US3468373A

US3468373A - Apparatus for severing well casing in a submarine environment

Info

Publication number: US3468373A
Application number: US705589*A
Authority: US
Inventors: Samuel H Smith
Original assignee: SAMUEL H SMITH
Current assignee: SAMUEL H SMITH
Priority date: 1968-01-02
Filing date: 1968-01-02
Publication date: 1969-09-23
Anticipated expiration: 1986-09-23

Description

sept. 23, 1969 S. H. SMITH APPARATUS FOR SEVERING WELL CASING IN A SUBMARINE ENVIRONMENT Drgnal Filed Sept. 9. 1966 2 Sheets-Sheet 1 Sept. 23, 1969 s. H. sM'lTH 3,468,373

APPARATUS FOR SEVERING WELL CASINGIN A SUBMARINE ENVIRONMENT Original Filed Sept. 9, 1966 2 Sheets-Sheet 2 l E74 f=' i INVENTOR.

SAMUEL H. 544/777' TTOP/VE-YS United States Patent O 3,468,373 APPARATUS FOR SEVERING WELL CASING IN A SUBMARINE ENVIRONMENT Samuel H. Smith, 2224 NW. 52nd St., Oklahoma City, Okla. 73112 Original application Sept. 9, 1966, Ser. No. 573,326, now Patent No. 3,378,072, dated Apr. 16, 1968. Divided and this application Jan. 2, 1968, Ser. No. 705,589

Int. Cl. E21h 29/00, 43/112 U.S. Cl. 166-55.8 3 Claims ABSTRACT OF THE DISCLOSURE Apparatus for cutting submerged multi-tubular well casing which includes an elongated tubing string dimensioned for passage into the innermost casing string and carrying a rotary casing cutting tool similarly dimensioned. The tool includes a plurality of elongated cutting members detachably and pivotally secured to the body of the tool for pivotation about a horizontal axis into cutting engagement with the innermost casing string, and shorter than required to Contact the internal wall of the outermost casing string. A piston mechanism is provided in the cutting tool for pivoting the cutting members into cutting position7 and a plurality of longer cutting members are provided for interchanging with those pivotally secured to the body ot' the cutting tool for the purpose of cutting through one or more casing strings located outwardly of the innermost casing string after the latter casing string has been severed. A plurality of variable length connecting subs are provided for insertion in the elongated tubing string in order to adjust the position of the cutting tool in the innermost casing string.

Related applications This application is a division of co-pending United States application Ser. No. 578,326 led Sept. 9, 1966, entitled Method and Apparatus for Severing Well Casing in a Submarine Environment, which application has now issued as United States Patent 3,378,072.

This invention relates to oit-shore or submarine hydrocarbon exploration and production techniques, and more specifically, but not by way of limitation, relates to an apparatus which can be employed for cutting or severing a well casing extended into the oor of the ocean or sea for the purpose of recovering hydrocarbons.

With the relatively recent advent of exploration and production of petroleum from subterranean deposits located beneath the oecans and seas, radical modifications in conventional drilling and production techniques used in onshore exploration and production have been demanded. Many problems which are not experienced in traditional drilling and production have been encountered in the case of offshore operations.

One of the difculties which has been experienced in olshore drilling and production is the problem of providing a sufficiently stable platform or Supporting structure on which the drilling equipment may be mounted, and from which the drill string or production tubing can be extended and made to function eliectively. In relatively deep waters where the use of a supporting structure rested upon the bottom of a body of water becomes impractical, drilling has been attempted and carried out with some success from oating platforms. In this case, however, difficulties and relatively greater expense continue to result from the necessity to accommodate the drilling equipment and steps employed to wave and swell action which continually change the position of the drilling barge or other point of origin of the drill string with respect to the location on the bottom of the ocean or sea where the 3,468,373 Patented Sept. 23, 1969 ICC actual bore hole is to be formed. Telescoping slip joints and similar structures have been provided in drill strings to permit a certain amount of play and variation in length of the string to randomly occur as may be required as a result from the necessity to accommodate thed rilling platform. There has also been recently developed, a swivel structure which is incorporated in the drill string and which cooperates with or rests upon the borehole casing to limit the movement of that portion of the drill string which is positioned within the casing, and thus make easier to carry out certain operations which must be carried out down hole by reason of improved stability in the location ofthe downhole tools.

