Hybrid threaded connection for expandable tubulars

An expandable threaded connection between segments of expandable tubulars. The present invention utilizes two complementary thread segments. The first segment of the threaded connection utilizes standard box and pin threads. In the second segment of the threaded connection, material is removed from the stab flank of the pin threads to reduce the standard width of the pin threads, while the box threads of the second segment are standard thread width. The use of the reduced thread width in the pin threads of the second segment allows for a loose fit between the pin threads of the second segment and the box threads of the second segment. The loose fit between the pin and box threads of the second segment allows radial and axial movement between those threads without causing disengagement of the threaded connection during the expansion process.

FIELD OF THE INVENTION

The present invention relates to threaded tubular connections particularly useful in the oil and gas industry. In particular, the invention relates to an expandable tubular threaded connection having a unique hybrid thread design.

BACKGROUND OF THE INVENTION

In the conventional drilling of an oil and gas well, a series of tubulars, typically strings of casing, liner, and/or screen segments connected together, are sequentially installed in the well bore until the depth of the producing zone of the formation is reached. Standard practice requires that each succeeding string of tubulars placed in the well bore has an outside diameter smaller than the preceding string of tubulars and/or bore hole such that the tubular segments can be passed through the preceding string of tubulars and/or bore hole to their downhole location. The reduction in the diameter of each successive string of tubular segments placed in the well bore results in a significant reduction in the diameter of the tubular through which hydrocarbons can be carried to the surface. More importantly, to achieve the desired tubular diameter in the producing zone, the initial bore hole size at the surface must be sufficiently large to allow for a large diameter casing. The large initial bore hole size requires increased drilling time and increased material costs, including increased use of materials such as drilling mud and casing cement.

The technology of expandable tubulars addresses these shortcomings in the conventional casing/liner/screen hanging operations. Technology that allows the permanent expansion of tubulars in oil and gas wells is rapidly developing. Through radial expansion of tubular segments until the outer wall of those segments contacts the inner wall of the host pipe, it is possible to create a tight fit between the expandable tubulars and the host pipe that holds the tubular segments in place and creates an annular seal. Further, it is possible to achieve a well bore of virtually uniform diameter (i.e., a monobore well) by the radial expansion of successive strings of tubular segments. The expandable tubulars are radially expanded by various means known in the art, including, but not limited to, pulling or pushing fixed or variable diameter expansion cones through the tubular, extruding the tubular off of a hydraulically-actuated expansion tool, or rotating an expansion tool while pulling or pushing it through the tubular.

The tubular segments to be expanded are typically coupled together using threaded connections in which the male end, or pin member, of one tubular is threadably connected to the female end, or box member, of an adjacent tubular. Alternatively, the ends of the adjacent tubulars may have a pin member at each end, with the box member being formed by a short coupling threaded onto one of the pin members. When a conventional threaded connection is made up, the nose of the pin member is typically in contact with or very close to the back of the box member. This threaded engagement between properly secured pin and box members creates a conventional tubular joint that effectively maintains a secure mechanical connection that holds the tubular segments together and that effectively seals the internal tubular area from the formation and vice versa. Often, the sealing ability of the threaded engagement is augmented through the use of Teflon® rings or other deformable seal rings entrapped in the thread area as well as the metal-to-metal seal formed by the contact between the pin and box members.

Problems have arisen, however, at the threaded connection point between tubular segments during and after expansion when using conventional threaded tubular connections and seals currently available in the industry. When the tubular string is radially expanded, a conventional threaded connection changes dimensionally in a way that can prevent the pin and box members from maintaining proper engagement and sealing. The radial expansion of a conventional threaded connection can cause the pin and box members to radially separate. Essentially, because the radius of curvature of the pin member is different than the radius of curvature of the box member during the expansion process, the pin and box members experience different displacements that the threads of a typical threaded connection cannot accommodate. As a result, the radial expansion weakens the coupling strength of the connections and degrades or lowers the pressure holding integrity of the connections. The threaded connection point thus becomes a source of potential weakness in the tubing string and of potential leaks during and after expansion of the tubular string.

Additionally, the radial expansion of the tubular string causes the pin and box members to undergo axial movement. The amount of axial movement experienced by the pin and box members is dependent on numerous factors, including, but not limited to, the amount of radial expansion of the tubular string, the geometry of the threaded connection (e.g., whether the pin and box members have any thin wall sections), and the method of radial expansion employed.

