Patent Application
20080302539
1. Field of the Invention
The present invention relates to apparatus and methods for lengthening a pipe string using friction stir welding and for installing a friction stir welded pipe string in a borehole. Specifically, the present invention relates to using friction stir welding to join a pipe segment to a pipe string that is suspended from a rig by a suspending device such as a spider, a landing table, a collar load support device, or other devices known in the art for suspending a pipe string from a rig.
2. Description of the Related Art
Conventional pipe strings that are installed in a borehole generally comprise pipe segments, typically 30 to 60 feet in length, threadedly connected to form a pipe string that can extend up to 10,000 feet or more. The pipe segments of conventional pipe strings are connected using threaded connections including an internally threaded sleeve that threadedly receives a first externally threaded pipe end into its first end and a second externally threaded pipe end into its second end to connect the two pipe ends together to form a pipe string. The pipe string is lowered through a rig floor into a borehole and suspended at the rig floor using a suspending device, such as a spider. The proximal end of the pipe string is positioned above the suspending device to facilitate the connection of additional (“add-on”) pipe segments to the pipe string, after which the lengthened pipe string is lowered further through the rig floor. This process is repeated until the pipe string reaches the desired length for being installed in a borehole and cemented into place, or otherwise applied for its purpose.
Except for drive pipe and conductor casing installed near the surface of a well, welding has not been practically used for forming long pipe strings for use in drilling, production or completion activities. Conventional welding, as that term is used herein, generally refers to those welding processes that can be referred to as fusion welding, such as electric arc welding. Conventional welding is an alternative method of connecting pipe segments to form a pipe string. For example, conventionally welded connections are used to connect pipe segments into pipe strings to form pipelines that can be used for transporting liquids or gas. Pipe segments are generally distributed along the route of the pipeline, and multiple conventional electrical arc welding machines are used to join the ends of adjacent pipe segments to form a continuous pipeline.
Conventional welding of long pipe strings suitable for use in connection with drilling, completion and production activities is not practical because the pipe string, which is generally vertically suspended at the suspending device, must be formed by joining one vertical add-on pipe segment (or stand) at a time to lengthen the pipe string, lowering the lengthened pipe string through the rig floor, and then repeating the process until the pipe string reaches its desired length. This process enables the positioning of the proximal end of the pipe string above the suspending device (such as a spider) that suspends the pipe string from the rig so that an add-on pipe segment can be welded to the proximal end of the pipe string to lengthen the pipe string. Conventional welding limits the rate of fabrication of a pipe string because, compared to assembling a pipe string using threaded connections, conventional welding is a slow process that may take up to 60 minutes or more to complete the weld required at each individual pipe joint, and also because the vertical orientation of the proximal end of the pipe string, and of the add-on pipe segment to be conventionally welded to the pipe string, allows welding of only one pipe joint at a time. Since a threaded pipe connection can be made-up much faster than a non-threaded connection can be conventionally welded, these limitations make the assembly and installation of a pipe string by conventional welding uneconomical. The opportunity cost of the rig makes using conventional threaded connections the far more attractive option, notwithstanding the higher cost of the materials used to form each threaded joint.
Another problem with the use of conventional welding for forming and installing a pipe string in a borehole is the difficulty in obtaining welded pipe connections that are free of weld defects and resistant to failure. Conventionally welded connections include heat-affected zones (“HAZ's”) that may, without proper stress relieving, adversely affect the strength and reliability of the welded joint. Although conventionally welded joints may be stress relieved to eliminate detrimental HAZ's, stress relieving would only increase the total amount of time consumed in forming each pipe joint.
