US3605896A

US3605896A - Liner top squeeze plug below retrievable tool

Info

Publication number: US3605896A
Application number: US830462A
Authority: US
Inventors: Lee E Perkins
Original assignee: Halliburton Co
Current assignee: Halliburton Co
Priority date: 1969-06-04
Filing date: 1969-06-04
Publication date: 1971-09-20
Anticipated expiration: 1988-09-20

Abstract

AN ANNULAR LINER PLUG IS RELEASABLY MOUNTED ON THE LOWER END OF A WELL BORE CEMENTING STRING BY MEANS OF A BALL-TYPE RETAINING AND RELEASING DEVICE. A RELEASING PLUG IS PUMPED DOWN THE CEMENTING STRING, FOLLOWING THE CEMENT USE TO CEMENT A LINER WITHIN THE WELL BORE, AND FORCEABLY ENGAGES WITHIN SLIDABLE SOCKET MEMBER WITHIN THE ANNULAR LINER PLUG. HYDROSTATIC PRESSURE ON THE RELEASING PLUG RESULTS IN THE SHEARING OF AN ATTACHMENT MEANS CONNECTING THE SLIDABLE SOCKET WITH THE INTERIOR OF THE ANNULAR LINER PLUG. THE SOCKET MEMBER SLIDES DOWNWARD, UNDER THE FORCE OF THE RELEASING PLUG AND PERMITS THE BALL DEVICE TO OPERATE SO AS TO RELEASE THE ANNULAR LINER PLUG FROM THE CEMENTING STRING. THE LINER PLUG IS PUMPED DOWNWARD AND, ULTIMATELY, SEATS OVER THE LINER AT THE BOTTOM OF A WELL BORE. THE LINER PLUG OPERATES TO SEAL OFF AN ANNULAR GAP BETWEEN THE LINER TOP AND A SURROUNDING CASING. THE RELEASING PLUG, ENGAGED WITHIN THE SOCKET MEMBER OF THE ANNULAR LINER PLUG, NOW OPERATES TO SEAL OFF THE CEMENT BELOW THIS ASSEMBLY FROM THE FLUID DISPOSED ABOVE THIS ASSEMBLY. LATCHING MEANS MAY BE PROVIDED FOR RETAINING THE RELEASING PLUG WITHIN THE ANNULAR LINER PLUG AGAINST ABRUPT BACK PRESSURES OR WELL "KICKING."

Description

. sept 20 1971 L. E. PERKINS 3,605,896

LINER TOP SQUEEZE PLUG BELOW RETRIEVABLE TOOL Filed June 4. 1969 2 Sheets-Sheet 1 Sept. '20, 1911 3,605,896

LINR TOP SAOUEEZE PLUG BELOW RETRIEVABLE TOOL Filed June 4, 1969 L. E. PERKINS 2 Sheets-Sheet 2 INVENTOR 'LEE E. PERKINS vm v om BY Burns, bow wm',

Sweater i M11 n .N ma

United States Patent O U.S. Cl. 166-290 10 Claims ABSTRACT F THE DISCLOSURE An annular liner plug is releasably mounted on the lower end of a well bore cementing string by meansof a ball-type retaining and releasing device. A releasing plug is pumped down the cementing string, following the cement used to cement a liner within the well bore, and forceably engages within slidable socket member within the annular liner plug. Hydrostatic pressure on the releasing plug results in the shearing of an attachment means connecting the slidable socket with the interior of the annular liner plug. The socket member slides downward, under the force of the releasing plug and permits the ball device to operate so as to release the annular liner plug from the cementing string.

The liner plug is pumped downward and, ultimately, seats over the liner at the bottom of a well bore. The liner plug operates to seal off an annular gap between the liner top and a surrounding casing. The releasing plug, engaged within the socket member of the annular liner plug, now operates to seal off the cement below this assembly from the fluid disposed above this assembly. Latching means may be provided for retaining the releasing plug within the annular liner plug against abrupt back pressures or well kicking This invention relates to oil well cementing and completion techniques, and more particularly to techniques for cementing the top of a liner disposed within the lower portion of a casing at the bottom of a well bore.

