Arcuate thread form fit

A threaded pipe connection includes a first tubular member having a pin end defining external threads, a second tubular member having a box end defining internal threads threadably engageable with the external threads of the pin end, and a thread profile that defines at least a portion of one of the internal or external threads and includes a crest, a root, and a transition surface extending between the crest and the root. The transition surface includes a first arcuate surface extending from a top of the crest at a first radius, a second arcuate surface extending from the first arcuate surface at a second radius, and a third arcuate surface extending from the second arcuate surface at a third radius. The first radius and the third radius are each smaller than the second radius.

BACKGROUND

In the oil and gas industry, several types of tubing and pipe are used in exploration, completion, and production operations to extract hydrocarbons from subterranean hydrocarbon-bearing formations. Typical types of oilfield tubing include drill pipe, casing (or liner), and production tubing. Relatively short pipe sections of 30 to 40 ft. or so in length are commonly coupled end-to-end to make a long string of tubing used to drill or complete a well, or to extract hydrocarbons from a completed well. Connected sections of drill pipe form a drill string used to deepen or work over the well, casing or liner pipe is used to encase the walls of the drilled wellbore and provide structural support for the well, and production pipe is used to convey the subsurface oil or gas to the well surface.

Each of the different types of pipe has a threaded end configuration specially designed to meet its intended purpose as it structurally secures and seals the pipe ends together. Common threaded connections include a male threaded member or “pin” at the end of a tubular section, which engages a female threaded member or “box” at the end of an adjoining tubular section. The box may be formed as an integral part of the tubular section or it may be formed by securing a coupling to a pin end of a tubular pipe section.

Threaded connections of oilfield tubulars generally engage each other in an interference fit, a shouldering fit, or a combination of interference and shouldering fits. In an interference fit, tapered pin and box ends are tightly wedged together as the pin threadably advances into the box. The resulting interference fit provides both structural and sealing connections between the pin and box ends. In contrast, a shouldering connection engages an annular shoulder on the pin end with an annular shoulder provided on the box end. The threads of the shouldering connection provide the structure holding the pin and box ends together, and the engaged shoulders help facilitate a sealed engagement.

Interference and shouldering threaded connections tend to fail in areas of stress concentrations that occur during makeup and working of the connections. A variety of thread designs, forms, and profiles have been suggested and introduced to change the distribution of torque stresses along the threaded connections of oilfield tubing.

DETAILED DESCRIPTION

This present disclosure is related to threaded connections and, more particularly, to threaded connections for downhole tubulars and pipes.

Embodiments disclosed herein describe threaded pipe connections that include a first tubular member having a pin end defining external threads, a second tubular member having a box end defining internal threads threadably engageable with the external threads of the pin end, and a thread profile that defines at least a portion of one of the internal or external threads and includes a crest, a root, and a transition surface extending between the crest and the root. The transition surface may include a first arcuate surface extending from a top of the crest at a first radius, a second arcuate surface extending from the first arcuate surface at a second radius, and a third arcuate surface extending from the second arcuate surface at a third radius. In some embodiments, the first radius and the third radius are each smaller than the second radius.

FIG. 1is a schematic diagram of an example drilling system100that may employ one or more principles of the present disclosure. Boreholes may be created by drilling into the earth102using the drilling system100. In the illustrated example, the drilling system100includes a bottom hole assembly (BHA)104positioned or otherwise arranged near the bottom of a drill string106extended into the earth102from a derrick108arranged at the surface110. The derrick108includes a kelly112and a traveling block113used to lower and raise the kelly112and simultaneously lower and raise the drill string106.

The BHA104includes a drill bit114operatively coupled to the end of a tool string116that extends axially within a drilled wellbore118. During operation, the drill bit114is rotated to grind and cut into the underlying rock formations and thereby progressively penetrate the earth102to create the wellbore118. The BHA104provides directional control of the drill bit114as it advances into the earth102and extends the wellbore118. Fluid or “mud” from a mud tank120may be pumped downhole using a mud pump122powered by an adjacent motor124. The mud is pumped from the mud tank120through a stand pipe126, which feeds the mud into the drill string106and conveys the same to the drill bit114. The mud exits one or more nozzles provided in the drill bit114and in the process cools the drill bit114as it operates. The mud then circulates back to the surface110via the annulus defined between the wellbore118and the drill string106, and in the process returns drill cuttings and debris to the surface. The cuttings and mud mixture are passed through a flow line128and are processed such that a cleaned mud is returned down hole through the stand pipe126once again.

Although the system100is described herein with respect to drilling for hydrocarbons, the principles described herein may be equally applicable to other types of applications such as, but not limited to, drilling for mineral exploration, environmental investigation, natural gas extraction, underground installation, mining operations, water wells, geothermal wells, sub-surface boring applications and construction assemblies, disposal wells, and the like. Moreover, while the system100is depicted as a land-based operation, it will be appreciated that the principles of the present disclosure could equally be applied in any offshore, sea-based, or sub-sea application where the service rig may be a floating platform, a semi-submersible platform, or a sub-surface wellhead installation as generally known in the art.

