US3561534A

US3561534A - Method and apparatus for cleaning oil wells

Info

Publication number: US3561534A
Application number: US855193A
Authority: US
Inventors: Daniel W Dendy
Original assignee: Individual
Current assignee: Individual
Priority date: 1969-09-04
Filing date: 1969-09-04
Publication date: 1971-02-09
Anticipated expiration: 1988-02-09

Abstract

A method for cleaning the perforations in an oil well casing liner set in an oil producing zone of the well hole including setting a cleaning tool initially adapted to produce high fluid pressure in the liner, depositing fluid in the well hole through a pipe, raising and lowering the tool to pump fluid into and create high fluid pressure in the liner so as to force the fluid through the perforations in the liner into the formation, converting the tool while in the well hole to a tool for producing a vacuum in the liner, and then raising and lowering the tool to produce a vacuum in the liner so as to draw the fluid from the formation through the perforations into the liner and to pump the fluid to the surface.

Description

United States Patent "i h a Primary Examiner-Stephen .I. Novosad Attorney-Miketta, Glenny, Poms and Smith ABSTRACT: A method for cleaning the perforations in an oil well casing liner set in an oil producing zone of the well hole including setting a cleaning tool initially adapted to produce high fluid pressure in the liner, depositing fluid in the well hole through a pipe, raising and lowering the tool to pump fluid into and create high fluid pressure in the liner so as to force the fluid through the perforations in the liner into the formation, converting the tool while in the well hole to a tool for producing a vacuum in the liner, and then raising and lowering the tool to produce a vacuum in the liner so as todraw the fluid from the formation through the perforations into the liner and to pump the fluid to the surface.

METHOD AND APPARATUS FOR CLEANING OIL WELLS BACKGROUND OF THE INVENTION AND PRIOR ART 'the hole extends down to the upper oil zone and then a 7% inch bit, for example, may be used to drill through the oil zone after which a reamer may be used to expand the diameter of the hole to 14 inches. Liner of 6% inches may then be set in the hole and gravel is packed around the outside of the liner within the reamed hole to provide a filter against silt or the like from stopping or plugging the holes in the perforated pipe but which allows the oil to enter the liner.

In an exemplary liner, the perforations may be l'rinches long when widths of .010 to .030 inches are employed and 2 inches long with widths from .030 to .500 inches. The width of the slot depends upon the overall diameter of the liner. The slots are longitudinally spaced approximately 6 inches apart commencing at approximately 12 inches from each end of the threaded section of the liner. The slots may be straight or undercut and may be staggered or aligned. The particular arrangement, size, overall ratio of perforate to imperforate material, etc. depends primarily upon the grain size of the sand or gravel surrounding the liner, strength limitations of the liner and the like.

Regardless of whether the liner is gravel packed, or is prepacked so as to provide a filter for attempting to maintain the perforations in the liner open, continued production generally gives rise to problems of plugging or clogging of the perforations in the liner during life of the well. lnsome instances, it may be desirable to wash such gravel pack or prepacked gravel liners when first installed. It will also be appreciated that these tools, while ordinarily referred to as cleaning tools, may also be used: (1) to relieve tightly packed sand conditions that might be present around the casing, (2) to loosen the sediment around a liner preparatory to pulling such liner from the hole, or (3) to wash the annular space around the casing and the walls of the formation so as to remove mud, filter cake, or similar formed materials which render production inefficient. Acid or other chemical solutions, clean oil or the like may be used as the cleaning fluid so as to dissolve paraffins, tars, etc. from the perforations and to remove such sediment from the well.

Of the more prevalent types of prior art devices and methods for cleaning or treating oil wells, one type is com monly referred to as a circulation washer." This system employs a downhole tool in which a small area'of the liner is washed or cleaned as the tool is moved up or down the liner with high pressure fluid pumped down into the liner from a large pump located above the ground. Some ofthe disadvantages of this system is the large amount of cleaning fluid required, for example, 150 to 200 barrels, and the concomitant large capacity storage for such fluid. Another apparent disadvantage is the considerable expense in the equipment and fluid.