Squeeze cementing has, for some time, been a common type of well cementing operation. The process involves applying hydrostatic pressure to force, or squeeze, a cement slurry into a formation through an open hole or through perforations formed in the casing. Engineers often find it desirable to squeeze cement liner tops which are axially overlapped by a casing.

Since cement slurry is not a true fluid, cement cannot be directly pumped into the interstices of many formations under a constant pressure without an undesirable amount of fluid loss. To cope with this situation, a hesitation squeeze process has been developed and is commonly employed. This method divides the squeeze cementing operation into pumping and Waiting periods in order to control the fluid loss from the slurry. It has been found that such a method properly results in the building of filter cake nodes on the formation while the parent slurry, within the casing, remains in a `fluid state.

When squeeze cementing is conducted in the zone Surrounding the top of a liner, however, additional problems are raised. These problems are aggravated by the use of the hesitation method but are offset by the present invention.

Essentially, the environment of the invention includes a liner conduit which is positioned at the bottom of a well bore. A well casing, with a diameter greater than the diameter of the liner, is fitted along the length of the well bore so as to extend down to the upper end of the liner and to overlap therewith to form an annular space. When squeeze cementing in the zone adjacent the overlap, with the hesitation method, the cement slurry dis- "ice i posed within the annular space and within the liner may be pressurized and displaced by hydrostatic fluid which is directed into the well bore immediately above the cement and used to develop the squeeze pressure.

When squeeze cementing, there may be a tendency for the mud following the cement to channel axially through a filter cake wall and thus fill the casing-liner overlap with mud rather than cement.

lf the well bore should deviate from the vertical to any appreciable degree, the displacing fluid may tend to overdisplace the cement slurry, i.e. channel between the Cement and the upper side of the deviated casing. This overdisplacement results in a condition where a hydrostatic fluid, such as mud, may occupy the annular overlap space instead of cement slurry.

Another problem, which may be encountered, arises where the formation will not support the hydrostatic head developed by the hydrostatic fluid after the hydrostatic fluid has been pumped into the formation. In this situation, the cement slurry is syphoned out of the annular space due to the continuous fluid flow so as to result in a defective cementing job.

-Due to the cementing defects caused by the above discussed problems, cementing jobs may have to be repeated two or three times before a satisfactory job is attained.

Therefore, it would be advantageous to develop a method and apparatus for cementing a liner, which apparatus and method would prevent channeling of mud into the overlap, prevent the overdisplacement of cement slurry within a well bore having a deviation from vertical, due to the overriding of a light hydrostatic fluid, and prevent the syphoning of cement slurry from the annular space in the overlap between the liner top and a surrounding casing.

OBJECTS AND SUMMARY OF INVENTION It is therefore an object of the present invention to provide an apparatus and a method for efficiently squeeze cementing the top of well liners so as to obviate or minimize problems of the type noted above.

It is another object of the present invention to provide an apparatus and a method for cementing the top of liners without permitting mud channeling of the column of cement disposed within the liner.

It is a further object of the present invention to provide an apparatus and a method for cementing liners within a well bore, which apparatus and method are simple and may be operated and performed using existing equipment requiring only minor adaptations.

It is still a further object of the presentinvention lt0 provide an apparatus and method for cementing the top of well liners, using the hesitation type of squeeze cementing, while offsetting the possibility of overdisplacing the cement with mnd or cement displacing fluid.

It is yet another object of the present invention to provide an apparatus and a method for cementing liners in deviated wells while preventing cement displacing fluid from channeling into the liner-casing overlap zone.

Briefly stated, the objects of the invention are carried out by providing a cementing string with an annular liner plug which is releasably secured to the bottom of the cementing string by attachment means which release the annular liner plug in response to the imposition of a predetermined force on the annular liner plug. The releasing force is provided by a releasing plug which is pumped down the cement string, engages the annular liner plug, seals a central channel defined by the annular liner plug, and cooperates with the annular liner plug to seal oil the top of the liner When the annular liner plug ultimately reaches a dinal position on top of the liner. The annular liner plug, itself, operates to seal off the annular gap between the liner and an overlapping casing.

