HK1213307B - Tubular connection with helically extending torque shoulder - Google Patents

Description

Tubular connection with helically extending torque shoulder

Cross-referencing

This application claims priority from U.S. provisional application serial No. 61/730,720, filed on day 11, 28, 2012 and U.S. patent application serial No. 13/798,330, filed on day 3, 13, 2013, which are incorporated herein by reference in their entirety.

Technical Field

The present application relates to tubular connections, and more particularly, to tubular connections having a helical torque shoulder arrangement.

Background

The oil and gas upstream production industry drills oil and gas wells of ever increasing depth and complexity to discover and produce the raw hydrocarbons. The industry commonly uses steel tubing (oil country tubular goods) to protect the wellbore (casing) and to control the fluids produced therein (production tubing). Casing and production tubing are manufactured and transported in relatively short lengths and installed one length at a time in the wellbore, each length being connected to the next. As the search for hydrocarbons drives companies to drill deeper and more difficult wells, the need for casing and production tubing grows proportionally greater in terms of tension and pressure. The development of slant and horizontal wells has exacerbated this trend, adding further consideration to the demand for casing and production tubing for increasing torsional loads.

There are two basic types of connectors within this field. Most commonly are threaded coupling connectors in which two male or external threads machined on the two long fitting ends of a pipe are connected by two female or internal threads machined on a relatively short member, which is a coupling having a larger outer diameter and substantially the same inner diameter than the pipe. The other is an integral connector in which the male fitting member is threaded onto one end of a full length fitting of pipe and the female fitting member is threaded into a second full length fitting. The two joints can then be directly connected without the need for an intermediate coupling member. The end of the pipe body may be further treated to facilitate the threaded connection of the connection.

The thread profile is generally defined by a thread root, a thread crest, a stab flank, and a load flank as generally shown in FIG. 1. In conventional threads, the "included angle", i.e. the angle between the load flank and the stab flank, is positive, meaning that the width of the thread crest is smaller than the width of the thread groove with which it is initially engaged. Thus, the pin teeth are easily positioned into the box groove when the threads are assembled by rotating one member into the other. In the final assembled position, one or both of the crest and root may engage, and a gap may exist between the load flanks or the stab flanks. This enables the threads to be easily assembled. As reflected in the exemplary thread positions shown in fig. 2A (stab position), 2B (engaged position) and 2C (fully tightened position), this clearance avoids situations where the load flanks and stab flanks form a positive interference with their mating surfaces that would cause the threads to "lock up" and not fully engage.

Many advances over the years have resulted in "premium" connectors. In contrast to connections explicitly proposed by API (american petroleum institute) and other similar organizations, one can generally conclude that these connections are characterized by: 1) more complex thread profiles; 2) one or more metal-to-metal sealing surfaces; and 3) one or more torque shoulders. The torque shoulder is a mechanism for geometrically locating the metal seal and reacting against the threads to resist externally applied torque while maintaining relatively low circumferential stress within the threaded portion of the connection. The torque resistance is a function of the torque shoulder area.

Another thread system that has been used in the art is known as a "wedge" thread, which is formed from a dovetail-shaped thread system having a varying width or varying pitch. This thread arrangement enables the threads to be easily engaged and assembled, but creates a positive interference between the opposing flanks of the threads in the fully assembled position. Wedge threads generally have greater torque resistance than other premium threaded connections. This "wedge thread" has certain disadvantages, the most important one being that it is more difficult to manufacture and measure than a thread having only a single pitch. Making wedge threads on the cone further increases the difficulty of the thread making and measuring process.

What is needed by drilling rigs and producers of deep high pressure thermal and/or deviated oil and gas wells is a threaded connection with high torque characteristics that is relatively easy to machine and relatively inexpensive to produce.

Disclosure of Invention

In one aspect, a method of joining tubular lengths of oil country tubular casing or tubing includes the steps of: using a first tubular member having an associated pin member with a first thread formation and a first helical torque shoulder axially spaced from the first thread formation along the pin member; using a second tubular member having an associated box member with a second thread formation and a second helical torque shoulder axially spaced from the second thread formation along the box member; engaging the pin member and the box member with one another into a stab position defined by interaction of the first thread formation and the second thread formation, in which the first helical torque shoulder does not contact or axially overlap the second helical torque shoulder; rotating at least one of the first or second tubular members such that interaction between the first and second threaded structures guides the first and second helical torque shoulders into cooperative alignment; continuing to rotate at least one of the first or second tubular members until the first helical torque shoulder is fully engaged with the second helical torque shoulder.