However, connecting pipe segments to form a pipe string by welding remains desirable because the welded connection offers advantages over a threaded connection. A welded connection is not subject to the risk of unbucking (“backing off” by inadvertent rotation), the welded connection is generally as strong as or stronger than the pipe between the connections, a welded connection is better suited to contain internal pressure without leaking, and because the exterior of a welded pipe string does not have shoulders that can hang up on borehole irregularities, such as borehole protrusions and restrictions, and slow pipe string installation. It is desirable to have the internal diameter and the external diameter of the pipe joint as close as possible to the internal diameter and the external diameter of the pipe body between the pipe joints because this configuration uses less of the borehole diameter for the pipe string, and because it allows a larger section of the borehole to be drilled out through the pipe string. Conventional connections consume a substantial amount of radial space due to the radially overlapping configuration of threaded connections. Also, for expandable pipe strings, conventional threaded connections make expansion more difficult since threaded sleeve connections offer substantially more resistance to forced radial expansion than the portions of the pipe wall between the threaded ends of the pipe. Threaded connections that offer good sealing performance in their original state do not reliably maintain the seal after being forcibly expanded or after being installed in a high-temperature service environment. By contrast, welded connections generally have mechanical properties that are very close that those of the pipe material, and welded connections generally expand uniformly with the adjacent pipe wall, either from forcible expansion or from increased temperatures. As a result, pipe strings having welded connections are easier to install in a borehole through the bore of an existing pipe string, and then more reliably expanded to nearly the same diameter as the existing pipe string to form a “monobore” or a “nearly monobore” pipe string. Wells drilled using a monobore well casing construction approach offer a substantial cost savings over the conventional pipe string multiple diameter technique because they require substantially less pipe material and require substantially smaller diameter boreholes compared to the conventional multiple diameter casing string that requires a “telescoping” structure formed by installing and connecting numerous progressively smaller casing strings as the depth of the borehole increases. Monobore casing strings may provide a substantial savings in drilling and completion costs if welded pipe strings could be economically welded and installed.
The monobore pipe strings described above are the subject of several pending and issued patents. For example, international applications WO 93/25799 (U.S. Pat. No. 5,348,095), WO 98/00626 (U.S. patent application Ser. No. 08/891,318) and WO 99/35368 (U.S. patent application Ser. No. 09/223,996), the contents of which are incorporated by reference, concern what is generally described in the industry as “expandable-tube” technology for well construction and borehole repair. Generally, expandable-tube technology enables a smaller diameter pipe string to be formed and installed in a borehole by passing it through the bore of an earlier-installed, larger diameter pipe string, and thereafter expanded to a larger diameter within the borehole. The expanded pipe string may serve as a casing string or as production tubing through which hydrocarbons are transported to the surface. Alternatively, the expandable pipe string may be expanded against the inner surface of an existing casing string to form a protective cladding for protecting the existing casing string against corrosive well fluids and from damage by tools that are lowered into the borehole for maintenance and work-over operations.
There are some reported methods of forming and installing expandable pipe strings using threaded connections, as opposed to welded connections, to form monobores. International application WO 93/25799 (U.S. Pat. No. 5,348,095) discloses the joining of expandable pipe strings having expandable threaded connections.
The advantage of using pipe strings made with threaded connections over these alternative methods is that the pipe string with threaded connections may be assembled on the rig to take any form or length desired simply by joining pipe segments or other devices on an as-needed basis. On the other hand, threaded connections may not provide a fluid-tight seal, especially after being expanded, and leaks at the joints may lead to undesirable consequences. Another drawback to using threaded connections to form and install expandable pipe strings involves the use of expansion tools to expand the pipe string within the borehole. The amount of force required to expand the threaded connection may be far more than the adjacent pipe wall is capable of handling without rupturing the pipe string. It would therefore be beneficial to achieve a method of joining pipe segments that is not hindered by threaded connections that expand differently than the adjacent portions of the pipe string. The method should be generally quick and safe to use on the rig floor, inexpensive to use, reliable, and avoid the limitations of conventional welding processes.