3 DRAWINGS While the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification, the preferred embodiment may best be understood by reference to the following detailed description taken in connection with accompanying drawings in which:

FIG. l is a cross-sectional view of a well bore having inserted therein the annular liner plug, of the present invention, detachably secured to the lowermost portion of a cementing string;

FIG. 2 shows a cross-sectional view of the well bore of FIG. l wherein the annular liner plug has been released and is being pumped in a downward direction;

FIG. 3 shows the lower portion of the well bore of FIG. 1 with the annular liner plug in a proper final position over the liner and sealing off cement within the liner and within an annular gap or axial overlap between the liner and an overlapping casing;

FIG. 4 shows a releasing plug used to release the annular liner plug from a cementing string;

FIG. 5 is a detailed cross-sectioned, elevational view of the annular liner plug of the present invention;

FIG. 6 shows the annular liner plug of FIG. 5 with the releasing plug of FIG. 4 forceably engaging therein so as to release a ball connection between the annular liner plug and the lower portion of the cementing string; and

FIG. 7 shows the annular liner plug with the releasing plug latched therein after separation of the annular liner plug from the lowermost portion of the cementing string.

GENERAL Referring now to the drawings in which like numerals are used to indicate like parts throughout the various views thereof, FIGS. l, 2 and 3 show the overall apparatus assemblage of the preferred embodiment being operated within an oil well bore 11 in accordance with the present invention.

A casing is positioned within the well bore 11 formed within a formation means 12.. A conventional well liner 14 is inserted into the bottom of the well bore 11, with the upper portion 14a of the liner 14 generally concentrically overlapped by the lower portion 10a of the casing 10 so as to form an annular space 15 therebetween. The liner 14 and the casing 10 generally comprise strong, non-corrosive metallic, cylindrical conduits. Liner 14 includes radial openings which may be slotlike or circular in nature.

A cementing string 16 is provided with a packer member 20 at a lowermost end 17 thereof. The packer member 20 is of the selectively actuable type used in testing, treating, and squeezing operations. Such packers are useful for isolating zones along the length of a well bore in order that cement may be forced into the formation at a particular permeable zone by applying hydrostatic pressure to force, or squeeze, the cement into contact with the formation. In this preferred embodiment, the packer used is the retrievable, test-treat, squeeze packer described on page 62 of Halliburton Services Sales and Service `Catalog for 1968, Halliburton Services, Duncan, Okla.

A cylindrical collar-like connector 22 is used to connect the lower end of the retrievable test-treat packer 20 with an annular liner plug 2'4. The attachment of the connector 22 with the annular liner plug 24 is designed to be releasable upon the applicable of a predetermined magnitude of uid generated force to the annular liner plug 24. A releasing plug 26, pumped through the string 16 under the pressure of a hydrostatic substance, such as mud, carries out the operation of applying the sufiicient force to the annular liner plug 24 in order to cause the release of the liner plug 24 from the cylindrical collarlike connector 22. In the preferred embodiment, the latch down plug shown on page 5l of the aforementioned Halliburton Services Sales and Service Catalog for 1968 was adapted for use as the releasing plug 26. The four members comprising the cementing string 16, the packer 2,0, the connector 22 and the plug 24 are all formed with axial passages 16a, 20a, 22a and 24a, respectively, which are aligned for the passage of cement slurry therethrough upon the conventional, threaded connection of the members.

In overall operation, the casing 1() and the liner 14 are conventionally positioned within a well bore 11. The cementing string 16 is then tted with the retrievable test-treat squeeze packer 2,0 at the lower end 17 of the string 16. The annular liner plug 24 is releasably attached .to the retrievable test-treat squeeze packer 20` by means of the collar-like cylindrical connector 22. The connection provided by the member 22, operatiing in combination with the retrievable test-treat squeeze packer 20 and the annular line plug 24, is described in detail later in the disclosure with reference to FIGS. 5, 6 and 7.

