Gravel Packer and Service Tool

This invention relates generally to equipment for preparing oil and gas wells for production, and more particularly to a novel and improved gravel packer and service tool combination.

Gravel packers are used to pack gravel around the screens through which the fluid production of the well enters the production apparatus. Without such gravel packed around the screens, sand will be produced with the fluids which must be removed. Further, there is a tendency for the screens to be eroded away by sand and the like.

It is normally the practice to lower a packer into the well with a service tool, which, after packing, is removed, leaving the packer in place. Generally in the past, the packer and service tool have been connected by a threaded connection which is released by rotating the service tool relative to the packer. The rotation of the service tool to remove it from the packer presents serious problems with deep wells, requiring a very long work string. Even greater problems are encountered in highly deviated, curved, or nonvertical wells.

In order to overcome such problems, packer and service tool combinations have been developed, utilizing fluid pressure to disconnect the service tool from the packer. U.S. Pat. No. 4,660,637 (assigned to the assignee of this invention) describes and claims such a packer/service tool combination. That patent is incorporated herein by reference.

In the packer/service tool combination of the '637 patent, the packer and service tool combination is lowered into the well until the packer is located in the desired location where gravel packing is required. A ball is then dropped down the work string to engage a ball seat in the service tool and seal off portions of the service tool so that tubing pressure can be applied to sequentially perform the various operations required.

When tubing pressure is applied to the service tool in a first relatively low pressure range, slips are radially extended from the packer into gripping engagement with the well casing to lock or set the packer in position within the casing. Thereafter, elastomeric seals are compressed longitudinally of the packer and caused to expand radially into sealing engagement with the well casing.

Subsequently, a higher tubing pressure is applied to release the threaded connection between the packer and service tool. Thereafter, a still higher tubing pressure is applied to move the ball seat to permit the gravel slurry to be pumped down through the service tool into the annulus between the packer and the well casing.

Shear screws are used which shear at progressively higher forces created by progressively higher pressures to provide the required sequence of operations.

In accordance with the present invention, an improved method and apparatus are provided in which back-up fluid pressure modes of operation are provided to operate the packer and service tool combination if the primary mode of operation fails for any reason. By providing back-up modes of operation, the reliability of the operation of the combination is greatly increased.

In the illustrated embodiment, the primary mode of operation of setting or locking the packer in the well casing and for extending the seals between the packer and the well casing is performed by applying tubing pressure in a first fluid pressure range. First shear screws shear off at a relatively low pressure, and the slips then extend into engagement with the well casing, where they bite into the casing to lock the packer in position within the well. As the pressure increases to a higher pressure, second shear screws shear, and the pressure causes compression of an elastomeric seal which expands radially to provide a seal between the packer and the well casing. A ratchet operates to lock the slips of the seal in their operated positions.

In the event subsequent pull tests and pressure testing establish that the primary mode of setting and sealing the packer has been unsuccessful, for example, as a result of the ball's failure to properly seat and seal, a second larger secondary ball is dropped down which seats in a secondary ball seat to seal off the service tool and permit setting and sealing of the packer. By providing such back-up mode of operation, operational reliability is improved.

After the packer is locked in place or set and sealed within the well, the next operation involves the release of the threaded connection between the service tool and the packer. Here again, primary and back-up modes of operation are provided.

With the primary mode of operation, the tubing pressure is increased to a higher value, causing a third set of shear screws to shear. This releases a hydraulic release piston, which then moves up to move a release ring from inside a threaded collet. The threaded collet then springs radially inward, causing release of the threaded connection.

Here again, if the primary mode of release is ineffective, a back-up mode of operation is available. With the back-up mode of operation, pressure is applied to the annulus between the packer/service tool combination and the well casing. When sufficient pressure differential is established between the high annulus pressure and the relatively low tubing pressure within the tool, the third set of shear screws shear and the hydraulic release piston is free to move in response to even lower tubing pressure. Such movement removes the release ring from the threaded collet and releases the threaded connection.

