the blunt arms


14


will return to the first position of substantial alignment with pump string


20


upon being raised from the cavity floor. Once the blunt arms


14


have been returned to a position of substantial alignment with pump string


20


, pump string


20


may be raised through and out of well bore


30


.





FIGS. 3A-B

are a series of drawings illustrating operation of tool


10


during production of fluid and gas from the cavity


32


. Referring to

FIG. 3A

, the pump string


20


is positioned in the cavity


32


for degasification operation of the coal seam


40


as previously described. The pump inlets


24


are positioned within the cavity


32


such that the pump inlets


24


are above rat hole


34


, but below the waterline of the fluids collected in cavity


32


.




As fluids are collected in the cavity


32


, particulate matter and other debris such as drilling cuttings and coal fines are also collected in the cavity


32


. Operation of the downhole pump


22


causes the suspended particulate matter and other debris to move through different locations within the body of fluid in cavity


32


. As the settling of particulate matter and other debris proceeds, the amount of particulate matter and other debris suspended in the fluid changes. Accordingly, different locations within the fluid body, or phases, have different concentrations of particulate matter and other debris. The heavier debris settles to the floor of cavity


32


and may eventually settle in rat hole


34


.




The relative size of the particulate matter and other debris changes across the different phases of the fluid body. The smallest particulate matter and other debris remains close to the surface in Phase III, as shown in FIG.


3


A. As the particulate matter and other debris coalesces or clumps together, the composite matter begins to settle through the phases and may eventually fill the rat hole


34


and form a solid layer of sludge on the floor of cavity


32


. Eventually, the depth of the sludge layer and size of the composite matter is such that the pump inlets


24


become clogged, causing production delays and added expense.




Referring to

FIG. 3B

, the blunt arms


14


are rotated in the cavity


32


about the longitudinal axis of pump string


20


by rotating the pump string


20


at the surface or by other suitable means. In one embodiment, the pump string is rotated at the surface by a tubing rotator, at approximately one rotation per day.




Rotating the blunt arms


14


agitates the fluid collected within the cavity


32


. In the absence of agitation the particulate matter and other debris may coalesce or clump together forming larger composite matter that would eventually clog the pump inlets


24


. With rotation of the blunt arms


14


, however, solids remain suspended in the fluid and are removed with the fluid. In addition, the distribution of the remaining particulate matter is pushed away from the pump inlets


24


, towards the sidewalls of cavity


32


.




As illustrated in

FIG. 3B

, rotation of the blunt arms


14


causes the levels or phases decrease in area. Furthermore, rotation causes the shape of the phases to become more sharply sloping from the sidewalls of cavity


32


towards the floor of cavity


32


. The change in shape of the phases prevents particulate matter from clumping in the liquid in the near vicinity of the pump inlets


24


. Thus, rotation of the blunt arms


14


decreases the concentration of large particulate matter and other debris surrounding the pump inlets


24


, and thereby greatly reduces clogging of the pump inlets


24


, and the increased costs associated therewith.




Although the present invention has been described in detail, it should be understood that various changes, alterations, substitutions, and modifications may be made to the teachings herein without departing from the spirit and scope of the present invention, which is solely defined by the appended claims.



