US3727685A

US3727685A - Method for thermally cutting tubing

Info

Publication number: US3727685A
Application number: US00198886A
Authority: US
Inventors: D Chestnut; C Morris
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1971-11-15
Filing date: 1971-11-15
Publication date: 1973-04-17
Anticipated expiration: 1990-04-17

Abstract

A method for thermally cutting tubing, such as below an internal restriction in a tubing string located in a well bore, which comprises placing in the tubing at the desired location a mixture of finely granulated aluminum with an oxide of iron or other metal and igniting the mixture while applying a tensile load to the tubing string.

Description

l 19g9 y m m ..l66/297 D United States Patent 1 1 011 3,727,685 Chestnut et al. 1 Apr. 17, 1973 [54 METHOD FOR THERMALLY CUTI'ING 2,436,036 2/1948 Defenbaugh ..166/55 TUBING 2,746,550 5/1956 Miu=11611 ..l66/255 2,839,143 6/1958 Alexander... ..l66/30l Inventors: Dwayne Chestnut, Lmleton, 3,076,507 2/1963 Sweetmon ..l66/297 C016; Clay A. Morris, Sugar Land, 3,115,184 12/1963 Jackson .1 ..166/55 x Tex.

[73] Assignee: Shell Oil Company, Houston, Tex. Examiner-Dav? H Brown Attorney-Theodore E. Bieber et al. [22] Filed: Nov. 15, 1971 211 Appl. No.2 198,886 [57] ABSTRACT A method for thermally cutting tubing, such as below 52 US. Cl. ..166/255, 166/297, 166/301, an internal resm'ction in a tubing string located in a /5 5 well bore, which comprises placing in the tubing at the 51 Int. Cl ..E21b 47/00, E2lb 29/02 desired location a mixture of finely granulated [58] Field of Search 166/250, 255, 297, mini-1m with a OXide of iron 01' other metal and ignit- 166/301, 315, 55, 63 ing the mixture while applying a tensile load to the tubing string. [56] References Cited 6C 2m UNITED STATES PATENTS PATENTEU APR 1 "/1975 FIG. 2

FIG. 2

METHOD FOR THERMALLY CUTTING TUBING BAKCGROUND OF THE INVENTION The invention relates to a method of removing par tially collapsed or deformed tubing by thermally cutting the tubing below the collapsed intervaland removing the tubing from the well bore.

DESCRIPTION OF THE PRIOR ART cutter. A chemical cutter, to be effective, requires a small diametrical clearance between its outer diameter and the inner diameter of the tubing to be cut. If the tubing has been deformed, that is, if the inner diameter has been reduced by a substantial amount, a chemical cutter cannot be employed to cut the tubing below the deformity as it will not pass through the restriction and still cut the tubing.

Another device that has been used is the string shot. The device is lowered into the well bore by a wire line through the tubing to the interval where the tubing is desired to be separated. The tubing is then rotated clockwise by suitable means at the surface of the well bore until the tubing is torqued up". The device is subsequently detonated by electrical means from the surface. By detonating the charge within the string shot device, the tubing is hopefully untorqued, and, if the operation is successful, the tubing will separate at a connection, that is, by a pin unscrewing from a collar. The disadvantage of this device is that if the well casing has been deformed such that it is in contact with the tubing, torque cannot be transmitted to the tubing below this point. In such a case the string shot device could not be used if it was desired to remove the tubing from the collapsed interval in the well casing.

A third device that has been employed to cut tubing in a well bore is through the use of mechanical cutters. These cutters can either be external or internal type cutters. An internal mechanical tubing cutter has blades that extend and contact the inner wall of the tubing when the cutter is rotated. The disadvantage of this device is that it too depends upon small diametrical clearance to be effective and, therefore, cannot be'effective if the tubing has been deformed to any great extent.

SUMMARY OF THE INVENTION The disadvantage inherent in these devices has been advantageously solved by applicant's invention such that tubing may be thermally cut below internal restrictions and removed from the well bore so that the well may be repaired and restored to production.

It is a further object of this invention to thermally cut tubing while applying a tensile load to tubing in an upward direction enabling the tubing to separate while leaving a relatively smooth surface at the top of the tubing left in the well bore.

It is even a further object of this invention to restore the well to production after removal of the deformed tubing from the well bore thereby precluding abandonment of a producing well that has significant hydrocarbon reserves or one that does not have sufficient reserves to profitably justify redrilling a replacement for the abandoned well.

BRIEF DESCRIPTION OF THE DRAWING The nature of the invention will be more fully appreciated with reference to the drawing in which:

.FIG. 1 is a sectional view showing a typical well in which the tubing string is restricted preventing normal removal;

FIG. 2 is a sectional view illustrating the equipment that may be utilized in the practice of the invention for cutting and removing the tubing in the restricted interval.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIG. 1, a well is shown in communication with a hydrocarbon bearing formation 15 and the earths surface 13 through well casing 14. A tubing string 16 is installed in well casing 14 and is held in tension by a packer or tubing anchor 17. The tubing anchor 17 forms an integral part of tubing string 16 and when properly actuated contacts well casing 14 such that the tubing string 16 may be maintained in tension. During normal operation if the tubing string 16 is required to be removed from well casing 14, the tubing anchor 17 is first released by rotation of tubing string 16 and then tubing string 16 is removed using conventional procedure, well known in the art. In abnormal circumstances, a collapse 30 may occur in well casing 14 such that a restriction 31 may develop in tubing string 16, preventing release of tubing anchor 17 thereby precluding removal of tubing string 16 from well casing 14. Even further if tubing anchor 17 is not installed in tubing string 16, conventional oil field tubulars are normally of the externally upset type which will also prevent removal of tubing string 16 from well casing 14. It is well known in the art that some oil field tubulars are flush in that they have a continuous external diameter such that they may be removed from well casing 14 even though the collapse 30 exists in well casing 14. In the case where the tubing string 16 has become restrained within well casing 14 such that it has a restriction 31 a conventional workover unit 11 is installed over the well bore and tubing string 16 is placed in tension with suitable means with which unit 11 is equipped. While the tubing string 16 is in tension wire line unit 12 is used to lower a free point instrument 18 that is electrically connected to wire line 19 into tubing string 16. Read out equipment on board wire unit 12 is used to indicate the interval in which tubing stirng 16 is restrained. Use of such equipment is well known to those skilled in the art and will not be discussed further.

