Pressure-controlled well tester operated by one or more selected actuating pressures

BACKGROUND OF THE INVENTION
This invention relates to full-bore drillstem testing apparatus; and, more particularly, this invention pertains to new and improved drillstem testing apparatus which is operated by selectively varying the pressure of the well bore fluids without needlessly risking damage to perforated well bore intervals.
BACKGROUND ART
It is customary to conduct so-called "drillstem tests" in cased well bores having one or more perforated intervals that provide fluid communication with earth formations penetrated by the well bore. One typical operating technique utilizes a full-bore packer that is positioned at a convenient depth location in the well bore and set for packing-off or isolating the formations which are to be tested from the completion fluids in the well bore. To conduct these drillstem tests, an assembly of tandemly-coupled full-bore tools is dependently suspended from a pipe string that is successively assembled and lowered into the cased well bore until a depending conduit or seal assembly arranged on the lower end of the tool string is inserted into a central seal bore in the packer and fluidly sealed therein. A normally-closed valve in the tool string is then selectively operated for opening fluid communication between the pipe string and the formations below the packer. In this manner, should the formations contain producible connate fluids, opening of the test valve will allow the fluids to flow to the surface by way of the tool string and the supporting pipe string. A series of pressure measurements are typically obtained by means of suitable pressure recorders included in the tool string. A sample-collecting tool is also typically included in the tool string whenever it is desired to collect one or more representative samples of the connate fluids produced during the testing operations.
Those skilled in the art recognize, of course, that many of the testing tools employed over the past few years have been controlled by selectively increasing the pressure of the well control fluids in the well bore above the packer to open the test valve and relieving the increased pressure when the valve is to be closed. Typical testing tools of this nature are described in Reissue Patent No. 29,638 and U.S. Pat. No. 3,901,314 issued to Nutter as well as in U.S. Pat. No. 4,440,230 issued to McGill, each of which are respectively assigned to the assignee of the present application and are hereby incorporated by reference. As fully described in these patents, these tools are operated by a pressure-responsive valve actuator having one pressure surface subjected to the pressure of the well bore fluids and its other pressure surface subjected to the pressure of a compressible gas such as nitrogen that is isolated in one portion of an enclosed chamber by a floating piston member. These tools respectively include inner and outer telescoping members that are arranged for controlling the communication between the well bore and the other portion of the enclosed chamber. In each of these tools, these telescoping members are initially positioned to communicate the well bore fluids with the other portion of the enclosed chamber so that the valve actuator will remain balanced in relation to the hydrostatic pressure of the well control fluids as the tools are being lowered into a well bore. Once these testing tools are positioned to conduct a test, the supporting pipe string is then slacked off to shift these inner and outer telescoped members to an alternate position which selectively closes off communication with the well bore and traps the well fluids in the other portion of the enclosed chamber and thereby maintain the compressible gas at the hydrostatic pressure of the well fluids. Since the other side of the valve actuator is still communicated with the well bore fluids, the test valve in each of these tools can thereafter be selectively opened and closed by selectively increasing and relieving the pressure of these fluids.
The test tool described in the above-identified Nutter reissue patent utilizes an actuator spring which is cooperatively arranged to reclose the test valve whenever the pressure in the well bore is again restored to its normal hydrostatic pressure. Nevertheless, it has been noted that the actuator spring in the Nutter testing tool lacked sufficient strength to reliably return the valve actuator to its normal valve-closing position in some operating situations. Accordingly, the new and improved testing tool shown in the above-identified McGill patent is arranged in keeping with the above-described inventive concepts of the Nutter reissue patent; but, as shown generally at "70" in this McGill patent, the McGill tester valve includes an additional pressureresponsive actuator which cooperatively utilizes the elevated pressure of the well bore fluids to supplement the closing force provided by the actuator spring.
The above-identified Nutter patent also shows a testing tool that also incorporates the inventive concepts of the Nutter reissue patent. As fully described in that patent, this later testing tool is uniquely modified to include an enclosed chamber that is normally closed by a rupture disc cooperatively arranged to fail if the pressure of the well bore fluids is inadvertently raised to an excessive level. Should the rupture disc fail, well bore fluids are admitted into a normally-isolated chamber in the test tool to impose an additional closing force on the valve actuator. Once the rupture disc fails, the valve member is permanently moved to its closed position and the testing tool must be returned to the surface before the valve member can be reopened.
When either of the above-described testing tools are utilized with a full-bore production packer that has been set in the well bore above a formation interval of interest, typically a slip joint is coupled to the lower end of the supporting pipe string above one or more drill collars for imposing a substantial downward force on the tool string to prevent a seal assembly that carries a perforated tail pipe on its lower end from being forced upwardly out of the packer as treating fluids are injected into the isolated well bore interval. It will, of course, be realized that when a test operation is conducted in a well bore that has a permanent packer, it is preferred to avoid having either a slip joint or one or more drill collars coupled in the pipe string.