After connecting the cementing string 16, the packer 20, the connector 22 and the annular liner plug 24 and after inserting this connected assemblage within the casing 10, the packer 20 is set, i.e. expanded radially outwardly into sealing engagement with casing 10. Thereafter, a mass or slug of cement is pumped through the axial passage, formed by the connection of these members, and into the area adjacent the lower end 10a of the casing 10. As the predetermined amount of cement is pumped into the casing 10 and into the liner 14 zone, the expanded packer 20 insures that cement exiting from passage 24a ows downwardly toward the liner 14 and into the annulus 15 between the liner 14 and casing end 10a.

To terminate the liner, squeeze cementing operation, the releasing plug 26 is placed in the axial passage 16a of the cementing string 16 while the last of the slug of cement is being directed into the well bore 11. Hydrostatic Huid, such as mud, is then directed, under pressure, into the cementing string 16 immediately behind the releasing plug 26 and operates to pump the releasing drill pipe plug 26 into forceable engagement with an upper portion of the annular line plug 24 so as to release the plug 24 from the connector 22.

FIG. 2 shows the releasing drill pipe plug 26 in engagement with the annular liner plug 24 at a moment in time shortly after release of the annular liner plug 24 from the cylindrical, collar-like connector 22. The fluid surrounding the upper surfaces of the annular liner plug and the releasing drill pipe plug comprises hydrostatic fluid such as mud As is shown in FIG. 2, the annular liner plug 24 is driven down toward the top 14a of the liner 14. The axial passage 24a, formed within the annular liner plug 24, is blocked olf by the releasing plug 26 after the plug 26 engages therein.

FIG. 3 shows the annular liner plug 24 resting in a proper final position over the well liner 14 and blocking the annular space 15 between the liner 14 and the casing 10.

With this arrangement and technique, the Ihydrostatic iiuid following the cement will not tend to overdsplace the cement and occupy the annular space 15 between the liner 14 and the casing 10. Likewise, if the hesitation method should be used, the hydrostatic fluid will not channel through the cement column below the annular liner plug 24. The drill pipe plug 26, engaged within the axial passage 24a of the liner plug 24, protects the column of cement within the liner 14 from any fundesiralble effects of the hydrostatic uid. The seal provided by the combined plugs 24 and 26 prevent a continued downward flow of fluid which might tend to siphon mud out of the space l5.

It should be understood that Ithe axis of the bore 11 may deviate as much as or more from the vertical.

When such is the case, overdisplacement of the cement by the lighter hydrostatic fluid along the upper portion of the casing is avoided.

Releasing plug FIG. 4 shows a detailed cross-sectional view of the releasing plug 26 used to force the annular liner plug 24 out of attachment with the cylindrical collar-like connector 22. The plug 26 is a composite unit, having a stem 3|() of drillable metal such as aluminum and a formed rubber plug body 32 which comprises four cuplike sections, each generally frustoconical in nature, and arranged one above the other.

The uppermost cup section 34 is deeper than the remaining cup sections and provides a greater inner surface area 35 upon which the pressure of the hydrostatic tluid may act. A rod-like nose member 36 is mounted on a lower portion 30a of the stem 30` by means of female threads 38 machined in an upper portion 36a of the nose member 36 and male threads 40 formed on a lower portion 30a of the stem 30x In order to ensure proper isolation of tluid disposed below the releasa'ble plug 2.6 from uid above the plug 26, a fluid seal 42 is provided and tits Within an annular groove 44 formed about the cylindrical periphery of the nose member 36. At a lower end of the nose 36, a male threaded projection 46 is formed and operates to retain a circumferentially and thus radially contractible split lock ring 48 and a. nose nut 50. The nose nut -`50 holds the lock ring 48 in a position llush against a shoulder 52 surrounding an upper portion of the threaded male projection 46. The purpose of the lock ring 48 is to latch the plug 26 within the annular liner plug 24 in a manner which will be explained later in the disclosure in connection with FIG. )6 of the drawings.