If in the unlikely event that the release is not achieved with either the primary or secondary pressure-operated modes of operation, a third release mode of operation is available, which involves rotating the service tool relative to the packer to unscrew the threaded connection therebetween.

After the connection between the service tool and the packer is released, the seal provided by the ball in the primary ball seat must be removed to allow the actual gravel packing operation. Here again, two modes of operation are available. In one mode of operation, a still higher tubing pressure is applied to shear a fourth set of shear screws and allow the ball seat to move clear of passages through which a slurry of gravel is pumped into the annulus around the packer. In the other mode of operation, the annulus pressure is raised above the tubing pressure to shear the fourth set of shear screws. Once these shear screws are sheared, a low tubing pressure is adequate to move the valve seat to a position for gravel packing.

Therefore, one important aspect of this invention is the provision of a packer/service tool combination in which multiple modes of operation are provided for each operational sequence. With such combinations, a successful packing operation of the well can be achieved even when problems are encountered.

Another important aspect of this invention involves a novel and improved structure which automatically aligns the locking slips and causes them to extend uniformly during the setting of the packer. The alignment structure also acts to prevent the slips from extending outwardly during any running or retrieving operation. Such structure also functions to ensure proper retraction of the slips when packer removal is required.

Another important aspect of this invention involves a novel and improved ratchet structure for locking the slips and the seal in their operative or set positions and which can be reliably released when the packer is to be moved from its set position. Such ratchet lock utilizes a ring which normally functions to lock the slips and the seal of the packer in their set positions, but can be released by axial force which moves a cam into an opening in the ring to spread the ring. The ring and its mounting structure are constructed to ensure that the ring remains substantially centered and releases the mating ratchet in a reliable manner.

Another important aspect of this invention involves the provision of a novel and improved release system for hydraulically disconnecting the service tool from a packer. Release can be accomplished with either of two modes of operation. The first mode involves increasing the tubing pressure above the annulus pressure to a predetermined value so as to release the connection between the service tool and the packer. The second mode of operation is performed by increasing the annulus pressure above the tubing pressure to a predetermined value, to shear a set of shear screws followed by the release of the connection by a relatively small differential pressure, in which the tubing pressure exceeds the annulus pressure.

Still another important aspect of this invention involves a novel and improved system for moving the valve seat so that the actual gravel packing operation can commence. Here again, two modes of operation are provided in which the valve seat can be hydraulically moved. In one mode of operation, a relatively high pressure is applied to the tubing, creating a substantial differential pressure between the annulus and the tubing which is sufficient to shear the shear screws associated with the valve seat. With the second mode of operation, the annulus pressure is increased above the tubing pressure to shear the screws. In this instance, a relatively low differential pressure is operable to perform the shearing operation.

In accordance with still another aspect of this invention, a novel and improved structure is provided to ensure that the annulus pressure exists below the primary valve seat during the hydraulic release of the coupling between the service tool and the packer to ensure that premature release of the valve seat does not occur.

These and other aspects of this invention are illustrated in the accompanying drawings and more fully described in the following specification.

FIG. 1 schematically illustrates a packer and service tool combination incorporating the present invention and which is assembled and lowered into a well for a gravel packing operation;

FIG. 2 is a longitudinal section of the packer and service tool;

FIGS. 3a through 3d are fragmentary, longitudinal sections of the portions of the service tool/packer combination designated in brackets in FIG. 2, and includes the portions of the tool which lock the tool in position within the well, form a seal with the well casing, and disconnect the mechanical connection between the service tool and the packer;

FIGS. 4a and 4b are additional enlarged, fragmentary sections, illustrating the portion of the tool combination indicated in brackets in FIG. 2;

FIG. 5a is a greatly enlarged, fragmentary, longitudinal section of the structure adjacent to the slips;

FIG. 5b is a cross section taken along line 5b--5b of FIG. 3d;