It will be realized that when tests are conducted in a well bore which has a permanent packer set above a perforated interval, the isolated formations might be damaged unless the pressure in that interval is controlled. For instance, a bypass vent passage should be provided at a convenient place in the tool string to accommodate the fluids displaced from the isolated interval as the seal assembly is inserted into the packer seal bore. If the formations are to be protected, the passage must be closed before increasing the pressure in the well bore annulus above the packer to open the test valve. Conversely, it will be recognized that once the seal assembly has been inserted into the packer seal bore, the pipe string is then typically elevated to properly position the test string before commencing a test. Thus, unless a bypass vent or relief passage is provided, the raising of the seal assembly in relation to the packer seal bore may reduce the pressure of the fluids in the isolated interval to an unacceptably-low level.
OBJECTS OF THE INVENTION
Accordingly, it is an object of the present invention to provide a new and improved drillstem testing tool which may be selectively operated from the surface without having to manipulate the supporting pipe string for trapping well bore fluids in a portion of an enclosed pressure reference chamber to provide an elevated pressure therein that can enhance the valve actuation of the tool.
It is a further object of the invention to provide a new and improved testing tool including a pressureresponsive relief valve which cooperatively responds to changes in the pressure differential between the interior and exterior of the pipe string for protecting the earth formations to be tested from adverse high or low pressures.
SUMMARY OF THE INVENTION
These and other objects of the present invention are attained by providing a pressure-actuated testing tool arranged to be connected in a pipe string and including a body defining a flow passage. Tester valve means, which may be full opening are cooperatively arranged in the tool body for selectively opening fluid communication through the flow passage in response to a selected increase in the well annulus pressure. An enclosed chamber is arranged in the body and is divided by a floating compensating piston into a first portion for containing a compressible fluid and a second portion adapted to contain well bore fluids that will act on the piston to maintain the compressible fluid at an elevated pressure corresponding to the pressure of the well annulus fluids in the second portion of the chamber. The testing tool further includes pressure-responsive valve means normally admitting well bore fluids into the second portion of the chamber and operable when the well annulus pressure increases to a selected level above atmospheric pressure for then closing to trap a supply of the well bore fluids at this increased pressure in the second chamber portion. The increased pressure provides a reference pressure to permit opening the test valve means in response to a further increase in annulus fluid pressure. When such further increased pressure is reduced, a mechanical coil spring that was compressed during valve opening forces the test valve means back to the closed position. Except for the feature of having a pressure-responsive reference valve, the foregoing summary is of equipment disclosed in the above-mentioned Nutter Re 29,638 patent and the McGill U.S. Pat. No. 4,440,230, to which reference has been made.
Although pressure-responsive reference valves are known generally (seen U.S. Pat. Nos. 3,976,136, 3,964,544, and 4,105,075) such prior valve structures have required a differential in pressure between annulus fluids and tubing fluids in order to produce a reference valve closing force. This requirement is highly undesirable for the principle reason that subsequent well service operations such as fracturing, acidizing or squeezing can employ such high tubing pressures as to cause the test valve to automatically close, and thus abruptly terminate the particular well service operation being performed. In accordance with the present invention, however, reference valve operation is totally insensitive to internal or tubing pressure and thus is a marked advance and improvement over the structures shown in the patents noted in the above parenthetical. The testing tool further includes bypass relief valve means initially controlling fluid communication between the well bore and the flow passage in the tool so that the isolated well bore interval is not subjected to unacceptable pressure differentials while the testing tool is being initially positioned before starting the testing operation.

BRIEF DESCRIPTION OF THE DRAWINGS
The several patentable features and distinctive aspects of the present invention are set forth with particularity in the appended claims. The arrangement and operation of the invention, together with further objects and various advantages thereof, may best be understood by way of the following written description of a preferred embodiment of apparatus incorporating the principles of the invention when taken in conjunction with the accompanying drawings, in which:
FIG. 1 shows a string of full-bore well tools such as may be typically used in a cased well bore and including a full-bore testing tool of the present invention; and
FIGS. 2A-2D are successive, elevational views which are partially cross-sectioned for showing a preferred embodiment of a new and improved full-bore testing tool incorporating the principles of the present invention.

DESCRIPTION OF A PREFERRED EMBODIMENT
Turning now to FIG. 1, a testing tool 10 arranged in accordance with the principles of the present invention is shown dependently coupled from the lower end of a pipe string 11 such as is typically assembled from a plurality of tandemly-coupled tubing joints. Although the new and improved testing tool 10 can be successfully employed to conduct drillstem tests in an uncased borehole, the testing tool is depicted as it might be utilized to conduct a drillstem test in a cased well bore as at 12. It will also be realized that although the new and improved testing tool 10 can be operated in conjunction with a retrievable packer that is tandemly coupled to the lower end of the testing tool, FIG. 1 shows a production packer 13 that has been previously set at a convenient location in the well bore 12 for isolating one or more earth formations, as at 14, which are in communication with the isolated well bore interval by means of one or more perforations as at 15.
