Swivel for subsea string

An improved swivel with increased sealing capability at fluid pressures up to 20 ksi and at fluid temperatures as high as 250° F. and as low as 35° F. The swivel may be relatively compact, being less than 8 feet in overall length and can operate unpressurized with axial loads of at high as 1,400,000 lbs. The swivel may comprise a swivel mandrel rotationally coupled with a swivel housing. Rotational bearings units can be securely held using cartridge carriers. A pressure seal may be formed between the swivel mandrel and swivel housing via a redundant seal stack.

BACKGROUND

In subsea operations, hydrocarbon fluids such as oil and natural gas are obtained from a subterranean geologic formation, referred to as a reservoir, by drilling a well that penetrates the hydrocarbon-bearing geologic formation. In various subsea applications, swivels are deployed along subsea landing strings to enable rotational motion of one system or component with respect to another. A swivel having components which rotate with respect to each other and provide a dynamic pressure seal often can be referred to as a dynamic swivel. The dynamic seal can be formed using O-rings or mechanical spring energized (MSE) seals. Such seals are able to hold axial and radial pressures. However, operating a swivel at relatively high pressures and under high axial loads can be challenging. Also, conventional bearing retention methods such as retaining rings/snap rings can be insufficient with respect to holding against axial, rotational, and bending forces. Known arrangements of components can also result in a dynamic swivel having substantial axial length. Furthermore, operating at high and low temperatures can also provide challenges for swivels, since the sealing mechanisms can be damaged and prone to leakage.

SUMMARY

According to some embodiments, a swivel is described that is configured for mounting along a tool string being deployed in an offshore environment. The swivel includes: a swivel mandrel having a first mechanical connector and a central bore through which pressurized well fluids are configured to pass; a swivel housing partially surrounding the swivel mandrel and including a second mechanical connector; first and second rotation bearing units together allowing for relative rotation about the central longitudinal axis, between the swivel mandrel and the swivel housing, thereby providing for relative rotation between one or more structures mounted to the first connector and one or more structures mounted to the second connector; first and second rotation bearing carriers configured to secure and retain the first and second rotation bearing units, respectively; a thrust bearing unit configured to allow for relative rotation between the swivel mandrel, the thrust bearing primarily supporting axial loads between the mandrel and housing in directions parallel to the longitudinal axis; and a rotating and pressure containing dynamic sealing system, the sealing system configured to contain pressurized well fluids flowing through the central bore.

According to some embodiments, the test string can include a subsea landing string configured for deployment through a subsea riser structure. The swivel can be configured to be vertically mounted with the first connection being made to the flowhead above the swivel, and the second connection being made to a master valve below the swivel. The first and second rotation bearing units can each include a plurality of cylindrical rolling bearing elements.

According to some embodiments, the improved design allows for a swivel being compact, with an overall length of less than 8 feet. The swivel can operate with the axial loads up to at least 1,200,000 pounds while the central bore is not pressurized. The dynamic sealing system can be configured to contain pressurized well fluids up to pressures of at least 18,000 psi.

According to some embodiments, each of the first and second bearing carriers have inner surfaces that are configured to securely engage the outer surfaces of the first and second rotation bearing units, respectively, and each of the carriers are mounted in a fixed relationship with respect to the swivel housing. Each of the first and second rotation bearing units can also have inner surfaces configured to engage outer surfaces on the swivel spindle.

According to some embodiments, the dynamic sealing system comprises a primary seal and a secondary seal. Each of the primary and secondary seals can include a plurality of elastomeric sealing elements having chevron-shaped cross-sections. The dynamic sealing system can be configured to contain well fluids as low as 35° F. and as high as 250° F.

As used herein, the term dynamic swivel is a swivel that includes one or more dynamic seals.

According to some embodiments, a swivel is described that is configured for mounting along a tool string being deployed in an offshore environment. The swivel includes: a swivel mandrel including a first mechanical connector and a central longitudinal bore through which pressurized well fluids are configured to pass; a swivel housing partially surrounding the swivel mandrel and including a second mechanical connector; first and second rotation bearing units together allowing for relative rotation about a central longitudinal axis, between the swivel mandrel and the swivel housing, thereby providing for relative rotation between one or more structures mounted to the first connector and one or more structures mounted to the second connector; a thrust bearing unit configured to allow for relative rotation between the swivel mandrel, the thrust bearing primarily supporting axial loads between the mandrel and housing in directions parallel to the longitudinal axis; and a rotating and pressure containing dynamic sealing system. The sealing system being configured to contain pressurized well fluids flowing through the central bore, the sealing system comprising a primary seal and a secondary seal, each of the primary seal and the secondary seal having a plurality of elastomeric sealing elements having chevron-shaped cross-sections.

