WO2012051148A2

WO2012051148A2 - Marine subsea assemblies

Info

Publication number: WO2012051148A2
Application number: PCT/US2011/055693
Authority: WO
Inventors: Roy Shilling; Kevin Kennelley; Robert W. Franklin; Vicki Corso; Adam L. Ballard; Ricky Thethi; Chau Nguyen; Steve Hatton
Original assignee: Bp Corporation North America Inc.
Priority date: 2010-10-12
Filing date: 2011-10-11
Publication date: 2012-04-19
Also published as: EP2627859A2; CN103228865A; EA201300439A1; EA026518B1; CA2811110A1; AU2011316731B2; MX2013003989A; AU2011316731A1; WO2012051148A3

Abstract

A lower riser assembly connects a riser to a seabed mooring and to a subsea hydrocarbon fluid source. The assembly includes sufficient intake ports to accommodate flow of hydrocarbons from the hydrocarbon fluid source, as well as optional flow assurance fluid. The upper end of the member has a profile suitable for fluidly connecting to the riser. The lower end of the member includes a connector suitable for connecting to the seabed mooring. An upper riser assembly connects the riser to a near-surface subsea buoyancy device and to a surface structure. The assembly includes sufficient outtake ports to accommodate flow of hydrocarbons from the riser through a subsea flexible conduit to the surface structure. The upper end of the member includes a connector for connecting to a subsea buoyancy device. The lower end of the member comprises a profile suitable for fluidly connecting to the riser.

Description

MARINE SUBSEA ASSEMBLIES

BACKGROUND INFORMATION

Technical Field

The present disclosure relates in general to assemblies useful in marine hydrocarbon exploration, production, well drilling, well completion, well intervention, and containment and disposal. More particularly, the present disclosure relates to upper and lower riser assemblies useful with risers in the above-listed end uses.

Background Art

Free-standing riser (FSR) systems have been used during production and completion operations. For a review, please see Hatton et al, Recent Developments in Free Standing Riser Technology, 3rd Workshop on Subsea Pipelines, December 3-4, 2002, Rio de Janeiro, Brazil. For other examples of FSR systems, see published U.S. Published Patent Application Nos. 20070044972 and 20080223583, as well as U.S. Pat. Nos. 4,234,047; 4,646,840; 4,762,180; 6,082,391, 6,321,844, and 7,434,624.

American Petroleum Institute (API) Recommended Practice 2RD, (API-RP-2RD, First Edition June 1998), Design of Risers for Floating Production Systems (FPSs) and Tension- Leg Platforms (TLPs), is a standard known by those practicing in the oil and gas production industry.

Szucs et al, Heavy Oil Gas Lift Using the COR, SPE 97749 (2005) discloses a lower riser assembly (LRA) in an FSR.

Tieback connectors have been characterized as "internal" and "external" tieback connectors, and each has been patented. Patents on internal tieback connectors are U.S. Patent Nos. 6,260,624; 5,299,642; 5,222,560; 5,259,459; 4,893,842; 4,976,458; 7,735,562; 5,279,369; and 5,775,427; and U.S. Published Patent Application No. 20090277645. Patents on external tieback connectors are U.S. Patent Nos. 4,606,557; 6,234,252; 6,540,024; 6,070,669; 6,293,343; 7,503,391; 7,337,848; 5,330,201; 5,255,743; 7,240,735. Drilling adapters and their connection to wellheads (casing head or tubing heads) are described in U.S. Published Patent Application No. 20090032265. Adjustable hangers are described in U.S. Patent Nos. 6,065,542; 6,557,644; and 7,219,738.

Due to the complexities of any given reservoir, well design, and riser system, while certain minimum standards such as presented in the above-referenced API riser standard may be known to persons of ordinary skill in the art, each individual oil or gas well may be a unique environment unto itself (see for example U.S. Patent No. 6,747,569). Riser systems that work for one reservoir/well/environment may not be suitable for use with other wells, even those wells located proximate thereto.

In the containment and disposal context, subsea risers (free-standing or not) have not been known as suitable for such use. In particular, until recently industry has not had to intervene with respect to subsea leaks at any significant depth, such as depths to 5,000 ft/1500 meters, or more. In particular, prior containment efforts did not address fluid properties produced by the combination of hydrocarbons with sea water at deep-ocean pressures and temperatures that contribute toward formation of gas hydrates.

Therefore, there remains an unmet need for more robust upper and lower riser assembly designs, particularly when flow assurance is a concern, both during normal production operations and during containment and disposal periods.

SUMMARY

In accordance with the present disclosure, marine subsea assemblies, and methods of making, installing, and using same are described which reduce or overcome many of the faults of previously known marine subsea assemblies.

A first aspect of the disclosure is an assembly for connecting a subsea riser to a seabed mooring and to a subsea hydrocarbon fluid source, comprising:

a generally cylindrical member having a longitudinal bore, a lower end, an upper end, and an external generally cylindrical surface, the member comprising sufficient intake ports extending from the external surface to the bore to accommodate flow of hydrocarbons from the hydrocarbon fluid source as well as inflow of a functional fluid (flow assurance fluid or other fluid, for example a corrosion or scale inhibitor, kill fluid, and the like), at least one of the intake ports fluidly connected to a production wing valve assembly,

the upper end of the member comprising a profile suitable for fluidly connecting to a subsea riser, and

the lower end of the member comprising a connector suitable for connecting to a seabed mooring.

In certain embodiments the generally cylindrical member comprises a subsea wellhead housing modified by connecting a transition joint thereto, the upper end of the subsea wellhead housing fluidly connected to an external tieback connector fluidly connecting the subsea wellhead housing to a riser stress joint.

In certain embodiments the subsea wellhead housing comprises an internal seal profile adapted to seal with an internal tieback connector, the internal tieback connector fluidly connecting an inner subsea riser to the internal seal profile of the subsea wellhead. In certain embodiments, the internal tieback connector comprises a nose seal which seals into the subsea wellhead profile of the subsea wellhead, the nose seal providing pressure integrity between an internal flow path in the inner riser and an annulus between the inner riser and a substantially concentric outer riser. In certain embodiments the internal tieback connector latches to both the subsea wellhead housing and to a riser stress joint, creating a preloaded structural connection between the subsea wellhead housing and the internal and external tieback connectors. In certain embodiments the latches comprise dogs. Certain embodiments comprise an external connector which latches the internal tie-back connector to the subsea wellhead housing.

In yet other assemblies, the production wing valve assembly is fluidly connected to a subsea source through one or more subsea flexible conduits.

In yet other assemblies the riser stress joint is in turn fluidly connected to an outer riser.

In yet other assemblies the transition joint is capped with a first padeye end forging serving as an anchor point for a free standing riser.

Yet other assemblies comprise ROV-operated valves for controlling flow through an internal flow path in the inner riser and through an annulus between the inner riser and a substantially concentric outer riser.

Still other assemblies comprise one or more pressure and/or temperature monitors.

Yet other assemblies comprise one or more hot stab ports for ROV intervention and/or maintenance.

In certain other embodiments the generally cylindrical member comprises a high-strength metal forging. These embodiments may comprise two intake ports connected to respective wing valve assemblies, and a third port including a sub suitable for connecting a source of functional fluid, for example a flow assurance fluid or other fluid. The sub may include one or more ROV -operable valves.

Certain embodiments comprise two or more intake ports connected to respective wing valve assemblies, and further comprising dual clamp supports for supporting respective dual subsea connectors, each fluidly connected to the forged high-strength steel member through respective block elbows, wherein each production wing valve assembly includes at least one ROV -operable valve. In certain embodiments, the generally cylindrical member comprises a third port suitable for connecting an annulus vent sub, the annulus vent sub connecting to the third port of the forged high-strength steel member through a third block elbow, the annulus vent sub providing a fluid connection to a source of a functional fluid, such as a flow assurance fluid or other fluid. In some embodiments, the annulus vent sub comprises one or more ROV- operable valves.

In certain embodiments, each wing valve assembly comprises a block elbow connector connecting the wing valve assembly to the metal forging, at least one ROV-operable valve connected to the block elbow, and a subsea connector for connecting to a subsea flexible conduit, the block elbow, ROV-operable valve, and subsea connector all fluidly connected by central bores allowing fluid communication from the subsea flexible conduit to the longitudinal bore of the metal forging.

Certain embodiments comprise a tie-back ring having an external threaded portion mating with threads on an internal surface of the metal forging, and an internal thread portion for mating with threads of an internal casing string.

In other embodiments, the forged high-strength steel member further comprises an internal surface, at least a portion of which is threaded, to threadedly engage mating threads of a tieback ring, the tieback ring including at least one set of internal threads which mate with a set of threads on the inner riser, and further including a seal element comprised of Inconel or other corrosion-resistant metal.

Certain embodiments comprise a hot stab assembly for injection of a functional fluid, the hot stab assembly allowing for a smaller flow rate of functional fluid than is possible through the annulus vent sub.

In other embodiments, the generally cylindrical member comprises a forged, high-strength steel intake spool fluidly connected to a gooseneck assembly, the gooseneck assembly fluidly connected to the lower flexible conduit, the intake spool also comprising a connector allowing connection to a source of a functional fluid. In embodiments, the gooseneck assembly comprises a subsea API flange connected in series to a tubing spool, a high- pressure subsea connector, another subsea API flange, and a bend restrictor. In other embodiments, the intake spool comprises an internal surface adapted to accept and fluidly connect with an internal tieback connector landed in the internal surface of intake spool, the intake spool further comprising a latching mechanism allowing the internal tieback connector to releasably connect to the intake spool, while an O-ring seal provides a fluid-tight seal between an external surface of the internal tieback connector and the internal surface of the intake spool.

