Fairing for marine drilling risers

Abstract

A fairing includes two half-shells of fiber reinforced plastic or fiberglass. The shell halves are shaped to close around the buoyancy modules (e.g., cylindrical syntactic foam buoyancy modules) commonly used on deep-water risers, but with an extended trailing edge. The fairing includes a tail that streamlines the riser and reduces / prevents formation of the vortex, which causes drag and vibration. Hinges at the tail join the halves and enable them to be opened for assembly around the riser pipe as it is being run into the water. The fairing may be fastened together by bolted stainless steel tensioners that tightly draw together straps of high strength aramid fiber, such as KEVLAR®. The fairing is positioned on the riser such that the fairing is free to swivel and rotate into the current, while integral buoyancy blocks support the tail. To prevent movement up or down the riser string, the fairing is held in place by a channel clamp gripping the outside diameter of the syntactic foam buoyancy module.

Description

PRIORITY INFORMATION[0001]This application claims priority under 35 U.S.C. §119(e) from U.S. provisional application Ser. No. 60 / 834,219 filed Jul. 28, 2006, which is hereby incorporated by reference.BACKGROUND OF THE INVENTION[0002]As offshore oil and gas exploration moves into deeper and more inhospitable waters, the danger of equipment failure increases. One of the hazards now being encountered is that of high-speed (e.g., 3 knots and greater) currents damaging the riser pipe that connects a floating drill rig to its wellhead on the ocean floor. Such currents exert a massive drag force on the pipe while causing it to shake violently in a phenomenon called vortex-induced vibration (VIV).[0003]Fairings, strakes, shrouds, and similar devices have been used for many years in an attempt to prevent riser damage by currents. These devices have been only partly successful because they were (1) overly complex and expensive; (2) difficult and time-consuming to assemble on board the rig; an...

AI Technical Summary

Benefits of technology

[0005]A fairing includes two half-shells of fiber reinforced plastic or fiberglass. The shell halves are shaped to close around the buoyancy modules (e.g., cylindrical syntactic foam buoyancy modules) commonly used on deep-water risers, but with an extended trailing edge. The fairing includes a tail that streamlines the riser and reduces / prevents formation of the vortex, which causes drag and vibration. Hinges at the tail join the halves and enable them to be opened for assembly around the riser pipe as it is being run into the water. The fairing may be fastened together by bolted stainless steel tensioners that tightly draw together straps of high strength aramid fiber, such as KEVLAR®. The fairing is positioned on the riser such that the fairing is free to swivel and rotate into the current, while integral buoyancy blocks support the tail. To prevent movement up or down the riser string, the fairing is held in place by a channel clamp gripping the outside diameter of the syntactic foam buoyancy module.

Problems solved by technology

As offshore oil and gas exploration moves into deeper and more inhospitable waters, the danger of equipment failure increases.

One of the hazards now being encountered is that of high-speed (e.g., 3 knots and greater) currents damaging the riser pipe that connects a floating drill rig to its wellhead on the ocean floor.

These devices have been only partly successful because they were (1) overly complex and expensive; (2) difficult and time-consuming to assemble on board the rig; and (3) lack the necessary robustness to withstand the rigors of shipboard use.

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