The overall construction of the releasing plug 26 is a compact, composite unit which may be pumped through the axial passage I16a of the cementing spring 16 and through the contiguous passages a and 22a by the action of the, hydrostatic fluid. The drill pipe plug travels down the overall string until the nose 36 of the plug 26 engages within the annular liner plug 24 and is latched therein as mentioned above. Since the material comprising the releasing drill pipe plug is drillable, the plug may be left within the well Ibore 11 and the ditcult process of retrieving the plug is thereby avoided.

Construction and operation of the annular liner plug FIG. 5 shows a cross-sectional view of the lower portion of the retrievable test-treat squeeze packer 20; the connecting collar member 22, and the annular liner plug The connecting collar member 22 is secured to a lower externally threaded projection 52 of the retrievable testtreating squeeze packer 20 by means of internal threads S4 formed on the upper inside wall of the collar 22. Longitudinally extending and circumferentially spaced slots 56 are formed as radial passages Within the collar 22 at the approximate midpoint along the axial length of the collar 22.

Slots `56 permit a reverse circulation of uid in the FIG. l assembly, i.e. a vilow of fluid down annulius 10a, through slots 56, and up passage means 20u to the wellhead.

The internally threaded wall portion of the collar 22 above the slots 56, in a conventional manner, is slightly divergent, with respect to the outer wall, from the area defining the slots 5'6 to an upper end 58 of the collar 22. A shoulder 59 is formed on the lower end of the packer 20 above and immediately adjacent the threaded projection 52. The upper inner wall of the collar 22 is formed with an annular recess -60` which fits over the shoulder 59 of the packer 20. This overall connection between members 20 and 221 provides strength against the loosenmg influence of cyclic transverse forces acting on the collar 22 and the annular liner plug 24.

The inner wall of the collar connector 22, beneath the slotted area K56, is substantially parallel with respect to the cylindrical outer wall thereof, to a point midway between the slots 56 and a lower end 61 of the collar 22. At this midpoint, the inside diameter of the collar connector is decreased so as to form a slight internal shoulder 62. An annular recess 63 is grooved within the inner Iwall of the connector 22 on the slight internal shoulder 62 midway along the axial length thereof. The annular recess 63 is utilized to retain an O-ring seal 66 which operates to preclude the leakage of fluid past the internal shoulder 62 when the collar connector member 22 is still connected with the annular liner plug 24.

The overall annular liner plug 24- is provided with a hollow, cylindrical, stem-like mandrel 68, the upper end of which tits within a lower end `61 of the connector member 22. A plurality of radial holes 70 is drilled near the upper end of the mandrel 68 and a steel locking ball 72 is placed within each radial hole 70. The diameter of each steel ball is somewhat larger than the thickness of the wall of the mandrel 68. The overall annular liner plug 24 includes an inner, hollow, socket or sleeve member 74 which is slidably mounted within the hollow, sternlike mandrel 68 and is connected thereto by means of a threaded brass shear screw 76 which exhibits a low shear strength. The outer cylindrical wall of the slidable socket member 74 forces each steel ball 72 to project slightly out of each hole 70l in the radially outward direction so as to bear upon the top of the shoulder 62 of the collar member 22 when the weight of plug 20 is vertically supported by the collar 22. In this manner, the plug 24 is vertically supported within the collar 22 only by the action of the balls 72. The weight of the plug 24 is transmitted to the balls 72 by the surface dening the top of each hole 70 bearing upon the top of each ball 72 and is transmitted to the collar 22 by the balls 72, in turn, bearing upon the top of the internal shoulder 62 of collar 22.

The socket member 74 is formed with a central axial passage 109 having a composite configuration. The diameter of the passage 109 is increased at the approximate midpoint of the axial extension thereof to form a recess 75 therein. This recess 75 is used to latchably engage the lock ring 48 of the drill pipe plug 26.

The hollow cylindrical mandrel 68 is threaded at a lower portion 78 thereof and there engages with a complementary threaded portion 80 of a shoe member 82 which consists of a drillable metal. A rubber cup member 84, which is annular in configuration, is positioned over the mandrel 68 and rests upon the top surface 85 of the shoe 82. In order to adapt the cup member 84 for use with mandrels existing in the eld, an adaptor 86 and a spacer 88 may be used to properly t the cup 84 with the mandrel 68 and the shoe member 82.