Another aspect of this disclosure comprises an assembly suitable for use as a subsea lower riser assembly comprising:

a subsea wellhead housing having a lower end and an upper end, the lower end modified by fluidly and mechanically connecting a transition joint thereto, the transition joint in turn fluidly and mechanically connected to a bottom forging, the bottom forging comprising sufficient intake ports to accommodate flow of production or containment fluids and flow assurance fluid, at least one of the ports connected to a source of a flow assurance fluid, at least one other intake port fluidly connected to a production wing valve assembly, the upper end of the subsea wellhead housing fluidly connected to an external tieback connector fluidly connecting the subsea wellhead housing to a riser stress joint, the subsea wellhead housing comprises an internal seal profile adapted to seal with an internal tieback connector, the internal tieback connector fluidly connecting an inner subsea riser to the internal seal profile of the subsea wellhead,

wherein the internal tieback connector comprises a nose seal which seals into the subsea wellhead profile of the subsea wellhead, the nose seal providing pressure integrity between an internal flow path in the inner riser and an annulus between the inner riser and a substantially concentric outer riser, and

wherein the internal tieback connector latches to both the subsea wellhead housing and to a riser stress joint, creating a preloaded structural connection between the subsea wellhead housing and the internal and external tieback connectors.

a generally cylindrical high-strength metal forging comprising a longitudinal bore, a lower end, an upper end, an external generally cylindrical surface, and sufficient intake ports to accommodate flow of production or containment fluids, at least one of the ports connected to a source of a flow assurance fluid, at least one other intake port fluidly connected to a production wing valve assembly,

the upper end of the metal forging comprising a profile suitable for fluidly connecting to an external subsea riser,

the lower end of the metal forging comprising a connector suitable for connecting to a subsea mooring,

a third port suitable for connecting an annulus vent sub, the annulus vent sub comprising one or more remotely-operated vehicle (ROV)-operable valves, and a tie-back ring having an external threaded portion mating with threads on an internal surface of the metal forging, and an internal threaded portion for mating with threads of an internal casing string.

a forged, high-strength steel, generally cylindrical intake spool fluidly connected to a gooseneck assembly, the gooseneck assembly fluidly connected to a lower flexible conduit, the intake spool also comprising a connector allowing connection to a source of a functional fluid;

the gooseneck assembly comprising a subsea API flange connected in series to a tubing spool, a high-pressure subsea connector, another subsea API flange, and a bend restrictor; and

wherein the intake spool comprises an internal surface adapted to accept and fluidly connect with an internal tieback connector landed in the internal surface of intake spool, the intake spool further comprising a latching mechanism allowing the internal tieback connector to releasably connect to the intake spool, while an O-ring seal provides a fluid-tight seal between an external surface of the internal tieback connector and the internal surface of the intake spool.

Another aspect of this disclosure is an assembly for connecting a subsea riser to a subsea buoyancy device and to a surface structure, comprising:

a generally cylindrical member having a longitudinal bore, a lower end, an upper end, and an external generally cylindrical surface, the member comprising sufficient outtake ports extending from the bore to the external generally cylindrical surface to accommodate flow of hydrocarbons from the riser, and at least one port allowing flow of a functional fluid into the longitudinal bore, at least one of the outtake ports fluidly connected to a production wing valve assembly for fluidly connecting the member to the surface structure with a subsea flexible conduit,

the upper end of the member comprising a connector suitable for connecting to a subsea buoyancy device, and

the lower end of the member comprising a profile suitable for fluidly connecting to the riser.

In certain embodiments the generally cylindrical member comprises a drilling spool adapter having a first end fluidly connected to a tubing head, the tubing head comprising the one or more outtake ports, the tubing head connected to a casing head having a stem joint fastened (for example, welded) thereto, the casing head also comprising one or more ports for admitting a functional fluid, and one or more production wing valve assemblies fluidly connected to respective outtake ports.

In certain embodiments of this aspect the stem joint is fluidly connected to an outer concentric riser.

In certain embodiments at least one of the production wing valve assemblies fluidly connects an outtake port to a collection vessel through a flexible conduit.

In certain embodiments the assembly comprises an adjustable tubing hanger fluidly connecting an inner riser to the tubing head.

In yet other embodiments of this aspect, the production wing valve assembly comprises first and second flow control valves for controlling flow in the bore of the inner riser and in an annulus between the inner riser and the outer riser.

In yet other embodiments, the production wing valve assembly comprises at least one emergency shutdown valve (ESD) selected from the group consisting of one hydraulically- operated ESD, one electrically-operated ESD, and one hydraulically-operated ESD and one electrically-operated ESD. In still yet other embodiments the production wing valve assembly comprises one or more ROV hot-stab ports allowing a functional fluid to flow into an inner riser and an annulus between the inner riser and an outer riser. In certain embodiments, the functional fluid is a flow assurance fluid selected from the group consisting of nitrogen or other gas phase, heated seawater or other water, and organic chemicals. In certain embodiments, the flow assurance fluid consists essentially of nitrogen.

In certain embodiments, the drilling spool adapter is connected to a shackle flange adapter capped on its top with a padeye end forging serving as an attachment point of the assembly to a near-surface subsea buoyancy assembly.

In other embodiments of this aspect of this disclosure, the generally cylindrical member comprises an offtake spool having the upper end and the lower end, a padeye flange connected to the upper end of the offtake spool, and a hanger spool connected to the lower end of the offtake spool, wherein the offtake spool and the hanger spool define the longitudinal bore.

In certain of these embodiments, the offtake spool comprises a second bore substantially perpendicular to the longitudinal bore and fluidly connecting the longitudinal bore to one of the production wing valve assemblies through one of the outtake ports.

In certain other embodiments, the production wing valve assembly comprises a gooseneck conduit and two emergency shutdown (ESD) valves fluidly connected inline of the gooseneck conduit, one of the ESDs being hydraulically actuated, and the second ESD being electronically actuated.

In certain other embodiments, the hanger spool comprises a third bore substantially perpendicular to the longitudinal bore and fluidly connecting an annulus defined by the hanger spool and an internal riser joint with an annulus access valve assembly. The annulus access valve assembly may comprise one or more ROV-operable valves. The annulus access valve assembly may be fluidly connected to a source of functional fluid. Certain embodiments comprise a riser locking assembly for interfacing with and retaining the internal riser joint within the offtake spool. The riser locking assembly may comprise a lockdown ring and a slip with T seals.

In certain embodiments, a dual ring seal and wire retainer arrangement is positioned on an inner surface of the offtake spool for providing a dual fluid seal between the annulus and the longitudinal bore.

In certain embodiments the URA comprises a production bore offtake spool fluidly and mechanically connected to a substantially vertical conduit and to a production tubing, the production tubing in turn fluidly connected to a bend restrictor through a subsea API flange, a high pressure subsea connector, another subsea API flange connection, and optionally a QDC subsea connector. The bend restrictor mechanically connects to the upper subsea flexible conduit which extends in a catenary loop to the collection surface vessel, and the substantially vertical conduit fluidly connects in series to an adapter which in turn fluidly connects to a hanger spool and API flange, a casing head via another API flange, a stem joint welded to the casing head, and to the outer riser via a threaded connection into a stem joint, the offtake spool including a shackle flange allowing connection to the subsea buoyancy device.

In certain embodiments the URA further comprises an ROV-operable ESD fluidly connected in a section of the conduit.

In certain embodiments the URA further comprises a support bracket which supports production tubing an angle σ to the conduit, and also supports a bend shield which provides a mechanical barrier between the production tubing and the conduit, where the angle σ ranges from 0 to about 180 degrees.

In certain embodiments the URA further comprises a connection to the hanger spool for connecting a gooseneck for delivery of heated water to the hanger spool from a surface vessel. In certain embodiments the gooseneck comprises, in order starting at the hanger spool, an API flange, a section of tubing, a high pressure subsea connector, a subsea API connector and API flange, and a bend restrictor.

In certain embodiments the inner riser is positioned inside of the adapter, the hanger spool, and the casing head, creating the annulus between an inner surface of the hanger spool and the inner riser.

In certain embodiments the URA comprises a pair of O-ring seals which seal the inner riser into the adapter, and one or more slips which wedge between an inner slanted surface of the hanger spool and the inner riser, firmly securing the inner riser in the hanger spool.

In embodiments, the URA further comprises components allowing circulation of a functional fluid, such as heated water, through the annulus.

In other embodiments, the URA also comprises an offtake spool fluidly connected to a hanger spool, the hanger spool in turn fluidly connectable to a tapered stress joint of the riser.

In yet other embodiments, the URA further comprises a shackle and chain tether allowing the URA to be mechanically connected to a near-surface buoyancy device.

Certain other embodiments comprise a first block elbow includes an inner bore which intersects with and is substantially perpendicular to a bore in the offtake spool, a second block elbow having an inner bore which is also substantially perpendicular to the offtake spool bore but which does not intersect the offtake spool bore, and a gooseneck conduit fluidly connected to the first block elbow providing a flow path for hydrocarbons in combination with first block elbow bore. In some instances, the URA comprises first and second emergency shutdown valves in the gooseneck conduit, the gooseneck conduit fluidly connected to a subsea connector in turn fluidly connected to the subsea flexible conduit.

In other embodiments, the assembly further comprises a bleed valve in the gooseneck conduit allowing shutting in the URA, bleeding off contents of the gooseneck conduit, and retrieving the subsea flexible conduit. In embodiments, the components allowing circulation of a functional fluid through the annulus comprises a subsea connector, a conduit and one or more valves in the conduit, the conduit fluidly connected to the hanger spool.

Yet another aspect of this disclosure is an assembly suitable for use as a subsea upper riser assembly, comprising

a drilling spool adapter having a first end fluidly connected to a tubing head, the tubing head comprising one or more outtake ports, the tubing head connected to a casing head having a stem joint fastened thereto, the casing head also comprising one or more ports for admitting a flow assurance fluid,

the stem joint fluidly connected to an outer concentric riser,

an adjustable tubing hanger for fluidly connecting an inner riser to the tubing head, forming an annulus between the inner riser and the outer concentric riser,

a production wing valve assembly fluidly connected to one of the respective outtake ports, the production wing valve assembly comprising first and second flow control valves for controlling flow in the inner riser and the annulus, and a hydraulically-operated emergency shut-down valve and an electrically-operated emergency shut-down valve, and the production wing valve assembly comprising one or more ROV hot-stab ports allowing a flow assurance fluid to flow into the inner riser and/or the annulus.

Still another aspect of this disclosure is an assembly suitable for use as a subsea upper riser assembly, comprising

an offtake spool having an upper end and a lower end, a padeye flange connected to the upper end, and a hanger spool connected to the lower end, wherein the offtake spool and the hanger spool define a longitudinal bore,

the offtake spool comprising a second bore substantially perpendicular to the longitudinal bore and fluidly connecting the longitudinal bore to a production wing valve assembly through an outtake port of the offtake spool,

the production wing valve assembly comprising a gooseneck conduit and two emergency shutdown (ESD) valves fluidly connected inline of the gooseneck conduit, one of the ESDs being hydraulically actuated, and the second ESD being electronically actuated, the hanger spool comprising a third bore substantially perpendicular to the longitudinal bore for fluidly connecting an annulus defined by the hanger spool and an internal riser joint with an annulus access valve assembly, the annulus access valve assembly comprising one or more ROV-operable valves,

a riser locking assembly for interfacing with and retaining the internal riser joint within the offtake spool, the riser locking assembly comprising a lockdown ring and a slip with T seals, and

a dual ring seal and wire retainer arrangement on an inner surface of the offtake spool providing a dual fluid seal between the annulus and the longitudinal bore.