FIG. 5c is a fragmentary, longitudinal section taken along line 5c--5c of FIG. 5b;

FIG. 6a is an enlarged, fragmentary section of the ratchet mechanism for maintaining the slips extended and the seal compressed;

FIG. 6b is a cross section taken along line 6b--6b of FIG. 3c;

FIG. 6c is a fragmentary section taken along line 6c--6c of FIG. 6b, with parts removed for purposes of illustration;

FIG. 7 is an enlarged, fragmentary, longitudinal section illustrating the structural detail of the mechanical connection between the service tool and the packer, along with the fluid pressure-responsive mechanism for releasing such connection; and

FIG. 8 is a fragmentary roll-out view of the cutter sleeve operable to shear the shear screws which lock the primary valve seat in position.

FIG. 1 schematically illustrates a packer 10 and service tool 13 combination positioned in a well having a casing 19 which has been perforated at 19a adjacent to the formation from which production is to be obtained. When the production formation is above the lower end of the well, a sump packer 19b is set within the casing below the perforations 19a to seal off the rat hole 19c. An extension 19d extends from the lower end of the packer to the screen 19e, through which the oil or gas enters after the packing is completed. During the gravel packing operation, gravel is positioned around the screen 19e to prevent sand and the like from eroding the screen and to filter sand out of the produced fluids.

FIG. 2 illustrates the overall gravel packer/service tool combination. The packer 10 is a tubular assembly which extends from an upper end at 11 to a lower end at 12. It includes a number of functioning subassemblies which will be hereinafter designated with a number designation to indicate an overall subassembly, with the individual parts of the subassembly indicated by such reference numeral followed by a letter.

The service tool 13 is also tubular and telescopes with the packer. The upper end of the service tool 14 is threaded to connect with the work string 15 used to lower the packer/service tool combination into the well to position it for the packing operation. The service tool extends the entire length of the packer to its lower end at 16. Here again, the service tool includes a number of distinct subassemblies, which are also referred to hereinafter by individual reference numerals, with the component parts of the subassembly indicated by such reference numeral followed by a letter designation.

FIGS. 3a through 3d are enlarged, fragmentary, longitudinal sections. The locations of each of the portions of the combination are designated in FIG. 2 with brackets. FIGS. 4a and 4b are also enlarged, fragmentary, longitudinal sections illustrating the portions of the combination, also indicated in FIG. 2 by brackets.

Before the service tool/packer is lowered into the well, the service tool is positioned within the packer and is mechanically connected by a threaded connection at 17, illustrated in FIG. 3b, so that the service tool and packer are mechanically locked together.

The various sequential steps of operation of the service tool and packer are performed by fluid pressure-operated subassemblies. These various subassemblies are responsive to differential pressures between the annulus 18 within the well casing 19 and the exterior of the service tool 13 and packer 10 combination (hereinafter referred to as "annulus pressure") and the pressure within the central passage 21 of the tool. Such passage is in communication through the service tool string with the well head and the pressure therein is hereinafter referred to as "tubing pressure." It should be recognized that the absolute pressure in the annulus in the vicinity of the tool is, to a large extent, dependent upon the depth of the tool within the well. Similarly, the absolute pressure within the passage 21 is a function of the depth of the tool assembly from the well head. The operational functions or steps of operation of the tool combination are determined by the differential pressure between the tubing pressure and the annulus pressure, as discussed in detail below, not upon the absolute pressure. Therefore, in the following specification, references to operating pressures and the like are to differential pressure, not static or absolute pressure.

As the service tool and packer are lowered into the well, the absolute pressure of the tool environment increases gradually until the tool is in the position at the formation in which production is to be achieved. A check valve 22, best illustrated in FIG. 4b, provides communication between the annulus 18 and an annular passage system 23 which extends up along the service tool 13 around the central passage 21 to lateral ports 24, illustrated in FIG. 3c. Seals 26 and 27, respectively located above and below the lateral passages 24, provide a sealing engagement with the adjacent inner tubing member 28 of the packer 10 to seal off the upper end of the passage system 23.