An operation which frequently must be conducted following a drilling operation which, for one reason or another has been terminated and no further utilization of the well head equipment contemplated, is the severance or cutting of the borehole casing at some point below the well head so that the upper portion of the casing and the valuable weil head equipment attached thereto can be recovered from the ocean oor and reutilized in other drilling and production operations. The difficulty of successfully and economically accomplishing such cutting and severance of the well casing has been considerably augmented in the case of oishore wells by the fact that it is the usual and conventional practice in such wells to provide a plurality of concentric casing strings, all of which must be cut through in order to permit the well head equipment which is attached to the top of these casing strings to be extracted or recovered from the ocean loor. The equipment which has been most widely employed for the purpose of cutting the casing a short distance below the well head has been a cutter tool usually including a plurality of cutter knives which are pivotally attached to the body of the cutting tool and can be extended radially outwardly therefrom into contact with the casing preparatory to the cutting operation. The tubing string which carries the cutting tool is then rotated within the casing so that the knives bear against the casing as they are rotated and eventually cut or abrade through the casing and permit the severed upper portion thereof to be removed.

While, in a few instances, cutting tools of this type have been satisfactory for the severance of the well casing, great diiculty has been experienced in reliably and quickly cutting through those casing structures most widely used in offshore drilling which include a plurality of concentric tubular casing members which must all be cut before the well head equipment can be freely moved. With the cutting tools and techniques previously in use, severing this multiple casing structure has been a. time consuming and expensive operation, and it has been extremely diicult on many occasions to know with certainty whether the cutting tool has completely severed the several concentric casing structures, with the result that frequently the operation is carried on much longer than necessary in order to be relatively assured of this fact.

The diiculty which has been experienced in the severance of the several concentric casing strings with the cutting tools previously in use has been largely due to the limited space which is available Within the innermost casing string, and the inability, because of such space limitations, to obtain adequate leverage and cutting efciency with cutting knives sufficiently large to extend completely through the outermost of the casing strings in the `tinal phases of the cutting operation.

The present invention involves an improved apparatus for accomplishing this severance or cutting of a submarine well casing of the type in which several tubular casing members are telescopingly disposed relatively to each other. The apparatus which is employed in permits such multiple concentric casing strings to be cut through in a much shorter time than prior techniques in use have permitted, and further gives a much greater assurance at the surface control point of the effectiveness and the success of the cutting operation, and of its progress over each interval of time.

The well casing severing apparatus of the invention includes a cutting tool of the type having pivotally secured thereto at least one elongated cutting member. The point at which the cutting tool is positioned within the innermost casing string will be selected according to current conventional practices, and will be based upon the necessary depth within the casing at which the cutting operation must be conducted in order to permit complete removal of the Well head equipment.

With the cutting tool positioned in this preselected position, and with the cutting members pivotally carried thereby being of a preselected length which is correlated to the diameter of the innermost of the casing strings, the cutting members are pivotally extended into contact with the internal wall of the innermost casing string preparatory to cutting through this casing string. The length of the cutting members is selected to provide maximum leverage against the innermost casing string, and thus to provide the most eicient cutting action through this tubular element. The cutting tool is then rotated within the innermost casing string to cause the cutting members carried thereby to cut through the innermost casing string to form an axially extending opening which extends around the entire circumference of the casing string.

