US3387863A - Safety joint - Google Patents

Description

R. TREESE SAFETY JOINT June 11, 1968 Filed Sept. 12, 1966 4, K fl'lwz,

ATTORNEY INVENTOR A0) 7RJ 3,387,863 SAFETY JOINT Roy Treese, Dallas, Tern, assignor to Bresser Industries, Inc., Daiias, Tern, a corporation of Delaware Filed Sept. 12, 1966, Ser. No. 578,565 6 Qiairns. {CL 285-2.)

ABSTRAQT OF THE DISCLUEBURE This invention relates generally to improved safety joints connectable in a string of tubing or the like arranged to be disposed in a well bore. More particularly, but not by way of limitation, this invention relates to an improved safety joint having a frangible portion that separates upon the application of a predetermined tensile force thereto, permittin separation of the tubing string.

In treating oil and gas wells, it is frequently necessary to set a well packer at a location deep within the well bore. One method utilized to place the packer in the desired position in the well bore and to set the packer therein is to connect the packer to the lower end of a tubing string that extends from the surface of the well. The string also provides the means for setting the packer after it has reached the desired depth.

Occasionally, the packer becomes stuck in the well bore to the extent that the packer cannot be released and retrieved on the tubing string. When this occurs, the tubing string must be released from the packer so that an overshot or other fishing tool may be lowered into the well bore to remove the packer. To permit separation of the tubing string from the packer, it is a common practice to connect a safety joint between the lower end of the tubing string and the upper end of the packer whereby separation thereof can be easily accomplished.

Various types of safety joints have been constructed in the past to permit the separation of the tubing string from the packer. Some have included relatively rotatable parts retained in a fixed position by one or more shear pins that shear or part upon the application of a torque exceeding their shear strength. Other types have included either J-slots or threaded connections that also require rotation of the tubing string relative to the packer.

As is well known to those skilled in the art, it is dangerous to rotate the tubing string due to the possibility of either unscrewing one of the many threaded joints in the tubing string or due to the possibility of twisting off the tubing string. In an effort to overcome the undesirable rotation, safety joints have been constructed utilizing a purely tensional force to separate the safety joint. In this type of joint, the wall thickness is reduced in a relatively small area providing a frangible portion wherein such separation will occur upon the application of the tensile force.

While this type of joint has been relatively successful, three primary difiiculties have been encountered. Firstly, in most treating operations involving the use of such equipment, the tubing string is tested with relatively high internal pressures and the frangible portions are not usually of sufficient thickness to withstand the test and/or tates Patent ice treating pressures. To alleviate this problem, the general practice has been to construct the joint 50 that the fluid under pressure is on both sides of the frangible portion thereby eliminating the fluid pressure differential across the frangible portion.

Secondly, and particularly when the fluid pressure is applied on both sides of the frangible portion to afford pressure equalization, the frangible portion is subjected to a tensile force resulting from said fluid pressure. It is therefore not possible to predict the precise tensile force necessary to separate the safety joint unless the precise internal fluid pressure is known when the joint is manufactured and sufiicient wall thickness is left to compensate for such pressure. Generally, the testing or treating pressures are not known in advance.

Thirdly, the frangible portion is subject to compressive loads placed on the tubing string. Manifestly, such loads, if sufficiently great, will buckle the frangible portion if it is not supported and most tension type joints are of relatively complex structure whereby such compressive loads are carried through the body of the joint avoiding the application of the loads to the frangible portion.

Summary of the invention This invention provides an improved safety joint connectable in a string of tubing and providing for the separation of the tubing upon the application of a predetermined tensile force, the safety joint comprising: a unitary tubular body member having end portions arranged for connection with the tubing string; and, an annular groove encircling the exterior thereof intermediate said portions forming a frangible portion thereon, the frangible portion having a predetermined tensile strength whereby the safety joint will part in the frangible portion when a tensile force is exerted on the tubing string exceeding the strength of the frangible portion.

One object of the invention is to provide an improved safety joint that will separate upon the application of a predetermined tensile force and that requires no rotation for separation.

A further object of the invention is to provide an improved safety joint wherein the joint will part upon the application of a tensile force exceeding the predetermined tensile strength of the safety joint and that is supported against compressive loads.

