Patent Application
20150252627
The field of the present invention relates to a mechanism that enables separation of a tool string into multiple segments downhole.
During drilling operations, there are instances when the drill string becomes stuck in the borehole. To remove the stuck portion of the drill string from the borehole, it is often necessary to separate the drill string into segments. The segments of the drill string can then be removed from the borehole with the aid of fishing tools as needed. Safety joints are weak joints that are intentionally built into a drill string at predetermined locations to allow separation of the drill string at the predetermined locations.
A safety joint that can be installed in a tool string, such as a drill string, and that can permit the tool string to be separated into individual segments at a later time is disclosed. The safety joint has the advantage of simplicity and enables separation of the tool string without timing of threads on connections.
In one illustrative embodiment, the safety joint comprises a first tubular joint body, a second tubular joint body, and a shear pin. The first tubular joint body has a first threaded surface and first hole section in which a plurality of first holes is formed. The first holes are spaced along a circumference of the first hole section. The second tubular joint body has a second threaded surface that is configured to engage the first threaded surface and a second hole section in which at least one second hole is formed. The first and second threaded surfaces and the first and second holes are configured such that the at least one second hole is aligned with one of the first holes when a threaded connection between the threaded surfaces is made up. The shear pin is inserted into the aligned first and second holes. The shear pin is configured to lie partly in each of the aligned first and second holes and to mechanically shear when a torque exceeding a combination of a break-out torque of the threaded connection and a shear strength of the shear pin is applied across the threaded connection.
In another illustrative embodiment, the safety joint comprises a first tubular joint body, a second tubular joint body, a torque ring, and a shear pin. The first tubular joint body has a first threaded surface and a second threaded surface. The second tubular joint body has a third threaded surface for engagement with the first threaded surface to form a first threaded connection between the first tubular joint body and the second tubular joint body. The second tubular joint body also has a first hole section in which at least one first hole is formed. The torque ring has a fourth threaded surface for engagement with the second threaded surface to form a second threaded connection between the torque ring and the first tubular joint body. The torque ring includes a second hole section in which at least one set of second holes is formed. The second holes are spaced along a circumference of the second hole section. The threaded sections and holes are configured such that the at least one first hole is aligned with one of the second holes in the at least one set of second holes in two orthogonal directions when the first and second threaded connections are made up. The shear pin is inserted into the aligned first and second holes. The shear pin is configured to lie partly in each of the aligned first and second holes and to shear when a torque exceeding a combination of a break-out torque of the first threaded connection and a shear strength of the shear pin is applied across the first threaded connection.
In yet another illustrative embodiment, a method of assembling a safety joint includes threading a torque ring into a first tubular joint body to form a threaded connection between the first tubular joint body and the torque ring. The method includes threading a second tubular joint body onto the first tubular joint body to form a threaded connection between the first tubular joint body and the second tubular joint body. The forming of the threaded connection between the first tubular joint body and the second tubular joint body will produce an alignment of a first hole in the second tubular joint body with a second hole in the torque ring, where the second hole is one of a set of second holes spaced along a circumference of the torque ring. The method includes inserting a shear pin into the aligned first and second holes.
In another illustrative embodiment, a method of separating a drill string includes providing a drill string having first and second segments connected by a safety joint, where the safety joint comprises a first tubular joint body threadedly engaged with a second tubular joint body and a shear pin coupling the first tubular joint body to the second tubular joint body. The method includes applying a torque to the drill string in a first direction until the shear pin is sheared. Then, a pull force is applied to the drill string while rotating the drill string in a second direction opposite to the first direction to disengage the first tubular joint body from the second tubular joint body.
It is to be understood that both the foregoing general description and the following detailed description are exemplary of the invention and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention and together with the description serve to explain the principles and operation of the invention.
The following is a description of the figures in the accompanying drawings. The figures are not necessarily to scale, and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness.