Upon completion of the cutting action lby the cutting member, the cutting tool is removed from the well casing, and at least one other elongated cutting member have a preselected length which is greater than the length of the rst mentioned cutting members is pivotally secured to the cutting tool. The tool is then again lowered to a preselected point or location within the innermost casing string. The preselected point or location of the cutting tool at this time will, as a general rule, be above the location which it occupied during the initial cutting operation, but in any event, the location of the pivotal axes of the several now and longer cutting members attached to the cutting tool will be above the location of the pivotal axes of the shorter cutting members used during the rst cutting operation to cut through and around the innermost casing string. The cutting members are then pivotally extended outwardly from the body of the cutting tool into the axially extending opening formed during the initial cutting operation with the preselected location of the cutting tool having been chosen to permit the new, longer cutting members to be extended through the axially extending opening in the innermost casing string. With the relatively longer cutting members extended into cutting position, the cutting tool is then rotated to cause the new cutting members to cut through at least one of the outer casing strings which surrounds the innermost casing string.

The described sequence of steps may be repeated several times with a substitution of a new and longer cutting member on the cutting tool if such repetition is required in order to completely cut through a plurality of telsecoped casing strings.

Though not an entirely critical or essential method of accomplishing such positioning, the preselection of the position which is to be occupied by the cutting tool in the well casing, and the manner in which the tool is brought to this position preferably entail mounting the cutting tool on the lower end of a tubing string which can be extended from the drilling platform or barge into the well casing, and which carries intermediate its length, an extensible slip joint, a supporting swivel assembly and an interconnecting sub which is located between the swivel assembly and the cutting tool. The swivel assembly s then rested upon a shoulder or abutment formed on the casing at some point, and acts as a point of suspension for that part of the tubing string which extends below the swivel assembly. To adjust the position of the cutting tool and the cutting members carried thereby with respect to the casing and the previous holes which have been cut therein by cutting members of other lengths, the length of the connecting sub which is positioned in the tubing string between the swivel assembly and the cutting tool is then varied to raise or lower the cutting tool to the required location.

The described method permits the length of the cutting members and their position within the multiple casing structure to be selected to yield maximum eiciency and optimum cutting performance. Though, of course, some time is involved in pulling the tubing string upon which the cutting tool is mounted for the purpose of exchangnig the variable length cutting members, and exchanging the connnecting subs connected in the string so as adjust the position of the cutting tool relative to the casing, the time involved in such pulling and changing operations is more than oifset and compensated by the eiciency obtained in the cutting operation, and the certainty with which the crew operating the cutting tool can be apprised of its effectiveness and time of cutting the plural casing strings.

The apparatus of the invention, as will appear from the foregoing discussion, includes an elongated tubing string; a rotary tool secured to one end of the tubing string, and having a plurality of elongated cutting members each detachably secured on said cutting tool for pivotation about a horizontal axis; piston means movably mounted relative to, and cooperating with, the elongated cutting members for pivoting the cutting 4members into a cutting position; additional elongated cutting members longer than the first mentioned cutting members adapted for detachable pivotal securement to the rotary cutting tool in place of the iirst mentioned cutting members; a swivel assembly rotatably mounted on and surrounding the tubing string intermediate its length; and a plurality of varying length connecting subs interchangeably connectable in said tubing string between said swivel assembly and said cutting tool for selectively adjusting the distance between the cutting tool and the swivel assembly.

From the foregoing description of the invention, it will have become apparent that it is an important object of the present invention to provide an improved apparatus for severing or cutting well casing located in a submarine environment.

An additional object of the present invention is to provide an apparatus which may be employed to more rapidly and eiciently cut through a plurality of concentrically or eccentrically disposed casing strings under circumstances where the cutting tool employed is suspended from a platform or supporting structure which varies randomly in its distance of separation from the cutting tool.

A further object of the invention is to provide an apparatus for cutting through, or severing, several telescoping tubing strings at a common location and from the inside outwardly with minimum wear occurring to the cutting elements used to accomplish such severance of the telescoped tubing strings.

In addition to the foregoing described objects and advantages, other meritorious features and beneficial results which can be obtained using the present invention will become apparent as the following detailed description of the invention is read in conjunction with the accompanying drawings which illustrate a typical embodiment of the invention.