The drill string106is made up of multiple pipes (alternately referred to herein as “tubular members” or “tubulars”) threadably connected together end-to-end. During oil and gas drilling operations, it is desirable that the threaded connections forming the drill string106have sufficient strength to withstand all expected service loads (e.g., torsion, tension, compression, etc.). Particularly, it is desirable that the threaded connections have sufficient torsional strength, which is a measure of the amount of torque applied about the centerline of the tubular connection required to cause failure. In order to optimize the torsional strength of the drill string106threaded connections, the threads must be designed to have a sufficient bearing and shear strength to avoid the common failures resulting from elevated torsion. Bearing strength is a measure of the amount of force required to cause deformation (e.g., plastic deformation) of engaged surfaces (e.g., thread flanks) of the threaded connection, and shear strength is a measure of the amount of force required to shear the threads between the thread flanks along a plane substantially parallel to the connection centerline.

According to embodiments of the present disclosure, a threaded pipe connection can provide a thread profile that includes a crest, a root, and a transition surface extending between the crest and the root. The transition surface may include at least three arcuate surfaces and a straight line portion extending from a top of the crest toward the root at varying radii. The three consecutive and contiguous arcuate surfaces followed by the straight-line portion provides less contact area between opposing stab flanks as the opposing curved surfaces are drawn together while making up (i.e., threading) the pin to the box, which results in reduced friction forces. Hydraulic lock caused by pipe lubricants may also be mitigated while making up the pin to the box.

FIG. 2is a cross-sectional side view of an example threaded connection200that may incorporate the principles of the present disclosure. As illustrated, the threaded connection200(also referred to as a “tool joint”) may include a pin202aof a first tubular member204aand a box202bof a second tubular member204b. The first and second tubular members204a,bmay comprise any type of tubing, pipe, or tubulars commonly used in the oil and gas industry and capable of being threadably connected end-to-end. Examples of the tubular members204a,binclude, but are not limited to, drill pipe, casing (or liner), production tubing, general tubular assemblies (e.g., a wellbore hanger, hydraulic fracturing tools, float equipment, etc.) and any combination thereof.

In the illustrated embodiment, the threaded connection200comprises a shouldered connection. As illustrated, the pin202aincludes an external shoulder206engageable with and end face208of the box202b. In operation, the face208functions as a box shoulder engaging the external pin shoulder206. In other embodiments, however, the threaded connection200may alternatively comprise an interference connection, or a combination shouldered and interference connection, without departing from the scope of the disclosure.

The pin202adefines or otherwise provides a helically extending external thread profile210athreadably engageable with a helically extending internal thread profile210bdefined or otherwise provided by the box202b. The external thread profile210aincludes a stab flank212and a load flank214, and the internal thread profile210bsimilarly includes a stab flank216and a load flank218. Accordingly, as the threaded connection110is made up, the stab flanks212,216oppose each other, and the load flanks214,218oppose each other.

As used herein, the term “thread profile” refers to the thread form or configuration of a thread in an axial plane and which is generally considered to include a crest, a root, and opposing stab and load flanks. Moreover, as used herein, the term “stab flank” is intended to designate those flanks of the pin and box threads that first engage as the pin is stabbed into the box, and the term “load flank” is intended to designate those contacting flanks of the pin and box threads that normally contact with an increasing bearing pressure in reaction to the load forces tending to separate the engaged pin and box axially.

Although not visible inFIG. 2, any gap between succeeding turns of the external and internal thread profiles210a,bwill progressively diminish, and the interference will increase between engaged threads after the gap closes in a direction from the engaged shoulder206and the end face208toward an axial end220of the pin202a. Moreover, as torque is applied to the threaded connection200, following engagement of the external shoulder206and the end face208, the pin202awill be drawn in tension and the box202bwill be pulled in compression.

FIG. 3is an enlarged cross-sectional side view of threaded engagement between the external and internal thread profiles210a,bofFIG. 2. The following description is related to the external thread profile210aof the pin202a, but is equally applicable to the internal thread profile210bof the box202b. As illustrated, the external thread profile210aprovides a tooth300that defines a crest302, a root304, a stab flank306a, and a load flank308a. The stab and load flanks306a,308aoppose corresponding stab and load flanks306b,308bof the internal thread profile210bof the box202b. In some embodiments, the crest302and the root304define substantially flat surfaces that are parallel to one another.

