US3543870A - Core barrel retrieval - Google Patents

Description

United States Patent 72] Inventor Lyle J. Martinsen Primary Examiner-James A. Leppink Murray, Utah Attorney-Lynn G. Foster [21] Appl. No. 808,205 [22] Filed March 18, 1969 [45] patented 1 970 ABSTRACT: Apparatus and method for retrieving a core bar- [73] Assignee Boyles Bum Drilling Company rel assembly from its core-receiving position at the leadlng end Salt Lake CiWUtah of a str1ng of drill pipe, the apparatus comprising an outer locking sleeve and an annular fitting disposed partly within the locking sleeve and featuring an annular seal ring interposed between the sleeve and fitting which (a) forms a fluid seal with [54] CORE BARREL RETRIEVAL the drill string when the annular fitting is advanced within the locking sleeve to foreshorten the overall apparatus and (b) 15 Claims, 4 Drawing Figs. I

breaks the fluid seal when the annular fitting 15 extended rela- [52] US. Cl 175/60; tive to the locking S]eeve An elongated Shaft aids in maintairb 166/153, 166/156 ing the locking sleeve and annular fitting in the foreshortened [51] Int. Cl EZlb 33/16; condmon within the drill String, to preserve the fluid Seal so E2 1 b 49/00 that the apparatus is displaced by the pressure of drilling fluid, [50] Field of Search 175/60; mil h haft is axially dis laced counter to a bias upon im- 166/ 15 5 pact thereof with overshot latching structure of the core barrel assembly atthe leading end of the drill string adjacent the [56] References Cited outer tube whereupon the annular fitting is relatively extended UNITED STATES PATENTS from the locking sleeve and the fluid seal is broken to accom- 2,589,656 3/1952 Armstrong 166/196 modate passage of drilling fluid by the apparatus as the core 0 8/ 1962 Culver tal. 166/153 barrel assembly and apparatus, to which the core barrel as- 3,052,302 9/1962 Lagucki u 6/1 sembly has latched are retrieved to the trailing end of the drill 3,070,167 12/1962 Loy III et a1. 166/155 string.

90 112 :30 I08 no s 2 62 |32\ 66 I24 56 5852 138 106 l "4] 4 6 I04 us I? as 95 1. il no 7 Q 122/100 176 I02 I66 1 CORE BARREL RETRIEVAL FIELD or rue INVENTION The present invention relates to retrieval of a core barrel assembly from the remote end of a string of drill pipe (drill string) and, more particularly, to novel method and apparatus accommodating hydraulic pressure displacement of the retrieval unit to the core barrel assembly, coupling of a novel retrieval unit to the core barrel assembly and subsequent retrieval of both the retrieval unit and coupled core barrel assembly without, at the same time, swabbing the hydraulic drilling fluid from the drill hole. The invention further relates to producing a hydraulic or fluid seal between the drill string and the retrieval unit during pressure displacement thereof to the drill site and automatically removing the hydraulic seal upon impact with the core barrel assembly and during said retrieval.

As used herein, drill string" means consecutive lengths of joined drill pipe, comprising a terminal outer tube, disposed in a hole and core barrel assembly means the combination of the core-receiving inner tube, the swivel mechanism and the outer tube-coupling latch structure and excludes the outer tube to which the latch structure is coupled during drilling.

BACKGROUND OF THE INVENTION It has been a longstanding problem in the core drilling art to efficiently displace a retrieval unit, particularly in a horizontal or in an up" hole to its coupling position with a core barrel assembly disposed adjacent an outer tube at the leading end of the drill string. Proposed prior art devices, to my knowledge, generally consist of a plurality of parts, which cooperate and which cause a hydraulic seal to be formed with the drill string to allow the core barrel assembly to'be displaced axially by hydraulic pressure. Conventional structure, attached to a wire line is required in order to retrieve the core barrel assembly from its drilling position. This wire line (cable) attachment dramatically curtails the rate at which the retrieval structure can be hydraulic-pressure-displaced within the drill string because the resistance to displacement comprises (a) the friction created by the seal of the retrieval structure, (b) the load or weight of the wire line, (c) the resistance of the packing gland seal at the pump end of the drill string which squeezes the wire line and (d) the low speed limitation imposed in order to avoid tangling with the wire line. More specifically with regard to (d), after the retrieval structure has coupled to the core barrel assembly for removal from an overhead hole, the drill string must be intentionally drained, at a controlled rate in order to maintain a fluid back pressure to control descent and thereby prevent wire line tangle. This retrieval process requires a substantial and expensive amount of time.