Another type of prior art system which requires no surface pumps are generally referred to as pressure and suction washers" which comprises two downhole tools which are successively used to perform the cleaning operation. The pressure washer is used to force the cleaning fluid through the perforations of the liners and through the annular space around the liner and into the formation. The pressure is created by raising and lowering of the run-in-string which creates the pumping action. After the fluid has been pumped into the surrounding formation, the tool is withdrawn from the hole and the suction washer is then run into the hole and removes the cleaning fluid and debris from the well. The disadvantages of this system is primarily thecost involved because of the valuable rig time used in removing the pressure washer from the hole and subsequently running in the suction washer to complete the entire operation. Moreover, in most instances, a separate scratching tool cannot be concurrently used with the pressure washer and suction washer system.

It is therefore a primary advantage and object of the present invention to provide a method and apparatus for cleaning or treating an oil well in which a single downhole tool can be used to provide fluid pressure or suction. It is another object of the present invention to provide a method and apparatus for cleaning the liner or perforated pipe in an oil well by pumping cleaning fluid through such perforations, and subsequently withdrawing such cleaning fluid from outside of the liner over substantial lengths of liner. Another object of the invention is to provide a method and apparatus for eliminating the time consuming pipe pulling and disjointing procedure and subsequent pipe connecting and lowering required in prior art devices by allowing the downhole tool or device to be converted from a pressure pump to a vacuum pump. Yet another object of the present invention is to provide a device as above described in which no surface pump is required and in which the pumping action is produced by lowering and raising the tool to provide approximately 60 foot strokes and high pressure and vacuum.

GENERAL SUMMARY OF THE INVENTION Generally, the method for cleaning oil wells in accordance with the present invention relates to the cleaning of perforations in an oil well casing liner set in an oil producing zone of a formation and includes the steps of downhole setting of a tool initially adapted for producing high fluid pressure in the liner, depositing fluid in the well hole through a pipe to the tool, raising and lowering the tool with a rig so as to pump fluid into and create high fluid pressure in the liner so as to force the fluid through the perforations in the liner into the formation thereby unplugging and unclogging the perforations, subsequently converting the tool while in the well hole to a tool for producing a vacuum in the liner, and raising and lowering the tool to produce a vacuum in the liner so as to draw the fluid from the formation through the perforations into the liner and to pump such fluid to the surface. In the exemplary embodiment shown and described, the method and apparatus for converting the tool while down hole includes a standing valve lowered downhole on a wire line which engages a check valve on the tool locking the check valve into open position so that while the check valve initially permitted downward fluid flow and prevented upward fluid flow, the standing valve will now permit and prevent fluid flow in the opposite directions.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic view of a portion of a well hole showing the formation and oil zone and the tool of the present invention set in a perforated liner preparatory to the cleaning operation;

FIG. 2a and 2b together comprise an enlarged view of an exemplary embodiment of a tool or apparatus for cleaning an oil well constructed in accordance with the present invention and shown in FIG. 1.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, there is shown a portion of a well hole in which an outer casing 2.0 has been set, down to approximately the upper end of an oil producing zone indicated generally at 21 of the formation in which the well hole has been drilled. Within the casing 20, a liner 22 i set having per forations 23 (schematically shown) through the zone 21 and up into the casing 20. Around the perforated liner there may be packed gravel 24 to provide a filter between the oil sand and the liner.

The present invention relates to a tool or apparatus indicated generally at and a method for maintaining the liner perforations 23 free, unplugged and unclogged so that oil from the zone 21 may freely enter the perforated liner 22 through which it may be pumped to the surface. Generally, tool 30 comprises means for centering the tool within the' perforated liner 22; scratching means, indicated generally at a first tubular section having at least one opening therein; a second tubular section having at least one opening therein; cup means, indicated generally at 55, mounted on second tubular section 50 above and below the opening; a check valve indicated generally at 70 mounted above the second tubular section 50, and a standing valve (see FIG. 2a) indicated generally at 80 selectively connected to the check valve 70 of the tool. The tool is set in the liner 22 at the end of a string indicated generally at 31 and comprising a plurality of pipe sections run into the hole in a conventional manner.

in the exemplary embodiment of tool 30, the means 35 for centering the tool within the casing comprises a standard casing centralizer including a plurality of bowed springs 36 carried by annular members 37 supported on pipe section 38 to which is attached a bullnose 39 at the lower end thereof. The eentralizer assures that the tool is centered in the liner particularly to aid in scratching the inner surface of the liner.

