Patent Application
20170159377
none
Not Applicable
1. Field of the Invention
The present invention generally relates to offshore oil and gas production. More particularly, it relates to steel catenary risers and their connection to floating vessels.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98.
A Steel Catenary Riser (SCR) is a steel pipe hung in a catenary configuration from a floating vessel in deep water that is used to transmit fluids such as oil, gas, injection water, etc. to or from pipelines or wellheads on the seafloor. The steel pipe of the SCR forms a catenary between its hang-off point on the floating or rigid platform, and the seabed.
A Floating Production System (FPS) typically consists of a floating unit such as a semi-submersible, FPSO or TLP which may be equipped with drilling and/or production equipment. It may be anchored in place with wire rope and chain, or can be dynamically positioned using rotating thrusters. Production from subsea wells is transported to equipment on the surface deck through production risers designed to accommodate platform motion. An FPS can be used in ultra-deep water.
A semi-submersible is a floating unit, with its deck supported by columns to enable the unit to become almost transparent to waves and provide favorable motion behavior. The unit stays on location using dynamic positioning and/or is anchored by means of catenary mooring lines terminating in piles or anchors in the seafloor.
A DeepDraftSemi® (SBM Offshore, 1255 Enclave Parkway, Houston Tex. 77077) is a semi-submersible unit fitted with oil and gas production facilities in ultra-deep water conditions. The unit is designed to optimize vessel motions to accommodate SCRs.
Floating Production Storage and Offloading system (FPSO) is a floating facility installed above or close to an offshore oil and/or gas field to receive, process, store and export hydrocarbons. It consists of a floater—typically, either new builds or converted tankers, permanently moored on site. The cargo capacity of the vessel is used as buffer storage for the oil produced. The process facilities (topsides) and accommodation are installed on the floater. The mooring configuration may be of the spread mooring type or a single point mooring system, generally a turret.
The high pressure mixture of produced fluids is delivered to the process facilities mounted on the deck of the tanker, where the oil, gas and water are separated. The water is discharged overboard after treatment to eliminate hydrocarbons. The stabilized crude oil is stored in the cargo tanks and subsequently transferred into shuttle tankers either via a buoy or by laying side by side or in tandem to the FPSO. The gas is used for enhancing the liquid production through gas lift, and for energy production onboard the vessel. The remainder is compressed and transported by pipeline to shore or reinjected into the reservoir.
In the case of a spread-moored FPSO/FSO, the tanker or process barge is moored in a fixed heading with anchor lines distributed over the bow and stern of the vessel to anchor points situated on the seabed. The heading is determined by the prevailing sea and weather conditions. The spread-moored FPSO/FSO can only be used in locations where currents, waves and winds are very moderate or normally come from a prevailing direction. With this type of FPSO/FSO, no turret or swivel stack is required, as the vessel does not change heading in relation to the risers connecting the tanker with the wells on the seabed. To offload crude from a spread moored FPSO/FSO, a separate tanker loading facility should be provided as the shuttle tanker cannot safely moor in tandem to the FPSO/FSO due to changing current, wind and wave direction, possible interference with the FPSO/FSO anchor lines, and high risk of collision. Deepwater CALM buoys have been designed as offloading facilities for deepwater spread moored FPSOs
In a turret mooring system, the turret system is integrated into or attached to the hull of the tanker, in most cases near the bow, and allows the tanker to weathervane around it and thereby take up the line of least resistance to the combined forces of wind, waves and current. A high-pressure oil and gas swivel stack is mounted onto the mooring system. This swivel stack is the connection between the risers from the subsea flowlines on the seabed to the piping onboard the vessel. It allows the flow of oil, gas and water onto the unit to continue without interruption while the FPSO weathervanes.
For reasons of size and cost, the number of swivels is kept to a minimum, and therefore the flow of oil and gas has to be manifolded in the turret area, particularly when the system produces from a large number of wells.
The turret mooring and high pressure swivel stack are thus the essential components of an FPSO.
Various flexible hang-off arrangements for catenary risers are disclosed in U.S. Pat. Nos. 8,550,171 and 8,689,882 the contents of which are hereby incorporated by reference in their entirety.