In the drawings:

FIG. l is a schematic illustration, partly in elevation and partly in section, of a typical off-shore well installation, and illustrating a cutting tool used in performing the method ot' the present invention and suspended in a multiple casing well bore from a oating drilling barge.

FIG. 2 is an enlarged detailed view, partially in sec tion and partially in elevation, depicting a typical cutting tool which can be used in practicing the method of the present invention, and illustrating this tool and its relation to the concentric casing strings employed for casing an off-shore oil well as the tool appears immediately prior to the commencement of a casing cutting operation.

FIG. 3 is a view similar to FIG. 2, but illustrating the use of the cutting tool in performing the first step of the casing cutting method of the present invention.

FIG. 4 is a view similar to FIGS. 2 and 3, but illustrating the cutting tool after it has been modified by the attachment of longer cutting Vmembers thereto and showing the tool as it is used in carrying out a subsequent step of the casing cutting operation.

FIG. 5 is a view of the cutting tool and telescoped casings similar to FIGS. 2-4, but illustrating the tool as further modified by the addition of yet longer cutting members, and showing the tool as it is being employed in the final step of the cutting operation.

Referring now to the drawings in detail and, initially to lFIG l, a drilling barge or platform is illustrated as oating on the surface of a body of water 12. A drilling rig 14 is mounted on the deck of the drilling barge 10 and supports a downwardly extending drilling string 16. The drilling string 16 includes along its length an extensible slip joint or telescoping connection 18 which permits the overall length of the drilling string to vary as the drilling barge 10 may be `caused to rise or fall with respect to the bottom of the body of water by wave actions, swells, etc.

The drilling string 16 extends downwardly into an inner casing 20 which is coaxially positioned inside an intermediate or central causing 22 and an exterior or outer casing 24, this telescoping casing construction being typical of that currently widely used for marine petroleum production. The exterior casing 24 is positioned in a bore hole 26 which extends into the bottom 28 beneath the body of water 12.

A marine swivel assembly 30 is connected in the drilling string 16, and is dimensioned to bear against and rest upon an upwardly facing shoulder 32 formed in the inner casing 20, preferably adjacent the upper end thereof. The function and mode of use of the marine swivel assembly 30 is explained in detail in my copending application for United States Letters Patent, Ser. No. 374,- 719, filed June 12, 1964. It will suffice for purposes of explanation of the present invention to point out that the swivel assembly 30 functions to provide a fixed point of suspension support within the well casing for that portion of the drilling string 16 which extends downwardly from the swivel assembly. Thus, the swivel assembly 30 in conjunction with the extensible slip joint 18 permit a relatively fixed location to be assumed by the cutting tool carried on the lower end of the drilling string 16 hereinafter described.

Secured to the lower end of the drilling string 16, and positioned in the FIG. l illustration below the well head at the top of the casing, is a cutting tool designated generally by reference character 34. The cutting tool 34 is illustrated as secured to the drilling string 16 through a connecting sub 36 of the box and pin type (see FIG. 2) It should be pointed out, however, that the location of the connecting sub 36 in this specific position relative to the drilling string 16 and cutting tool 34 is not critical or required for the performance of the method of the present invention, it only being necessary that the connecting sub be positioned in the drilling string at some point between the swivel lassembly 30 and the cutting tool 34. The role played by the connecting sub 36 in the practice of the method of the invention will be hereinafter described in greater detail.

In FIG. 2 of the drawings, some of the structural details of the cutting tool 34 are illustrated, and the tool is shown in the position which it should occupy at the commencement of the casing cutting operation. Although a variety of types of cutting tools can be employed in practicing the present invention, the type illustrated for explanatory purposes is one in which a tubular body 38 surrounds a slidingly mounted piston 40 which can be caused to reciprocate in the tubular body by fiuid directed through the drilling string 16 from the drilling barge I10. The piston 40 carries at its lower end a downwardly facing knife actuating member 42. The knife actuating member 42 is connected through a relatively small diameter rod 44 to a knife movement limiting member 46. A helical compression spring 48 is provided in the lower portion of the bore in the tubular body 38 and bears against the knife movement limiting member 46 for the purpose of `resiliently biasing the piston 40 to its inoperative position as depicted in FIGURE 2 when the fluid pressure directed against the piston via the drilling string 16 is relieved.