Another object of the invention is to provide an improved safety joint of the tension type that is unaffected by internal pressure in the tubing string or by compressive loads placed on the tubing string.

A still further object of the invention is to provide an improved tension type safety joint that will separate cleanly and leave no debris or junk in the well bore after separation.

Still another object of the invention is to provide an improved tension type safety joint that can be easily and economically manufactured.

The foregoing and additional objects and advantages of the invention will become more apparent as the following detailed description is read in conjunction with the accompanying drawings wherein like reference characters denote like parts in all views and wherein:

FIGURE 1 is a vertical cross-sectional view of a well bore illustrating a tubing string and packer disposed therein that are connected by a safety joint constructed in accordance with the invention;

FIGURE 2 is an enlarged cross-sectional view taken substantially along the line 2-2 of FIGURE 1 and showing the structure of the safety joint of FIGURE 1 in more detail; and

FIGURE 3 is an enlarged cross-sectional view similar to FIGURE 2, but illustrating the safety joint after the joint has been parted.

Referring to the drawing and to FIGURE 1 in particular shown therein is a cased well bore generally designated by the reference character 10, a packer 12 located in the well bore, a safety joint generally designated by the reference character 14 connected with the upper end of the packer 12, and a string of tubing 16 connected with the safety joint 14 and extending upwardly through the well bore to the surface (not shown) of the well. The packer 12 is illustrated as being fixed in the well bore 10 by a plurality of slips 18 that are expanded into holding engagement with the casing disposed in the well bore 1%. The tubing string 16 is made up of a plurality of sections of tubing 20 that are threadedly connected in end-to-end relationship as indicated by the box and pin joint 22.

FIGURE 2 illustrates the structure of the safety joint 14 in greater detail. As shown therein, the safety joint 14 includes a tubular body 24 having a bore 26 extending therethrongh. Threads 28 are formed in the bore 26 in the upper end portion of the tubular body 24 threadedly connecting the safety joint 14 with the lowermost section 20 of the tubing string 16. Threads 36 formed on the exterior of the lower end portion of the body member 24 threadedly connect the safety joint 14 with the upper end of the packer 12.

An annular groove 32 is provided in the exterior of the body 24 forming a frangible portion 33 and a downwardly facing annular shoulder 34 thereon. A second annular groove 36, spaced from the annular groove 32, encircles the body 24 forming an upwardly facing annular shoulder 38 thereon. As is apparent in FIGURE 2, the frangible portion 33 has a relatively small cross-sectional area so that the safety joint 14 will part therein as will be described more fully hereinafter.

An annular flange 49 is provided on the body 24 between the annular grooves 32 and 36. For reasons that will become more apparent hereinafter, the outer diameter of the annular flange 40 is less than the outer diameter of the body 24.

Disposed in close fitting relationship in the grooves 32 and 36 are a pair of support members 42. The support members 42 are preferably hemi-cylindrical in shape so that they can be easily inserted into the grooves 32 and 36, but they may be constructed in other segmented forms if desired.

It will also be noted that the support members 42 are each provided with an inwardly directed arcuate flange 44 that fits closely within the annular groove 32 and a second inwardly directed arcuate flange 46 that fits closely within the annular groove 36. The length of each of the support members 42 is substantially the same as the combined lengths of the grooves 32 and 36 and the flange 40 whereby the ends thereof are in supporting engagement with the downwardly facing annular shoulder 34 and the upwardly facing annular shoulder 38 located on the body 24. Thus, the support members 42 carry any compressive loads exerted on the body 24, preventing compressive buckling of the frangible portion 33.

In the preferred form of the safety joint 14, the support members 42 are constructed to the same dimensions for a given size of the safety joint regardless of the desired tensile strength of the frangible portion 33, that is, regardless of the desired parting strength. This is possible since the diameter of the bore 26 can be varied to vary the cross-sectional area of the frangible portion 33 and, thus, vary the parting strength thereof.

The diameter of the bore 26 can be varied to maintain a constant tensile strength for the frangible portion 33 when different lots of material are used in forming the body 24. Manifestly, the tensile strength of the material varies to some extent despite the manufacturers attempt to maintain the strength constant.

Also, varying the diameter of the bore 26 provides for the construction of a frangible portion 33 of a desired parting strength to meet special situations. Again, it should be pointed out that such parting strengths can be attained even though the support members 42 remain the same size. Thus, the manufacturing and inventory problems connected with the safety joint 14 are reduced to a minurnum.