When. it has been determined at which point or interval tubing string 16 is restrained within well casing 14 a suitable tubing plug 26 is lowered into tubing string 16 to a point below restriction 31 by suitable means such as wire line 19 or a sand line from workover unit 11. Tubing plug 26 may be any suitable means such as a conventional swab cup in its most simple form since all that is required in an obstruction within tubing string 16 below restriction 31 capable of creating a bridge.

After setting a tubing plug 26 some distance below restriction 31, say 15 to 20 and more preferably above the first tubing collar below casing collapse 30, a conventional slim hole dump-bailer is lowered in tubing string 16 by wire line 19 and is used to first place a predetermined volume of sand. A mixture of finely granulated aluminum with an oxide of iron or other metal, which is sold under the trademark Thermit 27 is then placed on top of the sand using wire line 19 and dump bailer. Preferably a volume of Thermit 27 equalling 6 to 18 of tubing volume is used. After placement of Thermit 27, dump bailer is removed from tubing string 16. Wire line 19 is then used to lower electrical squib 29 and starting Thermit into contact with Thermit 27 whereupon squib 29 is activated using wire line unit 12 thereby igniting starting Thermit which ignites Thermit 27 upon reaching a temperature of approximately 2200F. At a predetermined time after ignition of the starting Thermit, preferably l seconds, tension is pulled on tubing string 16 equalling 5,000 to 30,000 pounds over the weight of tubing string 16 in well casing 14 from the surface to the interval where tubing string is restrained in well casing 14. The resulting tubing cut after this operation is smooth, enabling conventional swaging techniques to be used to enlarge well casing 14 such that a conventional overshot may then be used to retrieve the remainder of tubing string 16 from well casing 14 without damage to well casing 14 from the thermal cutting of tubing string 16.

In another embodiment of the invention, if the tubing is old or has a low yield point, a conventional chemical cutter may be used to cut tubing string 16 at a point above the collapsed interval 30 of well casing 14, say l to 20 feet, after which the tubing string 16 above the cut is removed from well casing 14. A tubing overshot 20, safety joint 21, hydraulically operated jars 23, drill collars 24 are lowered in well casing 14 using a high strength work string 25 with workover unit 11. Preferably overshot 20 is of the type which has internal seals such that a pressure seal is present between tubing string 16 and overshot 20 after overshot 20 has come into gripping contact with tubing string 16. After overshot 20 has engaged tubing string 16 a tensile force is appliedto tubing string 16. The tubing is then thermally cut using the previously described procedure.

We claim as our invention:

1. A method for thermally cutting tubing in well casing below an internal restriction in said tubing, said method comprising the steps of:

determining the interval in which the tubing is restricted; plugging said tubing below said restriction by lowering suitable plugging means in said tubing a predetermined distance below said restriction;

placing a predetermined volume of Thermit using suitable means below said restriction and on top of said plugging means;

lowering starting Thermit and suitable ignition means into said tubing such that it is in contact with said thermit;

igniting said starting Thermit with said ignition means; applying a tensile force to said tubing at a predetermined time interval after igniting said starting Thermit; and

removing said tubing from said well.

2. The method of claim 1 wherein determining the interval in which the tubing is restricted is by freepointing said tubing string using suitable means.

3. The method of claim 1 wherein the volume of Thermit is equal to the volume of 6 to 18 inches of tubing volume.

4. The method of claim I wherein plugging the tubing a predetermined distance below said restriction is above the first tubing collar occurring below the restriction.

5. The method of claim 1 wherein a tensile force of 5,000 to 30,000 pounds over the weight of said tubing string is applied to said tubing string.

6. The method of claim 1 wherein the predetermined time interval ranges from 5 to l5 seconds.

Claims

1. A method for thermally cutting tubing in well casing below an internal restriction in said tubing, said method comprising the steps of: determining the interval in which the tubing is restricted; plugging said tubing below said restriction by lowering suitable plugging means in said tubing a predetermined distance below said restriction; placing a predetermined volume of Thermit using suitable means below said restriction and on top of said plugging means; lowering starting Thermit and suitable ignition means into said tubing such that it is in contact with said thermit; igniting said starting Thermit with said ignition means; applying a tensile force to said tubing at a predetermined time interval after igniting said starting Thermit; and removing said tubing from said well.

2. The method of claim 1 wherein determining the interval in which the tubing is restricted is by free-pointing said tubing string using suitable means.

4. The method of claim 1 wherein plugging the tubing a predetermined distance below said restriction is above the first tubing collar occurring below the restriction.

5. The method of claim 1 wherein a tensile force of 5,000 to 30, 000 pounds over the weight of said tubing string is applied to said tubing string.

6. The method of claim 1 wherein the predetermined time interval ranges from 5 to 15 seconds.