Exxon Production Research Company

Richard H Gunderson

Peter A Lunde

Terry N Gardner

Jerome Q Burns

William T Ilfrey

Stewart A Fox

Thomas G Choate

Peter J Guile

Michael P Piazza

Charles G Lyons

A releasable latch-type connector for a tension leg platform tether. A tether portion of the latch is provided with an annularly arranged set of shear lugs. The tether portion of the latch is adapted to be received within a generally cylindrical second portion of the latch. The second portion of the latch is also provided with an annularly arranged set of shear lugs. The two sets of shear lugs are arranged so that the tether portion of the latch may be inserted into the second portion of the latch and then rotated and lifted to cause the two sets of shear lugs to come into abutment, preventing further withdrawal of the tether portion of the latch. This connector is particularly well suited for securing the lower end of a tension leg platform tether to a foundation on the ocean bottom.

Tether connector for a tension leg platform

A fatigue-resistant threaded connector for connecting adjacent sections of a tubing string subject to cyclic dynamic stress variations is disclosed. The connector comprises a pin member which is threadedly engageable with a corresponding box member. In its preferred embodiment, the connector is radially preloaded. The connector has tapered threads with a straight load path having substantially no eccentricity. The preferred thread form is a modified buttress thread having a zero (or near zero) degree load flank, a 45 degree stab flank, and a large root radius. Additionally, the thread may include a small stab flank relief to reduce stress concentrations, and a differential between the pitch of the pin threads and the pitch of the box threads to compensate for the Poisson's ratio effect of the radial preload. The connector utilizes an elliptical stress relief groove at the base of the pin threads and elliptical contours on all thickness transitions to reduce peak stresses. The fully assembled and preloaded connector has a maximum stress-concentration-factor of less than 1.5 and its weight is less than 2.5 times the weight of an equivalent length of tubing.

Fatigue-resistant threaded connector

Described herein are a system for securing and tensioning the tethers 12 of a tension leg platform 10 and a TLP installation method incorporating such a system. The tethers 12 preferably extend upward from the ocean bottom 16 to a position slightly below the bottom of the unballasted TLP hull 20. At least one tether tensioning tool 26 is situated within the hull 20 for lowering a tether extender 22 to each tether 12 and then biasing each tether-tether extender unit upward to tension the tether 12. The use of a removeable tensioning tool 26 avoids the need for a dedicated tensioning system for each tether 12. The tensioning system 28 of the present invention permits use of a simplified method for installing a TLP 10. Because the tethers 12 extend to an elevation which, at least initially, is below the draft of the TLP hull 20, the tethers 12 may be installed offshore prior to hull installation. Following tether installation, the hull 20 is floated to a position above the tethers 12 and the securing and tensioning system 28 is used to lock the hull 20 to the tethers 12.

Method and apparatus for tensioning the tethers of a tension leg platform

A tether and tether tensioning system for a tension leg platform. A plurality of elongate tethers 12 are used to secure a tension leg platform hull 20 to a foundation 14 at the ocean floor. Each tether 12 has a lower end secured to the ocean floor foundation 14. The tethers 12 extend upward to a position slightly below the bottom of the hull 20. A tether securing and tensioning system 30 is positioned within the hull 20 for each tether 12. This system includes a tether extender 22 positioned within a shroud 28 in the hull bottom. The tether extender 22 includes a tether latch 24 at its lower end. The tensioning system is adapted to lower the tether extender 22 downward below the hull 20 to permit the tether extender 22 to latch to the tether 12. The securing and tensioning system 30 then raises the tether extender 22 to tension the tether 12. The tether tensioning system of the present invention permits use of a simplified method for installing TLPs. The tethers 12 extend upward to an elevation which, at least initially, is below the maximum draft of the tension leg platform hull 20. This permits the tethers to be installed offshore prior to installation of the hull 20. Following tether installation the hull 20 is floated to a position directly above the tethers 12 and the tether securing and tensioning system is used to lock the hull 20 to the tethers.

Tension leg platform and installation method therefor

A compliant offshore structure in which stabilization against excessive sway is provided by a resilient pile assemblies. A series of drive piles extend into the ocean floor beneath the base of the structure. Drive piles extend upward to a position proximate a pile attachment location on the structure a spaced distance above the ocean floor. The upper end of each drive pile is secured to the structure at the pile attachment location by a resilient coupling. The resilient coupling permits the structure to move upward and downward a slight distance relative to the substantially rigid drive pile. This accommodates sway of the structure. The resilient coupling biases the structure back to a vertical orientation in response to sway of the structure. In a preferred embodiment the pile attachment location is situated proximate the base of the offshore structure.