DETAILED DESCRIPTION

According to some embodiments, systems and methodologies are described for a compact dynamic swivel able to operate at high pressures and loading as well as at extreme temperatures. The compact swivel may comprise a swivel mandrel rotationally coupled with a swivel housing. A dynamic pressure seal may be formed between the swivel mandrel and swivel housing. Additionally, the rotational motion of the swivel mandrel relative to the swivel housing about the main longitudinal axis of the swivel is accommodated by rotational bearings, e.g. cylindrical roller bearings. Further, thrust loads between components are countered by a thrust bearing. According to some embodiments, a compact swivel is described that incorporates bearing structures which enable placement of the rotational bearings and the thrust bearing in close proximity to each other. The bearing arrangement enables construction of an axially compact swivel mandrel.

According to some embodiments, the swivel includes an improved rotational bearing configuration. The swivel incorporates rotational bearings, e.g. an upper rotational bearing unit and a lower rotational bearing unit. The bearing units are positioned in self-contained bearing cartridges that provide improved structural integrity to protect the bearings against axial, rotational, and bending forces. The cartridge design also allows for easy assembly of the various mechanical components while maintaining compact axial length as well as tolerance to high pressures and loads.

According to some embodiments, an improved swivel is described that includes high-level sealing capability even during rotational cycling at high temperatures, e.g. 250° F. and above, and low temperatures, e.g. 35° F. and below. A dynamic pressure seal may be formed between the swivel mandrel and swivel housing via a redundant seal stack. The redundant seal stack comprises redundant seals having a chevron-shaped cross section that are arranged to provide and maintain sealing even during rotational cycling at high and low temperatures.

FIG.1is a schematic diagram illustrating a subsea landing string configuration in which an improved swivel can be utilized, according to some embodiments. System100is shown being deployed in an offshore environment. The system100includes a flowhead120that supports the test string130, and provides a means of surface well control when completing, testing, and/or performing live well intervention operations. The flow head120is being deployed above rig floor110from an offshore oilfield rig such as semisubmersible vessel. According to some embodiments, the offshore rig can be some other type of mobile offshore drilling unit such as a jackup or submersible, other suitable vessel, platform or structure. According to some embodiments, the test string130is deployed from a platform or vessel that is not configured for drilling, such as from a floating production storage and offloading (FPSO) vessel. A riser112is shown extending from the rig, through the sea surface102, sea water104and the sea bottom surface106. At the sea bottom106a number of known well control devices are shown such as shear rams116and pipe rams118. Also shown above the rams is riser disconnect114.

Below flowhead120is an improved swivel150, according to some embodiments. The improved swivel150may be used in a variety of subsea landing strings to enable relative rotational movement of systems located downhole and uphole of the improved swivel. In particular, swivel150allows rotation of the string130without rotating the flowhead120, as illustrated by arrow152. Swivel150also prevents any rig movement from transferring torque into the structure of riser112or landing string130. Below swivel150is master valve126. Below master valve126, through the rig floor110and within riser112is test string130. Test string130can include lubricator valve132. Near the sea floor106is subsea test tree136and fluted hanger138. String140is shown deployed in the subsea well penetrating subterranean rock formation108. Not shown is one or more tools being deployed at the bottom of, or along, string140. The tools would be configured according to the intended purpose of the operation.

According to some embodiments, flowhead120includes several valves which are shown in greater detail inFIG.2. Handling sub128is shown attached to the top of the flowhead valve block120. Handling sub128is used to tension the flowhead120and the riser landing string130. According to some embodiments, handling sub128can also be configured to provide an interface to the surface wireline or coiled tubing equipment.

FIG.2is a schematic diagram illustrating further detail of a subsea landing string configuration in which an improved swivel can be utilized, according to some embodiments. Flowhead120is shown to include three separate valves: swab valve220, and wing valves222and224. According to some embodiments, swab valve220and master valve126can be configured as either manually or hydraulically operated. Wing valve222can be configured as a manual or hydraulic-operated fail-safe actuator for kill line122. Wing valve124can be configured as a hydraulic-operated fail-safe actuator for flow line124. The wing valves222and224in flowhead120thus connect to the kill line122and flow line124, respectively, for control of the flow of the wellbore fluids. According to some embodiments, valve actuators can be controlled from a console (not shown) located on the rig floor and can be linked to the emergency shutdown system for the flow wing valve224. This configuration allows for remote shut-in of the well at the flowhead120.