Prior to the lowering of the tool combination into the well, the passage system 23 above the check valve 22 is filled with air. As the tool combination is lowered into the well, the static pressure in the well causes the compression of this air, and ensures that the pressure in the passage system 23 is raised as the static pressure increases, and is therefore equal to the adjacent annulus pressure when the production formation is reached. Since the practice is to maintain well pressure above the pressure in the formation to control the operation of the well, it is important in the subsequent operation of the tool combination to establish and maintain the passage system 23 at the annulus pressure which exists prior to the setting and sealing of the packer. Once the packer is set and sealed, the pressure below the check valve will normally return to the lower pressure of the formation. The check valve 22, however, maintains the pressure in the portion of the passage system 23 immediately below the primary valve seat at the initial annulus pressure. This ensures that excessive differential pressure cannot occur across the primary valve seat during the pressure release of the connection 17 in the second mode of operation described below. Without the check valve, sufficient differential pressure could occur to cause premature shearing of the shear screws anchoring the primary valve seat.

After the packer is properly positioned in the well at the formation in which production is to be obtained, a first step in the operation of the tool is performed to expand slips 31 into locking engagement with the well casing 19. This locks the packer in such location against movement either up or down in the well. Immediately after the slips are extended to lock the packer against the well casing, elastomeric seal 32 is axially compressed and caused to expand radially into tight sealing engagement with the inner surface of the well casing. These operations are performed by establishing a differential pressure between the annulus pressure and the tubing pressure. Therefore, it is necessary to seal off the tubing so that such differential pressure can be established.

A primary valve seat member 33 is mounted in the service tool above the check valve 22. While the tool combination is being lowered into the well, communication is provided between the annulus and the central passage through the primary valve seat by lateral passages 34 in the packer 10, aligned lateral passages 36 in the service tool 13 and passages 33a and 33b in the primary valve seat assembly which open to the central passage 21 through a conical ball valve seat 33c. In order to seal off this connection between the central passage 21 and the annulus 18, a metal ball 37 is dropped down the service string and is moved by gravity down along the central passage 21 into sealing engagement with the ball valve seat 33c. FIG. 4a illustrates, in phantom, the ball 37 in engagement with the primary valve seat assembly.

Once the ball 37 is in engagement with the primary ball seat, it is possible to increase the tubing pressure in the central passage 21 to a pressure higher than the pressure of the annulus 18, and this pressure differential is utilized to expand the slips 31 into locking engagement with the casing and to then expand the seal 32 into sealing engagement with the casing so that the packer is set and sealed in position.

A fluid pressure-responsive setting and sealing assembly is provided for such operation. The assembly includes an upper piston 38a and a tandem lower piston 38b mounted in the service tool 13 around a central tube 13a. The setting and sealing assembly also includes engagement with the packer at an outer sleeve 39c connected to a threaded ring connector 39d, which in turn connects with a lower outer sleeve 39e of the packer.

Positioned within the lower outer sleeve 39e is an upper inner sleeve 39f which is connected by a ring connector 39g to a lower inner sleeve 39h which extends inside and past the seal 32. The inner lower sleeve 39h connects at its lower end to a slip expander 39i, providing a conical upper slip expanding cam surface 39j. The packer inner tubing member 28 extends down along the interior of the portion of the setting and the sealing assembly provided by the packer and is connected at its lower end to a lower slip expander member 28b. The expander member 28b provides an upwardly facing, conical slip expanding surface 28c. The two camming surfaces 28c and 39j cooperate when they move toward each other to radially expand the slips 31 into tight locking engagement with the well casing.

A first set of shear screws 41 extends through the upper outer sleeve 39c into a collet sleeve 42 provided by the service tool and locks the sleeves 39c and 39e against movement relative to the service tool. A second set of shear screws 43 extends from the slip expander 39i into the lower end of the lower inner sleeve 39h, and normally locks such members against relative longitudinal movement.