The outer diameter of a portion of the body 24 has been reduced forming a downwardly facing annular shoulder 43 thereon. A sleeve 50 encircles the reduced diameter portion of the body member 24 in close fitting relationship having its upper end abutting the annular shoulder 48 and having the lower end thereof connected to the body member 24 between the annular groove 36 and the lower end portion by welding, as illustrated by the reference character 52, or by another suitable means.

The sleeve 50 completely covers the grooves 32 and 36 and is in engagement with the exterior of the support members 42 thereby retaining the support members 42 in the grooves 32 and 36. The sleeve 5% also serves to resist bending of the safety joint .14 and aids in supporting compression loads exerted thereon through its engagement with the shoulder 48.

Operation To utilize the safety joint 14, the lower end thereof is threadedly connected with the upper end of the packer 12 and the upper end thereof threadedly connected with the lowermost section of tubing 20. The packer 1'2, safety joint 14, and lowermost section of tubing 20 are then lowered into the well bore 10. The desired number of additional sections of tubing 20 are connected in end-to-end relationship by the box and pin joints 22 until the packer 20 has reached the desired depth in the well bore 10.

After reaching the desired depth, the packer 12 is actuated through the tubing string 16 to set the packer 12 in the casing. Assuming that the packer 12 becomes stuck and cannot be retrieved from the well bore 10, an upwardly directed or tensile force is exerted on the tubing string 16 through apparatus (not shown) located on the surface thereby exerting a tensile force on the safety joint 14.

When the tensile force exerted on the tubing string 16 exceeds a predetermined value, the frangible portion 33 of the safety joint 14 parts as illustrated in FIGURE 3, permitting retrieval of the tubing string 16 and the upper portion of the body 24 of the safety joint 14. The lower portion of the body 24, sleeve 50, support members 42, and the packer 12 are left in the well bore 10.

As clearly illustrated in FIGURE 3, the support members 42 are retained in the second annular groove 36 between the sleeve 56 and the annular flange 49 that extends outwardly from the tubular body 24 into the recess in the support members 42 located between the inwardly directed flanges 44 and 46 thereon. Thus, there is no junk or debris left in the well bore 10 as a result of the parting of the safety joint 14 that might interfere with future operations therein.

From the foregoing detailed description of the structure and operation of the safety joint .14, it can be appreciated that the only movement of the tubing string necessary to part the safety joint 14 is in the upward direction, that is, only a tensile force need be exerted thereon. Thus, and even though the safety joint 14 is sufiiciently strong to permit actuation of the packer 12 by compression, rotation or tension, it is not necessary to rotate the tubing string 16 to part the safety joint 14.

It will also be apparent from the foregoing, that the smooth construction of the bore 26 avoids the imposition of tensile forces on the frangible portion 33 that may result from fluid pressure in the tubing string 16. This is an important feature due to the fact that frequently pressures in the neighborhood of 10 to 15 thousand pounds per square inch may be utilized in either testing the tubing string 16 or in the performance of certain treating operations in the well bore 10. The sleeve 50 and the support members 42 support the frangible portion 33 against outward deformation resulting from such pressure, whereby the fangible portion 33 is completely free from the effect of any pressure carried within the tubing string 16. Thus, it is possible to predict the precise tensile force necessary to separate the fangible portion 33.

Furthermore, an examination of FIGURES 2 and 3 clearly demonstrates that the safety joint 14 is of a relatively simple construction that may be quickly and economically constructed utilizing normal manufacturing procedures and equipment.

The single embodiment described herein is presented by Way of example only and it will be understood that many changes and modifications can be made thereto without departing from the spirit of the invention or the scope of the annexed claims.

What I claim is:

1. In a string of well tubing or the like adapted to be disposed in a well bore and to carry fluid under pressure, a safety joint connectable in said tubing providing means for the separation of the tubing upon application of a predetermined tensile force, said safety joint comprismg:

a unitary tubular body member having first and second end portions arranged for connection with the tubing string, and an annular groove encircling the exterior thereof intermediate said end portions forming a frangible portion thereon, said frangible portion having a predetermined tensile strength whereby said safety joint will part in said frangible portion when a tensile force is exerted on said tubing string exceeding the strength of said frangible portion; and support means at least partially disposed in said annular groove, said support means engaging said tubular body member in said groove to support said frangible portion against deformation by the fluid under pressure and against deformation resulting from compressive loads placed on said tubing string thereby avoiding compressive buckling of said frangible portion.