Later, the same prior art retrieval structure is used to again place the core barrel assembly in its drilling position, and, thereafter, when the retrieval structure is returned to the trailing end of the drill string the hole is once more swabbed dry, requiring additional time to subsequently refill the drill string with drilling fluid prior to resumption of drilling.

When drilling in a near horizontal down hole, the seal of commercial retrieval structures, undesirably will swab the hole dry of drilling fluid during retraction of the retrieval structure and core barrel assembly. Attempts to avoid swabbing the hole dry have recently been made for drilling in a down hole. For example, see US. Pat. No. 3,333,647. Nevertheless, the requirement that such devices use a wire line to operate properly, continues to inflict the problems above mentioned.

BRIEF SUMMARY AND OBJECTS OF THE PRESENT INVENTION It is a primary object of the present invention to overcome or alleviate problems of the mentioned type.

The mentioned primary object is accomplished by the present invention, which includes method and apparatus. The apparatus comprises a pump-in retrieval unit having structure for creating a hydraulic seal between the drill string and the pump-in unit for hydraulic displacement within the drill string prior to coupling of the retrieval unit with the core barrel assembly. The hydraulic seal is removed upon coupling with the core barrel assembly.

The pump-in or retrieval unit generally comprises telescopically interrelated members which are relatively axially displaceable between open and closed positions. Expandable seal structure is situated between the two members and rests upon bridging structure, so that when the unit is in the closed position, the seal structure will be expanded by the bridging structure outwardly beyond the periphery of the unit to form a fluidtight seal between the retrieval unit and the drill string.

When the members of the unit are in the open position, the seal structure is allowed by the bridging structure to contract away from the drill string thereby breaking the fluidtight seal.

The telescopically-interrelated members of the unit are displaced from the closed or retracted position to the open or extended position when the unit, being displaced within the drill string under pressure, strikes the latch structure of the core barrel assembly so that locking structure holding the members in the closed position is released to accommodate relative displacement of the two members away from each other.

Therefore, it is another primary object of the present invention to provide novel method and unique apparatus for displacement of a core barrel assembly retrieval structure to the leading end of a drill string by force of drilling fluid.

One still further significant object is to provide improved structure for selectively forming and breaking a seal with a pipe in which the structure is disposed.

Another paramount object is the provision of novel structure and method for retrieving a core barrel assembly such that a fluid seal is maintained between the apparatus and a drill string to accommodate displacement of the apparatus by pressure, the fluid seal being broken solely by impact between the apparatus and the core barrel assembly at the drilling site.

One still further important object of the present invention is to provide novel structure which maintains one member of a retrieval unit in a closed or retracted position relative to another telescopically-related member to maintain a fluid seal until the core barrel assembly is struck by the retrieval unit whereupon the members are unlocked accommodating limited relative movement therebetween into an open position.

It is another significant object of the present invention to provide a unique core barrel assembly retrieving apparatus and method which is particularly effective in up" and in generally horizontal holes, and which may be used without a wire line.

These and other objects and features of the present invention will become more fully apparent from the following description and appended claims taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a side elevation shown partially in cross section illustrating a presently preferred embodiment of a retrieval unit, constructed in accordance with the present invention and disposed in its locked, sealed condition;

FIGS. 2 and 3 are side elevations shown partially in cross section similar to FIG. 1 illustrating the retrieval unit of FIG. 1 (a) in the instantaneous position it assumed immediately upon impact with the core barrel assembly (FIG. 2) and (b) in the position it assumes immediately after the position of FIG. 2 is achieved (FIG. 3); and

FIG. 4 is a cross-sectional illustration of a wire line adapter which may be used with the embodiment of FIGS. 13.