According to one or more embodiments, a transition thread form or surface extends from the crest302to the root304and uses at least three consecutive and contiguous arcuate surfaces and a straight line surface extending from the last arcuate surface. More specifically, the stab flank306amay comprise a transition surface310extending between the crest302and the root304. The transition surface310may oppose a corresponding transition surface312provided on the stab flank306bof the internal thread profile210b. The transition surfaces310,312may be substantially similar, except in reverse and otherwise oppositely formed. Accordingly, while the present discussion is related to the transition surface310extending from the crest302to the root304of the pin202a, the principles of the present disclosure are equally applicable to the transition surface312extending from the root to the crest of the box202b, without departing from the scope of the disclosure.

As illustrated, the transition surface310may define or otherwise provide a first arcuate surface314aextending from the top of the crest302at a first radius R1. The first arcuate surface314atransitions into a second arcuate surface314bextending at a second radius R2, and the second arcuate surface314btransitions to a third arcuate surface314cextending at a third radius R3. The third arcuate surface314cthen transitions into a straight-line portion316that extends from the third arcuate surface314cto the root304at an angle Θ. A fourth arcuate surface314dextends from the straight-line portion316to the bottom of the root304at a fourth radius R4. Accordingly, in at least one embodiment, the transition surface310includes five contiguous and continuous surfaces, including the four arcuate surfaces314a-dand the straight-line portion316, extending from the crest302to the root304.

In some embodiments, the first and third radii R1, R3 are smaller than the second radius R2. The first and third radii R1, R3, for example, may range between about 0.008 inches and about 0.015 inches in magnitude, and the second radius R2 may range between about 0.200 inches and about 0.400 inches. In at least one embodiment, the second radius R2 may be about 0.250 inches. Moreover, in some embodiments, the fourth radius R4 may be smaller than the first, second, and third radii R1, R2, R3. In such embodiments, the fourth radius R4 may range between about 0.005 inches and about 0.012 inches. The length or “arc length” of the second arcuate surface314bwill generally be longer or of a greater magnitude than the length of the first or third arcuate surfaces314a,314c.

As its name suggests, the straight-line portion316extends from the third arcuate surface314cin a substantially straight line or course, with little or no curvature. The angle Θ of the straight-line portion316is measured from perpendicular to the pitch diameter line318of the tooth300(i.e., extending through the midpoint between the crest302and the root304) and may range between about 2° and about 10° offset from perpendicular to the pitch diameter line318. The angle Θ may be at least 1° greater than the angle of the load flank308a, thus making the angle of the stab flank306bat least 1° greater than the angle of the load flank308a. During the manufacturing process for the thread profile, in order to produce or form the proper angle of the stab flank308b, the insert needs to feed in at an angle that is at least 0.5° more to ensure that the finished angle is free from steps. If the insert is fed in at more than 1° than the angle, the stab flank306bwill not be free of steps as the tool is moving back more than the angle of the stab flank306band thereby leaving an un-machined surface outside the guidelines of the thread form finished product. As will be appreciated, however, the forgoing dimensions for the radii R1-R4 and the magnitude of the angle Θ may vary depending on the application.

In some embodiments, the third arcuate surface314cmay be centered at or near the pitch diameter line318of the tooth300. Accordingly, the transition surface310includes three contiguous and continuous surfaces extending from the crest302to the pitch diameter line318. The position of the third arcuate surface314c, however, may change due to taper angle of the pitch line318based off of the center line axis of the connection. In operation, the third arcuate surface314cmay provide a surface and/or location on the tooth300configured to hold the load flank308ain place, which helps reduce the chance of disengagement for compressive loads. More specifically, when fully engaged at the angle Θ, the load flank308awill be unable to move up without rotation due to the overhang of the angles, and the load flank308awill also be unable to move forward enough before contacting the third arcuate surface314cto move up without rotation.

In some embodiments, if the profile form of the first, second, and third arcuate surfaces314a-cwere replicated and mirrored, an ellipse would be created by the combination. More specifically, if the arcuate paths of the arcuate surfaces314a-cwere to continue in a mirror-image replication, the combination of all the arcuate surfaces would generate an elliptical shape. This may prove advantageous over prior art thread forms in that it reduces the contact area between the opposing two surfaces and allows the load flank308bto clear and as rotation is applied the load flank308abacks into the angle of the mating load flank308b.

At least one advantage to the three consecutive and contiguous arcuate surfaces314a-cfollowed by the straight-line portion316is less contact area between the stab flank306aof the external thread profile210aand the opposing stab flank306bof the internal thread profile210b. In contrast to prior art thread forms that have opposing flat surfaces sliding together at the opposing stab flanks, the transition surfaces310,312define opposing curved surfaces of opposing radii that are drawn together while making up (i.e., threading) the pin202ato the box202b. Consequently, there is less surface area contact (axial and radial) between the opposing stab flanks306a,bduring rotation (make-up), which results in reduced friction forces.