The testing tool 10 includes a pressure-operated tester valve 16 such as described in the above-identified McGill patent that is operated from the surface by selectively controlling the pressure of the fluids in the annulus of the well bore 12 above the packer 13. The drillstem testing tool 10 further includes a new and improved pressure reference tool 17 and a double-acting bypass valve 18 that are respectively arranged in accordance with the principles of the present invention. As will be subsequently described, the pressure reference tool 17 and bypass valve 18 are coupled in the tool string below the tester valve 16 and arranged to facilitate the operation of the testing tool to conduct one or more drillstem tests in the well bore 12. A seal assembly or socalled "stinger", as shown at 19, that is appropriately sized to be slidably and sealingly inserted into the upstanding seal bore of the packer 13 is tandemly coupled in the string of tools at a convenient location below the bypass valve 18.
To record the changes in pressure conditions in the well bore 12 during the course of a drillstem test, the testing tool 10 further includes one or more pressure recorders (not seen in the drawings) which are enclosed in a housing 21 arranged at a convenient location in the string of testing tools. It will, of course, depend upon the nature of any given testing operation and the condition of the well bore 12, but those skilled in the art will appreciate that one or more additional full-bore tools such as a sample collector, a jar and a safety joint (none of which are illustrated) may also be included in the tool string without affecting the operation of the drillstem testing tool 10. It will also be appreciated that, if necessary, a pressure-actuated perforating gun or so-called "tubing-conveyed perforator" (not seen in the drawings) such as the one described in U.S. Pat. No. 4,509,604 can be dependently coupled below the seal assembly 19 and appropriately arranged to be operated after the testing tool 10 has been positioned in the well bore 12.
Turning now to FIGS. 2A-2D, successive, partially cross-sectioned elevational view are shown for illustrating a preferred embodiment of the new and improved testing tool 10 of the present invention which (as previously described by reference to FIG. 1) is arranged for operation in a cased well bore, as at 12, that was previously perforated to communicate one or more formations, as at 14, with the isolated interval of the well bore below the packer 13. To facilitate the description of the tool 10, FIGS. 2A-2D have been simplified by eliminating some of the minor constructional details of the tool but without affecting the full and complete disclosure of the present invention.
Since the pressure-controlled tester valve 16 which is preferably included in the new and improved testing tool 10 is fully described in the above-identified McGill patent, in FIG. 2A only the lowermost portion of the tester valve is shown. As illustrated, the tester valve 16 has inner and outer coaxiallydisposed tubular body members 22 and 23 that are coupled at their lower ends to a tubular end member 24 and arranged for defining a full-bore axial passage 25 through the tester valve. To control the fluid communication through the axial passage 25, the tester valve 16 includes a movable valve member such as a rotatable ball (not seen in the drawings) which is selectively shifted between its open and closed positions by a pressure-responsive actuator (also not seen in the drawings) which is telescopically arranged in a higher portion of the inner body member 22. As described in the McGill patent, the tester valve 16 is cooperatively arranged so that it will be opened by selectively increasing the pressure of the fluids in the well bore 12 to at least a first pressure level and closed whenever the well bore pressure is subsequently reduced below that first pressure level. As described in the McGill patent, closing of the tester valve 16 is facilitated by providing a so-called "reference pressure" chamber in the tool.
Accordingly, in keeping with the McGill patent, the inner and outer body members 22 and 23 are arranged to define an annular chamber 26 above the end member 24 in which an annular piston 27 is slidably and sealingly arranged for dividing the chamber into first and second isolated portions, with the first or upper portion of the chamber being arranged for containing a compressible fluid such as nitrogen or some other suitable gas. A longitudinal passage 28 is arranged in the end member 24 to admit fluids in the well bore 12 into the lower portion of the chamber 26 before the pressure reference tool 17 is operated to block the passage. It will, of course, be appreciated that the upper portion of the piston chamber 26 which is isolated above the annular piston 27 functionally corresponds to the gas or nitrogen chamber seen at "62" in the McGill patent. In addition to isolating a suitable gas confined in the chamber 26 above the piston 27, the piston also serves to increase the pressure of that gas to the pressure level of the well bore fluids which are admitted by way of the longitudinal passage 28 into the lower portion of the chamber before the pressure reference tool 17 has permanently blocked further access to the passage to thereby trap a selected reference pressure in the chamber. The significance of this latter feature will subsequently become more apparent.
Turning now to FIGS. 2B-2D, a preferred embodiment of the new and improved pressure reference tool 17 and the bypass valve 18 of the invention are depicted as they will respectively appear when the drillstem testing tool 10 is in its initial or so-called "running-in" position. As illustrated, the pressure reference tool 17 and the bypass valve 18 have an elongated body 29 that is preferably arranged as a plurality of tandemly-coupled tubular sections which collectively define a continuation of the axial passage 25 in the tester valve 16 for providing a full-bore passage between the pipe string 11 and the seal assembly 19. To couple the tester valve 16 to the pressure reference tool 17 and the bypass valve 18, as illustrated in FIG. 2A, the end member 24 is threadedly coupled into the upper end of the body 29 and a reduced-diameter tubular extension 30 dependently coupled to the end member is coaxially fitted into and fluidly sealed, as at 31, within the upper end of the tubular body.