THE DETAILED DESCRIPTION OF THE ILLUSTRATED RETRIEVAL UNIT With reference to the FIGS., it should be observed that like numbers identify like parts throughout. With reference particularly to FIG. 1, the retrieval unit, generally designated 30, is illustrated in the closed and locked fluid sealed condition with the drill string 20. The retrieval unit 30 forwardly presents a shoe 32 having a hollow interior36, the shoe being adapted to couple with a core barrel assembly (not shown).

For coupling purposes, the interior 36 of the shoe 32 is provided with a bell-shaped recess 40 the trailingportion 38 of which is inwardly tapered to define a shoulder and the leading portion of which is provided with an annular core barrellatching shoulder 42 which extends through 360 of the interior surface of the shoe 32. Shoe 32 opens at the leading end 44 so that the spearhead latching structure 190 of a core barrel assembly may enter therethrough as shown in FIG. 2.

The spearhead latching structure 190 (FIG. 2) comprises prongs or resilient fingers 192 which are attached to the remainder of the core barrel assembly (not shown). The prongs 192 are outwardly biased, each having identical construction and comprising a coupling ridge 194 having outwardly diverging abutment surfaces 196 and 198 and an exterior arcuate mating surface 200 which couples directlywith the outer tube of the drill string 20.

Each prong 192 further comprises a spearhead hook 204 having an exterior tapered though arcuate surface 208 and an overshot latching shoulder 206 adapted toabut shoulder 42. The shoulder 206 is separated from the adjacent coupling ridge 194 by an arcuate groove 202 disposed in each prong.

The trailing end of shoe 32 is provided with a threaded aperture 34 which engages a threaded boss 52 comprising the leading end of an exterior housing or locking sleeve generally designated 50.

Locking sleeve 50 exteriorly presents a smooth cylindrical surface 70 which is chamfered at 56. The forward abutment face 58 adjacent the chamfer 56 provides a smooth surface against which the trailing end of the shoe 32 is contiguously disposed.

The locking sleeve 50 is centrally hollow and provided with a smooth interior surface 62, the hollow interior having a leading interior abutment surface60. A central aperture 55 exists through the center of threaded boss 52 of the locking sleeve 50 and opens to the interior of the locking sleeve 50 at the abutment surface 60. Also, one or more bleeder ports 54, which are essentially parallel to the aperture 55, are disposed in the boss 52 slightly spaced from aperture 55. Each bleeder port 54 accommodates passage of drilling fluid through the locking sleeve 50. Aperture S displaceably receives a central shaft generally designated 150, which will be subsequently more fully described. 7

The internal surface 62 0f the locking sleeve 50 is inter rupted adjacent the'trailing end 68 thereof with an annular groove 64. An annularly, outwardly tapered surface 66 is disposed between the groove 64 and the trailing end68 of the locking sleeve 50.

One or more stepped bores 72 are disposed intermediate the length of the locking sleeve 50, the reduced diameter portion of each bore 72 being threaded to threadedly receive set screw 74 at reduced shank portion 76. Shank 76 projects into the interior of the locking sleeve 50 beyond the smooth surface 62. The purpose and function of each setscrew 74 will be hereafter set forth.

Telescopically disposed within the interior 62 of the locking sleeve 50 is an inner annular fitting or core, generally designated 90, the core 90 having an annular leading end 92 disposed within and spaced slightly from the interior surface 62 and which presents a forward abutment face 94 which cooperates with abutment face 60 to confine a compression spring 95. Spring 95 continuously biases the annular core 90 axially away from the locking sleeve 50. The leading end 92 of the annular core is provided with (a) a central aperture 96 through which a portion of the central shaft 150 is reciprocably disposed and (b) a bleeder port 98 which provides for passage of drilling fluid. Aperture 96 and bleeder port 98 open at the trailing face 100 into a diametrically enlarged generally cylindrical chamber 102, which chamber terminates at the trailing surface 104.