Another aspect of the disclosure is an assembly suitable for use as a subsea upper riser assembly, comprising:

a production bore offtake spool fluidly and mechanically connected to a substantially vertical conduit and to a production tubing, the production tubing in turn fluidly connected to a bend restrictor through a subsea API flange, a high pressure subsea connector, another subsea API flange connection, and optionally a QDC subsea connector, the bend restrictor connected to the upper subsea flexible conduit which extends in a catenary loop to a surface structure,

wherein the substantially vertical conduit fluidly connects in series to an adapter which in turn fluidly connects to a hanger spool of an API flange, a casing head via another API flange, a stem joint welded to the casing head, and to an outer riser via a threaded connection into a stem joint, the offtake spool including a shackle flange allowing connection to a subsea buoyancy device;

an ROV-operable ESD fluidly connected in a section of the conduit;

a support bracket which supports production tubing an angle σ to the conduit, and also supports a bend shield which provides a mechanical barrier between the production tubing and the conduit, where the angle σ ranges from 0 to about 180 degrees;

a connection to the hanger spool for connecting a gooseneck for delivery of heated water to the hanger spool from a surface vessel, wherein the gooseneck comprises, in order starting at the hanger spool, an API flange, a section of tubing, a high pressure subsea connector, a subsea API connector and API flange, and a bend restrictor;

wherein the inner riser is positioned inside of the adapter, the hanger spool, and the casing head, creating the annulus between an inner surface of the hanger spool and the inner riser; and a pair of O-ring seals which seal the inner riser into the adapter, and one or more slips which wedge between an inner slanted surface of the hanger spool and the inner riser, firmly securing the inner riser in the hanger spool.

In certain embodiments, the subsea flexible conduits each comprise a lazy wave flexible jumper with distributed buoyancy modules connected to the subsea flexible conduit randomly or non-randomly from a point of connection of the subsea flexible conduit to the base of the free standing riser to a subsea manifold on the seafioor, the manifold fiuidly connected to the subsea source or sources.

In certain embodiments including an internal tieback connector fiuidly connecting the inner riser to the LRA, the internal tieback connector comprising a nose seal, in some embodiments the nose seal is an Inconel nose seal, which seals into a subsea wellhead profile of the subsea wellhead, the connector also latching with dogs both to the subsea wellhead and to the stress joint in order to create a preloaded structural connection between the subsea wellhead and the internal and external tieback connectors. Certain embodiments also comprise an additional external connector latch which latches the internal tie-back connector to the subsea wellhead. The nose seal provides pressure integrity between the internal flow path in the inner riser and the annulus between the inner and outer risers.

Certain embodiments include those wherein the URA production wing valve assembly comprises both hydraulically and manually operated emergency shutdown valves.

Certain embodiments include those wherein the URA production wing valve assembly comprises one or more subsea vessel hot- stab ports allowing a functional fluid to be injected into either one or both of the inner riser and the annulus. Examples of suitable functional fluids include flow assurance fluids such as a gas atmosphere, heated seawater or other water, or organic chemicals such as methanol, and the like. The gas atmosphere may be selected from nitrogen of various degrees of purity, such as nitrogen-enriched air, a noble gas such as argon, xenon and the like, carbon dioxide, and combinations thereof; hot seawater or other water pumped in the annulus and out the annulus vent sub, and methanol pumped in the annulus and out the vent sub. Certain hydrate inhibition fluids include liquid chemicals selected from the group consisting of alcohols and glycols. The flow assurance fluid may consist essentially of nitrogen, meaning the gas atmosphere comprises nitrogen and may include impurities which do not contribute to formation of, or themselves form, hydrates, and substantially excludes impurities that do form or contribute to forming hydrates.

Certain embodiments comprise external wet insulation adjacent at least a major portion of the outer surface of one or more of the wellheads, wing valves, casing heads, tubing heads, metal forgings, offtake spools, hanger spools, and the like. In certain embodiments the wet insulation comprises a polymeric material. The polymeric material may comprise a plurality of layers of polypropylene.

Certain URA and LRA embodiments include subs for allowance of a functional fluid, such as a flow assurance fluid, to flow into an inner riser and/or annular spaces between risers, and into the bores of the URA and LRA. Certain embodiments include subs for allowance of flow of hydrate inhibition fluid in these spaces. Certain embodiments include subs for allowance of hydrate remediation fluid in these spaces. Certain embodiments include subs for allowance of fluids for all of these uses. Once introduced into the inner riser and/or annular space, the flow assurance fluid, hydrate inhibition fluid, and/or hydrate remediation fluid may be stagnant or flowing, however mass and heat transfer favors a flowing fluid.

Certain other embodiments include those wherein at least some of the components of the LRA and/or URA comprise high-strength steel, although the use of steel is not required, other metals being possible for use. As used herein the term "high-strength steel" includes steels such as P-l 10, C-l 10, Q-125 and C-125, and titanium steels.

The assemblies described herein may be used with single or concentric risers systems. The assemblies described herein may be used with wet tree developments, including those employing an FPSO or other floating production systems (FPS), including, but not limited to, semi-submersible platforms. The assemblies described herein may also be used with dry tree developments, including those employing compliant towers, TLPs, spars or other FPSs. The assemblies described herein may also be used with so-called hybrid developments (such as TLP or spar with an FPSO or FPS). The assemblies described herein may be used with risers tensioned by air-can systems, hydro-pneumatic tensioners, or combinations thereof. These and other features of the systems, apparatus, and methods of the disclosure will become more apparent upon review of the brief description of the drawings, the detailed description, and the claims that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

The manner in which the objectives of this disclosure and other desirable characteristics can be obtained is explained in the following description and attached drawings in which:

FIGS. 1, 1A, and IB illustrate schematically, FIG. 1A in detailed cross-section, one embodiment of a riser system in which the assemblies of the present disclosure may be useful;

FIGS. 2A and 2B are schematic side-elevation and cross-sectional views, respectively, of a general embodiment of a lower riser assembly in accordance with the present disclosure;

FIGS. 3A-3G include various views, some in cross-section, of another embodiment of a lower riser assembly in accordance with the present disclosure;

FIGS. 4A is a perspective view, FIG. 4B a cross-sectional view, and FIG. 4C a more detailed cross-sectional view of a portion of the lower riser assembly embodiment of FIG.3;

FIGS. 5A and B illustrate schematic perspective views of another lower riser assembly in accordance with the present disclosure, and FIG. 5C is a schematic perspective view of an internal component useful with the lower riser assembly illustrated in FIGS. 5A and 5B; FIGS. 5D and 5E are cross-sectional views, and FIG. 5G is a plan view of the lower riser assembly illustrated in FIGS. 5A and 5B; and FIG. 5F is a detailed schematic view of a portion of the lower riser assembly illustrated in FIG. 5E;

FIG. 6 is a schematic side-elevation view, with portions cut away, of a general embodiment of an upper riser assembly in accordance with the present disclosure;

FIGS. 6A-6G include various views, some in cross-section, of another embodiment of an upper riser assembly in accordance with the present disclosure;

FIG. 6H is a schematic perspective view, and FIGS. 61 and 6 J are cross-sectional views, of a portion a of the upper riser assembly embodiment of FIG. 6; FIG. 6K is a perspective view of a seal test port; FIGS. 7A and 7B are schematic perspective views of another upper riser assembly embodiment in accordance with the present disclosure;

FIGS. 7C-7D are cross-sectional views of the embodiment of FIG. 7, and FIG. 7E is a detailed cross-sectional view of a portion of that embodiment; and

FIGS. 8 A and 8B are schematic side elevation and cross-sectional illustrations, respectively, of another URA embodiment, and FIGS. 8C and 8D are schematic side elevations and cross- sectional illustrations, respectively, of another LRA embodiment in accordance with the present disclosure.

It is to be noted, however, that the appended drawings are not to scale and illustrate only typical embodiments of this disclosure, and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments. Identical reference numerals are used throughout the several views for like or similar elements.

DETAILED DESCRIPTION

In the following description, numerous details are set forth to provide an understanding of the disclosed methods, systems, and apparatus. However, it will be understood by those skilled in the art that the methods, systems, and apparatus may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. All U.S. published patent applications and U.S. Patents referenced herein, as well as any non- published U.S. aptent applications and published non-patent literature are hereby explicitly incorporated herein by reference. In the event definitions of terms in the referenced patents and applications conflict with how those terms are defined in the present application, the definitions for those terms that are provided in the present application shall be deemed controlling.

The primary features of various embodiments of the present disclosure will now be described with reference to the drawing figures. The same reference numerals are used throughout to denote the same items in the figures, unless otherwise noted.

As noted previously, marine subsea assemblies, and methods of making, installing, and using same are described which may reduce or overcome many of the faults of previously known marine subsea assemblies.

As used herein the term "surface structure" means a surface vessel or other structure that may function to receive one or more fluids from one or more free-standing risers. In certain embodiments, the surface structure may also include facilities to enable the surface structure to perform one or more functions selected from the group consisting of storing, processing, and offloading of one or more fluids. As used herein the term "offloading" includes, but is not limited to, flaring (burning) of gaseous hydrocarbons. Suitable surface structures include, but are not limited to, one or more vessels; structures that may be partially submerged, such as semi-submersible structures; floating production and storage (FPS) structures; floating storage and offloading structures (FSO); floating production, storage, and offloading (FPSO) structures; mobile offshore drilling structures such as those known as mobile offshore drilling units (MODUs); spars; tension leg platforms (TLPs), and the like. As used herein the phrase "subsea source" includes, but is not limited to: 1) production sources such as subsea wellheads, subsea blow out preventers (BOPs), other subsea risers, subsea manifolds, subsea piping and pipelines, subsea storage facilities, and the like, whether producing, transporting and/or storing gas, liquids, or combination thereof, including both organic and inorganic materials; 2) subsea containment sources of all types, including leaking or damaged subsea BOPs, risers, manifolds, tanks, and the like; and 3) natural sources. Certain system embodiments include those wherein the containment source is a failed subsea blowout preventer.

The term "wellhead" is well-known in the hydrocarbon drilling and production art as a structure having a central bore and end connectors on both ends of varying nature, such as hubs, mandrel, dogs, and the like, and meeting API standards for strength and other parameters for wellheads, such as detailed in API specification 6A. As used herein, the terms "tubing head" and "casing head" are wellheads having relative strength ratings, such that a tubing head is generally stronger than a casing head, although this is not always the case. A subsea wellhead may either be a tubing head or a casing head, but is typically a casing head or even more robust construction due to conditions found subsea.