To communicate well bore fluids into the lower portion of the chamber 26 in the tester valve 16, as depicted in FIG. 2B, the pressure reference tool 17 has an annular valve chamber 32 and a passage 33 appropriately arranged in the upper portion of the body 29 to be communicated with the longitudinal passage 28 in the lower end member 24 of the tester valve 16 when the two tools are tandemly coupled together. To control the pressure of well bore fluids that will be isolated in the lower portion of the chamber 26 by the operation of the pressure reference tool 17, that tool is also provided with pressure-responsive relief valve means such as an annular valve member 34 and a downwardlyacting biasing spring 35 which are respectively arranged within the valve chamber 32 to control the fluid communication between an external port 36 and an internal port 37 in the body 29 that opens into the passage 33. The valve member 34 has an inwardlyprojecting upper portion 38 and a lower skirt portion 39 which respectively carry spaced sealing members 40 and 41 which engage the inner wall of the chamber 32 and are positioned to straddle the internal port 37 and thereby block that port so long as the force of the biasing spring 35 is able to retain the valve member in its illustrated normal port-closing position.
It will, of course, be recognized by those skilled in the art that since there are no external sealing members on the annular valve member 34, the pressure of the fluids in the well bore 12 outside of the tool body 29 will be acting on both ends of the annular valve member 34; and fluids in the longitudinal passage 33 will impose an upwardly-directed pressure force on the lower face of the enlarged upper portion 38 of the valve member which is countered by the downwardly-acting force of the biasing spring 35. Thus, as will be subsequently explained, the valve member 34 will remain in its illustrated port-closing position unless the pressure in the passage 33 exceeds the pressure in the well bore 12 by a predetermined differential which is dependent upon the performance characteristics of the spring 35 and the difference in the cross-sectional areas of the upper and lower portions 38 and 39 of the valve member.
To control the admission of well bore fluids into the lower portion of the chamber 26, the new and improved pressure reference tool 17 of the present invention further includes an elongated valve member or tubular mandrel 42 that, as shown in FIGS. 2B and 2C, is telescopically disposed in the tool body 29 and cooperatively arranged for moving longitudinally between its depicted lower or initial passage-opening position and a higher or final passage-closing position. The pressure reference tool 17 is provided with first or upper valve means 43 including a first pair of sealing members 44 and 45 cooperatively arranged on an upper portion of the mandrel 42 for controlling communication between a first set of longitudinally-spaced ports 46 and 47 in the inner wall of the body 29. In the preferred embodiment of the pressure reference tool 17, the upper port 46 is connected with the passage 33 and the lower port 47 is communicated with the well bore 12 by way of a longitudinal passage 48 leading to an annular space 49 in the body 29 that is, in turn, communicated with the exterior of the tool body by way of a port 50 in the outer wall of the tool body. As illustrated, the sealing members 44 and 45 are appropriately spaced on the mandrel 42 so that the seals will straddle the ports 46 and 47 to intercommunicate them so long as the valve mandrel stays in its initial passage-opening position as well as to locate the lower seal 45 between the ports for blocking communication therebetween once the mandrel has been shifted to its final passage-closing or upper operating position.
In keeping with the objects of the present invention, the pressure reference tool 17 also includes pressure-responsive actuating means 51 selectively operable for shifting the mandrel 42 to its elevated or final operating position only when the well bore pressure is raised to a second level. As seen in FIG. 2C, in the preferred embodiment of the actuating means 51, a piston member 52 is arranged on an intermediate portion of the mandrel 42 and sealingly disposed in an annular chamber 53 in the tool body 29. A sealing member 54 is positioned between the mandrel 42 and the body 29 for isolating the upper portion of the annular chamber 53 above the piston 52. A closure member 55 is sealingly fitted in a port 56 and cooperatively arranged to be selectively opened only in response to an increase of the well bore pressure for admitting fluids from the well bore into the lower portion of the annular chamber 53 below the piston 52. It must be realized, therefore, that so long as the port 56 remains blocked, the lower portion of the annular chamber 53 will stay at a modest pressure such as, for example, atmospheric pressure until the closure member 55 is opened. In the preferred embodiment of the tool 17, it is preferred to arrange the closure member 55 as a so-called "rupture disc" designed to fail in response to a predetermined pressure differential.