During the initial operation of setting and sealing, the tubing pressure is increased to a value above the annulus pressure by a first relatively low differential pressure to shear the screws 41. The tubing pressure is communicated to the two pistons 38a and 38b through ports 46 in the inner tubing 13a of the service tool. The tubing pressure from the ports 46 communicates with an upper piston chamber 47a and a lower piston chamber 47b. This first differential pressure created by the elevated tubing pressure results in an axially downward force on the packer outer sleeve 39c, which is resisted by the shear screws 41.

The shear screws 41 are sized so that when the pressure differential reaches such low first differential pressure, the shear screws 41 shear, allowing the outer sleeve 39c to move relative to the service tool and, in turn, relative to the inner tubing member 28. Such motion is transmitted on down to the slip expander 39i and results in movement of the upper slip expander cam surface 39j toward the lower slip expander cam member 28b. This causes radially outward movement of the slips 31. During such movement, the second set of shear screws 43 prevents relative movement between the slip expander 39i and the lower inner sleeve 39h. Therefore, the seal 32 is not expanded, and merely moves down with the assembly.

The slips 31 are provided with teeth 31a which bite into the well casing to mechanically lock the packer against movement along the well. The manner in which the slips are supported and aligned, described in greater detail below, provides improved setting of the packer within the well casing.

As the slips are forced out into biting engagement, further movement of the slip expander 39i is prevented so the differential pressure between the higher tubing pressure and lower annulus pressure increases to a second differential pressure higher than the first differential pressure until the second set of shear screws 43 shear. As soon as the second set of shear screws 43 shears, the lower inner sleeve 39h moves relative to the slip expander 39i which engages the lower edge of the seal 32. The ring connector 39g, which engages the upper end of the seal, moves toward the slip expander 39i, causing the seal 32 to be axially shortened and radially expanded. This action continues until the seal 32 is radially extended into tight sealing engagement with the well casing to isolate the upper annulus 18a from the lower annulus 18b.

An improved ratchet assembly 51, best illustrated in FIGS. 6a-6c, includes sawtooth ratchet teeth 51a formed along the outer surface of the inner tubing member 28 and a ratchet ring 51b formed with internal ratchet teeth 51c which interengage and mate with the external ratchet teeth 51a. As the slips are extended and the seal 32 is extended into sealing engagement with the well casing, the ratchet ring 51b is carried down along the inner tubing member 28. The ratchet ring is formed with a slot opening along one side (discussed in greater detail below) which allows the ratchet tooth to cam the ring open as it moves out along the inner ratchet teeth 51a. However, relative movement in the opposite direction is prevented. Therefore, at the completion of the setting and sealing operation, the slips 31 are locked in their extended position and the seal 32 is locked in its expanded and sealing position.

Before proceeding, the locking provided by the slip 31 and the seal provided by the seal 32 are tested. Alternate tensile and compressive forces are applied through the work string to test the locking of the slips. The function of the seal is tested by raising annulus pressure. A build-up of pressure differential indicates that the sealing is performed.

In some instances, difficulty is encountered in establishing the higher tubing pressure and a back-up mode of operation is provided. Such problem in building up tubing pressure can occur, for example, if scale or rust prevents proper sealing of the ball 37 in the primary ball seat 33c. The back-up mode of operation which is employed in the event of an unsuccessful setting and sealing operation utilizing the first mode of operation described above is then initiated.

A secondary valve seat 52 (illustrated in FIG. 3b) is mounted in the service tool above the primary valve seat assembly 33. The minimum diameter of the secondary valve seat is greater than the diameter of the ball 37, so that the ball 37 can pass the secondary valve seat and move to the primary valve seat. In the event of failure to operate with the first mode of operation utilizing the ball 37, a second ball 53 of larger diameter is dropped down the work string and moves into engagement with the secondary valve seat 52. This secondary ball 53 is not utilized if the primary ball 37 properly seats and seals. The ball 53 is usually formed of a phenolic resin or the like, and can be flushed up the well string and out of the well by reverse flow at a subsequent stage in the operation of the tool. After the secondary ball valve 53 is positioned, the slips are extended to set the packer, and the seal 32 is compressed to expand and seal by the application of a tubing pressure which is higher than the annulus pressure, in the same manner described above for the first mode of operation.