Claims
  • 1. A cavity positioning tool comprising:a head piece configured to receive a downhole string having a longitudinal axis; a plurality of blunt arms coupled to the head piece, the blunt arms configured to contact a surface of the cavity to position the tool in the cavity without substantial cutting of the surface of the cavity; and the arms operable to be radially extended outward from a first position of substantial alignment with the longitudinal axis to a second extended position.
  • 2. The cavity positioning tool of claim 1, wherein the blunt arms each comprise a rounded end distal from the head piece.
  • 3. The cavity positioning tool of claim 1, wherein the blunt arms each comprise at least one rounded side.
  • 4. The cavity positioning tool of claim 1, wherein each blunt arm comprises a rounded periphery.
  • 5. The cavity positioning tool of claim 1, wherein the blunt arms are pivotally connected to the head piece.
  • 6. The cavity positioning tool of claim 1, wherein the blunt arms are pivotally connected to the head piece by a pin.
  • 7. The cavity positioning tool of claim 1, wherein the blunt arms are operable to extend to the second extended position in response to rotation of the head piece.
  • 8. The cavity positioning tool of claim 1, wherein the head piece comprises:a clevis sized to receive a first end of each blunt arm; and a pin pivotally connecting the first end of the blunt arms to the clevis.
  • 9. The cavity positioning tool of claim 1, wherein the head piece is configured to receive a pump string.
  • 10. The cavity positioning tool of claim 1, wherein the head piece is configured to receive a pump inlet of a pump string.
  • 11. The cavity positioning tool of claim 1, further comprising stops for each blunt arm, the stops operable to limit the outward extension of the blunt arm from the first position.
  • 12. The cavity positioning tool of claim 11, wherein the stops are operable to limit the outward extension of the blunt arm from the first position to a position substantially perpendicular to the head piece.
  • 13. The cavity positioning tool of claim 1, wherein the blunt arms are operable to be rotated around the longitudinal axis.
  • 14. A method for positioning a downhole device relative to a subsurface cavity comprising:coupling the device to a plurality of blunt arms, the blunt arms configured to contact a surface of the cavity to position the tool in the cavity without substantial cutting of the surface of the cavity; lowering the blunt arms to the cavity through a restricted passageway with the blunt arms in a substantially retracted position; radially extending the blunt arms outward from the retracted position to an extended position within the cavity; and resting the blunt arms in the extended position on a floor of the cavity.
  • 15. The method of claim 14, wherein the blunt arms are pivotally extended.
  • 16. The method of claim 14, wherein the blunt arms are radially extended by centrifugal force.
  • 17. The method of claim 14, wherein the blunt arms are extended to a position substantially perpendicular to the head piece.
  • 18. The method of claim 14, wherein the device comprises an inlet for a pump string.
  • 19. The method of claim 14, further comprising slowly rotating the blunt arms about a longitudinal axis while the blunt arms are in the extended position.
  • 20. The method of claim 19, wherein the blunt arms are rotated at the rate of 10 revolutions per day, or less.
  • 21. The method of claim 19, wherein the blunt arms are rotated at the rate of 5 revolutions per day, or less.
  • 22. The method of claim 19, wherein the blunt arms are rotated at the rate of 1 revolution per day, or less.
  • 23. A method for positioning a pump inlet in a cavity for removing fluids from a subsurface formation, comprising:lowering an inlet of a pump through a well bore into a cavity, the cavity extending radially from the well bore; radially extending within the cavity a plurality of blunt arms coupled to the pump inlet, the blunt arms configured to contact a surface of the cavity to position the tool in the cavity without substantial cutting of the surface of the cavity; and resting the arms on a floor of the cavity.
  • 24. The method of claim 23, wherein the pump is a suction-rod pump.
  • 25. The method of claim 23, wherein the pump is a downhole pump.
  • 26. The method of claim 23, further comprising slowly rotating the blunt arms about a longitudinal axis while the blunt arms are in the extended position.
  • 27. The method of claim 26, wherein the blunt arms are rotated at the rate of 10 revolutions per day, or less.
  • 28. The method of claim 26, wherein the blunt arms are rotated at the rate of 5 revolutions per day, or less.
  • 29. The method of claim 26, wherein the blunt arms are rotated at the rate of 1 revolution per day, or less.
  • 30. A method for degasifying a coal seam, comprising:lowering an inlet of a pump through a well bore into a cavity formed in a coal seam, with a rat hole below the cavity, the cavity extending radially from the well bore; radially extending within the cavity a plurality of blunt arms coupled to the pump inlet; positioning the inlet in a lower part of the cavity above the rat hole by resting the blunt arms on a floor of the cavity; collecting fluids in the cavity; removing the fluids with the pump; and recovering gas through the well bore.
  • 31. The method of claim 30, further comprising slowly rotating the blunt arms about a longitudinal axis while the blunt arms are in the extended position.
  • 32. The method of claim 31, wherein the blunt arms are rotated at the rate of 10 revolutions per day, or less.
  • 33. The method of claim 31, wherein the blunt arms are rotated at the rate of 5 revolutions per day, or less.
  • 34. The method of claim 31, wherein the blunt arms are rotated at the rate of 1 revolution per day, or less.
  • 35. A method for removing particulate laden fluid from a subterranean zone, comprising:lowering an inlet of a pump through a well bore into a cavity formed in a subterranean zone, the cavity extending radially from the well bore; radially extending within the cavity a plurality of blunt arms coupled to the pump inlet, the blunt arms configured to contact a surface of the cavity to position the tool in the cavity without substantial cutting of the surface of the cavity; positioning the inlet in the cavity by resting the blunt arms on a floor of the cavity; collecting particulate laden fluids in the cavity; agitating the fluid by rotating the blunt arms about a longitudinal axis of the pump; and, removing the fluids with the pump.
  • 36. The method of claim 35, wherein the blunt arms are rotated at the rate of 10 revolutions per day, or less.
  • 37. The method of claim 35, wherein the blunt arms are rotated at the rate of 5 revolutions per day, or less.
  • 38. The method of claim 35, wherein the blunt arms are rotated at the rate of 1 revolution per day, or less.
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