As deeper wells and more difficult completions are attempted using expandable tubulars, the threaded connections that hold the expandable tubulars together must address these known problems and must be able to accommodate the higher pressures faced in such applications. What is needed is a threaded connection for expandable tubulars that maintains the coupling strength and the pressure integrity of the connection so that it will withstand high pressure during and after expansion. It is an object of the present invention to provide an apparatus and method for creating a threaded connection between segments of expandable tubulars that maintains the coupling strength and the pressure integrity of the expanded connection during and after expansion. Those and other objectives will become apparent to those of skill in the art from a review of the specification below.

SUMMARY OF THE INVENTION

An expandable threaded connection between segments of expandable tubulars that allows the threaded tubular connection to withstand the stresses and deformations imposed on the connection by the tubular expansion process is disclosed. The present invention is a unique hybrid threaded connection that utilizes two complementary thread segments to form the expandable threaded connection. The first segment of the threaded connection encompasses the area of the threaded connection between the back of the box member and approximately the mid-point of the threaded connection. The first segment of the threaded connection utilizes standard box and pin threads such that the threads on the pin member in the area of the first segment fully engage the mating threads on the box member in the area of the first segment. Additionally, the first segment of the threaded connection comprises a radial metal-to-metal seal, a resilient seal, and a thread seal. All of these seals are fully activated upon make-up of the threaded connection.

The second segment of the threaded connection begins where the first segment ends (i.e., at approximately the mid-point of the threaded connection) and extends to the face of the box member. The second segment of the threaded connection has the threads machined on the pin member in a manner such that the pin thread width is reduced. In machining the threads of the pin member in the area of the second segment, material is removed from the stab flank of the pin threads to reduce the standard width of the pin threads. In contrast to the pin threads of the second segment, the box threads of the second segment are standard thread width and, thus, are the same thread width as the box threads in the first segment.

The use of the reduced thread width in the pin threads of the second segment allows for a loose fit between the pin threads of the second segment and the box threads of the second segment. As the threaded connection is expanded, the loose fit between the pin and box threads of the second segment allows radial and axial movement between the pin and box threads of the second segments of the threaded connection without causing disengagement of the threaded connection. Thus, the disclosed hybrid threaded connection utilizes multiple thread segments in which the second thread segment accommodates the stresses and deformations generated by the radial expansion process while the threads of the first segment maintain pressure integrity where the metal to metal seal, the resilient seal, and the thread seal are all fully engaged upon make-up of the threaded connection.

Additionally, in the preferred embodiment the disclosed threaded connection utilizes a sleeve in the area of the back of the pin member that is placed onto a machined land that is machined into the outer diameter of the pin member. When placed on this land, the sleeve has an outer diameter substantially the same as the outer diameter of the box member such that upon make-up of the threaded connection, the sleeve abuts the box member. The use of such a sleeve protects the face of the box member from being damaged during running-in of the tubular string.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Referring toFIG. 1, an expandable tubular1is shown. In the typical application, multiple expandable tubulars1are connected together and sequentially installed in the well bore until the depth of the producing zone of the formation is reached. To accomplish this, expandable tubular1includes pin member10and box member20. Pin member10includes helical threads12and14extending along its length as discussed in more detail with reference toFIGS. 2 and 3. Box member20includes helical mating threads22that are shaped and sized to mate with helical threads12and14on pin member10during make-up of a threaded connection between separate tubular joints or segments. The interengaged threads of pin member10with the corresponding threads of box member20on an adjacent joint provide a threaded connection upon final make-up. In this way, multiple segments of expandable tubulars can be threadably connected.

The helical threads can be machined on plain end tubulars, tubulars with both ends upset, tubulars with one plain end and one upset end, or other connection types as typically used in the oil and gas industry. Additionally, the helical threads can be selected from a broad range of thread types used in the industry. One of skill in the art can appreciate that the present invention is not limited in application to only certain kinds of tubular ends or thread types.

FIG. 2is a side view of the hybrid threaded connection for expandable tubulars11of the present invention. As can be seen inFIG. 2, the hybrid threaded connection utilizes two complementary thread segments, Segment1and Segment2, to form the threaded connection. In Segment1, the pin threads14are sized and shaped to fully engage the box threads22upon make-up of the threaded connection. In contrast, in Segment2, the pin threads12are specially machined to have a reduced thread width such that when the connection is made-up, the pin threads12do not fully engage the box threads22. The result is the creation of a small gap25between the stab flank of the pin threads12and the adjacent flank of the box threads22. This small gap25allows radial and axial movement between the pin and box threads of Segment2without causing disengagement of the threaded connection as the connection is expanded.

