Exxon Production Research Company

Lyle D Finn

Kenneth M Steele

M Sidney Glasscock

Leo Donald Maus

Mark A Danaczko

Jerome Q Burns

George F Davenport

Michael P Piazza

Timothy Otis Weaver

Carl R Brinkmann

Bruce C Volkert

Michael M Brady

Jamie F Matthews, Jr

Donald A Hayes

Leonard D Power

A compliant offshore structure in which the primary restoring force to lateral displacement is provided by elongate flex elements. A gravity base is rigidly secured to the ocean bottom. A tower extends vertically upward from the base to a position above the ocean surface. A work deck is supported atop the tower. The tower is secured to the base by elongate flex elements which are arranged in an array surrounding the central axis of the structure. Each flex element has one end secured to the base and a second end secured to the tower. The flex elements permit the tower to pivot about its lower end, thus providing the tower and deck with a compliant response to environmental forces. The flex elements also support the tower above and free from contact with the base. This eliminates the need for a vertical load bearing joint between the tower and base.

Compliant offshore structure with fixed base

A flexible structural joint of 'flex joint' for use in an articulated structure is disclosed. The articulated structure has a first section and a second section which are located along a longitudinal axis of the structure, the first section being subject to lateral or transverse loads. The flex joint is located between the first and second sections and accommodates lateral pivoting of the first section with respect to the second section through elastic flexing or bending of certain of its members. No moving parts are used. In a first embodiment, the flex joint consists of an elongated axial load member and at least three shear and torsion links oriented so as to lie substantially in a plane perpendicular to the longitudinal axis of the structure. Each of the links is connected at one of its ends to the first section and at its other end to the second section. In a second embodiment of the invention, four shear and torsion links are joined to form a shear and torsion frame which lies in a plane that is substantially perpendicular to the longitudinal axis of the structure. The frame is connected to the first section of the structure at the opposite ends of a first diametral line lying in the plane of the frame. Similarly, the frame is connected to the second section of the structure at the opposite ends of a second diametral line lying in the plane of the frame. Preferably, the first and second diametral lines are substantially mutually perpendicular.

Flex joint

A complaint offshore platform in which the primary restoring force to lateral displacement is established by flex piles driven into the seafloor and fixedly secured to the platform legs a preselected distance above the seafloor. The platform includes a substantially rigid space-frame structure extending from the ocean bottom to a position above the ocean surface. A drilling and production deck is secured atop the space-frame structure. Shear piles extend through the base of the space-frame structure to prevent lateral displacement of the base while permitting the space-frame structure to pivot about its base. As the platform sways about its base in response to environmental forces, the flex piles establish a vertical couple at the location at which they are attached to the space frame structure. This couple resists movement of the platform away from a vertical orientation. In the preferred embodiment, the flex piles are secured to the platform at or near one-half the total height of the space-frame structure.

Compliant offshore platform

A pile assembly adapted for use in a compliant piled tower. A plurality of drive piles are driven into the ocean floor in a symetric array about a central, substantially vertical axis. A flex pile is secured to the upper end of each drive pile and extends upward to a preselected elevation above the ocean floor. The longitudinal axes of each drive pile flex pile pair are laterally offset from one another with the flex piles also being arranged in symetric array about the central axis. A tie member is provided to restrain the flex piles from lateral motion relative to one another. The tie member serves to balance the moments established by virtue of the eccentric axes of the flex pile drive pile pairs. The use of eccentric axes in the pile assemblies simplifies driving the drive piles, permits the drive piles to be placed relatively far from one another to minimize pile group effects and permits the flex pile to be designed without being constrained by driving considerations.

Pile assembly for an offshore structure

A hybrid offshore structure for conducting petroleum drilling and producing operations in very deep waters is disclosed. The structure consists primarily of a substantially rigid lower section extending upwardly from the bottom of the body of water to a pivot point located intermediate the bottom and the surface of the body of water, a compliant upper section extending upwardly from the pivot point to a deck located above the water surface, pivot means located proximate the pivot point and adapted to permit the compliant upper section to pivot laterally in response to environmental loads, and torsion means adapted to transmit torsional loads from the compliant upper section to the substantially rigid lower section. The lower section may comprise either a conventional trussed steel frame fixed to the bottom of the body of water by a plurality of piles or a concrete or steel gravity base. The compliant upper section may optionally be either a guyed tower or a buoyant tower. A variety of suitable pivot means and torsion means may be used. The pivot point is positioned so that the weight of the hybrid structure is substantially minimized while maintaining the flexural vibration period of the structure within acceptable limits. Generally, the pivot point will be located above the bottom of the body of water a distance of between about 10 percent and about 50 percent of the total depth of the body of water.

Hybrid offshore structure

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Growing community of inventors

Houston, TX, United States of America

Lyle D Finn