After the setting and sealing operation has been completed and successfully tested, the next step in the operation of the packer and service tool combination involves the release of the threaded mechanical connection 17 between the service tool and the packer so that the service tool can be moved axially relative to the packer. Here again, two modes of operation are provided so that in the event the first mode of operation fails for any reason, a separate and distinct mode of operation is available.

The mechanical connection 17 between the service tool 13 and the packer 10 is best illustrated in FIG. 7. The connection 17 is provided by internal threads formed of an inner tubing member 28 of the packer which mate with external threads on the collet sleeve 42 of the service tool. This threaded connection is a lefthand thread so that in the event the two fluid pressure-responsive modes of operation of the release of the service tool fail, the service tool can be threaded out of the packer by rotation of the service string.

The lower end of the collet sleeve 42 is provided with longitudinal slots (not illustrated) so that the collet sleeve per se is formed by a plurality of axially extending fingers 42a having the external threads at the lower ends thereof. These fingers 42a are held radially out in mating engagement with the threads on the tubing member 28 by a locking ring 42b positioned within the fingers 42a within the envelope of the threaded connection 17.

The threaded connection 17 is released to release the service tool from the packer by moving the lock ring upwardly to a release position in which the fingers 42a can then move radially inward to release the threaded connection 17. Such movement of the lock ring 42b is provided by a piston 42c connected to the lock ring 42b by a lost motion connection 42d. The plurality of shear screws 42e lock the piston 42c against movement relative to the service tool until the hydraulic release of the service tool is required. These shear screws are sheared by one of the two pressure-responsive modes of operation provided for the release of the service tool.

With the first mode of operation, the tubing pressure within the central passage 21 is increased above the annulus pressure within the annulus 18a and is communicated to the chamber 42f through lateral ports 42g. When the differential pressure reaches a third differential pressure higher than the second differential pressure, the shear screws 42e shear, causing upward movement of the piston 42c. After the piston has moved through the lost motion distance, further movement of the piston 42c raises the lock ring 42b and allows the fingers 42a to spring inwardly to release the threaded connection 17 between the service tool and the packer. The fingers 42a are prestressed so that as soon as the lock ring is moved upwardly, they spring inward to release the threaded connection 17.

In the event that the threaded connection 17 fails to release in response to elevated tubing pressure, a second mode of fluid pressure-responsive operation is provided in which the annulus pressure within the upper annulus 18a is increased to a value above the tubing pressure within the passage 21. When the annulus pressure is raised to a value above the tubing pressure by a third differential pressure, the screws 42e shear, allowing downward movement of the piston 42c. This movement, by itself, does not cause release of the lock ring 42b; however, after the screws 42e have sheared, the piston can be raised by a low differential pressure in which the tubing pressure exceeds the annulus pressure. Such low pressure can be achieved even if sufficient differential pressure cannot be obtained for the first mode of operation to shear the screws 42e. Therefore, in the second mode of operation, after the shear screws are sheared, the tubing pressure is raised above the annulus pressure to cause upward movement of the piston and release of the lock ring 42b.

In the unlikely event that both the first and second modes of operation for pressure release of the threaded connection 17 fail, as a third release mode of operation, the service tool can be rotated by the work string to thread the fingers out of the threads on the inner tubing member 28.

If the secondary ball valve 53 has been required and is positioned in the valve seat 52, reverse circulation is necessary to blow the ball valve 53 up the work string out of the well. For reverse circulation, the service tool is raised to lift the upper seals out of the packer so that fluid pumped down through the upper annulus 18a enters the central passage through the passages 36 and flows up the tubing to the surface. Such flow carries the secondary ball 53 up out of the well, clearing the tool system for further operations.