FIG.3is a schematic cross-sectional illustration of an example of an improved swivel, according to some embodiments. The improved swivel150is axially compact by stacking bearings in close proximity to each other. According to some embodiments, the overall length L of swivel150is less than nine feet (2.74 m). According to some embodiments, the overall length L of swivel150is less than eight feet (2.44 m). According to some embodiments, the overall length L of swivel150is less than 7.5 feet (2.29 m). The swivel provides structures for retaining the bearing units so as to hold and protect the bearings against axial, rotational, and bending forces. According to some embodiments, the structures may be in the form of an upper bearing cartridge340and a lower bearing cartridge342for holding upper rotational bearing unit330and lower rotational bearing unit332, which may include cylindrical roller bearings. The rotational bearing units330and332facilitate relative rotational motion about the central longitudinal axis304between the mandrel310and the housing320. The upper and lower bearing cartridges340and342are used instead of conventional retaining rings/snap rings to provide the desired protection of the bearings against axial, rotational, and bending forces experienced by the swivel. For example, a plurality of rotational bearings and a thrust bearing may be positioned in bearing support structures in a manner which places such bearings in close proximity to each other, thus shortening the axial length of the swivel. According to some embodiments, the improved design allows for two or more of the following criteria to be simultaneously met: compact overall length, high operating pressures, high operating load, and large operational temperature range. According to some embodiments, a swivel is provided that can operate at working pressures above 15,000 psi (15 ksi). According to some embodiments, the swivel can operate at working pressures up to 16 ksi or 18 ksi. According to some embodiments the swivel can operate at working pressures up to 20 ksi. According to some embodiments, the swivel has an axial tensile load rating of at least 1,000,000 lbf @ 0 psi. According to some embodiments, the swivel has an axial tensile load rating of at least 1,200,000 lbf @ psi. According to some embodiments, the swivel has an axial tensile load rating of at least 1,400,000 lbf @ 0 psi. According to some embodiments, the swivel has an axial tensile load rating of at least 650,000 lbf @ 18 ksi. According to some embodiments, the swivel has an axial tensile load rating of at least 750,000 lbf @ 20 ksi. According to some embodiments, the swivel is rated for a bending moment of at least 400,000 ft-lbf @ 300 psi and 938,000 lbs. tension. According to some embodiments, the swivel is rated for a bending moment of at least 500,000 ft-lbf @ 300 psi and 938,000 lbs. tension. According to some embodiments, the swivel has a temperature rating of 40° F. to at least 200° F. According to some embodiments, the swivel has a temperature rating of at least 35° F. to 250° F. Furthermore, the improved design has advantages in ease of manufacturing. In particular, various elements and parts of the swivel are configured for straight forward assembly.

Referring toFIG.3, the swivel150comprises a swivel mandrel310rotationally coupled with a swivel housing320. Although the swivel is shown horizontally oriented inFIG.3, swivel150is ordinarily mounted vertically, as shown inFIGS.1and2, such that the mandrel310is above swivel housing320. Swivel150includes a central bore300which in this example is nominally 5⅛ inches (actual inner diameter of bore300is 5.135 inches). The swivel150can be made having other dimensions of central bore diameter, outer diameter and overall length L. The outer diameter of the housing320is 30 inches. At the upper end of mandrel310is flange312, which is used for an upper connection (e.g. to the flowhead120shown inFIGS.1and2). The lower end of housing320is flange322which is used for a lower connection (e.g. to master valve126shown inFIGS.1and2).

The swivel150may have a variety of other components, such as rotational bearings, thrust bearings, load nuts, bearing covers, and/or other components, to facilitate reliable relative rotation between the swivel mandrel310and the swivel housing320about central axis304. In the example ofFIG.3, the relative rotational motion between mandrel310and housing320is facilitated by an upper rotational bearing330and a lower rotational bearing332, both denoted using dashed outline. The axial load (i.e. in directions parallel to axis304) of swivel150between the mandrel310and housing320is facilitated by thrust bearing334, also denoted using dashed outline. Some or all of bearings units330,332and332may include roller bearings, such as cylindrical roller bearings. The swivel150further comprises a rotating and pressure containing seal formed between the swivel mandrel310and swivel housing320via a redundant seal stack350. The redundant seal stack350comprises redundant chevron seals (shown in greater detail inFIG.5) arranged to provide and maintain sealing even during rotational cycling at high and low temperatures.

Note that both the upper bearing cartridge340and a lower bearing cartridge342are fixed to the housing320and thus rotate along with housing320. The inner surfaces of rotational bearing units330and332are seated with the outer surface of mandrel310, and the outer surfaces of rotational bearing units330and332are seated on the inner surfaces of cartridges340and342respectively. The upper rotational bearing unit330is prevented from moving longitudinally. In particular, upper bearing cartridge340and anti-backout retaining ring348are used for the outer side of bearing unit330. The retaining ring348is held in place with cap screws346. The inner side of upper bearing unit330is held in place by mandrel310and retaining ring341. The outer side of lower bearing unit332is held longitudinally by cartridge342and retaining ring343. The inner side of bearing unit332is held in place longitudinally by retaining rings346and348.