The cutting tool 34 has a plurality of axially extending slots 50 formed in the sides thereof for the accommodation of an equal number of cutting members or knives 52 which are pivotally secured to the tubular body 38 of the cutting tool by means of pivot pins 54. The cutting members or knives 52 each carry at their end most closely adjacent the pivot pins 54, an arcuately shaped or tapered ear 56 which extends into the slot or open space formed between the knife actuating member 42 and the knife movement limiting member 46. The ears 56 are thus positioned to be engaged by the knife actuating member 42 at such time as the piston 40 is moved downwardly within the tubular body 38 by the impress of fluid pressure directed through the drilling string 16. This construction Iand mode of operation of cutting tools of the general type described are well understood in the drilling technology at the present time, and constitute no part of the present invention except as tools of such general character are utilized in the practice of the method of the invention, and in the overall apparatus employed therefor as hereinafter described in greater det-ail.

A preferred method of practicing the present invention can best be related -by referring conjunctively to the several figures of the drawings in explaining the sequence -of perfomance of the several steps utilized. The occasion for using the method of the invention for severing or cutting the concentric casing strings arises at such time as a cased well has reached the end of its period of usefulness. At this time, it is economically desirable to recover the expensive well head equipment (not illustrated) which is positioned at the top of the casing, Iand it is also frequently necessary to remove the projecting portion of the casing and the well head equipment from the bottom of the ocean or sea in order to comply with certain legal requirements which apply to offshore drilling and production activities. In general, the casing cutting operation will be carried out ra relatively short distance below the well head, it only being necessary to be certain that the concentric casing strings are severed or cut at a location sufficiently low in the casing to permit these strings to be concurrently pulled from the bottom together with the well head equipment secured to the upper end thereof.

Knowing the depth within the casing where the cuting operation is to be carried out, the length of the drilling string 16 between the swivel assembly 30 and the cutting tool 34 is selected to effectively locate the cutting tool at the desired position in the casing when the swivel assembly 30 rests upon the casing shoulder 32 in the manner illustrated in FIG. l. Concurrently with the makeup of the drilling string 16 to meet the requirements of positioning the cutting tool 34 at the desired location, a Irelatively long connecting sub 36 is included in the tubing string 16 between the swivel assembly 30 and the cutting tool 34. Then the drilling string 16 with the cutting tool 34 attached thereto is run into the inner casing 20 until the swivel assembly 30 supports the lower portion of the drilling string and the cutting tool 34 within the casing in the manner illustrated in FIG. l.

A suitable hydraulic iluid is next directed down through the drilling string 16 against the piston 40 so as to move the piston downwardly in the tubular body 38 and thus extend the cutting members 52 against the internal wall of the inner casing string 20. The angle made by the longitudinal axis of each of the cutting members 52 with the substantially vertical axis of the drilling string and of the tubular -body 40 of the cutting tool 34 will be a relatively acute or slight angle at the time of initial contact of the cutting members with the inner `casing string 20. With the cutting members l52 continuously biased a-gainst the inner casing 20 by fluid pressure, the drilling string 16 is then rotated by a suitable rotary table or other equipment carried on the drilling barge 10, and such rotation of the drilling string causes the cutting tool 34 to be rotated within the inner casing 20. This rotational movement of the cutting tool 34 causes the cutting members 52 to bite into the inner casing 20, and cut through the casing until the cutting members have assumed a radially outwardly extending position such as that depicted in FIG. 3.