In another aspect, a tubular connection includes a male fitting component and a female fitting component. The pin member has a first thread formation and a helical torque shoulder axially spaced from the first thread formation along the pin member. The box member has a second thread formation and a second helical torque shoulder axially spaced from the second thread formation along the box member. The first and second thread structures are sized and positioned to control a stab position of the tubular connection in which the first helical torque shoulder does not engage or axially overlap the second helical torque shoulder.

In one example, the first and second thread structures may each be tapered constant pitch threads, and the first and second helical torque shoulders may be formed by respective non-tapered structures.

The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

Drawings

FIG. 1 is a schematic illustration of a thread pattern;

FIGS. 2A, 2B and 2C show a portion of the connection in a stabbed, engaged and tightened condition, respectively;

FIG. 3 illustrates an exemplary premium connection having a cylindrical torque shoulder surface;

FIG. 4 illustrates one embodiment of a connection in which a helical torque shoulder extends into a cylindrical torque shoulder;

FIGS. 5 and 6 illustrate another embodiment of a connection where the helical torque shoulder extends into the cylindrical torque shoulder;

FIG. 7 illustrates a connection embodiment in which the helical torque shoulder is formed by a dovetail wedge configuration.

Detailed Description

The present tubular connection provides a helical torque shoulder arrangement.

In this primary embodiment, a conventional circumferentially extending torque shoulder (e.g., a shoulder typically at the junction of the box base and pin nose of a threadingly coupled premium connection, or a center shoulder) is supplemented or replaced by a helically extending torque shoulder.

As previously mentioned, the most "premium" connection, FIG. 3, shows each of the illustrative partial pin 10 and box 12 connections, which includes threads 14, metal seals 16, and positive torque shoulders 18. When the first member of the connection is assembled into the second, mating member, the threads contact at some point on their respective "stab" flanks. When the first member 10 is rotated into the second member driven by a torque external to the member, the threads engage and the first member of the threaded connection moves into the second member constrained by the geometry of the engaged threads. As the threaded joint approaches full makeup, the two opposing structures, i.e., the "torque shoulders," are in contact.

A conventional torque shoulder typically at the interface of the pin nose and box base of a threadedly coupled premium connection is a cylindrical shoulder surface, as shown in fig. 3, which is approximately a complete circumferential surface of two components. The two shoulders lie in respective planes (e.g. 20) substantially perpendicular to the longitudinal axis 22 of the member/connector (e.g. only in case of radially extending shoulder surfaces, as shown) or are positioned along respective relatively narrow axial extensions (e.g. axial extensions 24 in case of shoulders extending at an angle to the radial direction). In either case, at any given radial distance from the central axis of the member/connector, the surface along that radial distance may define a line extending in a circumferential direction that will lie in a plane substantially perpendicular to the axis of the connector. When the metal sealing surface 16A of the first member contacts the metal sealing surface 16B of the second member, the reaction between the two creates a counter force and immediately prevents continued axial relative movement of the threaded members. The thread of the first member, driven by the external torque, continues to rotate, causing the conversion of the threaded contact from a stab flank engagement to a load flank engagement.

Once the load flanks of the threads are engaged, any additional increase in externally applied torque causes a reaction between the load flanks of the threads and a metal-to-metal seal, forcing the first member into the second member along the path defined by the thread geometry, further engaging the metal seal against the resistance of the seal's interference fit. Once the torque shoulder surface 18A of the first member contacts the torque shoulder surface 18B of the second member, no further rotation is possible. Contact between each member torque shoulder further resists movement in the circumferential direction.

If the external moment is large enough and the load capacity and shear capacity of the threads is large enough, the torque shoulders will yield themselves and the interaction force between the shoulders of each component becomes greater than the shear capacity or load capacity of the shoulders.