A tapered stress joint (TSJ) is a specialized riser joint with a tapered cross section used to distribute bending loads over a controlled length so that the bending stresses are acceptable. Typical locations of TSJs on dry tree production riser systems are at wellhead connection, above and below the keel joint in deep draft vessels. A tapered stress joint configuration for a subsea riser is described in U.S. Pat. No. 6,659,690.
A Remote Operated Vehicle (ROV) is a tethered underwater robot which has been designed to perform unmanned installation tasks or inspection in deep-water environments. They are linked to the installation vessel by an umbilical cable. Electrical power, video and data signals are transferred via the umbilical between the operator and the vehicle. High-power applications will often use hydraulics in addition to electrical cabling. Most ROVs are equipped with at least a video camera and lights. Additional equipment is commonly added to expand the vehicle's capabilities.
A removable riser hang-off connector equipped with a flexible element that, in one embodiment, comprises rubber-encapsulated steel plates, is designed for attachment to a hang-off collar on a steel catenary riser below the tapered stress joint or flex joint. Connection of the removable riser hang-off connector may be made by an ROV.
With the removable riser hang-off connector attached, the tapered stress joint and/or flex joint may be raised out of the water (for inspection, maintenance, repair or replacement) by lifting the upper end of the SCR out of the SCR porch receptacle with a chain jack (or other lifting device) and inserting the removable riser hang-off connector into the porch receptacle. This temporarily supports the SCR in an elevated state with the tapered stress joint or flex joint above the surface of the water.
In an alternative embodiment, the temporary riser hang-off connector may be configured as an adaptor designed for installation directly in the basket receptacle. In such an embodiment, the SCR (equipped with an auxiliary hang-off collar) may be raised out of the hang-off porch receptacle, the adaptor inserted into the porch receptacle (by an ROV or diver), and then the SCR may be re-inserted into the porch receptacle at the elevation of the hang-off collar. In this way, the SCR may be temporarily supported in the basket receptacle with its tapered stress joint and/or flex joint above the surface of the water.
This invention concerns a subsea apparatus (connector) for in-situ inspection and/or replacement of flexible and tapered stress joints (TSJ) used in steel catenary riser (SCR) hang-off systems. Recent exploration and production (E&P) in deepwater regions have raised the bar for production temperatures and pressure to upwards of 250° F. and 15,000 psi, respectively. These developments have introduced new challenges for SCR design, fabrication and operations.
Riser hang-off system selection is essential for ensuring safe and reliable production. Therefore, full-scale testing of the flex joints and stress joints for the hang-off system are now standard operating procedure. However, once offshore, there is an increasing need to inspect and replace the hang-off joints—specifically, elastomeric elements at the hang-off location(s). It is now a necessary requirement of production operators to periodically evaluate the integrity of the connection and to inspect and eliminate fatigue damage and/or seal leakage.
In the past, offshore intervention to remove and replace flex and stress joints was carried out using heavy-lift vessels (HLV) and diving operations. The connector of the present invention eliminates the requirements for diving and HLV assistance. The connector in one particular embodiment shown and described herein comprises a forged steel clamping and locking mechanism featuring a hinged connection on one side, and a locking pin on the opposite side. An elastomeric rubber housing is embedded in the connector to provide controlled compliance in all six degrees of freedom with respect to the SCR. An ROV-friendly locking pin and handles are also featured as part of the subsea diver-less installation. In certain other embodiments, the connector is an adaptor placed directly into the riser basket. The SCR pipe welded to the flex joint or stress joint, may be furnished with an integral hang-off collar and radial stoppers (upper and lower) during onshore pipe fabrication to allow for riser load transfer. The hang-off point may be furnished with a tapered joint to ensure appropriate stress distribution during flex joint and stress joints inspection and replacement.
The advantages and benefits of a method and apparatus according to the invention over the systems of the prior art include:
The invention may best be understood by reference to the exemplary embodiments shown in the drawing figures wherein the following figure elements are used:
Referring now to
In certain embodiments, hinged body 12 may be provided with one or more weight-saving recesses 16 in outer surface 14.