In the following detailed description, numerous specific details may be set forth in order to provide a thorough understanding of embodiments of the invention. However, it will be clear to one skilled in the art when embodiments of the invention may be practiced without some or all of these specific details. In other instances, well-known features or processes may not be described in detail so as not to unnecessarily obscure the invention. In addition, like or identical reference numerals may be used to identify common or similar elements. For purposes of this disclosure “threadably” means the connection of two components via a threaded connection.
The lower end portion 20 of the upper joint 12 has a cylindrical section 21 with an outer (or exterior) threaded surface 24. The upper end portion 22 of the lower joint 14 has a cylindrical section 25 with an inner (or interior) threaded surface 26 facing the axial bore 18. In the assembled state of the safety joint 10, the inner threaded surface 26 of the lower joint 14 engages with the outer threaded surface 24 of the upper joint 12 to form a threaded connection 27 that threadably couples the upper joint 12 and the lower joint 14. Left-hand threads may be used on the threaded surfaces 24, 26 in one embodiment. Other types of threads may be used on the threaded surfaces 24, 26 in other embodiments.
The upper joint 12 at its upper end 29 has an inner (or interior) threaded surface 28 facing the axial bore 16. The inner threaded surface 28 is for engagement with an upper segment (11a in
In
In
Referring to
In one embodiment, a combination of odd and even hole sets 34, 38 and equal hole spacing in the sets is used to achieve the alignment mentioned above without timing of the threads on the connection 27. That is, one of the hole sets 34, 38 has an odd number of holes and equal hole spacing, while the other has an even number of holes and equal hole spacing. In a particular embodiment, N, which is the number of holes in the outer hole set 38, is greater than M, which is the number of holes in the inner hole set 34, where both hole sets 34, 38 use equal hole spacing. Thus, for example, if the outer hole set 38 has ten holes, the inner hole set 34 may have 9 holes, 7 holes, 5 holes, 3 holes, or 1 hole. In a more particular embodiment, N is greater than M by 1 and equal hole spacing is used in the hole sets 34, 38. Thus, for example, if the outer hole set 38 has five holes, the inner hole set 34 will have four holes.
Referring to
A shear pin 46 is inserted in the aligned holes 34a, 38a. The shear pin 46 will prevent the upper joint 12 from unthreading from the lower joint 14 until it is mechanically sheared. The shear pin 46 can be mechanically sheared by applying a torque across the threaded connection 27 that is greater than a combination of a break-out torque of the threaded connection 27 and a shear strength of the shear pin 46. After the shear pin 46 is sheared, the upper joint 12 can be disengaged from the lower joint 14. This can be used to advantage when it is desired to separate the tool string (11 in
The shear pin 46 when inserted into the aligned holes 34a, 38a lies partly in each of the aligned holes 34a, 38a. In one embodiment, the holes of the inner hole set (34 in
The lower end portion 20 of the upper joint 12 includes a seal gland (or groove) 49 in which a sealing element 51 is mounted. This seal area including the seal gland 49 is located adjacent to the section 21 including the threaded surface 24. In the assembled state of the safety joint 10, the sealing element 51 will be disposed between the upper joint 12 and the lower joint 14 and will form a seal between the joint bodies 12, 14 generally proximate the threaded connection 27 formed by the threaded surfaces 24, 26.
The lower end portion 64 of the upper joint 52 includes an outer threaded surface 68. The upper end portion 64 of the lower joint 54 includes an inner threaded surface 70, which will engage the outer threaded surface 68 of the upper joint 52 to form a threaded connection 71 in the assembled state of the safety joint 50. The threaded surfaces 68, 70 may use square threads in one embodiment or a different type of thread in another embodiment. The lower end portion 64 of the upper joint 52 includes an inner threaded surface 72. The upper end portion 62 of the torque ring 56 includes an outer threaded surface 74, which will engage the inner threaded surface 72 of the upper joint 52 to form a threaded connection 75 in the assembled state of the safety joint 50.