The terms "flow assurance" and "flow assurance fluid" includes assurance of flow in light of hydrates, waxes, asphaltenes, and/or scale already present, and/or prevention of their formation, and are considered broader than the term "hydrate inhibition", which is used exclusively herein for prevention of hydrate formation. The term "hydrate remediation" means removing or reducing the amount of hydrates that have already formed in a given vessel, pipeline or other equipment. The term "functional fluid" includes flow assurance fluids, as well as fluids which may provide additional or separate functions, for example, corrosion resistance, hydrogen ion concentration (pH) adjustment, pressure adjustment, density adjustment, and the like, such as kill fluids.

As used herein the term "substantially vertical" means having an angle to vertical ranging from about 0 to about 45 degrees, or from about 0 to about 20 degrees, or from about 0 to about 5 degrees. As such the term "substantially vertical" includes and is broader than the term "near-vertical", as that term is used in describing the angle a riser may make with vertical. FIGS. 1, 1A, and IB illustrate schematically (FIG. 1A in detailed cross-section) one embodiment of a subsea riser system in which the assemblies described herein may be useful. It will be recognized that various other subsea riser systems may also benefit from use of the assemblies described herein. A free-standing riser (FSR) 2 is illustrated at an angle a with respect to vertical. Angle a may range from 0 to 90 degrees, or from 0 to 45 degrees, or from 0 to 20 degrees (considered "near vertical"). Another angle, β, is defined as the angle between vertical and a tangent line to flexible conduit 12 near the water surface 20. Angle β may range from 0 to about 90 degrees, or from 0 to about 45 degrees, or from 0 to about 20 degrees. A third angle γ, defined as the angle between a chain or other tether 58 (which may or may not be vertical) and an end section of a flexible conduit 14 near the base of the FSR, may range from about 5 to about 60 degrees, or from about 5 to about 30 degrees. A pile 16 is illustrated submerged into the seabed 10, and a chain tether 58 connects pile 16 to lower riser assembly 8 as further described herein. Subsea conduit 14 fluidly connects lower riser assembly 8 to a source of hydrocarbons, in this case a subsea manifold 26. An upper riser assembly 6 fluidly connects riser 2 with a flexible subsea conduit 12, which in turn fluidly connects to a surface vessel 32. Upper riser assembly 6 is also connected to primary and secondary air cans 18 and 19 in this embodiment.

FIG. 1A illustrates the relative locations of an inner riser 60, a substantially concentric outer riser 70, an outer surface 62 of inner riser 60, an outer surface 72 of outer riser 70, an inner surface 74 of outer riser 70, an annulus 76, and a flow path 64 in inner riser 60. Solid insulation 80 is placed adjacent at least a major portion of outer surface 72 of outer riser 70, and in certain embodiments, this solid insulation is adjacent the entire outer surface 72 of outer riser 70. Electrically heated risers may be an option in certain embodiments, although for operational reasons associated with the emergency quick disconnect (QDC) or hurricane evacuation scenarios, this option may not be attractive. Electrical heating may significantly complicate the QDC design.

Circulation of hot water in annulus 76 or other flow assurance fluid described herein, and insulation on the subsea manifolds, flowlines (including flexible subsea conduits 12 and 14, and flexible jumpers and goosenecks mentioned herein), and connectors, in addition to the free standing riser, may be included in many embodiments. "Circulation" may be continuous or discontinuous. In certain embodiments, the flow assurance fluid may be stagnant after filling the annulus. The ability to pump or otherwise inject one or more flow assurance fluids into one or more ROV hot stab receptacles is another option, as is the ability to pump or otherwise inject nitrogen or other gas phase into the bottom of the inner riser or at a subsea manifold into the flexible subsea conduits as a way to get the flow assurance fluid underneath an actual or potential, complete or partial hydrate plug. In certain embodiments such as illustrated in the figures, flow assurance fluid may be pumped or otherwise injected into a variety of locations, for example, but not limited to, the bottom of the inner riser 60, in the bottom of annulus 76, into the bottom (subsea) flexible 14, at the top of inner riser 60 and annulus 76 and into upper flexible conduit 12.

FIG. IB also illustrates schematically a tension monitoring system 52 on FSR 2. The location of the tension monitoring system is typically near the top of FSR 2, although the location may be anywhere along FSR 2, and may comprise a plurality of such monitoring systems randomly or non-randomly spaced along FSR 2. FIG. IB schematically illustrates a detail of the tension monitoring system illustrating a connector 54 and tension monitoring module 56.

Lower Riser Assembly (LRA)

FIGS. 2A and 2B are schematic side-elevation and cross-sectional views, respectively, of a general embodiment of a lower riser assembly (LRA) in accordance with the present disclosure. LRA 8 includes a generally cylindrical body CB, an upper end 8UE and a lower end 8LE, and five connections CI, C2, C3, C4, and C5 in this embodiment. Connection CI is a mechanical and fluid connection of cylindrical body CB to riser 2. Connection C4 is a mechanical connection of cylindrical body CB to a subsea mooring (not illustrated) through a chain or other functional tether 58. Connections C2, C3, and C5 are mechanical and fluid connections of conduits 8A, 8B, and 8C to cylindrical body CB though ports 8P in cylindrical body CB. Ports 8P extend from an inner surface 8IS to an external surface 8ES of cylindrical body CB.

Conduits 8A, 8B, and 8C may be, for example, wing valve assemblies connecting to subsea hydrocarbon sources, connections to sources of functional fluids such as flow assurance fluids, or connections to other subsea or surface equipment. Connections C2, C3, and C5 between ports 8P and conduits 8A, 8B, and 8C may be threaded connections, flange connections, welded connections, or other connections, and they may be the same or different with respect to type of connection, diameter and shape, depending on diameter and shape of ports 8P; for example, ports 8P could have a shape selected from the group consisting of slot, slit, oval, rectangular, triangular, circular, and the like. Connection CI may be a threaded, flanged, welded, or other connection, and may include one or more dogs, collet, split ring, or other features. In certain embodiments, the LRA may have the ability to connect to manifolds and other equipment, such as flexibles, within 270 degrees radius angle of approach.

Another embodiment of an LRA is illustrated in various views in FIGS. 3A-3G. FIG. 3A is a front elevation view of LRA 8, which in this embodiment comprises an external tie-back connector 102 connected to a subsea wellhead 104 (as further explained in relation to FIGS. 4A-C) and transition joint 105. Transition joint 105 is welded on its top end in this embodiment to the bottom of subsea wellhead 104, and to a bottom forging 106 including two machined flange connections 108 A and B and a padeye. Machined flanged connections 108 A and B are substantially perpendicular to a longitudinal axis common to wellhead 104, transition joint 105 and forging 106, and machined flanged connections 108 A and B define LRA intake ports. Bottom forging and padeye are one piece 106 in this embodiment, and transition joint 105 is a separate piece that welds bottom forging 106 to subsea wellhead 104. Transition joint 105 includes a padeye end forging 106, which engages a U-connector 119 and tether chain 58, leading to suction pile assembly 16 (not illustrated).

LRA 8 further comprises an ROV hot stab panel 110 for operating external tie-back connector 102 when making connection with subsea wellhead 104. External tieback connector 102 may be a slimline or ultra-slimline tieback connector such as available commercially from GE Oil and Gas, Houston, TX (formerly Vetco); FMC Technologies, Inc, Houston, TX; and possibly other suppliers. One such tieback connector is described in U.S. Pat. No. 7,537,057. Those skilled in the art will understand that known external tieback connectors are engineered with the understanding that as the design tension on the connector increases, the allowable bending moment decreases in an inverse relationship. Specific curves for these capacity relationships are available from the manufacturers.

A flange 111 connects a bend restrictor 112 and subsea flexible conduit 14 to a high-pressure subsea bend stiffener 180, the latter having an internal profile 81 (see FIG. 3F) allowing subsea flexible conduit 14 to fluidly connect with LRA gooseneck assembly 107. As illustrated schematically in FIG. 3F, bend stiffener 180 encases a flange connection 81 connecting subsea flexible conduit 14 to a high-pressure subsea connector 181, the latter used to mechanically and fluidly connected to conduit 107B of LRA 8. Bend stiffener 180 may take the moment off of flange connection 81 so that it is transferred directly from bend restrictor 112 to high-pressure subsea connector 181, which is coming out of the upper end of bend stiffener 180. Containment or production fluids flow upward through subsea flexible conduit 14 and flange connection 81 into a hub assembly 116B (two hub assemblies 116A and B are indicated in this embodiment), and further through an LRA production wing valve assembly 114B (two production wing valve assemblies 114A and B are indicated in this embodiment, FIG. 3A).

As illustrated in FIGS. 3 A and 3F, LRA production wing valve assemblies 114A and B each comprise respective block elbows 109A and 109B, and ROV-operated manual gate valves 115A and B as well as respective flow paths 115C and 115D (FIG. 3F). ROV hot stab panels 150A and B, respectively, may be provided for temperature and pressure monitoring. A subsea clamp structural support 118 provides support for subsea connectors 119A and 119B (such as available from Vector Subsea, Inc. under the trade designation OPTIMA). An ROV hot stab panel 121 with a mount to blind hub assembly 116A is provided, which may accommodate pressure and/or temperature monitoring sensors. Four swivel hoist rings 123 are also provided on structural support 118 in this embodiment.

FIG. 3C is a detailed view illustrating schematically hex bolts 94 welded at 93 to a clamp bolt retaining block 95. Block 95 is also welded at locations 97 to the body of subsea connector 119B. A similar arrangement is included on subsea connector 119 A, but is not illustrated.

FIG. 3D is a side elevation view, and FIG. 3E is a plan view of LRA 8. Gooseneck 107 may swivel through a wide angle as may be required during connection of flexible conduit 14, as viewed from the plan view, but once secured by connector 119B this motion is restricted.

FIG. 3F is a cross-sectional view taken along the dotted line of FIG. 3E, and illustrates certain internal features of LRA 8, most particularly the containment or production fluid flow path, as indicated by reference numerals 113, gooseneck conduit 107B (through connector 107A), 116C, 115C (through valve 115B and block elbow 109B), and finally flow path 64 through internal tieback connector 92 and inner riser 60. FIG. 3F also illustrates five casing (sometimes referred to in the art as lockdown) hangers 103 pre-installed into subsea wellhead 104, the upper most hanger latching internal tieback connector 92 into subsea wellhead 104, as explained further in reference to FIGS. 4 A, B and C. In certain embodiments there may be one, two, three, or more hangers 103. FIG. 3G indicates position of thermal insulation, designated INS, on portions of LRA 8.