Riser hang-off connector 10 may be secured in the closed position by locking pin 26 which may be configured to slide in locking pin sleeve 28 on upper surface 20. Limit machine screw 30 may be provided in a threaded bore in the side of locking pin 26. Limit machine screw 30 may be configured such that it contacts the upper end of locking pin sleeve 28 when locking pin 26 is in the fully engaged position. Locking pin latch 32 on the side of locking pin sleeve 28 may be configured to secure locking pin 26 in either the locked (inserted) or unlocked (withdrawn) positions. Limit machine screw 30 may also serve as a handle for raising and lowering locking pin 26 with the manipulator arm of an underwater Remotely Operated Vehicle (ROV).
In
Annular hang-off collar 38 may, in certain embodiments, be an integral part of SCR 18. In other embodiments, hang-off collar 38 may be welded or otherwise attached to the outer surface of SCR 18. Hang-off collar 38 is the load-bearing element which supports SCR 18 in riser hang-off connector 10 when riser hang-off connector is seated in the basket receptacle of a riser porch.
Landing stopper 40 and upper stopper 42 are annular flanges attached to or integral with the outer surface of SCR 18. They may be sized and configured to properly align riser hang-off connector 10 so that it may be closed around and properly engage hang-off collar 38.
In the exploded view of
In the side view of
In the cross-sectional view of
Also visible in
As shown in
A tolerance gap 56 may be provided between the lower end of hinged body 12 and landing stopper 42 to ensure that landing stopper 40 does not interfere with fully closing hinged body 12 around SCR 18.
As shown in
Additional details of an exemplary collar adapter 100 are shown in
When using collar adapter 100, landing stopper 40 and upper stopper 42 on SCR 18 may be omitted.
In the illustrated embodiment of
In the illustrated embodiment, the means for lifting SCR 18 into the elevated position is chain jack 220 mounted on gantry 222 which provides translational movement. Chain locker 224 may be provided to take in and let out lifting chain 84. Gantry 222 and chain locker 224 are supported by deck structure 218.
In
Following installation of hang-off connector 10 on hang-off collar 38, SCR 18 may be raised using chain jack 220 by an amount sufficient to clear bushing 76 from basket receptacle 88 on SCR porch 86. SCR 18 may then be extracted from basket receptacle 88 by translational movement of gantry 222. Lifting may then continue until TSJ 70 is sufficiently above the surface of the water to permit inspection, repair and/or replacement. The operation may be monitored to ensure clearance from adjacent risers, flowlines and the like by ROV 226. This state of the system is illustrated in
Lifting of SCR 18 may continue until riser hang-off connector 10 on hang-off collar 38 is elevated above basket receptacle 88 on SCR porch 86. SCR 18 may then be moved horizontally by translational movement of chain jack 220 on gantry 222 until SCR 18 is within the central axial opening of basket receptacle 88 at which point SCR 18 may be lowered until hang-off connector 10 is seated in basket receptacle 88 and the upper end of SCR 18 is supported by hang-off collar 38. This state is illustrated in
As will be appreciated by those skilled in the art, in the state illustrated in
Following inspection, maintenance and/or repair of TSJ 70 (or flex joint 94 for SCRs so-equipped), SCR 18 may be returned to service by reversing the steps of the above-described procedure—i.e., from the state illustrated in
A similar procedure may be used for the embodiment illustrated in
The invention may be embodied as a subsea riser hang-off connector comprising: a two-piece, generally cylindrical body having an outer surface, an upper surface, a lower surface, a central axial bore and divided axially into a front piece and a rear piece; a hinge connecting the front piece and the rear piece on a first side of the body; a lock releasably connecting the front piece and the rear piece on a second side of the body radially opposite the hinge on the first side of the body; an annular recess within the central, axial bore; and, an elastomeric element within the annular recess, said elastomeric element having a central axial bore.
The outer surface of the generally cylindrical body may be tapered from a first, larger, outside diameter proximate the upper surface to a second, smaller, outside diameter proximate the lower surface. The taper may correspond to an internal taper of a riser basket receptacle on a floating production system.
The elastomeric element may comprise an annular recess in the central axial bore thereof. The elastomeric element may be radially segmented.
The elastomeric element may comprise at least one bonded metal lamination or may comprise a plurality of metal laminations said laminations progressively varying in radial width.