The upper joint 52 has an inner threaded surface 76 at its upper end for engagement with an upper segment of tool string, such as segment 11 a in
Referring to
In
The axial spacing between the adjacent outer holes 88, 90 along the section 86 is the same as the axial spacing between the adjacent inner hole sets 82, 84 (in
In the assembled state of the safety joint 50, shear pins 92, 94 are inserted in the aligned holes 82a, 88 and 84a, 90, respectively. Plugs 96, 98 may be inserted into the holes 88, 90 to retain the shear pins 92, 94 in the holes. The shear pins 92, 94 will prevent the upper joint 52 from unthreading from the lower joint 54. However, when a torque is applied across the threaded connection 71 between the threaded surfaces 68, 70 that is greater than a combination of a break-out torque of the threaded connection 71 and a shear strength of either of the shear pins 92, 94, one or both of the shear pins 92, 94 will be mechanically sheared. The applied torque may be sufficient to shear both shear pins 92, 94 such that the upper joint 52 can be unthreaded from the lower joint 54. This would allow the tool string to which the safety joint 50 is attached to be separated into individual segments.
Although the safety joint 50 has been described with two inner hole sets 82, 84 on the torque ring 56 and two outer holes 88, 90 on the lower joint 54, it should be noted that the safety joint 50 could also work with one inner hole set on the torque ring and one outer hole on the lower joint 54.
One or more sealing elements 100 may be provided for sealing in between the lower joint 54 and the upper joint 52 generally near the threaded connection 71 formed between the threaded surfaces 68, 70. Similarly, one or more sealing elements 102 may be provided to seal between the upper joint 52 and the torque ring 56 proximate the threaded connection 75 formed between the threaded surfaces 72, 74. One or more sealing elements 104 may also be provided to seal between the torque ring 56 and the lower joint 54. The sealing elements 100, 102, 104 will prevent fluid from leaking out of the safety joint 50 through the various connections between the tubular joint bodies 52, 54 and torque ring 56.
To assemble the safety joint 50, the torque ring 56 is first threaded into the upper joint 52 until an outer shoulder 106 on the torque ring 56 meets a lower end face 108 of the upper joint 52. The lower joint 54 is then threaded onto the upper joint 52 until an upper end face 110 of the lower joint 54 meets an outer shoulder 112 of the upper joint 52. The two adjacent outer holes 88, 90 in the lower joint 54 should be aligned with two adjacent holes, e.g., 82a, 84a, from the two adjacent inner hole sets 82, 84 in the torque ring 56 when the threaded connections are completed. If the outer holes 88, 90 are not sufficiently aligned with holes 82a, 84a from the inner hole sets 82, 84 so that the shear pins 92, 94 can be dropped in the aligned holes seamlessly, then the torque ring 56 can be slightly rotated in either direction about the axial axis 61 of the safety joint 50 until the outer holes 88, 90 are sufficiently aligned with the holes 82a, 84a from the inner hole sets 82, 84. In order to align the holes of the torque ring 56 and the lower joint 54, the torque ring 56 may be rotated by inserting a cylindrical rod through holes 88, 90 of the lower joint and into holes 82, 84 of the torque ring 56. Once inserted, the cylindrical rod can be used to turn the torque ring 56 and align the holes by pushing the holes in a direction that would align the two sets of holes on the lower joint 54 and torque ring 56. To accept the shear pins 92, 94, the outer holes 88, 90 need to be aligned with the holes 82a, 84a in two orthogonal directions, i.e., along an axial direction and along a transverse direction. When the threaded connections are made up, the outer holes 88, 90 will be axially aligned with the inner holes 82a, 84a. Thus the pitch of the thread on the threaded surface 74 of the torque ring 56 should be fine such that slight rotation of the torque ring 56 to align the holes 88, 90 transversely with the holes 82a, 84a will not result in significant axial displacement of the torque ring 56. A significant axial displacement of the torque ring 56 may result in significant axial misalignment of the outer holes 88, 90 with the holes 82a, 84a.
After the holes 82a, 84a of the torque ring 56 and the holes 88, 90 of the lower joint 54 are aligned axially and transversely, the two shear pins 92, 94 are inserted into aligned holes. The plugs 96, 98 may then be threaded into the holes 88, 90 to retain the shear pins 92, 94 in the aligned holes.
While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.