The annular core terminates in an enlarged cylindrical portion which has a forward-directed annular shoulder 112 at the leading end and a trailing abutment surface 108. The cylindrical portion 110 is interiorly threaded at 106 between the trailing end 108 and the surface 104. The cylindrical member 110 has an outside diametral dimension which is substantially the same as the diametral dimension of the exterior housing or locking sleeve 50.

The exterior of the inner core 90, most of which is normally disposed telescopically within the locking sleeve 50, is provided with a diametrically tapered ramp 114 between the shoulder I12 and the essentially cylindrical surface portion 116. A plurality of transverse apertures 117 are disposed within the cylindrical portion 116 of the annular core 90. As illustrated in FIG. 1, each aperture 117 is adapted to be placed in substantial alinement with the annular groove or recess 64 of locking sleeve 50 when, the annular core 90 is retracted within the locking sIeeveJA spherical ball 65, preferably of surface-hardened metal, is loosely disposed within each aperture 117. Itis preferred that each ball 65 be slightly smaller in diameter than the associated aperture 117 and have a diametral dimension which is greater than the axial dimension of the aperture 117 (i.e., the thickness of the core 90 at each aperture 117) so that, in the closed or retracted position illustrated in FIG. 1, each ball 65 will project into the groove 64 to prevent axial displacement of the inner core 90 relative to the exterior locking sleeve 50.

Cylindrical portion 116 of the core 90 is also provided with an axially elongated exteriorly-open slot 120 for each setscrew 74, which receives the exposed shank 76 of the setscrew. Each slot 120 terminates in a forward end 124 and a trailing end 122, the ends 124 and 122 being adapted to abut the shank 76 of setscrew 74 to define the limit to which the annular core 90 may be axially displaced within and relative to the locking sleeve 50.

A resilient, expandable annular ring, such as an O-ring 118, is contiguously carried upon the tapered ramp surface 114 between the shoulder 112 and the abutment face 68 of the locking sleeve 50. When the annular core 90 and the locking sleeve 50 are in the retracted or closed position illustrated in FIG. 1, the inside and outside diameters of the annular ring 118 are forced to the diametrically enlarged left end of the ramp surface 114 so that the annular ring 118 is expanded radially outward tightly against the interior surface 22 of a drill string 20. Thus, a fluid seal is formed between the drill string 20 and retrieval unit 30 when the annular core 90 and the exterior housing or locking sleeve 50 are in the closed position of FIG. I.

An insert or cap, generally designated 130, in FIGS. 1-3, comprises a body 132 having, at the trailing end thereof, a smooth rear face 134 and, at transverse face 136 thereof, a forwardly projecting, exteriorly threaded annular boss 138 which is screw-secured into the cylindrical portion 110 of the annular core 90 at 106 until faces 108 and 136 meet. The boss 138 is provided with a planar abutment surface 140 which communicates with and is illustrated as being spaced slightly from the face 104 of the inner core 90. The abutment face 140 abuts one end of a compression spring 176 which biases the central shaft 150 toward its most projected rightward position, illustrated in FIG. 1.

If desired, the cap may be replaced by cap 250, shown in FIG. 4. Cap 250 resembles cap 130 in that it comprises the boss 138, abutment surface and face 136 and is attached to the annular core 90 in a substantially identical manner. The

' body 252 of the cap 250 is substantially longer than body 132 of cap 130 and body 252 is provided with an axial blind bore 254 having threads 256. The bore 254 opens into an annular recess 258, the recess 258-and threads 256 being adapted to receive a conventional wire line attachment (not shown). The embodiment of FIG. 4 is used with a wire line, for example, in horizontal or down holes where the force of gravity will not bring the retrieval unit to the trailing end of the drill string. However, it may also be used without a wire line.

The central shaft 150 comprises a smooth exterior portion 152 having a threaded leading end 154 which terminates in a substantially flat end 162. A retainer nut 156 and an impact nut 158 are threadedly attached to the end 154 of shaft 150, the impact nut 158 comprising an impact surface 160 which faces the opening 44 in the shoe 32.