2. The safety joint of claim 1 wherein said tubular body member also includes a substantially smooth interior, whereby fluid under pressure carried by said tubing string will not exert a significant tensile force on said frangible portion 3. The safety joint of claim 1 wherein said support means includes:

a plurality of segmented support members disposed in said groove in engagement with said body member; and

a sleeve member encircling a portion of said body member including said groove and engaging said support members to retain said support members in said groove.

4. The safety joint of claim 1 wherein said body member has a second annular groove proximate said first-mentioned annular groove forming an annular flange therebetween; and

said support means includes a plurality of segmented support members having an interior configuration mating with said annular grooves and said annular flange and engaging said body member to support said frangible portion against deformation by the fluid under pressure and to support said body member against compressive loads placed on said tubing string, thereby avoiding bucking of said frangible portion, and

a sleeve member encircling a portion of said body member including said grooves, said sleeve member being connected with said body member between said second annular groove and the end portion adjacent said second annular groove and engaging said segmented support members to hold said support members in said grooves until said frangible portion parts and to retain said segmented support members in said second annular groove at all times.

5. In a string of tubing or the like adapted to be disposed in a well bore and to carry fluid under pressure, a safety joint connectable in said tubing providing for the separation of the tubing upon application of a predetermined tensile force, said safety joint comprising:

a unitary tubular body member having first and second end portions arranged for connection with the tubing string,

a first annular groove encircling the exterior thereof intermediate said end portions forming a frangible portion and a downwardly facing annular abutment thereon, said frangible por tion having a predetermined tensile strength whereby said safety joint will part in said frangible portion when a tensile force is exerted on said tubing string exceeding the strength of said frangible portion,

a second annular groove encircling the exterior thereof proximate said first annular groove forming an annular flange having an outer diameter less than the outer diameter of said body member and forming an upwardly facing annular abutment, and

a substantially smooth interior, whereby fluid under pressure carried by said tubing string will not exert a significant tensile force on said frangible portion;

a pair of hemi-cylindrical support members disposed in said annular grooves, each of said support members being in engagement with said upwardly and downwardly facing annular abutments to support said tubular body against compressive forces exerted on said tubing string thereby avoiding compressive buckling of said frangible portion, each of said support members including a pair of spaced inwardly directed flanges, one of said inwardly directed flanges being located in said first annular groove in engagement with said frangible portion to support said frangible portion against deformation from the fluid pressure and the other inwardly directed flange being located in said second annular groove in engagement with said annular flange; and

a sleeve member encircling a portion of said body member including said grooves and connected with said body member between said second annular groove and the adjacent end portion, said sleeve member engaging said support members to retain said suppoit members in said grooves until said frangible portion parts and to retain said support members in said second annular groove at all times.

6. In a string of tubing or the like adapted to be disposed in a well bore and to carry fluid under pressure, a safety joint connectable in said tubing providing means for the separation of the tubing upon the application of a predetermined tensile force, said safety joint comprising:

a unitary tubular body member having first and second end portions arranged for connection with the tubing string, and

an annular groove encircling the exterior thereof intermediate said end portions forming a frangible portion thereon, said frangible portion having a predetermined tensile strength whereby said safety joint will part in said frangible portion when a tensile force is exerted on said tubing string exceeding the strength of said frangible portion; and

support means at least partially disposed in said groove, said support means engaging said tubular body member in said groove to support said frangible por- 7 tion against deformation by a force other than the predetermined tensile force exerted on said body member.

References Cited UNITED STATES PATENTS 1,814,800 7/1931 Heater 285-2 1,936,669 11/1933 Heeter 285-3 2,048,388 7/1936 Johnsen 285-4 X Boyles 85-61 Boynton 285-111 X Conrad et a1. 285-4 X Toelke 285-2 X EDWARD C. ALLEN, Primaly Examiner.

CARL W. TOMLIN, Examiner.

R. G. BERKLEY, Assistant Examiner.

Images