When the cutting members 52 have reached the outwardly extending position shown in FIG. 3, an axially extending slot or opening 53 has been cut into the inner casing 20, and such slot extends completely around this inner casing or, stated differently, the casing has been severed or cut into an upper and a lower portion. It is important to note at this point in the discussion of the present invention that the length of the cutting members 52 is initially selected with a knowledge of the internal diameter of the inner casing 20 so that sufficient leverage can be obtained on the cutting members to assure that they will cut easily and quickly through the inner casing. The limitations of diametric space within the inner casing 20 are such that the optimum length for the cutting members 52 utilized in the described initial cutting step can frequently not be suiciently great that such cutting members can extend to, or contact, the intermediate or central casing string 22. This is the situation which is illustrated in FIG. 3. On other occasions, however, it may be possible that some cutting of the central or intermediate casing string 22 can be accomplished with the initially used cutting members 52.

The cutting tool 34 may be, and preferably is, constructed with uid bypasses (not shown) which become open to the iiuid `driving the piston 40 at such time as the piston reaches its lowermost position and the cutter members 52 are fully outwardly extended as depicted in FIG. 3. The occurrence of some bypass or bleeding olf of the power uid at this time will permit a positive indication to be obtained on the drilling barge of the fact that the cutting members 52 have accomplished and completed their cutting operation, and that at least the inner casing string has been cut through. A further indication of the Lachievement of this status also results from a reduction in the torque which must be -applied to the drilling string 16 in order to drive it in rotary motion.

Upon completion of the step of the process by which the inner 4casing string 20 is cut through in the manner described, the drill string 16 is removed from the well casing and that portion of the string between the swivel assembly and the cutting tool 34 broken down and again made up, this time to include a relatively shorter connecting sub 60 than the connecting sub 36 which was utilized initially for the cutting operation by which the inner casing string 20 was severed. The cutting members 52 utilized on the cutting tool 34 are also replaced so that relatively longer cutting members or knives 62 are pivotally mounted on the tubular body in place of the shorter cutting members 52 which were originally employed (See FIG. 4). The length of the cutting members 62 which are used in the second cutting operation is selected so that these cutting members are substantially longer than the cutting rmembers initially used, and also so that, in most instances, though not necessarily all, the cutting members 62 will extend to, and be able to sever, the intermediate or central casing string 22 during the subsequent cutting operation to be described. The size of the connecting sub 60 is selected to correlate with the length of the cutting members 62 which are used so that the free ends of the cutting members 62 will be able to pass through the axially extending slots or openings 53 formed in the inner casing string 20, and will either initially be in a position in the annulus between the inner and intermediate casing strings 20 and 22, or will bear against the internal surface of the intermediate casing string. Viewed in another way, the sub 60 is selected so that without alteration of any other part of the portion of the drill string 16 which is positioned `between the swivel assembly 30 and the cutting tool 34, the length of this portion of the string is shortened so as to bring the cutting tool to a relatively higher position in which the longer cutting members 62 can move into and through the relatively small slot or opening formed through the inner casing string 20 by the initial cutting operation using the relatively shorter cutting members 52.

With the lower portion of the drilling string 16 made up in the described fashion, the drilling string is again lowered into the inner casing string 20 until the swivel 30 comes to rest upon the supporting shoulder 32 of the well casing. The hydraulic fluid is then again directed through the hollow interior of the drilling string 16 against the piston 40 and forces the piston downwardly against the ears 56 of the cutting members `62. Thus, the cutting members 62 are biased radially outwardly so that their upper edge bears against, or is in contact with the downwardly facing upper edge of the slot 53, which was cut through the inner casing string 20 during the initial cutting operation. The drilling string 16 is then rotated, and the rotative motion of the cutting tool 34 secured thereto coupled with the constant outward bias of the cutting members 62 results in the slot or opening 53 being enlarged in an axially upward direction, and also results in the tips of the cutting members 62 being extended further in a radial direction with respect to the cutting tool 34 and with respect to the inner casing string 20.