The mandrel 68 is formed with an external shoulder 90 formed above the threaded portion 78 thereof and the shoulder 90 engages within a complemntary recess 92 formed on the inner wall of spacer member 88. When the shoe member 82 is tightly threaded on the mandrel 68, an outer shoulder 94 of the spacer 88 presses a portion of the cup 84 against the adaptor member 86 and simultanously presses both the cup 84 and the adaptor member 86 down against the top surface 85 of the shoe member 82 in order to form a composite, integral plug configuration.

An annular groove 95 and an O-ring seal 96 are provided on the inside surface of the adaptor 86, to prevent the passage of lluid between the adaptor 86 and an outer surface of the spacer 88. A similar annular groove 97 and an O-ring seal 98 are provided on the outer surface of the mandrel 68 adjacent the spacer member 88 in order to prevent the passage of uid between the mandrel 68 and the spacer 88. An O-ring seal 99 and groove 100 arrangement is also provided on the outer surface of the slidable socket member 74 to cooperate with an adjacent interior wall 108 of the mandrel 68 and thereby to form a fluid tight seal therebetween.

Radial ports 102 are formed in the mandrel 68 and in the slidable socket member 74. The alignment of the ports 102 is such that, when the brass rod 76 is properly connecting the socket member 74 with the mandrel member 68, there is a direct fluid communicating relationship between the space surrounding the outside of the mandrel 68 and the axial passage 109 inside the hollow slidable socket member 74. Since the axial space 109 communicates with the space below the overall liner plug 24, equalization of pressure is effected between the spaces above and below the plug 24 before the drill pipe plug 26 is engaged within the liner plug 24.

This arrangement is especially useful for equalizing pressures while running the overall apparatus into a well bore at operational speeds or for reverse circulation around the packer if a squeeze pressure should develop before the liner plug 24 is released. Also, it may become necessary to retrieve the string from the bore with the plug 24 still attached thereto and the provision of pressure equalizing slots 56 and ports 102 prevents swabbing of the bore during such a retrieval.

Ports 102 and slots or ports 56 provide a continuously operable, reverse circulation system. If sleeve 74 should be moved downwardly, as shown in FIG. 6, to close port means 102, ports 56 will still provide a reverse circulation path. If plug 26 should engage sleeve 74 so as to block port means 56, but not move sleeve 74 downwardly, port means 102 would remain open to permit reverse circulation.

An annular groove 104, which retains an outwardly expansible, split lock ring 106, is formed in an outer surface 111 of the slidable socket member 74. The lock ring 106 bears against the inside surface 108 of the mandrel 68. This inside surface 108 is of substantially constant diameter from the upper end 69 of the mandrel 68 to an internal recess 110 formed just above the threaded area 78 of the mandrel 68. At this recess 110, the inside diameter of the mandrel 68 is increased for a short axial distance beneath annular shoulder 116, and then decreased for another short axial distance at 112 before again being increased to form a second recess 114. The operational purpose of this composite inner wall 108 configuration of the mandrel 68 may be best understood in connection with FIG. 6.

FIG. 6 shows, in partial cross-section, the packer 20, the connecting collar 22, the overall annular liner plug 24, and the releasing drill pipe plug 26 properly engaged Within the slidable, socket member 74 of the overall annular liner plug 24.

The releasing drill pipe plug 26 is pumped down through the cementing string 16, through the retrievable test-treat squeeze packer 20 and into the socket member 74. The nose portion 36 of the releasing drill pipe plug 26 fits within the slidable socket member 74 and passes therethrough until the lock ring 48 of the plug 26 engages within the internal recess 75 of the socket 74 wherein the lock ring 48 expands in recess 7411 and is retained by shoulder 74C. The lock ring 48 thereby latches the drill pipe plug 26 within the socket member 74 of the overall annular liner plug 24. The socket member 74, being forced downward within the hollow stem-like mandrel 68 by the force transmitting drill pipe plug 26, is, in turn, latched within the mandrel 68 by the action of the socket member carried lock ring 106 expanding within recess 110 being retained by the shoulder 116 at the upper end of the internal annular recess 110 of the mandrel 68. This overall latch arrangement holds the plug 26 against any overriding reverse pressure which might result from kick back forces due to abrupt release of fluid deposits into the bore 11 beneath the annular liner plug 24.