The subsequent and last step of operation prior to the actual gravel packing requires the movement of the primary ball seat, with the primary ball 37 seated therein down until the passages 36 are open. Here again, two distinct modes of operation are available to ensure the reliability of operation of the tool. The primary valve seat assembly 33 is also locked in its normal position illustrated in FIG. 4a by a plurality of shear screws 33d threaded into a shear screw receiving ring 33e. As illustrated in the roll-out view of FIG. 8, these screws are in abutment on their upper sides by a downwardly facing flat surface 33f on the primary valve seat member 33 and which prevent downward movement of such member until the shear screws 33d are sheared. Positioned below the shear screws is a sleeve 33g which is threaded onto the lower end of the primary valve seat member 33. The upper ends of the sleeve 33g are formed with grooves 33h, with one groove 33h adjacent to each of the shear screws 33d. As best illustrated in FIG. 8, the depth of the grooves 33h is progressively increased so that in one mode of operation for shearing the shear screws 33d, only a single screw is fractured or sheared at any given time and the shear screws are progressively but singly sheared.

In a first mode of operation, tubing pressure higher than annulus pressure is utilized to shear the screws 33d to allow downward movement of the primary valve seat 33. Before the shearing operation is commenced, the service tool is raised a sufficient distance so that the seals 26 clear the upper end of the tubing member 28, to provide direct communication through the ports 24 between the annulus 18a and the portion of the passage system 23 immediately below the primary valve seat member 33. In the first mode of operation, the tubing pressure is again raised to a value above the pressure in the upper annulus (and the passage system 23) until a fourth differential pressure higher than the third differential pressure is reached. At such differential pressure, the shear screws 33d shear and the primary valve seat member 33 is carried downwardly until it clears the passages 36. At such time, the packing operation can be commenced.

In the event that the first mode of operation fails to cause shearing of the shear screws 33d for any reason, a second mode of operation is again provided to release the primary valve seat member 33 so that it can be moved down clear of the passages 36. The annulus pressure is then raised above the tubing pressure, producing an upward force on the primary valve seat member. This upward force causes the sleeve to move in an upward direction.

In this instance, only a single shear screw resists such upward movement at any given time, since the shear screw associated with the groove 33h of least depth is the only shear screw initially engaged. Therefore, the full pressure resultant force in an upward direction is applied to a single shear screw and results in shearing of such screw when the annulus pressure exceeds the tubing pressure by a fifth differential pressure which is substantially lower than the fourth differential pressure. As soon as the first screw shears, the assembly moves up until the groove 33h, which is slightly greater in length, engages and shears one more shear screw. This action continues progressively until all of the shear screws 33d are sheared, thereby releasing the primary valve seat member 33. With this structure, in which the shear screws 33d are progressively sheared rather than simultaneously sheared, the shearing operation to be performed with very low differential pressure compared to the pressure required in the first mode of operation. If desired, the grooves can be structured to simultaneously shear two or more screws. However, in such case, a higher differential pressure is required. Once all of the shear screws have been sheared, the pressure differential is reversed to establish a higher tubing pressure than annulus pressure and a relatively low differential pressure is all that is required to overcome the friction and move the primary valve seat member down clear of the passages 36. A ratchet ring 33i engages external ratchet teeth to ensure that once the primary valve seat is moved down clear of the passages 36, it remains in such operating position.

Gravel packing is accomplished by lowering the service tool back until the seals enter the packer so that gravel pumped down along the tubing passes out through the passages 36 and 34 into the lower annulus 18b.

Once the gravel packing is completed, the service tool is removed and a production tool string is lowered into the well and is connected to the upper end of the packer.