The present invention relates to a solution to increase the torque resistance of a connection by increasing the surface area of the torque shoulder, since the contact stress is directly proportional to the force and inversely proportional to the area. For a given pipe wall thickness, the threads must use a certain percentage of the radial depth of the wall thickness to create the required load bearing and shear area necessary for the threads to transmit the pipe load. The actual percentage of cross-sectional area is a function of the thread geometry: pitch, thread height, and thread taper. The remainder of the radial depth or thickness of the wall portion may be used for the metal-to-metal sealing surface and the torque shoulder.

Cold forming the forward end of the pin to reduce the pin member inner diameter enables designers to increase torque shoulder surface area, but has limitations. One of the most important requirements of oil country tubular goods is the "drift diameter", i.e. the largest cylinder of a specific diameter and length that is to be passed through the assembled pipes and connections. The drift diameter is only slightly less than the nominal internal diameter of the pipe body. Thus, the male fitting can only be formed by a small amount, thereby limiting the increase in shoulder surface area to a small amount.

In the embodiment shown in fig. 4-6, the conventional torque shoulder 30, which is typically at the junction of the box base and pin nose of a threadingly coupled premium connection, is supplemented by a set of helical surfaces 32 and 34 machined on a cylindrical section 36 of the pipe body parallel to its longitudinal axis 38. The helical torque shoulder of the male component 10 has two flanks 32A, 34A connected by a root and a crest that spiral around three turns. The female fitting component 12 has corresponding mating torque shoulder flanks. Each of these surfaces has the potential to add surface area to the cylindrical torque shoulder. Although the extension of the surfaces may vary from less than one revolution to more than three revolutions, the main problem is to find that these surfaces will support the main torque shoulder surfaces 30A and 30B (still cylindrical) against the reaction of the thread load flank surfaces of the connection.

In the illustrated embodiment, the helical torque shoulder is a trapezoidal "flank to flank" design. As seen in fig. 6, the helical torque shoulder may include a start chamfer 50. The box member may also include a clearance area 52 between the box metal seal surface 16B and the start of the box torque shoulder surface 34B to allow the connection start of the pin nose and the pin helical torque shoulder to go to a position that shortens (e.g., axially to the right in the view of fig. 6) the start of the box torque shoulder surface 34B. During assembly, both of the shoulder surfaces of the helically extending flanks/helical torque shoulders of one component contact the shoulder surfaces of the mating flanks/helical shoulders of the other component prior to full assembly (e.g., as the helical torque shoulder on the pin 10 moves into the helical torque shoulder on the box body 12).

The machined flank surface at a slight angle (mil angle) measured from a direction perpendicular to the longitudinal axis of the tubular body allows further rotation of the connection member driven by an externally applied torque. As these flank surfaces are driven further together, the normal force between the flank surfaces increases, resulting in increased friction against the externally applied torque, i.e., it requires more torque, to continue driving the two members together.

When the components are fully assembled, the helical torque shoulder forms the end and the two cylindrical torque shoulder surfaces engage, significantly increasing the assembly torque requirement. Furthermore, once the engaged components are stopped by the vertical cylindrical shoulder, any increased externally applied torque continues to force an increasingly greater reaction between the load flank of the helical torque shoulder surface and the cylindrical shoulder surface.

When the load flank of the female joint forces the load flank and the entire male joint member into the female joint member, the reaction between the load flank of the male joint and the load flank of the female joint results in a pressure force acting on the male joint member. When the load flank of the pin forces the load flank and the entire box member away from the cylindrical torque shoulder, the reaction between the load flank of the box and the load flank of the pin results in a tensile force acting on the box member.

As these forces increase as a result of the drive of the increasing external torque, the poisson effect drives the male and female joint members: radially enlarging an outer peripheral surface of the male joint in a compressed state; the outer peripheral surface of the female joint in a tensioned state is radially reduced. This reaction begins at the cylindrical shoulder surface and is transmitted back to the connection starting from the helical torque shoulder. The poisson effect starts at the intersection of the cylindrical torque shoulder and locks the helical surface through the helical torque shoulder in the direction of the thread. The locking mechanism enables both flanks of the helical torque shoulder to increase the effective area of the combined torque shoulder.

This embodiment of the invention provides a number of advantages.