Further details of this embodiment of an LRA are illustrated in FIGS. 4A, B, and C, which illustrate use of two locking hangers 704, 724. In addition to previously detailed features, FIGS. 4A, B, and C illustrate a plurality of connector lock indicator rods 720 that travel up and down and show whether external tieback connector 102 is open or fully locked. Also illustrated are one of two secondary mechanical lockdown plates 702 (the other being hidden in FIG. 4A), as well as tubing 11 OA for flow of hydraulic fluid via hot stabs 110. Hot stabs and tubing 11 OA, which passes through end cap HOB (or through other exterior ports in connector 102) are parts of an upper active locking system 102A for external tieback connector 102. A lower passive locking system 102F is also included in this embodiment. An example of mechanical details and operation of upper active locking system 102A and lower passive locking system 102F are provided in U.S. Pat. No. 6,540,024. Briefly, upper active locking system 102 A comprises an inner sleeve 102C, a hydraulically, axially movable piston 102D, and an upper locking element 102E, which may be a split ring, collet, or plurality of dogs circumferentially disposed within a chamber formed between an inner surface of outer tieback connector 102 and a lower portion of piston 102D.

Some details of lower passive locking system 102F of external tieback connector 102, as well as some details of inner tieback connector 92, are illustrated schematically in cross-section in FIG. 4C. Lockdown hangers 704 and 724 are provided, hanger 704 providing about 2 million lb_f (about 0.9 million Kg_f) of lockdown capacity in this embodiment. FIG. 4C further illustrates an internal tieback connector outer body or sleeve 708, and an inner body or mandrel 709. A set of lock down dogs 717 is provided to lock lockdown casing hanger 704 to subsea wellhead housing 104. Another set of locking dogs 901 are provided for locking external tieback connector 102 to subsea wellhead housing 104. A lower set of locking dogs 706 lock sleeve 708 of internal tieback connector 92 to lockdown casing hanger 704, and thus also locking to subsea wellhead housing 104.

Still referring to FIG. 4C, a similar set of upper locking dogs 740 lock internal tieback connector 92 to stress joint 2FJB and thus to external tieback connector 102. The lower and upper sets of dogs provide a secondary lock of the riser to subsea wellhead 104 and may maintain pressure integrity with the nose seal 92A fully engaged should external tieback connector 102 become unlocked from subsea wellhead 104 for whatever reason.

Also illustrated schematically in FIG. 4C are packoff assemblies 710, 711, and 715, and a landing surface 712 on an internal portion of casing hanger 704 for landing internal tieback connector nose seal 92A. Packoff 711 includes a wedge 711 A which forces dogs 717 into a set of internal mating grooves 717A of wellhead housing 104. Dogs 901 are positioned within a grooved window 902 in external tieback connector 102. FIG. 4C further illustrates a wellhead gasket 716. As will be understood by those of skill in the art, one or more of the dogs described herein maybe replaced by a split ring, collet or other functional equivalent.

Internal tieback connector 92 has a nose seal 92A, which may be Inconel, which seals into landing surface 712 of lockdown hanger 704. Internal tieback connector 92 latches with dogs 706 both to lockdown hanger 704 and to stress joint 2FJB in order to create a preloaded structural connection between subsea wellhead 104 and internal and external tieback connectors 102 and 92 (in addition to the external active connector latch to the wellhead - so there is multiple redundancy). Nose seal 92A may provide pressure integrity between the internal flow path 64 and annulus 76 between the inner and outer risers 60, 70. Hence, as illustrated in FIG. 3F, oil and gas to be contained or produced coming up through subsea flexible jumper 14 through a passage defined by inner surface 113 of flexible 14, enters the wing valve assembly through passages 107B and 116C, and flows through elbow block 109B and forging 106. With nose seal 92 A engaged, the produced fluids have only one way to go and that is up through inner riser 60 through passage 64 to the URA and ultimately through flexible conduit 12 to containment vessel 32 in this embodiment.

Another embodiment of a lower riser assembly is provided schematically in FIGS. 5A-5G. In this embodiment, a substantially cylindrical member 220 is provided, which is a forged high- strength steel member. Member 220 is fluidly connected to a production riser pup joint 221 via a lower cross-over joint 222 and threaded connector 242. A padeye flange 223 allows connection of member 220 to a pile assembly on the seabed. Dual clamp supports 224A and 224B support subsea connectors 225A and 225B, respectively. Two production wing valves assemblies 226A and 226B are provided, each fluidly connected to member 220 through respective block elbows 23 OA and 230B. Each assembly 226 A and B includes an ROV- operable valve 227A and 227B. An additional assembly or sub 228 is provided, fiuidly connecting to member 220 through a block elbow 229. Assembly or sub 228 may provide a fluid connection to a source of a functional fluid, such as a flow assurance fluid or other fluid. In this embodiment, block elbow 229 is smaller than block elbows 230A and 230B, but this is not necessarily so. Another assembly 231 is a hot stab assembly for injection of a functional fluid. In this embodiment, hot stab assembly 231 provides for a smaller flow rate of functional fluid than is possible through assembly 228, but once again this is not necessarily so in all embodiments. A small diameter conduit 241 (FIG. 5F) allows delivery of the functional fluid.

FIG. 5C illustrates a perspective view of a production tubing or casing 232 that connects to an internal surface of member 220. Production tubing 232 includes a tieback ring 233 and a seal element 234, which may be an S-type seal element. Seal element 234 may be comprised of Inconel or other corrosion-resistant metal. As further illustrated schematically in FIGS. 5D and 5E, tieback ring 233 includes at least one set of internal threads 235 which mate with a set of threads on production tubing 232. Tieback ring 233 also includes at least one set of external threads 236 which mate with threads on an internal surface of member 220. FIG. 5E illustrates dual inline ROV-operable valves 237 A and 237B for functional fluid injection (or circulation out) included in annulus vent sub 228, which includes a bore 238 providing access to an annulus between production tubing 232 and member 220 and lower cross-over joint 222. A flange connection 239 or other connection may be provided for this purpose. Each production wing valve assembly 226 includes a connector 240 (240A and B) which allows connection to subsea flexible conduits, as illustrated in the plan view of FIG. 5G. Connectors 240A and 240B may be connectors known under the trade designation OPTIMA, available from Vector Subsea, Inc.

FIG. 8C is a side elevation view of another LRA assembly in accordance with the present disclosure. This LRA embodiment may include a forged, high-strength steel intake spool 920, a connector 921 and gooseneck 944, subsea API flange 945, tubing spool 946, high-pressure subsea connector 180, another subsea API flange 111, bend restrictor 112, and subsea flexible conduit 14 which may connect to a subsea source of hydrocarbons (not illustrated). Another connector 947 on intake spool 920 may allow connection to a source of functional fluid. FIG. 8D illustrates, in cross-section denoted 8D-8D in FIG. 8C, details of this embodiment of LRA, illustrating an internal tieback connector 92 landed in an internal surface of intake spool 920. A latching mechanism 930 allows internal tieback connector 92 to releasably connect to intake spool, while an O-ring seal 928 may provide a fluid-tight seal between the bore of internal tieback connector 92 and annulus 76. Flex joint 2FJB is connected to intake spool in known fashion, for example by split rings, collets, or dogs as described herein for other embodiments.

Upper Riser Assembly (URA)

FIG. 6 is a schematic side-elevation view, with portions cut away, of a general embodiment of an upper riser assembly 6 in accordance with the present disclosure. Upper riser assembly (URA) 6 in this embodiment is a generally cylindrical member including an upper end 6UE and a lower end 6LE, and defines an inner bore 6IB. URA 6 shares a common bore with outer riser 70 in this embodiment and may share more than one common bore therewith. Conduits 6A and 6B are fluidly connected to URA through offtake ports 60T, conduit 6A being fluidly connected to the inner bore of inner riser 60 while conduit 6B fluidly connects with an annular space created by URA inner bore 6IB and inner riser 60. URA upper end 6UE is connectable to a near-surface buoyancy device (not illustrated) through a chain tether or other connector 127.

FIGS. 6A-6G include various views, some in cross-section, of another embodiment of an upper riser assembly in accordance with the present disclosure. FIG. 6H is a schematic perspective view, and FIGS. 61 and 6J are cross-sectional views, of a portion of the upper riser assembly embodiment of FIG. 6; FIG. 6K is a perspective view of a seal test port. URA 6 in this embodiment includes a tubing head 122, which serves as fluid connection between a casing head and stem joint 124 manufactured by GE Oil & Gas, and a drilling adapter spool 120. Drilling adapter spool 120 and tubing head 122 are mechanically connected together using a plurality of lockdown assemblies 120 A, while tubing head 122 and casing head and stem joint 124 are also mechanically connected using a second plurality of lockdown assemblies 122B. Lockdown assemblies 120A and 122B may be the same or different, and may be lockdown screw assemblies or other locking assemblies known in the art. One non- limiting example of a lockdown screw assembly is provided in U.S. Pat. No. 4,606,557. Also included are a shackle adapter flange 126, padeye end forging 128, and U-link 125 which provides a connection for tether chain 127. All of these items (except the shackle flange) are available from GE Oil & Gas.

Tubing head 122 may be machined with a 5-1/8" 10K API flange connection, and production wing valve assembly 136 attached with one hydraulically actuated 5-inch (13cm) 10,000 psi (69 MPa) emergency shutdown valve, 137B, and one ROV-operated 10,000 psi (69 MPa) emergency shutdown valve, 131. A pressure and temperature monitoring ROV hot stab port panel 139 may be provided in certain embodiments, and a nitrogen (or other fluid) injection ROV panel 152 may be provided in certain embodiments for injection of nitrogen or other gas atmosphere into the riser annulus. Tubing 158 for nitrogen or other gas atmosphere injection into the annulus may be included in this embodiment, as well as pressure, temperature and bleed ports (through ROV access panel 153) between the valves on the production flow path. A burst disc 156 on ROV panel 152 may be provided. ROV hot stab ports and pressure gauges may be provided in between the two ESD valves on the URA in order to circulate functional fluid back through flexible conduit 12 to the surface structure and to bleed pressure from the line if necessary (while keeping the first valve closed). An umbilical mounting bracket 155 is supplied. A series of outtake ports 130 may be provided in tubing head 122 (see FIG. 6A), as well as a plurality of intervention ports 135.

As illustrated in FIG. 6B, a flange connection 133 may connect a high pressure subsea connector 184 to a bend restrictor 134. Also provided are a kick-off spool 138 and bend restrictor adapter 157. A lifting eye 129 A may be provided for lifting the production wing valve assembly 136, but not when subsea flexible conduit 12 is attached.