Many attempts have been made to adapt conventional welding to the formation of pipe strings in order to avoid the many complications and problems that come with the use of threaded connections. The difficulties presented by using conventional threaded connections for expandable pipe strings prompted some to experiment with different welding techniques for joining pipe segments to form a pipe string. Conventional welding techniques that have been considered are submerged arc welding, tungsten inert gas welding and gas metal arc welding, among others. However, safety does not generally permit conventional welding techniques requiring an open ignition source at or near the borehole where hydrocarbon gases could be ignited. For the same reasons, other newer forms of welding such as electrical resistance welding, radial friction welding, flash welding (U.S. Pat. No. 6,935,429), metallurgical bonding (U.S. Pat. No. 6,860,420), explosive welding (U.S. Pat. No. 6,953,141), amorphous bonding (U.S. Pat. No. 6,078,031), forge welding (U.S. Pat. No. 7,181,821) and laser welding (U.S. Pat. No. 7,150,328) are also generally unacceptable or impractical. These other newer forms of welding have individual drawbacks associated with each technique including, but not limited to, electrical spark generation, production of toxic fumes, visual limitations due to involved arc flash, other sources of ignition, workpiece pre-heating requirements, equipment limitations (cost, size, etc), environmental restrictions (rain, moisture, wind, humidity, etc.), lack of reliable weld quality, repeatability and speed of weld production. Therefore, these other newer forms of welding, like conventional welding techniques, are too risky to use near a borehole.
A need exists for a method and an apparatus that employs welding to connect pipe segments or stands together to form a pipe string. A need exists for a method and apparatus for forming and installing pipe strings that eliminates losses related to unbucking of threaded connections. A need exists for a method and an apparatus for joining pipe segments to pipe strings to form joints that are as strong as or stronger than the pipe adjacent to the pipe joint. A need exists for a method and an apparatus for forming pipe strings that are better suited for containing internal pressure, even after being expanded within a borehole. A need exists for a method and an apparatus for joining pipe segments to a pipe string on a rig that avoids the introduction of ignition sources near the borehole.
The present invention satisfies one or all of the above-stated needs, and others. Aspects of the present invention provide an apparatus and a method of connecting pipe segments to form a pipe string using friction stir welding. Friction stir welding is described in U.S. Pat. No. 5,460,317, which is incorporated herein by reference.
The present invention relates to a method and an apparatus for lengthening a pipe string by using friction stir welding to join add-on pipe segments to the pipe string while it is supported within a borehole using a suspending device. The suspending device used to suspend the pipe string within the borehole may be a spider, a collar load support device, landing tables, a dual elevator system with landing tables, or any combination of these or other devices known in the art for suspending a pipe string from a rig.
The apparatus for joining add-on pipe segments to a pipe string comprises a friction stir welding machine having a rotatable probe for being forcibly inserted into an abutment between the lower end of the add-on pipe segment and the proximal end of the pipe string, or into a gap between the nearly abutting and adjacent ends of a pipe segment and a pipe string where the gap is substantially smaller than the rotatable friction stir welding probe. The friction stir welding machine further comprises an assembly for movably securing the friction stir welding machine into position for applying the force necessary to cause the rotating probe to be inserted into the abutment or the gap and to stir the material of the pipe segment and the pipe string immediately adjacent to the abutment or the gap. The assembly may include an internal clamp or an external clamp, or both, for gripping and restraining the abutment or the gap between the add-on pipe segment and the pipe string in a manner to oppose movement of the pipe segment and the pipe string away from the rotating probe during probe insertion. In one embodiment, the pipe segment and the pipe string are both aligned and secured in the abutting or nearly abutting position using an internal clamp that is inserted into, and later withdrawn from, the top end of the pipe segment and positioned at the abutment or gap between the two workpieces. In an alternate embodiment, the friction stir welding machine may comprise a clamp assembly that grips the exterior of the lower end of the add-on pipe segment using a superior (upper) clamp, and that grips the exterior of the pipe string under the proximal end of the pipe string using an inferior (lower) clamp that is generally aligned with the superior clamp. In one embodiment, a clamp assembly applies a restraining force to the pipe segment and the pipe string to maintain the abutment or the gap between the pipe string and the add-on pipe segment. The clamp assembly may operate, alone or in conjunction with other devices, to resist separation of the pipe segment from the pipe string at the abutment or gap upon forcible insertion of the rotating stir probe into the abutment or gap.