The helical torque shoulder requires only a few helical machined surfaces.

These surfaces resemble a pattern of threads, although having different functions, but can be machined in a similar manner to threads.

The helical torque shoulder of the illustrated embodiment is machined on a cylindrical path parallel to the longitudinal axis of the pipe body, further simplifying machining and measuring the surface. However, in other embodiments, the helical torque shoulder may be machined on a tapered path.

The surface area of the joint can be enlarged by changing the profile (e.g. for thicker walled tubes the height of the surface can be increased, or the pitch changed).

Other embodiments of the invention may provide additional or supplemental advantages. For example, the above description describes a trapezoidal surface having a slight angle with respect to a direction perpendicular to the axis of the tube. Even a slight angle will generate some radial force. These radial forces will tend to force the two members apart, with the greatest detrimental effect on members having thinner cross-sections; in the embodiment shown the male fitting. An alternative embodiment may use a helical surface having a square or rectangular shape, wherein the angle between the flank surfaces and with respect to a direction perpendicular to the longitudinal axis of the pipe is zero or close to zero.

Other embodiments may use more complex forms, with some flanks having negative or dovetail angles. The helical torque shoulder illustrated has a cylindrical profile relative to the axis of the connection, thus eliminating the need for axial engagement clearance as in the form of make-up threads used in oil field casing or production tubing equipment. The threaded connection must have features that enable assembly on the drilling machine. This requires some "stabbing" depth to stabilize the length of pipe suspended in the derrick tower while the rig crew initiates contact between the two components and rotates them together. The main thread 14 in the connection performs this function, while the helical torque shoulder need only be optimized to react to externally applied torque (i.e., "make-up" torque). Thus, in contemplated connections, the helical torque shoulder surfaces will not engage or axially overlap when the two members are in a stab position defined by the main threads controlling the make-up operation. Only after relative rotation of one member causes the members to move axially together will the helical shoulder surfaces begin to axially overlap and move into each other.

Other embodiments may actually use variable width versions of square, near square, or dovetail designs, where flank contact may be enhanced by the aforementioned wedging mechanism of the wedge threads. The increased maximum torque (torquecapacity) is a function of the increased surface contact area of the two flanks of the spline pair within the wedged torque shoulder. This value can be optimized based on the available cross-sectional height and make-up rotation of the main drive threads (with the conventional threads in any location on the connection). Figure 7 shows by way of example an embodiment in which the helical shoulders have a trapezoidal shape resulting from a wedge shape (e.g. when the helical torque shoulder 100 of the pin member moves into the helical torque shoulder 104 of the box member, these shoulders wedge after full pull-up; a metal-to-metal seal is shown at 124).

The torque capacity is also enhanced by any conventional torque shoulder that may be present in a threaded connection and that should be used in conjunction with the helical torque shoulder described above. The conventional torque shoulder may be an extension of the helical torque shoulder or positioned in other locations within the connection independent of the helical torque shoulder.

A premium connection has shoulders in different locations, and in some cases, multiple shoulders. The main positions are:

the pin nose/box base intersects the inside diameter of the connection (example given here).

A male joint base/female joint surface; i.e. intersecting the outer diameter of the connecting element.

The intermediate wall portion of the connector, "center shoulder" (each shoulder location shown, for example, in U.S. patent No. 5,415,442, which is incorporated herein by reference).

Those skilled in the art will appreciate that the concept of a helical torque shoulder may be used in any and all of these shoulder configurations with suitable modifications.

While a metal seal may or may not be present within the threaded connection, the configuration using a metal-to-metal seal between the helical torque shoulder and the conventional threads has the additional advantage over conventional premium connections in that the helical torque shoulder isolates the metal-to-metal seal from the compressive loads experienced by the pin member.

The metal seal is formed by interferingly fitting two smooth metal surfaces together. During the loading of the compression load, the metal seal portion (particularly, the metal seal portion of the male joint member) deforms due to the excessive compression load. The two surfaces attempt to separate due to the contact pressure created by the interference fit. Although conventional designs use techniques that hold the two surfaces together, analysis shows some separation and resulting loss of contact pressure. The helical torque shoulder will isolate the sealing surface from axial load effects and produce a more stable consistent metal seal under a variety of loading conditions.