Scratching means 40 in the exemplary embodiment comprLes a section of pipe 61 on which stiff wire bundles 42 are mounted around the circumference, as in a spiral pattern, to scratch paraffin, tars, etc. from the liner inner wall surfaces. The particular scratching means, is of no importance to the present invention but it should be noted that the scratching means forms a part of the tool so that the scratching operation may be performed at the same time that the liner is cleaned with the fluid, so as to avoid an extra step in the operation.

Above the scratching means 40, there is mounted the first tubular section 45 having a plurality of openings 46, three being shown, although it will be understood that any number of openings may be provided. Mounted immediately above first tubular section 45 is second tubular section 50 also having at least one opening 511.

On second tubular section 50 there is mounted cup means indicated generally at and in the exemplary embodiment such means 55 includes a plurality of individual resilient generally frustoconically-shaped cups. The cups are designed to provide a seal against a pressure difi'erential in one direction in which the higher fluid pressure expands the cup forcing it into sealing engagement with the surrounding liner. It is therefore apparent that it is important to the successful assembly and operation of the tool of the present invention that the plurality of cups be properly oriented at the respective positions at which they are mounted in longitudinally spaced apart relation. Referring to FIG. 2b, cups 56, S7, 58 and 59 are mounted above opening 51 in the second tubular section 50 while

cups

68, 61, 62 and 63 are mounted below the opening 51. The two

cups

58, 59 comprising the first adjacent cups above opening 51 and

cups

60, 61 comprising the first adjacent cups below opening 51 are oriented to provide a seal when the pressure in the annular chamber 64 is greater than the pressure in the chamber 65 below the cup means 55. The

lowemiost cups

62, 63 of the cup means are oriented so as to prevent fluid from below the cups in chamber 65 from flowing upwardly between the tool and the liner when the tool is lowered so that the pressure in chamber 65 exceeds the pressure in chamber 64 and thereabove. Similarly, the

uppermost cups

56, 57 are oriented so as to prevent fluid deposited above the tool from flowing downwardly between the tool and the liner when the tool is lowered so that the pressure in chamber 66 above the cup means 55 is greater than the pressure in chamber 64. It will therefore be seen that the individual cups are oriented so that during the cleaning operation there is provided a seal regardless of which of the

chambers

64, 65 or 66 is at a higher pressure than the adjacent chamber separated only by the cups.

Mounted above the second tubular section 50 issthe check valve indicated generally at 70 which may be any conventional check valve used in downhole oil well operations and which may exemplarily include a pipe section housing 71, a valve member 72, a valve seat 73 secured in housing 71 by sleeve 74 secured in position by pipe section collar 75. A spring support member 76 is fixedly positioned in the lower portion of check valve housing 71 and supports a spring 77 for biasing valve member 72 into closed position. The upper end of valve member 72 is provided with a shoulder 78 having a plurality of fluid orifices 79 therein. Check valve 70 allows fluid to pass downwardly but prevents the upward flow of fluid since a higher pressure within the housing 71 and second tubular section 50 than in the pipe string 31 produces a pressure differential across the check valve so as to close valve member 72 on seat 73. A reversal of the pressure differential last described will be seen to produce a downward flow of the fluid through the check valve which will remain open under the pressure differential.

in the exemplary embodiment of tool 30, the tool may be selectively fitted with standing valve 80 to convert the tool while in the downhole position from its initial capacity for producing high fluid pressure in the liner to now function to produce a vacuum in the liner, i.e., chamber 65. The standing valve 80 disposed in pipe section 81 includes a body 82 having an inner chamber 83 open at the bottom and through the sides, a valve seat 84, and a ball valve 85. The standing valve 80 allows fluid to pass upwardly therethrough when the pressure in the housing 81 below the ball valve 85 is greater than the pressure of the fluid above the standing valve. When the pressure differential is reversed, fluid is prevented from flowing downwardly. The standing valve includes means for rendering the check valve 70 inactive which is carried'by body 82 and comprises circumferentially spaced locking prongs or legs 86 having an upwardly facing annular stop shoulder 87. Stop shoulder 87 is adapted to seat below radially inwardly extending annular housing shoulder 88 so as to depress check valve member 72 opening the check valve 70 when the standing valve 80 is lowered into engagement with the tool. The standing valve is releasably locked in position since its downward force when lowered into the tool will cause temporary deflection of the prongs 86 so that the feet of the prongs may bear against valve member 72 until the stop shoulder 87 on the legs 86 engage the housing shoulder 88 whereupon upward bias by spring 77 on valve member 72 will maintain the standing valve 80 in proper position.