To retain the valve mandrel 42 in its lower operating position until the pressure-responsive actuating means 51 have operated to shift the mandrel to its elevated operating position, the pressure reference tool 17 is provided with mandrel-retaining means 57 including a sleeve 58 which, as illustrated in FIG. 2B, is loosely disposed in the annular space 49. The sleeve 58 is longitudinally slotted at circumferentially-spaced intervals for defining a plurality of depending flexible collet fingers 59 cooperatively arranged with inwardly-directed heads 60 on their lower ends that are releasably coupled to the mandrel 42 by means such as complemental internal and external threads 61 which are respectively formed in the heads and around the adjacent portion of the mandrel 42. As depicted in FIGS. 2B and 2C, it will be seen that the threads 61 are cooperatively arranged so that the overall length of the external mandrel threads is at least equal to the longitudinal spacing between the lower and upper operating positions of the mandrel 42 so that the internally-threaded heads 60 on the collet fingers 59 will always be cooperatively engaged with the mandrel threads. The annular space 49 around the collet fingers 59 is appropriately sized for accommodating the outward movement of the collet heads 60 as the collet fingers are being successively flexed inwardly and outwardly by the upward travel of the mandrel 42.
In FIGS. 2C and 2D, a preferred embodiment of the new and improved double-acting bypass valve 18 of the invention is illustrated in its initial or so-called "running-in" position. As depicted, a lateral port 62 is arranged in the tool body 29 a short distance below the port 56 and the interior of the body is cooperatively formed to define an enlarged-diameter annular space 63 just below the port 62. A sleeve 64 is loosely disposed in the annular space 63 to define a fluid passage between the sleeve and the interior wall of the tool body 29 communicating a port 65 in a thick-walled upper portion of the sleeve with one or more circumferentially-spaced ports or elongated slots 66 in a thinwalled lower portion of the sleeve. A seal 67 is arranged around the sleeve 64 above the port 65 to seal the upper portion of the sleeve in relation to the tool body 29.
The bypass valve 18 also includes second valve means 68 comprising a tubular mandrel 69 which is telescopically disposed in the lower portion of the full-bore passage 25 in the tool body 29 and adapted to be moved longitudinally between its illustrated elevated position and one or more lower operating positions. As depicted in FIG. 2D, biasing means such as a coiled spring or a stack of Belleville washers 70 are cooperatively arranged on the mandrel 69 between an upwardly-facing body shoulder 71 and the lower face of a mandrel shoulder 72 to impose a moderate upward force thereon that normally maintains the mandrel in its elevated position. To selectively control fluid communication between the full-bore passage 25 and the well bore above the packer 13, as shown in FIG. 2C the mandrel 69 includes an enlarged upper portion 73 that is slidably disposed within the lower portion of the sleeve 64. A seal 74 is arranged on the enlarged mandrel portion 73 to be located above the ports 66 so long as the mandrel 69 is in its elevated port-closing position and to at least partially uncover the ports 66 when the mandrel is moved downwardly toward one or more of its lower operating positions during the operation of the bypass valve 18.
In keeping with the objects of the present invention, the new and improved double-acting bypass valve 18 also includes pressure-responsive means 75 cooperatively arranged to respond to predetermined changes in the well bore pressure conditions for increasing the overall force required for shifting the mandrel 69 downwardly from its elevated flow-blocking position. As shown in FIG. 2D, in the preferred embodiment of the force-controlling means 75, an annular piston 76 carrying inner and outer seals 77 and 78 is slidably arranged around an intermediate portion of the mandrel 69 and is disposed in an annular chamber 79 in the tool body 29 so that the upper face of the piston is normally engaged against a downwardly-facing shoulder 80 defining the upper end of the chamber. The piston 76 includes a depending skirt portion 81 which will ordinarily be kept in engagement with the upper face of the mandrel shoulder 72 by virtue of the upward force of the biasing springs 70 on the mandrel 69.
In keeping with the objects of the present invention, the force-controlling means 75 also include force-supplementing means 82 cooperatively associated with the piston 76 and adapted for significantly increasing the overall force required to shift the mandrel 69 downwardly from its normal flow-blocking position should there be a predetermined change in the well bore pressure conditions. To accomplish this, the force-supplementing means 82 include a sleeve 83 that is loosely disposed in the space 79 and has an upper portion longitudinally slotted at circumferentially-spaced intervals for defining a plurality of upstanding flexible collet fingers 84 extending upwardly around the mandrel shoulder 72 and terminating adjacent to the upper face of that shoulder. The upper ends of the fingers 84 are shaped to provide inwardly-directed camming surfaces 85 adapted for cooperative engagement by outwardly-directed camming surfaces 86 on the lower end of the depending skirt portion 81. It will, of course, be appreciated that although the opposing end or camming surfaces 85 and 86 are complementally shaped so that downward travel of the piston 76 relative to the collet fingers 84 will expand the fingers as the skirt 81 is driven into the fingers, the piston can not be moved downwardly until the downward force acting on the piston 76 is sufficient to overcome the force resisting the outward expansion of the collet fingers.
Accordingly, as will subsequently be more apparent, the mandrel 69 is normally supported in its elevated flow-blocking position by the moderate force provided by the biasing springs 70. It will, of course, be realized that so long as the opposing end surfaces 85 and 86 are abutted against one another, the valve mandrel 69 is free to move downwardly in relation to the piston 76 and the sleeve 83 against the moderate biasing force developed by the springs 70 as they are compressed between the opposing shoulders 71 and 72. On the other hand, it will be realized that since the skirt portion 81 of the piston 76 can abut on the mandrel shoulder 72, the valve mandrel 69 can also be shifted downwardly in relation to the tool body 29 should the pressure forces imposed on the piston 76 be of such magnitude that the substantial predetermined upward biasing force developed by the force-supplementing means 82 is no longer adequate to maintain the mandrel in its elevated flow-blocking position.