FIG. 6D is a side elevation view of the URA 6, and FIG. 6E is a cross-sectional view through section A-A of FIG. 6D. As illustrated in FIG. 6E, a URA adjustable hanger 159 is provided in this embodiment. Also indicated is the containment fluid flow path, first upward through bore 64, then laterally through passage 137D in block elbow 137A and connection 132, then downward through a passage 137C in valve 137B and passage 131 A in valve 131, and finally out URA through flow path 184B in subsea connector 184A, which is connected to flexible conduit 12 through flange 184C, and flow path 12A through flexible conduit 12 to containment vessel 32 at the sea surface in this embodiment. [0128] FIG. 6F is a plan view of URA 6, illustrating in more detail some of the previously mentioned features. Further details of this embodiment of an URA are illustrated in FIGS. 6H-K. A nitrogen injection port 158A is illustrated, as well as a lower portion 122 A of tubing head 122, the lower portion including a seal test port 718. Further illustrated is a seal ring 720 between tubing head 122 and casing head 124; a metal-to-metal seal 722; a torque tool profile 724, a crossover connection 726, and a hanger support load ring 728, as well as a packoff 730. FIG. 6J further illustrates a URA forging 734 having ports 732 therein suitable for attaching pressure and temperature gauges. Finally, a seal ring 736 is illustrated positioned between drilling adapter spool 120 and tubing head 122. FIG. 6H and 61 illustrate casing head and stem joint 124 comprise a casing head lower portion 124A and a stem joint 124B welded at 124C to casing head lower portion 124 A.

FIG. 6G is a schematic perspective view of the URA 6, illustrating the placement of insulation material, INS, around valves 137B and 131, as well as associated piping.

FIGS. 7A and 7B are schematic perspective views of another upper riser assembly (URA) embodiment in accordance with the present disclosure, FIGS. 7C-7D are cross-sectional views of the embodiment of FIGS. 7A and 7B, and FIG. 7E is a detailed cross-sectional view of a portion of this embodiment. This URA embodiment is a different from the URA embodiment illustrated in FIGS. 6 A - 6K primarily as it allows circulating a functional fluid, such as heated water, through the annulus. The URA embodiment illustrated schematically in FIGS. 7A - 7E, replaces two of the large wing valves and the large diameter passages of the embodiment schematically illustrated in FIGS. 6 A - 6K with ROV stab functionality to inject a functional fluid such as nitrogen. In the embodiment illustrated in FIGS. 7A-E, another flexible conduit (not illustrated for clarity) may be connected to the URA via subsea connector 818 and extend to a surface vessel if continuous or semi-continuous circulation in or through the annulus is desired.

An offtake spool 804 is fluidly connected to a hanger spool 803. Hanger spool in turn is connected in this embodiment to a tapered stress joint 802, which is not a part of the URA per se but is illustrated for completeness and to show how the URA may connect to a riser system. A shackle 806 and chain tether 807 allow the URA to be mechanically connected to a near-surface buoyancy device (not illustrated). As best illustrated in FIG. 7D, block elbow 808 includes an inner bore 808A which intersects with and is substantially perpendicular to a bore 804A in offtake spool 804. Also included in this embodiment is a block elbow 809 and inner bore 809A which is also substantially perpendicular to bore 804A but which does not intersect bore 804A.

A gooseneck conduit 810 provides, in embodiments, a flow path for hydrocarbons in combination with elbow bore 808A, first emergency shutdown (ESD) valve 811 and second ESD valve 812. An outlet 813 in connector 813A may connect to a subsea flexible conduit 12 for production or containment operations. Connector 813A may be a connector known under the trade designation OPTIMA, or other connector suitable for subsea use. An ROV connection 814 is provided for operation of connector 813A. A bleed valve 815 may also be provided, serving to allow shutting in the URA, bleeding off contents of the gooseneck assembly 810, and retrieving the subsea flexible, for example for a hurricane or other unplanned event, or a planned event.

Valves 816 and 817 are provided for annulus circulation and/or production and/or functional fluid injection through connector 818. Valves 816 and 817 may be ROV-operable. A functional fluid may also be injected into the annulus via another ROV-operable valve 819 and connector 820, which may be a flange connector.

FIG. 7E is a detailed cross-sectional view of an area where offtake spool 804 and hanger spool 803 connect. Two ring seal and wire retainer arrangements 822 provide dual seals between fluid flowing in bore 825 A in tubing 825 and chamber 827 holding slips 824. Further included may be a passage 826 allowing access arrangements 822.

Another embodiment of an upper riser assembly in accordance with the present disclosure is illustrated schematically in side elevation in FIG. 8A. URS 6 includes, in embodiments, a production bore offtake spool 910 fluidly connected to a conduit 911 and to a production tubing 913. Production tubing 913 is fluidly connected to a bend restrictor 134 through a subsea API flange 905, a high pressure subsea connector 184, another subsea API flange connection 133, and optionally a subsea connector (such as available from Vector Subsea, Inc. under the trade designation OPTIMA). Bend restrictor 134 may connect to a subsea flexible conduit 12, which extends in a catenary loop to a surface structure in known fashion. An ESD 915 is provided in this embodiment in tubing section 911, which may be ROV- operable. A support bracket 916 is provided in this embodiment, which in addition to supporting tubing 913 at an angle σ, also supports a bend shield 942 that provides a mechanical barrier between wing assemblies. Angle σ may range from 0 to about 180 degrees, or from about 30 degrees to about 90 degrees, or from about 30 to about 45 degrees. Tubing 911 fluidly connects to an adapter 926, which in turn fluidly connects to a hanger spool 912 via an API flange 917, casing head 124 via another API flange 918, stem joint 124B welded to casing head 124, and riser 2 threaded into stem joint 124B. Offtake spool 910 may include a shackle flange 127 allowing connection to a chain tether 125 and near- surface buoyancy device (not illustrated).

Another feature of this embodiment, illustrated in FIG. 8A, is provision of a connection 906 in hanger spool 912 for connecting a gooseneck 907, API flange 908, tubing 909, high pressure subsea connection 940, another subsea API connector 940 and API flange 941, and bend restrictor 923 for a subsea flexible 919 for delivering heated water (or other flow assurance fluid) to hanger spool 912 from a surface structure. The heated water (or other flow assurance fluid) may then either circulate in the annulus, or traverse through the annulus generally downward toward an LRA and exit the annulus through one or more annulus vent sub valves, such as illustrated at 142, 144 in FIG. 8C.

FIG. 8B illustrates, in cross-section denoted 8B-8B in FIG. 8A, details of this embodiment of URA. An inner riser 60 is illustrated positioned inside of adapter 926, hanger spool 912, and casing head 124, creating an annular space 76 between in inner surface 912A of hanger spool 912 and inner riser 60. A pair of O-ring seals 925 seal inner riser 60 into adapter 926 in this embodiment. One or more slips 924 wedge between an inner slanted surface 943 of hanger spool 912 and inner riser 60, firmly securing inner riser 60 in hanger spool 912.

FIG. 8C is a side elevation view of another LRA assembly in accordance with the present disclosure. This LRA embodiment includes a forged, high-strength steel intake spool 920, a connector 921 and gooseneck 944, subsea API flange 945, tubing spool 946, high-pressure subsea connector 180, another subsea API flange 111, bend restrictor 112, and subsea flexible conduit 14 which connects to a subsea source of hydrocarbons (not illustrated). Another connector 947 on intake spool 920 allows connection to a source of functional fluid.

FIG. 8D illustrates, in cross-section denoted 8D-8D in FIG. 8C, details of this embodiment of LRA, illustrating an internal tieback connector 92 landed in an internal surface of intake spool 920. A latching mechanism 930 allows internal tieback connector 92 to releasably connect to intake spool, while an O-ring seal 928 provides a fluid-tight seal between the bore of internal tieback connector 92 and annulus 76. Flex joint 2FJB is connected to intake spool in known fashion, for example by split rings, collets, or dogs as described herein for other embodiments.

Flow assurance calculations may indicate that an FSR could be designed with a 5-layer, 3- inch (7.6cm) thick polypropylene thermal insulation coating applied to the outer riser, while the annulus between the inner and outer riser would be displaced with low pressure nitrogen. During operation, this scheme may substantially maintain the temperature of the hydrocarbons from a subsea source to their arrival on the surface structure.

Materials, Methods of Construction, and Installation

Aside from gaskets, hoses, flexible conduits and other components which are not considered a part of the present disclosure, the primary components of the LRAs and URAs described herein (offtake spools, intake spools, hanger spools, generally cylindrical members, riser sections, tubing heads, casing heads, tubing spools, high pressure subsea connectors, stem joints, riser stress joints, and the like) may largely be comprised of steel alloys. While low alloy steels may be useful in certain embodiments where water depth is not greater than a few thousand feet, activities in water of greater depths, with wells reaching 20,000 ft (6000 meters) and beyond may result in above-normal operating temperatures and pressures. In these "high temperature, high pressure" (HPHT) applications, high strength low alloy steel metallurgies such as C-l 10 and C-125 steel may be more appropriate.

The Research Partnership to Secure Energy for America (RPSEA) and Deepstar programs have initiated a long term, large scale prequalification program to develop databases of fatigue data and derive derating factors on high strength materials for riser applications with the contribution of major operators, engineering firms and material vendors. High-strength steels (such as X-100, C-l 10, Q-125, C-125, V-140), Titanium (such as Grade 29 and possibly newer alloys) and other possible material candidates in the higher strength category may be tested for pipe applications, and pending those results, they may be useful as materials for risers, LRAs, and URAs as described herein. Higher strength forging materials (such as F22, 4330M, Inconel 718 and Inconel 725) either have been or will soon be tested for component applications in the coming years, and may prove useful for one or more components of the described LRA and/or URA assemblies, and/or risers. The test matrix may be designed to reflect various production environments and different types of riser configurations such as single catenary risers (SCR's), dry tree risers, drilling and completion risers. The project is currently scheduled to be divided into 3 separate Phases: Phase 1 will address tensile and fracture toughness, FCGR and S-N tests (both smooth and notched) on strip specimens of high strength pipes, high strength forging materials and nickel base alloy forgings in air, seawater, seawater plus Cathodic Protection (CP) and sour environment (non-inhibited) and a completion fluid known as INSULGEL (BJ Services Company, USA) with sour environment (non-inhibited) contamination (2008). Phase 2 is scheduled to be Intermediate Scale Testing (2009), and Phase 3 Full Scale Testing with H2S/C02/Sea water (2010). For further information, please see Shilling, et al, Development of Fatigue Resistant Heavy Wall Riser Connectors for Deepwater HPHT Dry Tree Riser Systems, OMAE (2009) 79518 (copyright 2009 ASME). See also RPSEA RFP2007DW1403, Fatigue Performance of High Strength Riser Materials, Nov. 28, 2007. The skilled artisan, having knowledge of the particular depth, pressure, temperature, and available materials, may design a system for each particular application without undue experimentation.