In the preferred embodiment of the present invention, the pin threads12of Segment2are machined on the pin member10in a manner such that the pin thread width is reduced by approximately one-third of the original, standard thread width. In machining the pin threads12in the area of Segment2, material is removed from the stab flank of the pin threads12to reduce the standard width of the pin threads12. In contrast to the pin threads12of Segment2, the box threads22of Segment2are standard thread width and, thus, are the same thread width as the box threads22in Segment1.

Although the width of the pin threads12of Segment2is reduced by approximately one-third of standard width in the preferred embodiment, one of skill in the art will appreciate that the pin thread width may be reduced by more than one-third or less than one-third of the standard thread width depending on numerous factors, including, but not limited to, the geometry of the expansion tool performing the tubular expansion, the amount of bending experienced by the threaded connection, the wall thickness of the expandable tubulars, the grade of material used for the expandable tubulars, and the percent expansion of the tubulars.

Additionally, one of skill in the art will appreciate that alternative embodiments exists in which the pin threads may be of a uniform width across the entire length of the pin member10while the box threads of the box member20may be machined such that the box member20has multiple thread segments, including a thread segment wherein the box threads have a reduced thread width such that a gap is formed between the stabbing flank of the pin threads and the adjacent flank on the box threads, for accomplishing the objectives of the present invention. Such an alternative embodiment is illustrated inFIG. 7.

Further, although the preferred embodiment utilizes a pin member10comprising two thread segments, one of skill in the art will appreciate that alternative embodiments exist in which a pin member (or box member) with more than two thread segments having varying thread widths may be used to accomplish the objectives of the present invention. Moreover, although the preferred embodiment utilizes threads of a uniform width reduction in Segment2of either the pin or box member, one of skill in the art will appreciate that the threads of Segment2of either the pin member or the box member could be cut such that the reduction in width of the threads progressively increases (i.e., the threads could be cut at an accelerating lead resulting in each “shaved” thread having a slightly smaller width than the preceding thread).

FIG. 2also shows the four-point seal that is created in the disclosed threaded connection upon make-up of the connection. Specifically, upon make-up of the disclosed threaded connection, radial metal-to-metal seals30and40will be created by the area of engagement between the pin member10and the box member20as shown inFIG. 2, while the engagement of pin threads14and box threads22in the area of Segment1will also create a “thread seal.” Additionally, a resilient seal ring35, such as a Teflon® ring, may be placed in a groove between the pin and box threads in Segment1. The use of a resilient seal ring35augments the sealing capacity of the threaded connection. The resilient seal ring35can be selected from any suitable downhole sealing material known in the industry, and can be shaped and sized to effect the greatest possible sealing arrangement. Thus, as shown inFIG. 2, the disclosed hybrid threaded connection utilizes multiple thread segments, Segments1and2, in which the threads of Segment2accommodate the stresses and deformations generated by the radial expansion process while the threads of Segment1maintain pressure integrity where the metal-to-metal seal30, the resilient seal ring35, and the seal between engaged threads14and22are all fully activated upon make-up of the threaded connection.

FIG. 2also discloses the use of a sleeve55that resides on a machined land50that is machined into the outer diameter of the expandable tubular1adjacent the pin member10. In the preferred embodiment, the sleeve55has an outer diameter substantially identical to the outer diameter of the box member20and abuts up against, but does not cover, the end of box member20. The benefits of utilizing sleeve55on machined land50are discussed in more detail below with reference toFIG. 3.

FIG. 3is a close up view of the pin threads12and the box threads22of Segment2of the hybrid threaded connection ofFIG. 2.FIG. 3shows the gap25created by the engagement of the box threads22with the reduced width pin threads12in more detail.

FIG. 3also shows the use of sleeve55on machined land50in more detail. In the preferred embodiment, box member20is machined on an area of the expandable tubular1that has a slightly larger outer diameter than the remaining portion of the expandable tubular1. The outer diameter of the box member20is then “turned down” to the desired outside diameter—which is slightly larger than the outside diameter of the pin member10in the preferred embodiment. This special turned down box member20will allow for a better inspection of the box member20by different methods of non-destructive testing. The pin member10is machined on the other end of the expandable tubular1such that the outside diameter of the pin member10is the same as that of the expandable tubular1outside diameter.