At the top end of body 82 of the standing valve 80 is mounted a retriever nose 90 adapted to cooperate with a conventional retrieving tool assembly (not shown), such as that manufactured and sold by the Fluid Packed Pump Division of Armco Steel Corp., Los Nietos, Calif. As in standard practice, the retriever assembly is engaged with the standing valve through the nose at the surface and lowered downhole on a wire line by its own weight. When the check valve member 72 is engaged and the standing valve legs 86 are engaged with the housing shoulders 88 so as to position the standing valve the retriever assembly will automatically release the standing valve when the assembly is pulled upwardly. When it is desired to return the standing valve to the surface, after the cleaning is complete, the retriever assembly is lowered and will automati- Y, cally grasp the nose 90 upon contact therewith so that raising the retriever assembly will disengage the legs 86 from the housing shoulders 88 whereby the entire standing valve may be raised to the surface.

Having described the structure of an exemplary apparatus of a tool constructed in accordance with the present invention, the operation of such tool and the method for cleaning the perforations in the oil well casing liner will now be described. The tool 30 is run into the hole in accordance with conventional practice at the end of the pipe string 31. When the tool has been lowered to the oil producing zone so as to be positioned in the perforated portion of the casing, the cleaning operation commences. It will be appreciated that during all movements of the tool relative to the liner 22, the scratching means 40 will aid in the cleaning of, the liner by scraping or scratching sediment from the inner wall surface. It will be understood, that the liner 22, at this point of the operation, will be full of oil, water and other fluids. The tool 30, however, will sink to the bottom of the liner or to the position desired.

It must also be appreciated that'when the tool is set for the commencement of the operation, the tool is initially adapted for producing a high fluid pressure in the liner since the standing valve is not engaged with the tool, as explained more fully in detail hereinafter.

Cleaning fluid is now deposited into the tool and liner from the surface. The tool is then raised and lowered, in 60 foot strokes, by a conventional drilling rig. On the first upstroke, the fluid, oil, etc. within the tool will flow through the check valve 70, second tubular section 50 and into first tubular section 45 and out of the openings 46 since the cup means 55 will form a vacuum in chamber 65. At the top of the first upstroke, the fluid will have completely filled the chamber 65 below the tool 30 and the cup means 55 but will not be forced through the perforations in the liner. The tool is now lowered on its first downstroke whereupon the check valve 70 will close because of the pressure differential created so as to prevent fluid flow through the tool. Simultaneously, the cup means 55 will prevent the upward flow of fluid between the tool and the inner surface of the perforated liner. The fluid in chamber 65 is therefore forced through the openings46 in first tubular section 45 and upward into second tubular section 50. The pressure in chamber 65 will exceed the pressure in chamber 64 so that the fluid will be forced out of opening 51 in second tubular section 50 and will be prevented from passing between the tool and the liner by

cups

59, 60 so that the fluid is forced with great pressure through the perforations 23 in the liner 22 as the tool moves downwardly in the liner. It is believed that pressures as high as 1,000 psi are created in chamber 64 by the above-described pumping action. It will be seen that sections of substantially 60 foot length are cleaned by the raising and lowering of the tool with the present invention. The pressure operation continues with further fluid being deposited into the liner and tool and pumped through the perforations in. the liner through the gravel, and into the formation. When the perforations are satisfactorily cleaned, the tool may be converted to a suction pump so that the cleaning fluid may be reclaimed, and the sediment and other foreign materials removed from the liner and the surrounding formation.