Where the cutting members 62 are of sufficient length to extend into contact with the intermediate or central casing string 22, the cutting action of these members will continue on the inner surface of the intermediate casing string until this casing string has been cut through, and the cutting members 62 attain the horizontal status depicted in full lines in FIG. 4 of the drawings. Thus, both the inner and intermediate casing strings 20 and 22 have then been cut completely through, and there remains only the outer casing string 24 which has not been severed. It should be pointed out here, however, that in some types of casing installations, the intermediate casing string 22 may be suiliciently larger than the inner casing string 20 that the cutting members 62 which are necessarily used in the second step of the cutting procedure will not reach to, or engage, the intermediate casing string 22. In such eventuality, the steps of the method as hereinafter described are nevertheless followed, and eventually cutting members of sufiicient size to extend through and sever all of the telescoped casing strings will be utilized, and all of the casing strings will be cleanly and eiciently cut at the desired location.

The attainment by the cutting members 62 of the fully extended, substantially horizontal position shown in FIG. 4 will be known at the surface from the torque reduction and the hydraulic power fluid pressure reduction herein- Abefore described. At this time, the uid pressure on the piston 4i) is released to permit the spring 48 to bias the cutting members 62 to their retracted positions, and the drilling string 16 is again withdrawn from the well casing to permit a relatively shorter connecting sub 66 to be connected in the string in place of the connecting sub 60. Also after the removal of the drilling string 16 from the well, new cutting members 68 of yet greater length are pivotally secured on the tubular body 38 of thecutting tool 34 with the cutting members 68 being selected to permit them to extend through the opening in the inner and intermediate casing strings 20 and 22, and into contact with the outer casing string 24. The length of the connecting sub 66 is selected so that the lower free ends of the cutting members 68 will be adjacent, or slightly above, the lower edge of the slot or opening 53 formed in the internal casing string 20 when the swivel assembly 30 occupies its position of support at the top of the well casing.

With the drill string 16 made up in this way, the string is again lowered into the casing until the swivel 30 comes to rest on the supporting shoulder 32. When the drilling string 16 is thus positioned, the cutting tool 34 will occupy the position illustrated in FIG. 5, and the cutting members 68 carried thereby will be in their retracted positions as shown in dashed lines in FIG. 5. The hydraulic uid is then directed through the hollow interior of the tubular drilling string 16 to bias the piston 40 forcibly downwardly and cause the relatively long cutting members 68 to be pivoted outwardly through the openings previously cut in the internal and intermediate casing strings 20 and 22, and to bear against either the internal surface of the outer casing string 24, or against the upper edges of the openings cut through the inner and intermediate casing strings 20 and 22. In either event, with the continued downward bias of the piston 40 by hydraulic pressure, the rotation of the drilling string 16 is commenced, and the cutting members 68 commence to either enlarge the slots or openings formed through the inner and intermediate casing strings 20 and 22, or to cut through the outer casing string 24, or both of these reaming and cutting operations may occur simultaneously.

After a brief period of rotation of the drill string 16 with continued downward bias of the piston 40, the cutting members 68 are ultimately completely extended so that they occupy the horizontal status depicted in FIG. 5. At this time, all of the telescoped casing strings 20, 22, and 24 have been completely cut through by the cutting operations hereinbefore described. The completion of the cutting of the outer casing string 24 is reflected on the drilling barge by a reduction in the torque required to rotate the drilling string 16, and by a reduction in the pressure being applied to the hydraulic uid which biases the piston 40 downwardly. At this time, the hydraulic pressure on the piston 40 can be released to permit the spring 48 to bias the piston upwardly and the cutting members 68 to be retracted. The tubing string and the cutting tool 34 carried thereby can then be retrieved from the well casing, and appropriate tools can be connected to the well head or equipment attached thereto to lift the upper portion of the severed casing and the well head equipment to the surface so that it can be loaded onto the drilling barge 10 and thus completely salvaged.

From the foregoing description of the invention, it will have become apparent that this invention provides a highly effective apparatus for quickly cutting through a plurality of concentrically or eccentrically disposed strings of Well casing so that the portion of the casing strings adjacent the well head can be removed from the earth, and all of the equipment which is secured to the well head can be recovered. The method can be easily practiced, involves a minimum of wear and breakage of apparatus used in practicing the method, and affords positive and easily recognized indications to operating personnel of the times at which the several cutting steps involved in the method have been completed.