Load nut302is fixed to mandrel310, for example, by a threaded connection. The thrust bearing unit334thus is sandwiched between the lower surface of cartridge340(that is fixed to housing320) and the upper surface of load nut302(that is fixed to mandrel310). A rotational bore seal is also positioned between the swivel mandrel and the swivel housing. The rotational bore seal stack350provides the pressure containing dynamic seal which is able to maintain functionality during rotational cycling at high and low temperatures.

According to some embodiments, the swivel mandrel310and swivel housing320may initially be held together by, for example, bolts inserted into holes306and then released to enable the relative rotation with respect to each other. According to some embodiments, one or more of bearing units330,332and334can be engineered cartridge-type bearing units, such as manufactured by Timken Company.

FIGS.4A and4Bare exploded perspective view diagrams illustrating further detail of some of the upper and lower rotational bearing components, respectively, according to some embodiments. As described, supra, the rotational bearings may be in the form of upper cylindrical rotational bearing unit330and lower cylindrical rotational bearing unit332. The upper bearing unit330is protected against axial, rotational, and bending forces by an upper bearing cartridge340, as further illustrated inFIG.4A. The upper bearing unit330is secured on its outer side by upper bearing cartridge340(including ridge member440) and anti-backout ring348. According to some embodiments, the anti-backout ring348is held in place with a plurality of screws, e.g. four cap screws346.

Referring toFIG.4B, the outer side of lower bearing unit332is secured on its outer side by the inner surface of cartridge342(including ridge member420) and retaining ring343(shown inFIG.3). According to some embodiments, a lower bearing cartridge may be secured to the housing320via a number of threaded fasteners (not shown) positioned through a plurality of openings410. According to an example, 16 fasteners (or other suitable number of fasteners) may be positioned to extend axially through the lower bearing cartridge342so as to secure the lower bearing cartridge in place and to support the lower rotational bearing unit332. It should be noted the upper bearing cartridge340and the lower bearing cartridge342can enable an improved swivel150to be more reliable than conventional swivels. The bearing cartridges340and342allow the swivel150to hold more axial load than conventional swivels, and the bearing cartridges can be scaled to various types and sizes of swivels.

FIG.5is a cross section view illustrating further detail of dynamic sealing mechanisms using in an improved swivel, according to some embodiments. Visible is a detailed view of a cross section of the redundant seal stack350. As can be seen, the stack350is made up of a primary seal500and the secondary seal502. In the view shown inFIG.5, downhole is to the right side (as inFIG.3). The primary and secondary seals500and502, as well as the other elements longitudinally aligned with those seals are mounted fixed to the outer portion (upper inFIG.5) of mandrel310. Therefore, the relative motion and the dynamic sealing will be formed between the outer portion (upper inFIG.5) of the seals500and502and the inner surface (lower inFIG.5) of housing320. According to some embodiments, rotating and pressure containing seals500and502may each comprise a dual, unidirectional chevron stack separated by a spacer ring, e.g. a plastic spacer ring. In particular, the primary seal500includes two elastomeric sealing elements510and512having chevron-shaped cross sections separated by a plastic spacer ring522. Seal500also includes further plastic spacers below (520) and above524and526of the sealing elements510and512. Similarly, the secondary seal502includes two elastomeric sealing elements514and516having chevron-shaped cross sections separated by a plastic spacer ring532. Seal502also includes further plastic spacers below (530) and above534and536of the sealing elements514and516. This a dual chevron stack provides a primary and a secondary rotational and pressure containing seal for the swivel. According to some embodiments, additional retainers, spacers, and/or retention mechanisms may be used to secure the pressure containing and rotating seals500and502at a desired location between the swivel mandrel and the swivel housing. Note that in the illustrated example, the chevron seals510,512,514and516of both the primary seal500and the secondary seal502are unidirectional, although various arrangements and orientations of chevron seals may be used to accommodate parameters of a given operation.

The pressure containing and rotating seal stack350provides reliable pressure containment during relative rotation of the swivel components and may be used in, for example, an in-riser subsea landing string. The pressure containing and rotating seal350enables simple, dependable operation and also may be used to retrofit existing swivels. In other words, the pressure containing and rotating seal350may be sized and configured to fit within existing seal cavities. In some embodiments, the seal cavity may be modified to accommodate the pressure containing and rotating seal with increased length or size. For example, the seal cavity length of the swivel mandrel could be modified to accommodate the desired pressure containing and rotating seal. The construction of the pressure containing and rotating seal350also enables use of the swivel in subsea 20K (20,000 psi) system applications.