As previously related, the double-acting bypass valve 18 of the present invention is cooperatively arranged to respond to changes in the direction of the pressure differential between the interior and exterior of the bypass valve as will be required to protect the earth formations 14 from adverse pressure changes before the pressure reference tool 17 is initially operated. It will be appreciated, of course, that so long as the mandrel 42 of the pressure reference tool 17 remains in its initial operating position illustrated in FIGS. 2B-2C, sealing members 87 and 88 respectively arranged on the mandrel 42 and incorporated with the second valve means 68 will be straddling the ports 62 and 65. In that initial flow-blocking position of the mandrel 42, the fluids in the well bore 12 above the packer 13 are in communication with the enclosed annular space 63 defined between the sealing member 67 and the upper face of the piston member 76. At the same time, so long as the tester valve 16 has not been opened, the fluids in the full-bore axial passage 25 below the closed tester valve will be communicated through the unsealed annular clearance space 89 (FIG. 2D) around the lower portion of the mandrel 69 into the annular space 79 below the lower face of the piston member 76. Moreover, until such time that the pressure reference tool 17 is initially operated, the fluids in the full-bore axial passage 25 will also simultaneously impose a downward pressure force on the enlarged-diameter upper portion 73 of the mandrel 69 that will be jointly opposed by the moderate upwardly-directed biasing force of the stacked Belleville washers 70 against the mandrel shoulder 72 as well as any upward pressure force imposed against the upper mandrel portion by the well bore fluids in the annular space 63 therebelow.
Accordingly, it will be appreciated that so long as the tester valve 16 remains closed and the pressure reference tool 17 has not yet been operated to permanently block the communication between the ports 62 and 65, the second valve means 68 cooperate to longitudinally position the mandrel 69 of the double-acting bypass valve 18 in accordance with the direction and magnitude of the pressure differential at any given moment between the fluids in the well annulus 12 and the fluids in the full-bore passage 25. For instance, those skilled in the art will recognize that with the tester valve 16 closed, when the seal assembly 19 is first lowered into the seal bore of a previously-installed packer, as at 19, if it were not for unique operation of the double-acting bypass valve 18 of the invention, there would be a substantial increase in the pressure of the fluids in the isolated portion of the well bore 12 below the packer. It will be appreciated that any substantial increase in the pressure of the well bore fluids in the isolated interval below the packer 13 might potentially damage the adjacent earth formations 14.
In keeping with the objects of the present invention, therefore, the new and improved double-acting bypass valve 18 is cooperatively arranged for operating as necessary to prevent the pressure in the isolated zone of the well bore 12 from exceeding a predetermined moderate pressure level that is considered to be sufficiently low to avoid potential damage to the formations 14. Referring again to FIGS. 2C and 2D, it will be recognized that whenever the pressure in the axial passage 25 below the stillclosed tester valve 16 is increased above the pressure of the fluids in the well bore 12 outside of the body 29, there will be a corresponding increase in the net pressure forces acting on the mandrel 69 that will begin shifting the valve mandrel downwardly against the moderate biasing force of the springs 70. These increased forces will be effective, therefore, for shifting the mandrel 69 downwardly until the seal 74 begins to pass or uncover the ports 66. Once the ports 66 have been at least partially uncovered, the higher pressure of the fluids within the mandrel 69 will be reduced as these fluids escape into the annular space 63. This reduced pressure will, of course, be effective for correspondingly reducing the downwardly-directed pressure forces on the mandrel 69 so that the biasing springs 70 will shift the mandrel back upwardly toward its normal port-closing position.
It will be appreciated that the mandrel 69 may move upwardly and downwardly several times as the seal assembly 19 is being positioned in the packer 13. Ultimately, however, the pressure differential will again stabilize so that the biasing springs 70 will again retain the valve mandrel 69 in its depicted normal elevated port-closing position. It will, of course, be recalled that the opposing end surfaces 85 and 86 will remain abutted against one another so long as the pressure inside of the mandrel 69 is not reduced below the pressure outside of the tool 18. This will, therefore, leave the mandrel 69 wholly free to move downwardly relative to the piston 76 and the sleeve 83 and be opposed by the moderate biasing force developed by the springs 70 as they are compressed between the opposing shoulders 71 and 72 in addition to the force due to outside pressure.
