Exxon Production Research Company

Jerome Q Burns

Richard H Gunderson

Lyle D Finn

Peter A Lunde

Stewart A Fox

George F Davenport

Michael P Piazza

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

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 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.

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San Diego, CA, United States of America

Jerome Q Burns