The helical torque shoulder structure described herein provides a torque shoulder surface that extends through more than 360 degrees, preferably through more than 720 degrees. When following the helical shoulder surfaces at a given radial distance from the longitudinal centre axis, the resulting trajectory will not lie in a plane substantially perpendicular to the longitudinal axis of the pipe or connector body, or even have a narrow extension as suggested in fig. 3 due to the helical character of these surfaces.

In one embodiment, the axial length L of the helical torque shoulder_HTSMay be 30% or less of the total length L of the connection, and the length L of the main thread_PTWhich may be about 50% or more (e.g., 60% or more) of the overall length L of the connection, it should be understood that the length L of the connection is defined as the axial distance between: (i) a shoulder, metal-to-metal seal or thread located furthest from one end of the connection; and (ii) a shoulder, metal-to-metal seal, or thread shoulder located furthest from the other end of the connection.

In one embodiment, the axial length L of the helical torque shoulder_HTSMay be the axial length L of the main thread_PTBetween about 15% and 45%.

In one embodiment, the helical torque shoulder extends through no more than 4 turns, while the main thread pattern extends through at least 10 turns.

It is to be clearly understood that the above description is intended to be illustrative and exemplary only and is not intended to be limiting, and that other variations and modifications are possible. For example, while tapered constant pitch threads of the type used in Premium connections (such as ULTRA-DQX, ULTRA-FJ, ULTRA-QX, and ULTRA-SF connections available from Ultra Premium OilfieldProducts of Houston, Tex.) have been primarily described in connection with helical torque shoulder threads, other thread configurations may be used in place of the Premium connection threads, such as API round threads, API buttress threads, or other threads.

Claims (21)

1. A tubular connection, comprising:

a male joint member having:

a first tapered constant pitch thread having a root, a crest, a stab flank, and a load flank;

a first helical torque shoulder surface axially spaced from the first tapered constant pitch thread along the pin member, the first helical torque shoulder surface being non-tapered;

a female fitting member having:

a second tapered constant pitch thread having a root, a crest, a stab flank, and a load flank;

a second helical torque shoulder surface axially spaced from the second tapered constant pitch thread along the box member, the second helical torque shoulder surface being non-tapered;

the pin member and the box member are configured such that the first helical torque shoulder surface does not engage or overlap the second helical torque shoulder surface in a stab position.

2. The tubular connection of claim 1, wherein (i) the first tapered constant pitch thread and the first helical torque shoulder surface are sized and positioned relative to one another, and (ii) the second tapered constant pitch thread and the second helical torque shoulder surface are sized and positioned relative to one another, such that the first helical torque shoulder surface is guided into cooperative alignment with the second helical torque shoulder surface during rotational pull-up of the pin member and the box member under control of interaction between the first tapered constant pitch thread and the second tapered constant pitch thread.

3. The tubular connection of claim 2, wherein upon final make-up of the pin member and box member, the first helical torque shoulder surface moves into wedging engagement with the second helical torque shoulder surface.

4. The tubular connection of claim 1, wherein: the first helical torque shoulder surface and the second helical torque shoulder surface have a variable width form.

5. The tubular connection of claim 4, wherein: the load flank lead of the first helical torque shoulder surface and the second helical torque shoulder surface is greater than the stab flank lead.

6. The tubular connection of claim 1, wherein:

a root diameter of the first helical torque shoulder surface is less than a starting root diameter of the first tapered constant pitch thread and an ending root diameter of the first tapered constant pitch thread;

a root diameter of the second helical torque shoulder surface is less than a starting root diameter of the second tapered constant pitch thread and an ending root diameter of the second tapered constant pitch thread.

7. The tubular connection of claim 6, wherein:

the pin member includes a first transition region in an axial direction between the first helical torque shoulder surface and the first tapered constant pitch thread, the first transition region including a first sealing surface;

the female joint member includes a second transition region in an axial direction between the second helical torque shoulder surface and the second tapered constant pitch thread, the second transition region including a second sealing surface;

in a fully tightened state, the first sealing surface engages the second sealing surface for sealing.