Over the past several years, the assignee herein has participated in development of a comprehensive 15/20Ksi (103/138 MPa) dry tree riser qualification program which focuses on demonstrating the suitability of using high strength steel materials and specially designed thread and coupled (T&C) connections that are machined directly on the riser joints at the mill. See Shilling et al., "Development of Fatigue Resistant Heavy Wall Riser Connectors for Deepwater HPHT Dry Tree Riser Systems", OMAE2009-79518. These connections may eliminate the need for welding and facilitate the use of high strength materials like C-l 10 and C-125 metallurgies that are NACE qualified. (As used herein, "NACE" refers to the corrosion prevention organization formerly known as the National Association of Corrosion Engineers, now operating under the name NACE International, Houston, Texas.)

Use of high-strength steel and other high-strength materials may limit the wall thickness required, enabling riser systems to be designed to withstand pressures much greater than can be handled by X-80 materials and installed in much greater water depths due to the reduced weight and hence tension requirements. The T&C connections may reduce the need for third party forgings and expensive welding processes - considerably improving system delivery time and overall cost. Using these materials and connectors to design a fully rated second generation 15Ksi (103/138 MPa) FSR containment system, the outer riser can actually be downsized from the 13.813 inch (35.085cm) OD to 10.75 inch (27.305cm) OD x 0.75 inch (1.91cm) WT with a 7 inch (17.8cm) OD x 0.453 inch (1.15cm) WT C-l 10 inner riser. It will be understood, however, that the use of third party forgings and welding is not ruled out for URAs, LRAs, and risers described herein, and may actually be preferable in certain situations. The skilled artisan, having knowledge of the particular depth, pressure, temperature, and available materials, may design a system for each particular application without undue experimentation.

Connections of assemblies described herein to risers, and intra-assembly connections, such as drilling spool adapter to tubing head connections, and connections of substantially cylindrical members to risers, and the like, may include threading such as described in the above- mentioned Shilling et al., article, as well as those described in the following patent documents: WO2005093309; WO2005059422; U.S. Pat. Nos. 6,752,436 and

6,729,658. Further information may be found in the following publications: Sches et al.; Fatigue Resistant Threaded and Coupled Connectors: the New Standard for Deep Water Riser Applications, OMAE 2007-29263; Sches et al, Fatigue Resistant Threaded and Coupled Connectors for Deepwater Riser Systems: Design and Performance Evaluation by Analysis and Full Scale Tests, OMAE 2008-57603; and Shilling et al., Developments in Riser Technology for the Next Generation Ultra-Deep HPHT Wells, DOT Conference, 2008 Proceedings.

Materials of construction for gaskets, flexible conduits, and hoses useful in conjunction with the assemblies and methods described herein will depend on the specific water depth, temperature and pressure at which the assemblies are employed. Although elastomeric gaskets may be employed in certain situations, metal gaskets have been increasingly used in subsea application. For a review of the art circa 1992, please see Milberger, et al, "Evolution of Metal Seal Principles and Their Application in Subsea Drilling and Production", OTC- 6994, Offshore Technology Conference, Houston Texas, 1992. See also API Std 601 - Standard for Metallic Gaskets for Raised-face Pipe Flanges & Flanged Connections and API Spec 6A - Specification for Wellhead and Christmas Tree Equipment. Gaskets are not, per se, a part of the assemblies and methods of the present disclosure, but as certain LRA and URA embodiments may employ gaskets (such as wellhead gasket 716 mentioned in connection with the LRA embodiment of FIG. 3J), mention is made of the following U.S. Patents which describe gaskets which may be suitable for use in particular embodiments, U.S. Pat. No. 3,637,223, 3,918,485, 4,597,448, 4,294,477, and 7,467,663. In certain embodiments, the gasket material known as DX gasket rated for 20 ksi may be employed.

Another gasket that may be used subsea is that known under the trade designation Pikotek VCS, available from Pikotek, Inc., Wheat Ridge, Colorado (USA). This type of gasket is believed to be described in U. S. Pat. No. 4,776,600, incorporated by reference herein.

In certain embodiments the URA may have a retrievable burst disk, allowing venting of the URA to the atmosphere. In certain embodiments this burst disk may be a retrievable burst disk. Burst disks may allow, among other things, venting of the annulus above the LRA, and in certain embodiments may allow pumping of a functional fluid such as nitrogen into the annulus near the top of the FSR. Burst disks may allow pressure and/or temperature measurement of the flow stream (inside inner riser) or annulus between inner and outer risers. In addition to burst disks, high flow hot stabs may be employed in various types of equipment, for example, in the emergency disconnect systems.

Subsea flexible conduits, sometimes referred to herein as simply as "flexibles", or "flexible jumpers", are known to skilled artisans in the subsea hydrocarbon drilling and production art. For example, U.S. Pat. No. 6,039,083 discloses that flexible conduits are commonly employed to convey liquids and gases between submerged pipelines and offshore oil and gas production facilities and other installations. These conduits are subjected to high internal and external pressures, as well as chemical actions associated with the seawater surrounding the submerged conduits and the fluids being transported within the conduits. U.S. Pat. No. 6,263,982 discloses subsea flexible conduits may comprise a flexible steel pipe such as manufactured by Coflexip International of France, under the trademark "COFLEXIP", such as their 5 -inch (12.7cm) internal diameter flexible pipe, or shorter segments of rigid pipe connected by flexible joints and other flexible conduit known to those of skill in the art. Other patents of interest, assigned to Coflexip and/or Coflexip International, include U.S. Pat. Nos. 6,282,933; 6,067,829; 6,401,760; 6,016,847; 6,053,213 and 5,514,312. Other possibly useful flexible conduits are described in U.S. Pat. No. 7,770,603, assigned to Technip, Paris, France. U.S. Pat. No. 7,445,030, also assigned to Technip, describes a flexible tubular pipe comprising successive independent layers including helical coils of strips or different sections and at least one polymer sheath. At least one of the coils is a strip or strips of polytetrafluoroethylene (PTFE). This list is not meant to be inclusive of all flexible conduits useable in systems and methods of the present disclosure.

Hoses, which may also be referred to herein as flexible jumpers in certain embodiments, suitable for use in the systems and methods of this disclosure may be selected from a variety of materials or combination of materials suitable for subsea use, in other words having high temperature resistance, high chemical resistance and low permeation rates. Some f ouropolymers and nylons are particularly suitable for this application except for conduits of extremely long length (several kilometers or more) where permeation may be problematic. A good survey of hoses and materials may be found in US Pat. No. 6,901,968, presently assigned to Oceaneering International Services, London, Great Britain, which describes so called "High Collapse Resistant Hoses" of the type used in deep sea applications, which, in use, must be able to resist collapsing due to the very large pressures exerted thereon.

In certain embodiments it may be necessary or desirable to splice one hose to another hose, or to replace a damaged hose. In these instances, the ROV-operable hose splicing devices of assignee's serial numbers 61479486 and 61479489, both filed April 27, 2011 may be useful. The '486 application describes ROV-operable hydraulically-powered hose splicing devices, while the '489 application describes ROV-operable non-hydraulically-powered (mechanical) hose splicing devices. Each device provides a full-bore connector while allowing full- pressure service that may be preferred for applications that require high flow rates and high pressure. A simple stab motion employing a guide funnel minimizes the dexterity required of the ROV pilot. The hydraulically-powered devices include at least two chambers and a least one self-engaging mechanical lock per chamber, wherein after a hose is stabbed into a chamber, the ROV pilot energizes the device and the connection is made without further need to move the ROV manipulators, and the hydraulic pressure can be released from the chambers. An ROV hot stab may be used in certain embodiments to connect the device to an ROV hydraulic power unit to energize and operate the device. The assemblies described herein may be useful with either a single pipe (Single Line Offset Riser - SLOR) or a pipe in pipe design (Concentric Offset Riser - COR) that provides additional insulation and allows riser base gas lift or active heating through the annulus. These risers can be either welded or threaded construction and may be tensioned by an upper aircan located at 50- 150m below the surface depending on the environmental conditions, or by hydro-pneumatic tensioners, or both. Each freestanding riser may be connected to the surface structure (for example, a surface vessel or production platform) by a shallow water flexible jumper.

In certain embodiments, riser tension is maintained using a non-integral aircan system chain tethered above the riser string. The aircans provides the necessary buoyancy upthrust required for global stability and motion performance control and ensures that positive 100 kips (45,000 Kg) effective tension is experienced at the base of the riser under all loading conditions, including failure of one or more aircan chambers. In one embodiment, an LRA manufactured generally in accordance with FIGS. 3 and 4 weighs approximately 30 kips (13,600 Kg) in air, 26 kips (11,800 Kg) submerged. It may be attached to the suction pile with 90 feet (27 m) of 117mm R-4 studless chain with a breaking strength of 2,915 kips (1,300,000 Kg) and a 250 ton (230,000 Kg) Crosby G-2140 shackle with a breaking strength of 2,750 kips (1,230,000 Kg). The LRA in this embodiment is comprised of a 15Ksi (103 MPa) GE Oil & Gas (Vetco) H-4 subsea wellhead, specially machined with 2 x 7-1/6 inch (5.08 x 18.2cm) 10,000 psi (69 MPa) inlets to accommodate either multiple flexible jumper connections, or as illustrated in FIG. 3, one production jumper and an ROV interface for methanol injection.

The FSR containment or production concept which employs the assemblies disclosed herein is scalable over a wide range of water depths and well pressures and conditions. Flow assurance calculations indicate that the FSRs, and LRA and URA employed, are capable of handling over 40,000 bbls per day (6400 m³/day) each with a 6-inch (15cm) ID flow path. Existing dry tree riser hardware may be used to construct the FSRs as it is readily available. The outer riser joints may be 13.813-inch (35.085cm) OD x 0.563-inch (1.43cm) wall X-80 material and rated to 6,500 psi (45 MPa). X-80 material may be used to weld on premium riser connectors with external and internal metal to metal seals and fatigue performance for the anticipated service life. Riser systems employing URA and/or LRA assemblies of the present disclosure may be installed, in certain embodiments, by a MODU and then accommodate upper flexible jumper installation after the riser has been run. The upper flexible may be connected to the URA during installation from the drilling MODU and optionally clamped at intervals hanging vertically along the riser. The lower subsea flexible may be connected several days later to the LRA by subsea installation vessels after the FSR is connected and tensioned to the suction pile.