A subsea riser hang-off connector according to the invention may comprise at least one handle on the upper surface. The handle may be sized and configured for manipulation by a subsea remotely operated vehicle.
A subsea riser hang-off connector according to the invention may comprise at least one padeye on the upper surface.
A subsea riser hang-off connector according to the invention may comprise a hinge pin within the hinge connecting the front piece and the rear piece.
A subsea riser hang-off connector according to the invention may incorporate a lock that comprises a locking pin and a locking pin sleeve attached to the upper surface of the generally cylindrical body, the locking pin configured to slide within the locking pin sleeve between a raised position wherein the lock is unlatched to a lowered position wherein the lock is latched. The locking pin may comprise a radial bolt configured to rest on an upper end of the locking pin sleeve when the lock is latched and limit the travel of the locking pin within the locking pin sleeve.
A subsea riser hang-off connector according to the invention may comprise a first annular recess on the locking pin and a locking pin latch on the locking pin sleeve comprising a latch pin sized and configured to engage the first annular recess on the locking pin and thereby secure the locking pin in the latched position. A second annular recess may be provided on the locking pin, said second annular recess sized and configured to be engaged by the latch pin and thereby secure the locking pin in the unlatched position. The locking pin latch may comprise a sleeve projecting radially from the locking pin sleeve, said locking pin latch sleeve having an L-shaped slot in a wall thereof and a radial projection on the latch pin sized and configured to slide within the L-shaped slot and secure the latch pin in a latched condition.
A subsea riser hang-off collar adapter according to the invention may comprise a generally cylindrical body having a tapered outer surface, an upper surface, a lower surface, and a central axial bore, a radial opening in the generally cylindrical body extending from the upper surface to the lower surface and from the central axial bore to the outer surface, and a shoulder within the central axial bore. The taper of the tapered outer surface corresponds to an internal taper of a riser basket receptacle on a floating production system. The subsea riser hang-off collar adapter may further comprise a pair of opposing, radially projecting plates flanking the radial opening in the generally cylindrical body. The radially projecting plates may extend radially beyond the outer surface of the generally cylindrical body.
The invention may be embodied as a steel catenary riser comprising an annular hang-off collar projecting radially from the outer surface of the steel catenary riser proximate an upper end thereof, said hang-off collar sized and configured to fit within the above-described elastomeric element of a subsea riser hang-off connector according to the invention. The annular hang-off collar may be integral with the wall of the steel catenary riser. The steel catenary riser may further comprise an annular, radially projecting landing stopper on the steel catenary riser below the annular hang-off collar, said landing stopper sized and configured to support a subsea riser hang-off connector as described above when said subsea riser hang-off connector is in an open position. The radially projecting landing stopper on the steel catenary riser may be sized and configured to be axially spaced apart from the lower surface of a subsea riser hang-off connector according to the invention when said subsea riser hang-off connector is in a closed position.
A steel catenary riser according to the invention may further comprising an annular, radially projecting upper stopper on the steel catenary riser above the annular hang-off collar, said upper stopper sized and configured to engage the upper end of the annular recess in a subsea riser hang-off connector according to the invention when said subsea riser hang-off connector is in a closed position.
In another embodiment, a steel catenary riser according to the invention may comprise an annular hang-off collar projecting radially from the outer surface of the steel catenary riser proximate an upper end thereof, said hang-off collar sized and configured to fit within a subsea collar adapter according to the invention and bear upon the shoulder within the central axial bore thereof. The steel catenary riser may further comprise a first tapered portion of the steel catenary riser above the annular hang-off collar wherein the outer diameter of the riser progressively decreases from a larger outer diameter proximate the hang-off collar to a smaller, nominal outer diameter of the steel catenary riser at a location distal from the hang-off collar, and a second tapered portion of the steel catenary riser below the annular hang-off collar wherein the outer diameter of the riser progressively decreases from a larger outer diameter proximate the hang-off collar to a smaller, nominal outer diameter of the steel catenary riser at a location distal from the hang-off collar.