The tool may now be converted while in the downhole position to a tool for producing a vacuum in the chamber 65 of the liner. The conversion is accomplished by lowering the tool to the bottom of the liner and then lowering the standing valve 80 on a wire or cable line which engages the check valve 70 so as to lock the check valve in open position, the standing valve automatically seating and released by a retriever assembly with which the valve is lowered. On the following upstroke, the standing valve 80 will be closed so that a vacuum is created in the tubular sections below the standing valve. Also, a vacuum will be created below the cup means 55 so that fluid will flow in from the formation through the gravel and the perforations in the liner into chamber 65. The chamber 65 is now filled with the fluid. On the succeeding downstroke, the tool will force the fluid in chamber 65 through the openings 46 in first tubular section 45 and upward through second tubular section 50 passed the check valve 70 and the standing valve 80 which is now open. The fluid is thus forced to the surface. Some small amount of fluid during the downstroke will pass out of the opening 51 in second tubular section 50 to further wash the liner depending upon the restriction in the standing valve 80. When all of the fluid has been reclaimed, the cleaning operation is complete, and the tool may be returned to the surface.

As is well known in the oil well drilling and production art, it is always desirable to raise a pipe string which is dry, i.e., each section of the pipe is not filled with the fluid from the wellhead so that when the sections are disconnected, the fluid will not pour out onto the surface working area. The tool of the present invention may be raised dry by lowering the retriever assembly on the wire line so as to grasp the nose 90 of the standing valve and which may be raised so as to bring the standing valve 80 to the surface. Thereafter, as a pipe string is raised, the fluid therewithin will have a pressure head greater than the chamber in the first and second tubular sections of the tool so that the fluid in the pipe string will open the check valve 70 flowing through the valve into the first and second tubular sections and out of the

openings

46 and 51. Moreover, the check valve will function to prevent any inadvertent blowout of the well.

From the above-detailed description of an exemplary. embodiment of an apparatus constructed in accordance with the present invention and a description of an exemplary method for cleaning an oil well, it will be seen that all of the objects and advantages previously set forth for the present invention are attained. The present invention will provide considerable savings in labor and equipment expenses by its unique feature wherein the cleaning tool may be converted from a pressure to a suction operating tool while in the downhole position.

While the above description has been specific, it will be apparent to those skilled in the art that means other than those specifically described above may be employed to accomplish the objects of the present invention. Many modifications and variations of this invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

I claim:

1. A method for cleaning the perforations in an oil well casing liner set in an oil producing zone of the formation comprising the steps of:

setting a tool initially adapted for producing high fluid pressure in the liner into the oil producing zone on a pipe string; depositing fluid in said liner and pipe string; raising and lowering the tool to pump fluid into and create high fluid pressure in the liner so as to force the fluid through the perforations in the liner into the formation;

converting the tool while in the well hole to a tool for producing a vacuum in the liner; and

raising and lowering the tool to produce a vacuum in the liner so as to draw the fluid from the formation through the perforations into the liner and to pump the fluid to the surface.

2. The method of claim 1 wherein said tool is initially set so that raising the tool allows the fluid deposited into the well hole to flow through the tool into the liner and lowering the tool prevents fluid from flowing through the tool or between the tool and liner thereby forcing the fluid through the liner perforations.

3. The method of claim 2 wherein the tool is converted while in the well hole so that raising the tool draws fluid into the liner through the vacuum created in the liner and tool and lowering the tool forces fluid through the tool and up the pipe string to the surface.

4. The method of claim 3 wherein the tool is converted while in the well hole by lowering a standing valve on a wire line to engage a check valve on the tool so as to lock the check valve into open position.

5. The method of claim 4 additionally including the steps of retrieving the standing valve with a wire line and raising the tool to the surface, the tool allowing lfluid from above to flow therethrough when raised so as to come up dry.

6. A tool for cleaning, unplugging and unclogging the perforations in the casing liner set in a well hole oil producing zone comprising:

means for centering the tool in the liner;

a first tubular section mounted above said centering means and having at least one opening in the sidewall thereof;

a second tubular section mounted above said first tubular section and having at least one opening disposed in the sidewall thereof, resilient annular cup means mounted on said section above and below said opening;

a check valve mounted above said second tubular section preventing fluid below the valve within said sections from passing upwardly when the tool is lowered, and allowing fluid deposited above the valve to pass downwardly when said tool is raised in the well hole;

said cup means forcing fluid in the liner below said means through said opening in said first tubular section into said first tubular section and upwardly out of said opening in said second tubular section and through the perforations in the liner when said tool is lowered in the well hole;

a standing valve selectively mounted above said check valve for converting said tool while in the well hole from producing pressure in the liner below said tool to producing a vacuum in the liner below said tool, including means for rendering said check valve inactive; and

said cup means and standing valve creating a vacuum therebelow after conversion of said tool, allowing fluid to pass through said perforations into the liner when said tool is raised, and forcing fluid through said openings in said first tubular section into said tool and upwardly through said standing valve to the surface when said tool is lowered.