In some instances, it is necessary to remove a set and sealed packer. When this is necessary, a recovery tool is lowered into the well and connects with the outer sleeve 39c at its upper end. An upward force is then applied of sufficient magnitude to shear a set of shear screws 51d, allowing the lower outer sleeve 39e to move up and cam the ratchet ring 51b open out of engagement with the external ratchet teeth 51a. FIGS. 6a through 6c best illustrate the structure of the ratchet ring 51b and a cam 51e, which operates to spread the ratchet ring after the shear screws 51d have sheared. The ratchet ring 51b is formed as a split ring, stressed inwardly to maintain engagement between the external ratchet teeth 51a and the internal ratchet teeth 51c. The cam 51e is formed on the interior of the outer sleeve 39e and shaped to enter the opening 51f and spread the ring when the outer sleeve 39e is pulled upward by the recovery tool.

The clearance 51g provided between the outer surface of the ratchet ring 51b and the inner surface of the outer sleeve 39e is proportioned with respect to the dimensions of the cam 51e so that the cam spreads the ratchet ring a sufficient amount to ensure that the internal ratchet teeth 51c clear the external ratchet teeth 51a even when the ratchet ring 51b moves off center a maximum distance permitted by such clearance 51g. The cam, however, is sized so that even when the cam fully spreads the ratchet ring, the diameter of the outer surface of the ratchet ring 51b is still less than the diameter of the inner surface of the sleeve 39e. This ensures that jamming does not occur in the event that scale or other debris collects around the ratchet ring during the time the packer is in the well.

Once the ratchet ring releases, the sleeve 39e is moved upward by the tension applied by the recovery tool and the compression of the seal 39h is released. Similarly, such motion is transmitted to the slip expander 39i, which also moves upwardly to release the slips. As discussed in greater detail below, the slips are retained in a slip retaining ring 31b, which is connected to the slip expander 39i for movement therewith. If the lower ends of the slips fail to release by moving upwardly relative to the lower slip expanding cam member 28b, the upward movement of the slip retainer 31b lifts the slips up and ensures their release. Once the slips are released and the compression in the seal is released, the packer is free to be removed from the well by the recovery tool.

FIGS. 5a through 5c illustrate the structural detail of improved mounting of the slips 31 and their operating cams. The slips 31 are formed with a generally U-shape illustrated in FIG. 5b, and provide legs 31d which extend out through longitudinal slots 31c in the slip retainer sleeve 31b. A spring 31e is positioned between the legs 31d and normally maintains the slips in their retracted position against the inner tubing member 28.

In order to ensure that all of the slips remain retracted while the packer is run down the well, the forward end of the cam surface 39j is provided with a tongue 39k which extends into a mating recess 31f in the slips and engages the end of the recess with abutting engagement. This engagement prevents contact between the slips and the casing from causing the slips to expand while the packer is being lowered. However, during the expansion of the packer, the movement of the slips along the surface 28c tips the recess out from the tongue 38k and allows expansion of the slips.

When the slips 31 are released for retrieval of the packer from the well, the upward movement of the slip expander 39i causes the slip retainer 31b to engage the lower ends of the slips and ensures that none of the slips hang up on the lower slip expander cam surface 28c. Such engagement also ensures that the slips do not extend during retrieval of the packer.

With the present invention, the reliability of operation is substantially improved by providing alternate modes of operation for each of the operating steps required in the preparation of the packer for the actual gravel packing. Further, individual subcomponents or combinations are structured for improved reliability in operation. For example, the check valve 22 prevents premature shearing of the shear screws which lock the primary valve seat in position. The slips are supported and structured for reliable, uniform operation. The shearing of the shear screws locking the primary valve seat in position can be accomplished with low differential pressure in the mode of operation involving an annulus pressure higher than tubing pressure. Further, the ratchet system for holding the slips extended and the seal compressed operates reliably and can be released in a reliable manner when the packer is to be retrieved.

Although the preferred embodiment of this invention has been shown and described, it should be understood that various modifications and rearrangements of the parts may be resorted to without departing from the scope of the invention as disclosed and claimed herein.