Compliant offshore structure stabilized by resilient pile assemblies

A buoyancy system for a tension leg platform tether 10 or other element extending a significant vertical distance through a body of water. A series of bulkheads 25 divide the interior of the tether 10 into individual buoyancy cells 31. A central access tube 32 extends along the central axis of the tether 10, passing through a sealed penetration in each bulkhead 25. A series of cascade conduits 42 are provided the lower portion of each buoyancy cell 31 in fluid communication with the buoyancy cell 31 immediately above. A tool 82 is provided for injecting air into a selected buoyancy cell 31. As air is injected, water exists through the central access tube 32 until the buoyancy cell 32 is emptied of water, at which point air passes through the cascade conduit 42 into the adjacent upper buoyancy cell. The tool 82 can also be used to selectively flood individual buoyancy cells 31.

Buoyancy system for submerged structural member

A pressure balanced tether buoyancy system 12 useful for reducing the load imposed on a tension leg offshore platform 24 by the tethers 10 securing it to the ocean bottom. The tether 10 has tubular tether walls 11 defining a central cavity 15 isolated from the surrounding seawater. A series of bulkheads 25 extend laterally across the interior of the tether 10, dividing it into a series of individual buoyancy cells 31. Each bulkhead 25 is provided with a differential pressure valve 34 establishing selective fluid communication between the two buoyancy cells 31 separated by the bulkhead 25. Preferably, each differential pressure valve 34 is adapted to open in response to a differential pressure across the bulkhead 25 exceeding the differential hydrostatic existing across the vertical distance separating adjacent bulkheads 25. This permits a pressure gradient to be established interior to the tether 10 approximating that of the seawater in which the tether 10 is located. A central access tube 32 can be provided interior to and extending the length of the tether 10. The central access tube 32 can be used to pass tools through the tether 10 and to ballast and deballast individual buoyancy cells 31.

Pressure balanced buoyant tether for subsea use

A subsea connection unit for securing an offshore structure to a marine bottom is disclosed. The unit comprises a base adapted to be positioned on the marine bottom and an insert member adapted to be connected to the lower end of the offshore structure. The base has a recess thereon adapted to receive the insert member. Releasable vertical latch means comprised of a plurality of tapered shear blocks are carried by the insert member and cooperate with tapered lugs in the recess to lock the insert member against vertical movement within the recess. Releasable horizontal latch means comprised of a plurality of wedge members are positioned on the base around the recess and cooperate with load surfaces on the insert member to center and lock the insert member against horizontal movement within the recess.

Connection unit for securing offshore structures to marine bottom

There is disclosed a universal joint for multiple conduit system wherein all of the conduits pass through the interior of the joint. The conduits which pass through the universal joint on axes offset from the pivot axes of the joint are provided with first and second pivot means which are preferably fluid swivels. The fluid swivels provide the requisite flexibility to the conduits when the universal joint is flexed.

Universal joint for multiple conduit system

A pressure energized seal to seal an annulus between two concentric cylindrical members, particularly well suited to be used as an annular casing seal in an oil and gas well. A circular sealing ring has both its upper and lower surfaces channeled to leave two upper sealing lips and two lower sealing lips which effect the seal by being forced against the sealing surfaces of the cylindrical members. Two circular setting rings can be used to spread the sealing lips into sealing engagement with the sealing surfaces of the cylindrical members. The setting rings would be partially disposed within the channels of the sealing ring and adapted to spread the sealing lips when the setting rings are moved toward the sealing ring.

Annular seal

The disclosure is directed to a coupling assembly which serves to connect a pipelaying stinger to a pipelaying vessel and is of the type wherein laterally spaced, disconnectable joints interconnect the stinger and vessel. The spaced joints are each comprised of a tapered male member and a mating female member, normally a pin and receptacle, and are preferably axially aligned to form a hinge which permits the stinger to rotate about a horizontal axis. When the two spaced joints are both engaged the stinger is prevented from rotating in a non-axial manner. However, when one joint is disengaged, the other will disengage as the male and female members rotate about their rotational point of contact.

Stinger coupling

Apparatus for supporting pipe as it is laid from a vessel in a body of water is described. The apparatus includes a stinger movable from an operating position supporting the pipe to a protected position beneath the vessel. Apparatus for moving the stinger from the operating position to the protected position and securing it to the vessel is also provided.

Growing community of inventors

Houston, TX, United States of America

Richard H Gunderson