Another advantage to the three consecutive and contiguous arcuate surfaces314a-cfollowed by the straight-line portion316is the mitigation of hydraulic lock while making up the pin202ato the box202b. More specifically, a lubricant (e.g., thread dope) is commonly applied on the internal and/or external thread forms110a,bto help ease the make-up process. Once the pin202amates with the box202b, contact will occur on the crest302, the root304, and the load flank306a, and the lubricant will need somewhere to flow. Since the opposing transition surfaces310,312combine multiple radii on the opposing stab flanks306a,b, it opens up gaps on either side of the radius to receive and gather the lubricant. This not only helps to seal the connection, but also mitigate hydraulic lock.

FIGS. 4A-4Eare cross-sectional side views of the threaded engagement between the external and internal thread profiles210a,bshowing progressive engagement showing how the pin and box connections202a,bcome together during make up, according to one or more embodiments. As illustrated, when the pin and box connections202a,bare stabbed together for make-up, the clearance between the opposing curved surfaces and radii of the two stab flanks306a,ballows the load flanks308a,bto clear each other. Moreover, during the make-up rotation, the radii of the stab flanks306a,bclose in a reverse axial movement, which correspondingly closes the distance between the load flanks308a,buntil fully engaged. As shown inFIG. 4C, the thread profiles210a,bdescribed herein allow the load flanks308a,bto pass by each other until the stab flanks306a,bmake contact on their larger radii. Once the stab flanks306a,bengage each other, a reactive force is created that drives the load flanks308a,btogether, as shown inFIG. 4D. The load flanks308a,bcome together due to the negative angle Θ (FIG. 3) of the straight-line portion316(FIG. 3).

A. A threaded connection that includes a first tubular member having a pin end defining external threads, a second tubular member having a box end defining internal threads threadably engageable with the external threads of the pin end, and a thread profile that defines at least a portion of one of the internal or external threads and includes a crest, a root, and a transition surface extending between the crest and the root, the transition surface comprising a first arcuate surface extending from a top of the crest at a first radius, a second arcuate surface extending from the first arcuate surface at a second radius, and a third arcuate surface extending from the second arcuate surface at a third radius, wherein the first radius and the third radius are each smaller than the second radius.

B. A thread profile that includes a crest, a root, and a transition surface extending between the crest and the root and comprising a first arcuate surface extending from a top of the crest at a first radius, a second arcuate surface extending from the first arcuate surface at a second radius, a third arcuate surface extending from the second arcuate surface at a third radius, and a straight-line portion extending from the third arcuate surface toward the root at an angle offset from perpendicular to a pitch diameter line extending through a midpoint between the crest and the root.

Each of embodiments A and B may have one or more of the following additional elements in any combination: Element 1: wherein the pin and box ends are threadably engaged in a shouldered connection, an interference connection, or a combination of shouldered and interference connection. Element 2: wherein the first and second tubular members are selected from the group consisting of drill pipe, casing, liner, production tubing, a general tubular assembly, and any combination thereof. Element 3: wherein the transition surface further comprises a straight-line portion extending from the third arcuate surface toward the root at an angle offset from perpendicular to a pitch diameter line of the thread profile. Element 4: wherein the transition surface further comprises a fourth arcuate surface extending from the straight-line portion to a bottom of the root at a fourth radius. Element 5: wherein the fourth radius is smaller than the first radius, the second radius, and the third radius. Element 6: wherein the first, second, and third arcuate surfaces extend from the crest to a pitch diameter line of the thread profile. Element 7: wherein the third arcuate surface is centered at the pitch diameter line. Element 8: wherein the thread profile is helical. Element 9: wherein the crest and the root comprise flat surfaces that are parallel to one another. Element 10: wherein the thread profile of the internal and external threads is provided on opposing stab flanks, and wherein the first, second, and third arcuate surfaces of each stab flank result in a minimal amount of surface area contact between the opposing stab flanks, and thereby reducing friction forces during make up.

Element 11: wherein the first radius and the third radius are each smaller than the second radius. Element 12: wherein the transition surface further comprises a fourth arcuate surface extending from the straight-line portion to a bottom of the root at a fourth radius. Element 13: wherein the fourth radius is smaller than the first radius, the second radius, and the third radius. Element 14: wherein the first, second, and third arcuate surfaces extend from the crest to the pitch diameter line. Element 15: wherein the third arcuate surface is centered at the pitch diameter line. Element 16: wherein the crest and the root comprise flat surfaces that are parallel to one another. Element 17: wherein the thread profile of the internal and external threads is provided on opposing stab flanks, and wherein the first, second, and third arcuate surfaces of each stab flank result in a minimal amount of surface area contact between the opposing stab flanks, and thereby reducing friction forces during make up.

By way of non-limiting example, exemplary combinations applicable to A and B include: Element 3 with Element 4; Element 4 with Element 5; Element 6 with Element 7; Element 12 with Element 13; and Element 14 with Element 15.