The invention may also be embodied as a method for supporting a flex joint or tapered stress joint (TSJ) proximate an upper end of a subsea riser above the surface of the water comprising: attaching a riser hang-off connector to a hang-off collar on the riser; attaching a pull head to the upper end of the riser; attaching a lifting device to the pull head; raising the upper end of the riser with the lifting device to a first position wherein a support bushing or a flex joint on the riser is fully disengaged above a corresponding basket receptacle on a riser porch on a floating production system; moving the riser horizontally to a second position wherein the riser is displaced from the basket receptacle; raising the upper end of the riser with the lifting device to a third position wherein the riser hang-off connector attached to the hang-off collar on the riser is at an elevation higher than the elevation of the basket receptacle; moving the riser horizontally to a fourth position wherein the riser is within the basket receptacle and the riser hang-off connector attached to the hang-off collar on the riser is at an elevation higher than the elevation of the basket receptacle; and, lowering the riser by reverse movement of the lifting device to a fifth position wherein the riser hang-off connector is seated within the basket receptacle. The riser may be a Steel Catenary Riser (SCR). The lifting device may be a chain jack having a chain connected to the pull head. The chain jack may be mounted on a gantry and moving the riser horizontally may comprise moving the gantry. Attaching the riser hang-off connector to a hang-off collar on the riser may be performed by a subsea remotely operated vehicle (ROV). The riser hang-off connector may be a hinged riser hang-off connector according to the invention, as described above.
The method may further comprise performing inspection, maintenance, or replacement of a flex joint or TSJ on the riser while the riser is in the fifth position. The method may comprise providing scaffolding supported below a deck of the floating production system.
Following inspection, maintenance or repair, the riser may be returned to service by: raising the riser from the fifth position to the fourth position; moving the riser horizontally from the fourth position to the third position; lowering the riser to the second position; moving the riser horizontally from the second position to the first position; and, lowering the riser sufficiently to seat the bushing or flex joint in the basket receptacle on the riser porch of the floating production system. The method may further comprise detaching the riser hang-off connector from the hang-off collar on the riser.
The invention may be embodied as a method for supporting a flex joint or tapered stress joint (TSJ) proximate an upper end of a subsea riser above the surface of the water comprising: providing a hang-off collar on the riser; attaching a pull head to the upper end of the riser; attaching a lifting device to the pull head; raising the upper end of the riser with the lifting device to a first position wherein a support bushing or a flex joint on the riser is fully disengaged above a corresponding basket receptacle on a riser porch on a floating production system; moving the riser horizontally to a second position wherein the riser is displaced from the basket receptacle; installing a collar adapter in the basket receptacle; raising the upper end of the riser with the lifting device to a third position wherein the hang-off collar on the riser is at an elevation higher than the elevation of the basket receptacle; moving the riser horizontally to a fourth position wherein the riser is within the basket receptacle and the hang-off collar on the riser is at an elevation higher than the elevation of the basket receptacle; and, lowering the riser by reverse movement of the lifting device to a fifth position wherein the riser hang-off collar is seated in the collar adapter in the basket receptacle. The collar adapter may be a collar adapter according to the above-described collar adapter. Installing the collar adapter in the basket receptacle may be accomplished with at least one diver or with at least one subsea remotely operated vehicle (ROV). The method may further comprise providing a first tapered outside diameter portion on the riser above the hang-off collar and a second tapered outside diameter portion on the riser below the hang-off collar wherein the wall thickness of the riser in the first and second tapered portions may be greater than the nominal wall thickness of the riser.
The riser may be returned to service by: raising the riser from the fifth position to the fourth position; moving the riser horizontally from the fourth position to the third position; removing the collar adapter from the basket receptacle; lowering the riser to the second position; moving the riser horizontally from the second position to the first position; and, lowering the riser sufficiently to seat the bushing or flex joint in the basket receptacle on the riser porch of the floating production system.
The foregoing presents particular embodiments of a system embodying the principles of the invention. Those skilled in the art will be able to devise alternatives and variations which, even if not explicitly disclosed herein, embody those principles and are thus within the scope of the invention. Although particular embodiments of the present invention have been shown and described, they are not intended to limit what this patent covers. One skilled in the art will understand that various changes and modifications may be made without departing from the scope of the present invention as literally and equivalently covered by the following claims.