Machined land50is machined into the outer diameter of the expandable tubular1such that sleeve55can be secured on the pin end of the expandable tubular1on the machined land50by a shrink fit method or any other suitable method such as the use of epoxy compounds. Machined land50extends from the external shoulder of pin member10to a point on the expandable tubular1that is approximately 2.0 inches from the threaded connection. One of skill in the art will appreciate that the length of machined land50can be greater than or less than 2.0 inches and still achieve the objectives of the present invention. In the preferred embodiment, sleeve55has an outside diameter equal to that of box member20. Sleeve55can be made of steel or other suitable material, including resilient materials.

During the running in of the tubular string in a well, the pin member10will be run in the “pin up” position, i.e., the position in which the pin nose is pointing towards the surface of the well. This is done to facilitate the movement of the expansion cone or tool through the threaded connection as is customary with such applications. In this position, box member20will be facing downward. Because the outside diameter of box member20is slightly larger than the outside diameter of pin member10, it is possible that box member20may get “hung up” or damaged during the running in of the tubular string. Such damage can weaken the connection, as most expandable tubulars are thin-walled. Because the sleeve55outside diameter is machined to equal that of the box member20outside diameter, the sleeve55serves to protect the exposed end of the box member20, thus reducing or eliminating the risk of damaging the face of the box member20while running the string inside the host tubular or borehole.

Moreover, because sleeve55is not designed to cover box member20, sleeve55does not increase the effective wall thickness of box member20and, thus, does not affect the expansion capabilities of the tubular in the area of box member20and does not interfere with the metal-to-metal contact between a host pipe and an expanded tubular. Although sleeve55is used in the preferred embodiment of the present invention, one of skill in the art will appreciate that alternative embodiments of the present invention may not use sleeve55or machined land50.

FIG. 4is a close up view of the pin threads14and the box threads22of Segment1of the hybrid threaded connection ofFIG. 2. AsFIG. 4shows, the pin threads14of Segment1are standard width such that they fully engage the box threads22in the area of Segment1.FIG. 4also shows the metal-to-metal seal30and resilient seal35that are created or are functional when threads14and22are fully engaged upon make-up of the threaded connection.

In an alternative embodiment of the present invention shown inFIG. 5, pin threads12and14and box threads22could be machined on pre-expanded ends of expandable tubulars to reduce the amount of expansion of the connection versus the amount of expansion of the tubular itself. The use of pre-expanded ends on expandable tubulars is disclosed and claimed in U.S. patent application Ser. No. 10/442,859 filed on May 21, 2003 (which is incorporated herein in its entirety).

In another alternative embodiment of the present invention shown inFIG. 6, pin members10could be machined on both ends of the expandable tubulars1such that a coupling member100is used to form a threaded and coupled connection. In such a connection, coupling member100would serve as the box members20with box threads22that would engage pin threads12and14consistent with the teachings of the present invention. Generally, the inside diameter of coupling member100will be machined to equal that of the expandable tubular1inside diameter to facilitate the transition of the expansion tool through the expandable tubular1during the expansion operation. Although the coupling member100shown inFIG. 6is shown as a double box member coupling, one of skill in the art will appreciate that coupling member100is not limited to such a configuration and could be any configuration that allows for threadably coupling two expandable tubulars together with pin threads12and14and box threads22as disclosed herein.

Further, during the expansion operation, a solid cone of suitable material such as hardened steel, machined to exact dimensions, is pulled through the expandable tubulars and the threaded connections in the preferred embodiment. One of skill in the art will appreciate, however, that this is not the only applicable expansion method that can be applied to expand the present invention. For example, the expansion cone could be pushed through the expandable tubular rather than being pulled through, the expansion operation could be performed using a rotary expansion method, or the expansion operation could be performed using a combination of such methods in either a single or multiple pass expansion operation.

Similarly, one of skill in the art will appreciate that the expansion cone or expansion tool itself could be of different designs depending on the size and grade of the material to be expanded and the desired results. For example, the expansion cone could be a “bullet” shape, a sphere, or a combination of such shapes. Further, the expansion cone or expansion tool could be either solid or a hollow “shell,” or could be a “shell” filled with a different material than that of the shell itself.

While the apparatus, compositions and methods of this invention have been described in terms of preferred or illustrative embodiments, it will be apparent to those of skill in the art that variations may be applied to the process described herein without departing from the concept and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the scope and concept of the invention as it is set out in the following claims.