On the other hand, it will be appreciated that so long as the tester valve 16 remains closed and the pressure reference tool 17 has not yet been operated for permanently blocking the communication between the ports 62 and 65, the second valve means 68 cooperate also to position the mandrel 69 of the double-acting bypass valve 18 as needed to counter a significant decrease in the pressure in the full-bore passage 25. For example, with the tester valve 16 closed, when the seal assembly 19 is positioned in a previously-installed packer, as at 19, if it were not for the new and improved bypass valve 18 there could be substantial decreases in the pressure of the fluids in the isolated portion of the well bore 12 below the packer should it be desired to raise the testing tool 10 to a slightly-higher depth location. It will be recognized that substantial pressure reductions in the isolated interval below the packer 13 can be undesirable.
In keeping with the objects of the present invention, therefore, the new and improved double-acting bypass valve 18 is cooperatively arranged for operating as necessary to prevent the pressure in the isolated zone of the well bore 12 from dropping below a predetermined moderate pressure level that would make it unnecessarily difficult to raise the tool string in the well bore 12. Referring again to FIGS. 2C and 2D, it will be recognized that so long as the pressure reference tool 17 has not yet been initially operated, as the pressure in the full-bore passage 25 begins to fall below the pressure of the well bore fluids outside of the tool body 29, there will be a corresponding increase in the net pressure forces acting upwardly on the mandrel 69 as the hydrostatic pressure of the well bore fluids in the annular space 63 is imposed on the lower face of the enlarged mandrel portion 73. It will be appreciated, however, that the hydrostatic pressure within the annular space 63 is also imposed against the upper face of the piston member 80. Thus, whenever the pressure in the bore 25 and the space 79 becomes lower than the pressure in the space 63, there will be a downward pressure force acting on the piston 76 that will be opposed by the collet fingers 84 acting on the lower end of the skirt 81. It will, of course, be recalled from the previous description of the force-supplementing means 82 that although the opposing end or camming surfaces 85 and 86 are shaped so that the downward travel of the piston 76 relative to the collet fingers 84 will expand the fingers as the skirt 81 is driven into them, the piston can not move downwardly until the downward pressure forces acting on the piston overcome the force resisting the outward expansion of the collet fingers. This can, of course, require a substantial pressure differential which, as will be subsequently described, will be predetermined as needed to assure the reliable operation of the testing tool 10.
At any rate, whenever the differential between the hydrostatic pressure in the chamber 63 and the fluid pressure in the passage 25 reaches this predetermined pressure differential, this pressure differential will be effective for forcibly urging the piston 76 downwardly unitl the collet fingers 84 are expanded outwardly and the piston skirt 81 can enter the expanded space therebetween. Once the higher level of force is attained, the downward pressure force on the piston member 76 will, of course, be effective for urging the mandrel 69 downwardly until the seal 74 begins to uncover the ports 66. At this time, as the ports 66 are at least partially uncovered, the fluids in the annular space 63 will escape into the axial bore 25. This flow of fluids into the bore 25 will, of course, be effective for correspondingly reducing the downwardly-directed pressure forces on the mandrel shoulder 72 until such time that the force of the biasing springs 70 will shift the mandrel upwardly toward its normal port-closing position. It will be appreciated that once the mandrel 69 is moved upwardly a sufficient distance that the piston skirt 81 is retracted from within the collet fingers 84, it will again be necessary for the pressure in the bore 25 to drop to a level sufficient for driving the piston skirt back under the collet fingers. Nevertheless, the testing tool 10 can be raised to a depth level that can cause the skirt 81 to move into and out of the collet fingers 84 several times as the stinger 19 is being positioned in relation to the packer 13. Finally, however, the pressure differential will again stabilize so that ultimately the biasing springs 70 will again hold the mandrel 69 in its depicted normal elevated port-closing position.
It will, therefore, be realized that the double-acting bypass valve 18 functions to maintain the pressure differential between the well bore 12 and the full-bore passage 25 within a desired range. When, for example, the pressure in the passage 25 becomes excessive, the piston 76 will remain in engagement with the shoulder 80 and the mandrel 69 will be shifted downwardly in relation to the piston 76 until the sealing member 74 is at least partway uncovering the ports 66. Hereagain, when the ports 66 are at least partially uncovered, any excessive pressure in the full-bore axial passage 25 will be relieved as pressured fluids in the passage are discharged into the well bore 12. Conversely, when the pressure in the full-bore passage 25 becomes unduly low, the mandrel 69 will remain in its elevated position until such time that the pressure differential is sufficiently high to drive the skirt 81 into the collet fingers 84. Again, in keeping with the objects of the present invention, it must be kept in mind that the above-described actions of the bypass valve 18 can take place only so long as the pressure reference tool 17 remains in its depicted running-in position where its mandrel 42 is in its illustrated lower position with the seals 87 and 88 straddling the ports 62 and 65 to maintain communication between the well bore fluids and the passage 63. As will be described, once the pressure reference tool 17 is operated, communication between the well bore fluids and the bypass valve 18 will be discontinued for the remainder of the testing operation.