8. The tubular connection of claim 7, wherein:

an axial length of the first helical torque shoulder surface is less than an axial length of the first tapered constant pitch thread;

the second helical torque shoulder surface has an axial length less than an axial length of the second tapered constant pitch thread.

9. The tubular connection of claim 8, wherein:

an axial length of the first helical torque shoulder surface is substantially less than an axial length of the first tapered constant pitch thread;

the axial length of the second helical torque shoulder surface is substantially less than the axial length of the second tapered constant pitch thread.

10. The tubular connection of claim 6, wherein:

the first helical torque shoulder surface extends a number of turns substantially less than the number of turns of the first tapered constant pitch thread;

the second helical torque shoulder surface extends a number of turns substantially less than the second tapered constant pitch thread.

11. The tubular connection of claim 1, wherein the first helical torque shoulder surface extends into a first generally cylindrical torque shoulder surface of the pin member, the second helical torque shoulder surface extends into a second generally cylindrical torque shoulder surface of the box member, the first generally cylindrical torque shoulder surface engages the second generally cylindrical torque shoulder surface and the first helical torque shoulder surface engages the second helical torque shoulder surface in a fully made-up position of the tubular connection, resulting in a combined cylindrical and helical torque shoulder.

12. The tubular connection of claim 2, wherein upon final make-up of the pin member and the box member, the first helical torque shoulder surface and the second helical torque shoulder surface engage at one of: (i) at a pin nose/box base location that intersects an inner diameter of the tubular connection, (ii) at a pin base/box surface location that intersects an outer diameter of the tubular connection, or (iii) at an intermediate wall portion of the tubular connection that is a center shoulder of the tubular connection.

13. A tubular connection, comprising:

a male joint member having:

a first thread formation;

a first helical torque shoulder axially spaced from the first thread formation along the pin member;

a female fitting member having:

a second thread formation;

a second helical torque shoulder axially spaced from the second threaded structure along the box member;

wherein the first and second thread structures are sized and positioned to control a stab position of the tubular connection in which threads of the first helical torque shoulder do not engage or overlap with the second helical torque shoulder.

14. The tubular connection of claim 13, wherein: the first helical torque shoulder and the second helical torque shoulder have a variable width form.

15. The tubular connection of claim 14, wherein: the load flank lead of the first helical torque shoulder and the second helical torque shoulder is greater than the stab flank lead.

16. The tubular connection of claim 13, wherein:

(i) the first thread formation and the first helical torque shoulder are sized and positioned relative to one another, and (ii) the second thread formation and the second helical torque shoulder are sized and positioned relative to one another such that the first helical torque shoulder is directed into cooperative alignment with the second helical torque shoulder during rotational make-up of the pin member and the box member under control of interaction between the first thread formation and the second thread formation.

17. The tubular connection of claim 14, wherein the first helical torque shoulder extends into a first generally cylindrical torque shoulder of the pin member, the second helical torque shoulder extends into a second generally cylindrical torque shoulder of the box member, the first generally cylindrical torque shoulder engages the second generally cylindrical torque shoulder and the first helical torque shoulder engages the second helical torque shoulder in a fully made-up position of the tubular connection, resulting in a combined cylindrical and helical torque shoulder.

18. A method of joining tubular lengths of oil country tubular casing or tubing, the method comprising:

using a first tubular member having an associated pin member with a first thread formation and a first helical torque shoulder axially spaced from the first thread formation along the pin member;

using a second tubular member having an associated box member with a second thread formation and a second helical torque shoulder axially spaced from the second thread formation along the box member;

engaging the pin member and the box member with one another to a stab position defined by interaction of the first thread formation and the second thread formation, in which the first helical torque shoulder does not contact or axially overlap the second helical torque shoulder;

rotating at least one of the first or second tubular members such that interaction between the first and second threaded structures guides the first and second helical torque shoulders into cooperative alignment.

19. The method of claim 18, comprising:

continuing to rotate at least one of the first or second tubular members until the first helical torque shoulder wedges with the second helical torque shoulder.

20. The method of claim 19, wherein the male fitting member is integrally formed with the first tubular member and the female fitting member is integrally formed with the second tubular member.

21. The method of claim 19, wherein the first thread structure is a tapered constant pitch thread and the second thread structure is a tapered constant pitch thread.