In this connection, it will be appreciated that as nose 36 enters sleeve 74, resiliently expansible ring 48 will be contracted by sleeve cam 74a and then automatically re- 8 expanded adjacent sleeve wall 74b to be latched to sleeve 74 beneath sleeve shoulder 74C. Similarly, resiliently expansible ring 106 will expand in recess 110 to be latched to mandrel 68 beneath shoulder 116.

Briefly summarizing the operation of the overall annular liner plug 24, the force of the releasing drill pipe plug 26 acting down on the slidable socket member 74, shears the brass rod 76 and causes the slidable socket member 74 to latch into a position clear of the area defining the radial holes 70 which retain the steel balls 72. The steel balls no longer being confined to the radial holes 70, the slidable socket member 74 may move downwardly and so the balls 72 may roll radially inwardly from the retaining holes 70 and into the interior of the stem-like mandrel 68.

As the steel balls 72 are removed from position, lthe connecton between the collar 22 and the mandrel 68 is thereby also removed. Consequently, the overall annular liner plug 24, with the releasing drill pipe plug 26 latched within the slidable socket 74 and blocking the central axial passageway 109 therethrough, may drop away from the connecting collar 22 as shown in FIG. 7. The pressure of the hydrostatic fluid above the plug 24 then `may force the overall annular liner plug 24 into operational position on top of the liner 14 as shown in FIG. 3. The annular liner plug may now block off the annular space 15 between the casing 10 and the liner 14. The column of cement within the liner 14 is similarly protected by the drill pipe plug 26.

SUMMARY OF ADVANTAGES AND SCOPE OF INVENTION A principal advantage of the invention resides in the provision of plug means for preventing the channeling of mud, or other cement displacing fluid, into an annular zone which is desired to be cemented.

The invention is particularly advantageous when applied to the cementing of the annular zone between a liner conduit and a previously installed well casing.

The utilization of the liner plug in conjunction with cementing operations conducted in deviated wells is particularly significant in that the plug offsets the normal tendency of the cement displacing fluid to channel past the top of the cement on the upper side of the Well.

The latching of the releasing plug to the actuating fluid or sleeve, and the latching of this sleeve to the body of the liner plug provides a significant locking arrangement tending to offset problems that might develop during the liner plug releasing operation, if sudden pressure should be generated beneath the cementing tool.

The circulating port arrangement provides a continuously effective system for inducing reverse circulation operations if such should become necessary.

As will be recognized, the invention may be practiced while employing liner plug and releasing plug arrangements significantly different from those described in detail. Changes in plug seal structures, plug body structures, releasing and latching mechanisms, and overall plug configurations are well within the purview of the invention.

Changes of these natures as well as yother substitutions, modifications and deletions are deemed to fall within the purview of this invention as defined in the appended claims.

I claim:

1. Apparatus for cementing well conduits, comprising:

(a) a cementing string having a cementing packer positioned at a lower end of said cementing string;

(b) an elongated annular plug having a mandrel `on one end and a plug body on the other end, said mandrel having a slidable socket member disposed therein;

(c) a releasing plug;

(d) means for releasably mounting said annular plug to a lower end of said packer; and

(e) said means for releasably mounting said annular plug to a lower end of said packer being 'operable to release said annular plug from the lower end of said packer in response to a forced engagement of said releasing plug witin said annular plug.

2. Well production apparatus comprising:

(a) a well bore;

(b) a well liner disposed within a lower end of said well bore;

(c) a well casing having a diameter greater than the diameter of said well liner and disposed along a substantial length of said bore;

(d) said well casing axially overlapping said well liner so to define an annular space therebetween;

(e) a cementing string inserted in said well bore;

(f) said cementing string being adapted for connection with a source of cement slurry;

(g) an annular liner plug;

(h) a releasing plug;

(i) means for releasably securing said annular liner plug to a lower end of said cementing string; and

(j) said means for releasably securing said annular liner plug to a lower end of said cementing string being operable to release said annular liner plug from the lower end of said cementing string in response to a forced engagement of said releasing plug within said annular liner plug; and

(k) said annular liner plug being operable to cover the annular space between said casing and said liner upon release of said annular liner plug from said cementing string.