The central shaft 150 is disposed through both aperture 55 in the exterior housing 50 and aperture 96 in the inner core 90. The shaft 150 terminates at the trailing left end thereof in a stepped annular enlargement having a lower step 164 with a forwardly directed abutment face 166 and rearwardly merging with the annularly enlarged upper step 170 over an annular ramp surface 168. The annularly enlarged step 170 terminates rearwardly in a tapered edge 172 and a planar face 174 upon which the compression spring 176 bears to urge the central shaft 150 in the projected position illustrated in FIG. 1.

OPERATION OF THE RETRIEVAL UNIT When it is desired to use the retrieval unit in a horizontal or up hole and to propel the retrieval unit to a core barrel assembly at the leading end of the drill hole by the hydraulic pressure of drilling fluid, the retrieval unit 30 is placed in the contracted position by forcing the inner core 90 telescopically withinthe locking sleeve 50 against the bias of compression spring 95 until each aperture 117 is alined with the annular groove 64. This causes the central shaft 150 to be drawn to the projected position illustrated in FIG. 1 so that the spherical ball 65 within each aperture 117 will ride up the ramp 168 and rest upon the annularly enlarged portion 170 of the shaft 150. In this position, a portion of each ball 65 is within the associated annular groove 64 and another portion is within the associated aperture 117 to releaseably lock the inner core 90 and the locking sleeve 50 in the position illustrated in FIG. 1.

The retracted or closed position of the inner core 90 relative to the locking sleeve 50 forces the resilient annular ring 118 to the diametrically enlarged portion of ramp 114 at the left so that the ring 118 radially expands and forms a fluidtight seal with the smooth interior surface 22 of the drill string 20. In this position, hydraulic fluid acting primarily upon the surface 134 of the cap 130 (see the arrows of FIG. 2) will propel the retrieval unit 30 through the drill string to the location of the core barrel assembly at the drilling site.

As illustrated in FIG. 2, when the overshot bell receives the spearhead hook 204 of the prongs 192, the prongs 192 are gathered together within the shoe 32 until the leading end 210 of each prong 192 strikesthe impact surface 160 of nut 158. instantaneously the impact force is communicated from the prongs 192 through the impact locknut 158 to the central shaft 150 and displaces the central shaft 150 axially rearward (left) against the bias of compression spring 176 until each spherical ball follows the ramp 68 to the reduced stepped portion 164 of the shaft 150. In the FIG. 2 position, which is the instantaneous position at impact, the spherical balls 65 are forced radially inward through apertures 117 toward shaft 150. The compression spring 95 then instantaneously axially displaces the inner core 90 re'arwardly (left) relative to the exterior housing 50 to the extended position illustrated in FIG. 3. Engagement of the balls 65 with interior surface 62 of the housing 50 and with the ramp surface 168 of the shaft 150 restrains the shaft in the position'of FIG. 3 counter to the bias of spring 176. The amount of displacement of the inner core 90 relative to the exterior housing or locking'sleeve 50 is limited by engagement of the abutment shoulders 122 and 124 by the shank 76 of each setscrew 74.

In the extended position, illustrated in FIG. 3, the radially expandable resilient ring 118, which is made of wear resistant material with memory, will have moved along the ramp surface 114 to the diametrally reduced cylindrical portion 116 of the annular core 90 due to the memory of the material. As the expandable ring 118 moves to the reduced diametral portion, the inside and outside diameters of the ring 118' concurrently contract due to said resilience or memory to move the ring 118 out of sealed relation with the surface 22 of the drill string 20 thereby breaking the fluid seal between the retrieval unit 30 and the drill string 20.

When the retrieval unit 30 is axially displaced through the outer tube 20 toward the trailing end of the drill string, the lower coupling shoulder 206 of the prongs 192 will engage the annular core barrel latching shoulder 42 so that the core barrel assembly is withdrawn along the the retrieval unit. In an up" hole, the return of the retrieval unit 30 and core barrel assembly is preferably accommodated without a wire line by force of gravity with the drill pipe being drained as rapidly as possible until only enough drilling fluid remains to adequately cushion the fall of the retrieval unit at the trailing end of the drill string.