The surface structure may be equipped with a quick disconnect system (QDC) for the upper flexible. Embodiments of a quick connect/disconnect coupling feature are described in assignee's United States provisional application serial number 61480368, filed April 28, 2011. A disconnectable buoy may be used to support the surface structure end of the upper flexible during an emergency disconnect. The buoy may be attached to provide both buoyancy and drag and ensure the upper flexible is not damaged by too rapid a decent (i.e. excessive compression exceeding the minimum bend radius) after it released to free fall. In the event of a hurricane or a planned disconnect, the 6- inch (15cm) upper flexible is disconnected from the surface structure in a controlled manner and lowered by a support vessel to hang along the side of the FSR, where it is clamped in place via ROV.

In certain concentric riser embodiments in which one or more of the LRAs and/or URAs described herein may be useful, the URA may allow for flow control of both the inner riser, as well as, the annulus between the inner and outer risers. The inner riser flow path may have provisions for pressure and temperature sensors; a fail close hydraulic actuated ESD valve controlled from the surface structure; a ROV hot stab pressure bleed port; and/or an ROV operated manual gate valve. The annulus may incorporate provision for ROV hot stab nitrogen injection, and a temperature and pressure sensor. A pressure safety valve (PSV) set at 4,500 psi (31 MPa) on the riser annulus may prevent failure due to over pressure of the outer riser in the event of a hydrocarbon leak from the inner riser.

In certain embodiments the LRA provides ROV hot stab access to both the riser annulus and production flow path for injection, venting, pressure and temperature monitoring. Two ROV operated 3-inch (7.5cm) valves on the annulus vent sub provide larger bore access to the annulus for nitrogen purging and venting operations, or other functional operation. In certain embodiments, the LRA flow path is comprised of two spools, each equipped with an ROV operated 5 -inch (13cm) lOKsi (69 MPa) valve and ROV operated clamps (such as supplied by Vector Subsea) for subsea connection of flexible production jumpers.

In certain embodiments, LRA and URA assemblies described herein may be used as components of a containment and disposal, or production, system. In such systems, a hydrate inhibition system (HIS) may be integrated into the systems and methods. Hydrate inhibition chemical supply lines from a surface vessel may supply chemical to a subsea BOP stack cap, BOP, and to subsea flexible conduits through a subsea manifold. When circulating the chemical, it may return to the vessel through a return line. Chemical may also be delivered to choke and kill lines of the subsea BOP via a choke/kill manifold.

From the foregoing detailed description of specific embodiments, it should be apparent that patentable assemblies and methods have been described. Although specific embodiments of the disclosure have been described herein in some detail, this has been done solely for the purposes of describing various features and aspects of the methods and apparatus, and is not intended to be limiting with respect to the scope of the assemblies and methods. It is contemplated that various substitutions, alterations, and/or modifications, including but not limited to those implementation variations which may have been suggested herein, may be made to the described embodiments without departing from the scope of the appended claims.

Claims

1. An assembly for connecting a subsea riser to a seabed mooring and to a subsea hydrocarbon fluid source, comprising:

a generally cylindrical member having a longitudinal bore, a lower end, an upper end, and an external generally cylindrical surface, the member comprising sufficient intake ports extending from the external surface to the bore to accommodate flow of hydrocarbons from the hydrocarbon fluid source as well as inflow of a functional fluid, at least one of the intake ports fluidly connected to a production wing valve assembly,

2. The assembly of claim 1 wherein the generally cylindrical member comprises:

a subsea wellhead housing, the lower end modified by connecting a transition joint thereto, the transition joint comprising said sufficient intake ports,

the upper end of the subsea wellhead housing fluidly connected to an external tieback connector fluidly connecting the subsea wellhead housing to a riser stress joint,

the subsea wellhead housing having an internal seal profile adapted to seal with an internal tieback connector, the internal tieback connector fluidly connecting an inner subsea riser to the internal seal profile, and

the internal tieback connector having a nose seal which seals into the subsea wellhead internal seal profile, the nose seal providing pressure integrity between an internal flow path in the inner riser and an annulus between the inner riser and a substantially concentric outer riser.

3. The assembly of claim 2 wherein the production wing valve assembly is fluidly connected to a subsea source through a subsea flexible conduit.

4. The assembly of claim 2 wherein the riser stress joint is in turn fluidly connected to the outer riser.

5. The assembly of claim 2 comprising ROV-operated valves for controlling flow through the internal flow path in the inner riser and the annulus.

6. The assembly of claim 2 comprising one or more hot stab ports for ROV intervention and/or maintenance.

7. The assembly of claim 1 wherein

the generally cylindrical member comprises a high-strength metal forging fluidly connected to a production riser pup joint via a lower cross-over joint and threaded connector, the forging comprising said longitudinal bore, lower end, upper end, external generally cylindrical surface, and said sufficient intake ports,

the lower end of the metal forging comprising the connector suitable for connecting to the subsea mooring.

8. The assembly of claim 1, wherein the generally cylindrical member comprises a forged, high-strength steel intake spool fluidly connected to a gooseneck assembly, the gooseneck assembly fluidly connected to a subsea source through a subsea flexible conduit, the intake spool also comprising a connector allowing connection to a source of a functional fluid.

9. An assembly for connecting a subsea riser to a subsea buoyancy device and to a surface structure comprising:

a generally cylindrical member having a longitudinal bore, a lower end, an upper end, and an external generally cylindrical surface, the member comprising sufficient outtake ports extending from the bore to the external generally cylindrical surface to accommodate flow of hydrocarbons from the riser, and at least one port allowing flow of a functional fluid in the longitudinal bore, at least one of the outtake ports fluidly connected to a production wing valve assembly for fluidly connecting the member to the surface structure with a subsea flexible conduit,

10. The assembly of claim 9 wherein the member comprises a drilling spool adapter having a first end fluidly connected to a tubing head, the tubing head comprising one or more outtake ports, the tubing head connected to a casing head having a stem joint fastened thereto, the casing head also comprising one or more ports for admitting a flow assurance fluid.

11. The assembly of claim 10 wherein the stem joint is fluidly connected to an outer concentric riser.

12. The assembly of claim 11 comprising an adjustable tubing hanger fluidly connecting an inner riser to the tubing head.

13. The assembly of claim 12, wherein the production wing valve assembly comprises first and second flow control valves for controlling flow in the inner riser and in an annulus between the inner riser and the outer riser.

14. The assembly of claim 9 wherein the production wing valve assembly comprises one or more ROV hot-stab ports allowing a flow assurance fluid to flow into an inner riser and an annulus between the inner riser and an outer riser, the flow assurance fluid selected from the group consisting of nitrogen or other gas phase, heated seawater or other water, and organic chemicals.

15. The assembly of claim 9 wherein the generally cylindrical member comprises an offtake spool having the upper end and the lower end, a padeye flange connected to the upper end of the offtake spool, and a hanger spool connected to the lower end of the offtake spool, wherein the offtake spool and the hanger spool define the longitudinal bore.

16. The assembly of claim 15 wherein the offtake spool comprises a second bore substantially perpendicular to the longitudinal bore and fluidly connecting the longitudinal bore to one of the production wing valve assemblies through one of the outtake ports.

17. The assembly of claim 16 wherein the production wing valve assembly comprises a gooseneck conduit and two emergency shutdown (ESD) valves fluidly connected inline of the gooseneck conduit, one of the ESDs being hydraulically actuated, and the second ESD being electronically actuated.

18. The assembly of claim 15 wherein the hanger spool comprises a third bore substantially perpendicular to the longitudinal bore and fluidly connecting an annulus defined by the hanger spool and an internal riser joint with an annulus access valve assembly.

19. The assembly of claim 18 wherein the annulus access valve assembly comprises one or more ROV-operable valves.

20. The assembly of claim 19 wherein the annulus access valve assembly is fluidly connected to a source of flow assurance fluid.

21. The assembly of claim 9 further comprising a production bore offtake spool fluidly and mechanically connected to a substantially vertical conduit and to a production tubing, the production tubing in turn fluidly connected to a bend restrictor through a subsea API flange, a high pressure subsea connector, another subsea API flange connection, and optionally a QDC subsea connector, the bend restrictor connected to the upper subsea flexible conduit which extends in a catenary loop to the surface structure, and wherein the substantially vertical conduit fluidly connects in series to an adapter which in turn fluidly connects to a hanger spool, an API flange, a casing head via another API flange, a stem joint welded to the casing head, and to the outer riser via a threaded connection into a stem joint, the offtake spool including a shackle flange allowing connection to the subsea buoyancy device.

22. The assembly of claim 21 further comprising an ROV-operable ESD fluidly connected in a section of the conduit.

23. The assembly of claim 22 further comprising a support bracket which supports production tubing an angle σ to the conduit, and also supports a bend shield which provides a mechanical barrier between the production tubing and the conduit, where the angle σ ranges from 0 to about 180 degrees.

24. The assembly of claim 23 further comprising a connection to the hanger spool for connecting a gooseneck for delivery of heated water to the hanger spool from a surface vessel.

25. The assembly of claim 24 wherein the gooseneck comprises, in order starting at the hanger spool, an API flange, a section of tubing, a high pressure subsea connector, a subsea API connector and API flange, and a bend restrictor.

26. The assembly of claim 25, wherein the inner riser is positioned inside of the adapter, the hanger spool, and the casing head, creating the annulus between an inner surface of the hanger spool and the inner riser.

27. The assembly according to claim 9, further comprising components allowing circulation of a functional fluid, such as heated water, through the annulus.

28. The assembly according to claim 27 comprising an offtake spool fluidly connected to a hanger spool, the hanger spool in turn fluidly connectable to a tapered stress joint of the free standing riser.

29. The assembly according to claim 28, further comprising a first block elbow includes an inner bore which intersects with and is substantially perpendicular to a bore in the offtake spool, a second block elbow having an inner bore which is also substantially perpendicular to the offtake spool bore but which does not intersect the offtake spool bore, and a gooseneck conduit fluidly connected to the first block elbow providing a flow path for hydrocarbons in combination with first block elbow bore.

30. The assembly according to claim 29, further comprising first and second emergency shutdown valves in the gooseneck conduit, the gooseneck conduit fluidly connected to a subsea connector in turn fluidly connected to the upper subsea flexible conduit.

31. The assembly according to claim 27, wherein the components allowing circulation of a functional fluid through the annulus comprises a subsea connector, a conduit and one or more valves in the conduit, the conduit fluidly connected to the hanger spool.