3. Cementing apparatus comprising:

(a) a mandrel having a hollow cylindrical wall, said wall formed to define at least one radial hole;

(b) a ball disposed in each of said at least one hole, each said ball having a diameter greater than the thickness of said cylindrical `wall of said mandrel;

(c) an annular plug body mounted on a lower end of said mandrel;

(d) a hollow slidable socket member releasably secured by fastening means within said mandrel, said lmember being so disposed within said mandrel as to cover each said at least one hole and to retain each said ball from moving radially inward;

(e) said fastening means being releasable in response to the imposition of a predetermined magnitude of force on said slidable socket member.

4. In an apparatus according to claim 3 wherein said mandrel is connected with a lower end of a cement string, the addition of:

(a) a hollow cylindrical connector member;

(b) said hollow cylindrical connector member being connected at an upper axial end with a lower end of said cementing string;

(c) a lower axial end of said hollow cylindrical connector member being secured about the upper axial end of said mandrel so as to prevent each said ball from moving radially outward from each said at least one hole;

(d) shoulder means formed on an inside surface of said hollow cylindrical connector and bearing on an underside of each said ball for transmitting the weight of said hollow mandrel, said annular plug body, and said slidable socket member, to said hollow cylindrical connector;

(e) said shoulder means disengaging each said ball in response to a releasing of said fastening means and a predetermined axial movement of said slidable socket member away from said at least one hole whereby each said ball moves radially inward and out of engagement with said shoulder means.

5. An apparatus according to claim 4 wherein said hollow cylindrical connector member is formed with at least one radial opening whereby uid may be circulated between an outer surface of said hollow cylindrical connector member and a hollow inner passage thereof.

6. An apparatus according to claim 3 with the addition of latch means for preventing axial movement of said slidable socket within said mandrel upon the sliding of said slidable socket a predetermined axial distance within said mandrel.

7. An apparatus according to claim 6 wherein said latch means comprises:

(a) an annular recess formed in an inner surface of said cylindrical wall of said hollow mandrel adjacent the lower end thereof, and

(b) lock ring means on said slidable socket member operable to lockingly engage said annular recess.

8. An apparatus according to claim 7 wherein (a) said hollow mandrel and said slidable sleeve member are formed to define radial ports extending entirely through said slidable sleeve member and said mandrel; and

(b) said radial ports are aligned so as to place the outer surface of said mandrel in fluid pressure communication relationship with the inner surface of said slidable socket member upon attachment of said slidable socket member within said mandrel by said fastening means.

9. A method for cementing a well liner to a well casing comprising the steps of:

(a) providing a cementing string;

(b) releasably mounting an annular liner plug on a lower end of the cementing string;

(c) inserting the string and plug into the well casing;

(d) pumping a quantity of cement slurry through the cementing string and annular liner plug into the liner;

(e) placing a releasing plug generally adjacent the end of the cement slurry;

(f) pumping the releasing plug through the cement string and into engagement with the annular liner plug;

(g) releasing the annular liner plug from the cementing string in response to the engagement of the releasing plug with the annular liner plug; and

(h) pumping the annular liner plug with the releasing plug engaged therein into a position on top of the well liner so as to block an annular space formed in the axial overlap between the liner and casing.

10. A method according to claim 9 with the additional step of latching the releasing plug within the annular liner plug.

References Cited UNITED STATES PATENTS 1,594,498 8/1926 Day 166290X 2,738,011 3/1956 Mabry `166-290X 3,090,442 5/1963 Cochran et al. 166-224X 3,231,020 1/1966 Greene 166-117X 3,364,996 1/1968 Brown 166-208X FOREIGN PATENTS 1,183,039 12/1964 Germany 166-290 DAVID H. BROWN, Primary Examiner U.S. Cl. X.R. 166-15 4