In another embodiment, the clamp positions the pipe segment to maintain a gap between the lower end of the pipe segment and the upper end of the pipe string that is substantially smaller than the rotatable pin, or probe, that engages and stirs the material of the pipe segment and the pipe string to create the joint. While there may be no specific advantage to creating a gap between the two workpieces, it should be recognized that friction stir welding, like some other methods of welding, does not necessarily require abutment of the workpieces in order to join the workpieces. In one embodiment, a spacer or insert may be used to establish or maintain the desired gap.
In another embodiment, an internal clamp may be used either in place of or with external clamps to align the pipe segment with the pipe string, either to form an abutment or to form a gap substantially smaller than the diameter of the rotating friction stir welding probe. The internal clamp may be inserted into the bore of the pipe segment and positioned to straddle the abutment or the gap between the lower end of the pipe string and the proximal end of the pipe segment. The internal clamp is expandable to grip the pipe string and the pipe segment to maintain the abutment or the gap and may also be designed to resist separation of the pipe segment from the pipe string during friction stir welding. An internal clamp may also be coupled to a source of inert gas for displacing air from the vicinity of the friction stir welded joint to prevent unwanted oxidation of the material that is heated by the friction stir welding process.
In another embodiment, an internal alignment device may be used to provide reinforcement to the wall of the pipe segment and the pipe string to resist deformation under the large forces applied by the friction stir welding probe as it is forcibly inserted into the abutment or the gap, and as it is forced into the abutment or the gap to join the pipe segment to the pipe string. The internal alignment device may also be coupled to a source of inert gas for displacing air from the vicinity of the friction stir welded joint to prevent oxidation of heated material. The internal alignment device may be especially useful in joining pipe segments and pipe strings having a thin pipe wall that might otherwise deform under the load applied by the friction stir welding machine.
In another embodiment of the method of the present invention, the lower end of the pipe segment and the proximal end of the pipe string may be formed for mating engagement to resist radial movement of one relative to the other during friction stir welding. For example, the weld bevels on the lower end of the pipe segment may be tapered to form the radially exterior surface of a truncated conical frustum, and the weld bevels on the proximal end of the pipe string may be reverse tapered to form the radially interior surface of a truncated conical frustum so that the lower end of the pipe segment may be received into the proximal end of the pipe string to form an interface that is not purely horizontal relative to the axis of the workpieces. This type of mating interface is generally self-aligning; that is, the interface tends to secure the pipe segment and the pipe string in the aligned condition.
The friction stir welding apparatus of the present invention may further comprise an orbital movement assembly that imparts controlled orbital movement of the rotatable probe about the abutment or the gap to provide a fully circumferential friction stir weld. The orbital movement assembly may be hydraulically, pneumatically or electrically-powered, or any combination thereof, to forcibly move the friction stir welding machine, including the rotatable stir probe, about the abutment or the gap. Similarly, the clamp assembly described above may be hydraulically, pneumatically or electrically-powered, or any combination thereof, to grip the lower end of the add-on pipe segment with the superior clamp and the proximal end of the pipe string with the inferior clamp. The friction stir welding machine may be hydraulically, pneumatically or electrically-powered, or any combination thereof, to rotate the stir probe within the abutment or the gap while the orbital movement assembly imparts orbital movement to move the rotating stir probe through the seam to friction stir weld the add-on pipe segment to the pipe string. In one embodiment, the orbital movement assembly cooperates with an external clamp assembly, and the superior clamp and the inferior clamp assist in supporting the friction stir welding machine and in securing the orbital movement assembly in position to forcibly impart the orbital movement to the friction stir welding machine.
In one embodiment of the method of the present invention, the pipe string lengthened using the method of the present invention is expanded after being installed in the borehole. There are several methods for expanding a pipe member after it is installed within a borehole. In one embodiment, the present invention provides an expansion mandrel for forcibly expanding the pipe string as the mandrel is axially forced to move through the bore of the lengthened pipe string. This method is described in U.S. Pat. No. 5,348,095, which is incorporated by reference herein. In another embodiment of the method of the present invention, the pipe string is expanded within the borehole using a rotary expansion device such as that described in U.S. Pat. No. 6,935,430. An expandable pipe string formed using the method and apparatus of the present invention may be expanded within the borehole while maintaining a fluid-tight seal at the expanded friction stir welded joints formed between adjacent pipe segments.