However, in a down" hole, the return must be effectuated by a wire line attached to the cap embodiment 250 (FIG. 4), secured as described to the retrieval unit 30. In either case, the present invention forms a seal with the drill string prior to latching with the core barrel assembly which seal is automatically broken when the core barrel assembly is impacted by the novel retrieval unit 30.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore to be embraced therein.

Iclaim:

1. Apparatus for fluid pressure displacement through a string of drill pipe terminating in an outer tube to latch with and retrieve a core barrel assembly disposed within and coupled to the outer tube during drilling comprising:

an exterior housing having a maximum transverse dimension less than the inside transverse dimension of the outer tube and the drill pipe;

resilient seal means adjacent the exterior housing which,

when in one position, are radially expanded to a transverse size slightly greater than the inside transverse dimension of the outer tube and the drill pipe to create a seal between the drill pipe or the outer tube and the apparatus adjacent the periphery of the housing to prevent drilling fluid from passing between the apparatus and the drill pipe or outer tube;

axially displaceable substantially water-impenetrable means telescopically carried at least partially within the housing and relatively displaceable from an extended disposition to a fluid-obstructing retracted disposition for expanding the seal means into the one position and thereafter maintaining the seal means in the one position so long as the axially displaceable means are in the retracted disposition; and

means partially telescopically disposed within both the housing and the axially displaceable means and responsive to the impact of the apparatus against the core barrel assembly, the responsive means comprising locking means releasably coupling the housing and the displaceable means when in the fluid-obstructing retracted disposition and means transferring the impact force to the locking means to release the locking means and effect relative axial displacement of the displaceable means from the retracted disposition to the extended disposition accommodating transverse contraction of the seal means due to the resilience thereof to terminate said seal and allow for fluid flow between the apparatus and the drill pipe or the outer tube.

2. Apparatus of the type defined-in claim 1 wherein said seal means comprise an annular ring composed of a material with memory.

3. Apparatus of the type defined in claim 1 wherein one end of the housing abuts the seal means and the axially displaceable means comprise a diametrically tapered ramp fitted through a hollow center of the seal means so that movement of the displaceable means from the extended to the retracted disposition drives the seal means up the ramp by reason of the abutment with the housing thereby radially expanding the inside and outside transverse dimensions of the hollow seal means to create said seal.

. 4. Apparatus of the type defined in claim 1 wherein the responsive means comprise a central shaft partially telescopically disposed within the axially displaceable means, the shaft being adapted to be contacted by the core barrel assembly upon impact and thereby axially displaced accommodating release of the locking means to provide for relative movement of the displaceable means and the housing into the extended disposition.

5. Apparatus of the type defined in claim 4 wherein the locking means are interposed between the housing and the central shaft and are urged against the housing by an enlarged portion of the shaft when the axially displaceable means are in the retracted disposition, the locking means moving away from the housing when the enlarged portion is displaced away from the locking means upon impact of the apparatus against the core barrel assembly.

6. Apparatus of the type defined in claim 1 further comprising means interposed between the axially displaceable means and the responsive means urging the axially displaceable means and the responsive means away from each other.

7. Apparatus of the type defined in claim 1 further comprising means interposed between the housing and the axially displaceable means biasing the axially displaceable means toward the extended disposition.

8. Apparatus of the type defined in claim 1 further comprising stop means interposed between the housing and the axially displaceable means limiting the permissible relative movement therebetween and thereby defining the extended and retracted dispositions.

9. Apparatus of the type defined in claim 1 further comprising coupling means integral and coaxial with the exterior housing at the leading end thereof for latching the apparatus to the core barrel assembly upon impact.