7. The tool of claim 6 additionally including liner inner wall scratching means carried by said tool.

*1. The tool of claim 6 additionally including retriever means selectively attached to said standing valve and a wire line for lowering said retriever means and standing valve down to said tool to convert said tool, said retriever means being lowered into the hole and releasing said standing valve upon engagement with said tool and thereafter withdrawn from the well hole, said retriever means being lowered by said wire line back into said hole upon completion of said cleaning operation so as to attach said standing valve-and thereafter be withdrawn therewith from the well hole, whereby said tool may be raised dry.

9. The tool of claim 6 wherein said cup means comprises a plurality of individual sealing cups, each of said cups preventing fluid flow in one direction upon movement of said tool and cups relative to the perforated liner, the cups first adjacent said opening in said second tubular section oriented so as to prevent fluid pumped through said opening from flowing between said tool and the liner so as to force the fluid through the liner perforations and into the formation.

10. The tool of claim 9 wherein at least the lowermost cup is oriented so as to prevent fluid below said cups from flowing upwardly between said tool and said liner when said tool is lowered.

11. The tool of claim 10 wherein at least the uppermost cup is oriented so as to prevent fluid deposited above the tool from flowing downwardly between said tool and liner when said tool is lowered.

Claims

1. A method for cleaning the perforations in an oil well casing liner set in an oil producing zone of the formation comprising the steps of: setting a tool initially adapted for producing high fluid pressure in the liner into the oil producing zone on a pipe string; depositing fluid in said liner and pipe string; raising and lowering the tool to pump fluid into and create high fluid pressure in the liner so as to force the fluid through the perforations in the liner into the formation; converting the tool while in the well hole to a tool for producing a vacuum in the liner; and raising and lowering the tool to produce a vacuum in the liner so as to draw the fluid from the formation through the perforations into the liner and to pump the fluid to the surface.

5. The method of claim 4 additionally including the steps of retrieving the standing valve with a wire line and raising the tool to the surface, the tool allowing fluid from above to flow therethrough when raised so as to come up dry.

6. A tool for cleaning, unplugging and unclogging the perforations in the casing liner set in a well hole oil producing zone comprising: means for centering the tool in the liner; a first tubular section mounted above said centering means and having at least one opening in the sidewall thereof; a second tubular section mounted above said first tubular section and having at least one opening disposed in the sidewall thereof, resilient annular cup means mounted on said section above and below said opening; a check valve mounted above said second tubular section preventing fluid below the valve within said sections from passing upwardly when the tool is lowered, and allowing fluid deposited above the valve to pass downwardly when said tool is raised in the well hole; said cup means forcing fluid in the liner below said means through said opening in said first tubular section into said first tubular section and upwardly out of said opening in said second tubular section and through the perforations in the liner when said tool is lowered in the well hole; a standing valve selectively mounted above said check valve for converting said tool while in the well hole from producing pressure in the liner below said tool to producing a vacuum in the liner below said tool, including means for rendering said check valve inactive; and said cup means and standing valve creating a vacuum therebelow after conversion of said tool, allowing fluid to pass through said perforations into the liner when said tool is raised, and forcing fluid through said openings in said first tubular section into said tool and upwardly through said standing valve to the surface when said tool is lowered.

8. The tool of claim 6 additionally including retriever means selectively attached to said standing valve and a wire line for lowering said retriever means and standing valve down to said tool to convert said tool, said retriever means being lowered into the hole and releasing said standing valve upon engagement with said tool and thereafter withdrawn from the well hole, said retriever means being lowered by said wire line back into said hole upon completion of said cleaning operation so as to attach said standing valve and thereafter be withdrawn therewith from the well hole, whereby said tool may be raised dry.