The joining of adjacent pipe segments utilizes a stir probe formed of a material that may be substantially harder than the material of the pipe segment and pipe string being joined, and by rotating and forcibly inserting the probe into an abutment between the pipe segment and the pipe string, or into a gap between the adjacent ends of the pipe segment and the pipe string, to plasticize and stir at least a portion of the material at the adjacent ends of each of the pipe segment and the pipe string to join the pipe segment and the pipe string into a lengthened pipe string. The stir probe used to make the friction stir weld between the pipe segment and the pipe string may be a tungsten-rhenium alloy, a polycrystalline cubic boron nitride, or some other material that is suitable for forcibly engaging and stirring steel, steel alloys and other metals that can be used to form pipes.
In a preferred embodiment, the friction stir welding machine cooperates with a clamp assembly to operatively secure the friction stir welding machine into position to be moved in an orbital path about the abutment or the gap between the lower end of the pipe segment and the proximal end of the pipe string. In one embodiment, the friction stir welding machine and the clamp assembly may together be disposed within a frame that can be controllably supported and moved on the rig floor, such as within a groove or on a track, toward well center to engage the pipe segment and the pipe string for joining them together, and later controllably moved away from well center to remove the friction stir welding machine and the clamp assembly, and to clear the rig floor for other activity. The frame may be adapted for automated repetitive movement to and from well center, and it may be remotely controlled.
In one embodiment, the friction stir welding machine may be disposed within the bore of the pipe segment and positioned at the abutment or the gap between the pipe segment and the pipe string to join the lower end of the pipe segment to the proximal end of the pipe string from the inside. This embodiment is more applicable to larger diameter pipe, and can be used with either internal clamps, external clamps, or a combination thereof, for gripping the pipe segment and the pipe string, and for maintaining the abutment or the gap between the pipe segment and the pipe string during the friction stir welding process.
The method of the present invention uses the friction stir welding process to provide a pipe string comprising a plurality of joined pipe segments, the pipe string having a generally uniform wall thickness at the welded connections that is substantially the same thickness as the adjacent pipe wall, and highly reliable for expansion, along with the non-welded portions of the pipe string, to form an expanded pipe string having a larger diameter.
In one embodiment of the present invention, the method for forming and installing a pipe string in a borehole using friction stir welding includes the step of joining a pipe segment to a pipe string by simultaneously using two or more friction stir welding probes distributed about the abutting seam or the gap formed between the lower end of the pipe segment and the proximal end of the pipe string. This method includes the step of distributing the rotatable friction stir welding probes about the abutting seam or the gap, and simultaneously engaging and welding the abutment or the gap using two or more rotating friction stir welding probes. In one embodiment, the distributed friction stir welding probes are distributed so as to generally balance the insertion forces imparted to the abutting or nearly abutting pipe segment and pipe string by the forcible insertion of the rotating probes to mechanically stir the material of the pipe segment and the pipe string adjacent to the abutting seam or the gap. Similarly, the corresponding apparatus of the present invention comprises two or more rotatable stir probes, each coupled to a press for forcibly disposing the probe into the abutting seam or gap between the pipe segment and the pipe string, and for controlled orbital rotation about the abutment or gap to join the pipe segment to the pipe string. The probes may be disposed and moved about the abutting seam or gap while generally opposed one to the other to offset the forces or, alternately, the probes may be staggered so that a first probe preconditions the workpieces at or near the abutment or gap to facilitate improved joining of the workpieces using the second, or trailing, probe.
The number of friction stir welding probes that can be simultaneously engaged with the workpieces may depend on the size of the pipe and size of the friction stir welding machines, the diameter of the weld being made and the desired proximity of the rotating friction stir welding probes one to the others. It should be noted, however, that two or more friction stir welding probes may require a substantially increased amount of force to controllably move the rotating probes through the abutting seam or gap to join the workpieces.