10. A pump-in unit for fluid pressure displacement through a string of drill pipe to an outer tube comprising the terminal section of the string to latch with and retrieve a core barrel assembly disposed adjacent and coupled to the outer tube comprising:

a central axially directed shaft having an annularly enlarged portion near the trailing 'endof the shaft;

a locking sleeve concentrically circumscribing the enlarged portion of the central shaft having an internal annular locking groove;

a generally annular core disposed between the central shaft and the locking. sleeve, the core having a plurality of transverse apertures opening to both the central shaft and the locking sleeve and an external ramp surface at least part of which is disposed rearward beyond the trailing end of the sleeve and defining a gradually rearwardly increasing radial dimension;

spherical balls loosely disposed one in each of the apertures in the core, each ball having a diameter somewhat greater than the end-to-end length of the aperture so as to be projectable into the annular groove in the locking sleeve when the central shaft is so disposed that the enlarged portion is in locking position contiguous with the balls and to be removed frorn'the annular recess toward the shaft when the enlarged portion is displaced away from the balls; and diametrally expandable O-ring carried upon-the exterior ramp surface of the core which is expandable into fluidsealing relation with the drill-pipe or outer tube by relative displacement of the O-ring with respect to the ramp surface in a rearward direction until the balls are continuous with the annular groove in the locking sleeve and is contracted out of fluid-sealing relation with the drill pipe or outer tube by relative displacement of the O-ring with 11. A pump-in unit of the type defined in claim 10 wherein said core is normally biased in an axial direction away from the locking sleeve so that the core will move relative to the locking sleeve automatically when the spherical balls are away from the annular groove.

12. In a method of coupling and retrieving a core barrel assembly disposed at the leading end of the string of drill pipe using a retrieving unit:

positioning an inner core of the retrieving unit having an exterior ramp surface relative to an exterior housing of the retrieving unit so that an expandable seal resting upon the ramp surface is expanded by relative displacement of the ramp surface with respect to the seal to form a fluid seal with the string; restraining the seal in the expanded fluid-seal position; displacing the retrieving unit under pressure of drilling fluid through the string causing the unit to strike and couple with the core barrel assembly free of the string; and

changing the relative positions of the inner core and the exterior housing upon striking the core barrel assembly to relatively displace the ramp surface with respect to the seal so as to cause the expandable seal to contract thereby terminating the fluid seal.

13. In a method of the type defined in claim 12 further comprising returning the retrieving unit and the coupled core barrel assembly to the trailing terminal end of the string while simultaneously allowing relative flow of the drilling fluid between the string and the retrieving unit.

14. Apparatus for retrieving a core barrel assembly from its drilling position at the leading end of a drill string:

a resilient annular seal;

a water-impenetrable diametrically tapered section passing through and contiguous with the hollow of the annular seal;

means restraining the annular seal to accommodate enlargement of the inside and outside diameters of the sea] by relative displacement of the tapered section with respect to the annular seal from an open to a closed position, the outside diameter of the annular seal in the closed position being slightly greater than the inside diameter of the drill string to create a fluidtight relation therebetween when the apparatus is in the drill string;

means (a) for reversibly coupling the tapered section and restraining means to maintain the annular seal in the closed position while the apparatus is displaced under pressure of drilling fluid until the apparatus reaches the core barrel assembly and (b) for incoupling the tapered section and the restraining means to return the annular seal to the open position with the inside and outside diameters of the annular seal being contracted due to the resilience of the seal following contact with the core barrel assembly to terminate the fluidtight relation; and

means for coupling the apparatus to the core barrel assembly for retrieving the core barrel assembly.

15. Apparatus for transversely sealing the interior of a pipe against fluid flow across the apparatus:

first and second telescopically-interrelated members which are selectively displaceable with a tapered section disposed therebetween, said members each having a maximum transverse dimension less than the inside diameter of the pipe and together obstructing fluid passage except between the exterior periphery of the members and the interior periphery of the pipe;

structure for relatively positioning and reversibly restraining the members in an open extended position or a closed retracted position; and

an endless annular seal made of a material having memory mounted between portions of said first and second members upon the tapered section at a central opening in the seal which opening is sized to cause the seal to concausing the inside and outside diameters of the endless seal to be enlarged when the members are relatively displaced toward each other until the closed position is obtained where the outside diameter of the seal is greater than the inside diameter of the pipe.

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