Although a specific embodiment of the apparatus of the invention has been hereinbefore defined in order to provide typical examples of the manner in which the invention is to be practiced, it rwill be understood that various changes and modifications can be made in the various structural elements of the apparatus used without departing from the basic principles of the invention. All changes and modifications of this type are therefore deemed to be circumscribed by the spirit and scope of the invention except as the same may be necessarily limited by the appended claims, or reasonable equivalents thereof.

What is claimed is:

1 Apparatus for severing a plurality of telescoped well casmgs comprising:

(a) an elongated tubing string diametrically dimensioned to facilitate insertion of a major portion of said tubing string in the innermost one of said telescoped well casings;

(b) a rotary cutting tool secured to one end of Said elongated tubing string on said major portion of the tubing string and dimensioned for insertion in the innermost casing, said cutting tool having (l) a plurality of elongated cutting members each detachably secured on said cutting tool for pivotation about a horizontal axis, and of a length to contact the internal wall of said innermost casing and shorter than required to contact the internal wall of the outermost casing of said telescoped well casings, and

(2) piston means movably mounted relative to, and cooperating with7 said elongated cutting members for pivoting said cutting members into a cutting position in contact with the internal wall of said innermost casing when said piston means is moved under the impress of a hydraulic fluid directed through the tubing string;

(c) additional elongated cutting -members longer than said rst-mentioned cutting members adapted for detachable, pivotal securement to said rotary cutting tool in place of said lirst-mentioned cutting members;

(d) a swivel assembly rotatably mounted on, and surrounding, said tubing string intermediate its length, said swivel assembly being diametrically dimensioned to contact and engage one of said casings when the portion of said tubing string carrying said cutting tool is lowered into said innermost casing; and

(e) a plurality of varying length connecting subs interchangeably connectable in said tubing string between said swivel assembly and said cutting tool for selectively adjusting the distance between said cutting tool and said swivel assembly.

2. Apparatus as defined in claim 1 and further characterized to include an extensible slip joint connected in said tubing string on the opposite side of said swivel `assembly from said cutting tool.

3. Apparatus for severing a plurality of concentrically disposed well casings from the inside of such casings outwardly comprising:

(a) an elongated tubing string adapted for insertion of a portion thereof in the innermost one of said concentric well casings;

(b) a rotary cutting tool secured to one end of said elongated tubing string for insertion in the innermost casing of said concentric casings, said cutting tool comprising:

(l) a tubular body having elongated axially extending slots formed in the sides thereof;

(2) an elongated cutting member detachably mounted in each of said slots and having a portion projecting into the interior of said tubular body, each of said slots being at least twice the length of said elongated cutting member to facilitate accommodation of detachably mounted cutting members of lengths substantially longer than said first mentioned cutting members; and

(3) piston means movably mounted in said tubu- 11 lar body relative to said elongated cutting niembers and cooperating with said cutting members for pivoting said cutting members into a cutting position for cutting the internal wall of the innermost casing of said concentric casings when said piston means is moved downwardly in said tubular body;

(c) a swivel assembly rotatably mounted on, and surrounding, said tubing string intermediate its length for permitting said tubing string to rotate within said swivel assembly when said swivel assembly is held stationary;

(d) a connecting sub quick detachably connected in said tubing string between said swivel assembly and said tubular body for quick detachment and replacement by connecting subs of various lengths; and

(e) an extensible slip joint connected in said tubing string on the opposite side of said swivel assembly from said cutting tool.

12' References Cited UNITED STATES PATENTS DTHER REFERENCES Composite Catalog of Oil Field Equipment and Services, 1962-63, Houston, Tex., Gulf Pub. Co., vol. 3, p. 4634.

CHARLES E. OCONNELL, Primary Examiner l. A. CALVERT, Assistant Examiner US. Cl. X.R. 166-78