It will be understood by those skilled in the art that the methods and apparatus of the present invention are compatible with the use of fill-up and circulation tools for intermittently introducing fluid into the bore of the lengthened pipe string to generally maintain a hydrostatic balance between the bore of the lengthened pipe string and the annulus between the pipe string and the wall of the borehole over the length of the pipe string. It will also be understood by those skilled in the art that the present invention may be used and implemented on a conventional rig having a drawworks for supporting a block, and a string elevator supported from the block, a top drive, or any other rig having a vertically reciprocatable support for positioning a pipe segment or for suspending and lowering a pipe string into a borehole.
The use of friction stir welding with the present invention to join pipe segments to a pipe string offers many advantages that cannot be achieved by using conventional welding. Friction stir welding eliminates many safety hazards associated with conventional welding such as open ignition sources, toxic fumes, weld spatter, transportation of and connections to bottled or tanked industrial gasses, and visual sensitivity of humans to the arcs produced during conventional welding. Also, unlike with conventional welding, the entire length of the pipe string does not become a part of an electrical circuit with friction stir welding. Other costly and time-consuming activities associated with conventional welding are also eliminated, such as beveling of surfaces to be welded, weldor training and skills certifications, preheating of workpieces to a minimum temperature, and post-weld cooling of workpieces to a maximum temperature prior to loading.
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. However, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
The motor 47 shown in
When closed, the superior clamp 42a and inferior clamp 42b prevent separation of the friction stir welding machine 40 from the abutment 24 or gap as the probe 48 is powered by the extending gear and rack assembly to penetrate the abutment 24 or gap and powered by the motor 47 to rotate and stir the material of the pipe segment and the pipe string. The powered rotation of the superior drive gear 46a and the inferior drive gear 46b against the superior external gear 43a and the inferior external gear 43b disposed on the external surfaces of the superior clamp 42a and the inferior clamp 42b, respectively, may be provided by one or more auxiliary motors that may be driven using the same high pressure hydraulic fluid supply provided to operate the motor to drive the probe. Alternately, the powered rotation of the superior drive gear 46a and the inferior drive gear 46b against the superior external gear 43a and inferior external gear 43b, respectively, disposed on the external surfaces of the superior clamp 42a and the inferior clamp 42b may be provided by a gear train driven by the motor 47. The power needed to forcibly close the superior clamp 42a and the inferior clamp 42b and to thereby forcibly grip the pipe segment 22 and the pipe string 20, respectively, may be provided from the same high pressure hydraulic fluid supply provided to drive the motor 47 to rotate the probe 48.
It should be understood that the closure of superior clamp and the inferior clamp to grip the pipe segment and pipe string, the rotation of the probe, and the rotation of the drive gears may be mechanically enabled using a variety of power sources, including hydraulic pressure, pneumatic pressure, electricity, mechanical linkages, etc. It is preferred that these devices be hydraulically-powered in order to eliminate spark-ignition sources from the near-borehole area and also due to the need to deliver generally high-density power to the friction stir welding machine. While pneumatically-powered devices generally avoid or minimize the potential for unwanted ignition sources, the motor and the cylinders would need to be substantially larger to use compressed air as the power fluid to generate the same clamping force, gear torque, motor torque and speed, etc. However, it should be recognized that modern intrinsically-safe or explosion-proof electrical devices may be adapted for powering the various devices of the apparatus of the present invention without introducing an ignition risk.
In another aspect, the friction stir welding machine 40 may include a supply tube or hose within the power bundle 57 that supplies a stream of an inert gas to supplant or dilute the air in the immediate region of the FSW weld probe to decrease the possibility of oxide forming on the weld as a result of the high temperatures from friction between the probe and the workpieces. Impurities, such as oxide formed during the FSW process, are undesirable because they weaken the bond between the joined pipe members. In one embodiment, the inert gas stream may be delivered to the near-weld region through one or more ports formed in the friction stir welding machine 40 adjacent to the stir probe 48.
After additional add-on pipe segments have been welded to the pipe string and the desired length of the pipe string has been achieved, the pipe string may be lowered into the borehole and then radially expanded using an expander tool. Examples of expander tools include cone-shaped mandrels such as that shown in
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