Referring again to FIGS. 2B and 2C, from the previous description of the pressure reference tool 17 it will be recalled that the tool mandrel 42 will remain in its illustrated position until the pressure in the well bore 12 is increased sufficiently to cause the rupture disc 55 to fail and allow the fluids in the well bore to enter the lower portion of the piston chamber 53. From the preceding description of the operation of the bypass valve 18, it will, of course, be appreciated that a substantial increase in the well bore pressure is required to move the piston 76 downwardly. On the other hand, as described in more detail in the above-identified McGill patent, the pressure-operated tester valve 16 is operated by successively increasing and relieving the well bore pressure. Thus, in considering the overall operation of the drillstem testing tool 10, since the pressure reference tool 17 must be operated before opening the tester valve 16 for the first time in a given testing operation, it has been found preferable to design the rupture disc 55 so that it can be opened at a modest pressure differential that is well below the pressure differential required to operate any other tool in the string of tools that might be incorporated with the testing tool and still protect the formations as at 14. By way of example, the rupture disc 55 might be chosen to open in response to a modest pressure differential in the order of 500 or 1,000-psi. so that the tester valve 16 can be selectively operated by increases in the pressure in the well bore in the magnitude of 1,500 to 2,000-psig above the normal hydrostatic pressure.
Accordingly, upon consideration of FIGS. 2B and 2C, it will be realized that once the rupture disc 55 is broken, the fluids in the well bore 12 will enter the lower portion of the piston chamber 53 and, as a result, shift the mandrel 42 upwardly to its upper or final operating position. At this time, the seal 88 will be elevated above the port 65 to permanently discontinue fluid communication between the pressure reference tool 17 and the bypass valve 18. It will also be appreciated that once the mandrel 42 is shifted upwardly to its final operating position, the upper valve means 43 will have functioned to block further communication between the well bore 12 and the pressure reference tool 17 once the sealing member 45 moves above the port 47. When that occurs, the well bore fluids that had previously entered the passage 33 by way of the ports 46 and 47 will then be permanently trapped in the passage 33 and will initially be at the well bore pressure that existed at the time that the rupture disc 55 was opened. This so-called "reference pressure" will, therefore, be also trapped in the lower portion of the chamber 26 (FIG. 2A) by way of the intercommunication of the passages 28 and 33.
Hereagain, as fully described in the above-identified McGill patent, this trapped reference pressure will be utilized to facilitate the operation of the tester valve 16. In order to control the level of the reference pressure, the new and improved pressure reference tool 17 is preferably arranged so that the spring 35 in the upper chamber 32 functions to allow the valve member 34 to move upwardly in response to only a modest pressure differential in the order of 200 to 300-psi. This selection of the spring 35 to respond to pressure differentials in that range will allow the nitrogen reference pressure to bleed down to such level as the tools are being withdrawn from the well. The mandrel 42 will be retained in its elevated or final operating position by the pressure of the fluids that entered the lower portion of the piston chamber 53 upon the opening of the rupture disc 55. At this point in the testing operation, the pressure reference tool 17 has also completed its final operation to uniquely establish a predetermined reference pressure in the tester valve 16 and the drillstem operation can then begin as is fully described in the above-identified McGill patent.
It should be particularly recognized that since the new and improved pressure reference tool 17 can not be reopened until the tool is returned to the surface, the well bore fluids will remain trapped in the lower portion of the chamber 26 and the two passages 28 and 33 as well as in that portion of the chamber 32 lying between the seals 40 and 41 on the valve member 34. Thus, whenever a testing operation has concluded and the testing tool 10 is being returned to the surface, the valve member 34 will periodically function as needed to keep the reference pressure in the chamber 26 at a modest increased pressure level above the hydrostatic pressure at any given depth as the tools are being withdrawn from the well bore 12.
Accordingly, it will be appreciated that the new and improved pressure reference tool and bypass valve of the present invention have provided tools which can be incorporated in a tool string including a pressure-controlled tester valve to facilitate the operation of the tester valve without risking damage to the earth formations that are to be tested. In particular, the new and improved tools described herein respectively cooperate for providing a full-bore drillstem testing tool which is capable of being selectively operated from the surface without having to manipulate the supporting pipe string for trapping well bore fluids in an enclosed chamber to provide a source of fluids at an elevated pressure that will enhance the actuation of the tool. Moreover, these new and improved tools cooperatively respond to changes in the pressure differential between the interior and exterior of the pipe string for protecting the earth formations to be tested from adverse pressure changes.
While a particular embodiment of the present invention has been shown and described, it is apparent that changes and modifications can be made without departing from this invention in its broader aspects; and, therefore, the aim in the appended claims is to cover all such changes and modifications as may fall within the true spirit and scope of this invention.

Number	Name	Date
RE29638	Nutter	May 1978
3856085	Holden et al.	Dec 1974
3860069	Wray et al.	Jan 1975
3901314	Nutter	Aug 1975
3964544	Farley et al.	Jun 1976
3976136	Farley et al.	Aug 1976
4105075	Helmus	Aug 1978
4361188	Russell	Nov 1982
4440230	McGill	Apr 1984
4609005	Upchurch	Sep 1986
4617999	Beck	Oct 1986

Pressure-controlled well tester operated by one or more selected actuating pressures

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