Other

Sea Engineering Associates, Inc.

David N Dunlop

Pieter G Wybro

A compact offshore tension leg platform having a deck, a hull, and a plurality of elongate tendons securing the hull to an ocean floor foundation provides full well workover and production capabilities for autonomous operation and can be installed and operated in any waterdepth and sustain any environmential loading conditions. The hull supports the well risers of well trees located below the water surface at an elevation in close proximity to the connections of the tendons to the hull. Alternatively the risers and trees may be supported by the deck. A well workover platform, supported by a circular perimeter trackway on the deck may be positioned over any of the well risers for workover operations. Liquid products may be exported from the platform via a seabed pipeline or to a floating tanker moored to a mobile offtake on the deck support column. The hull is configured to minimize loadings in the tendons. All components, except the deck, are installed by a drilling vessel without the need for specialist installation vessels and equipment. The tendons are arranged in groups offset from the hull body to resist platform overturning loadings, and to reduce the tendons pretension required to prevent platform pitch and roll motions. The wells are drilled prior to installation of the hull using a drilling vessel. After installation of the platform, all operations required on the wells are performed autonomously from the platform without the need for another drilling vessel or equipment.

Tension leg platform and method of instalation therefor

A method and apparatus for installing and tensioning mooring tethers or tendons between a subsea foundation and a tension leg platform. Load bearing porch members secured on the platform columns near the hull receive the threaded upper end of tethers which are engaged at their lower ends in the foundation. Movable hoists on the platform deck position the upper ends of the tethers on the porches. A platform arrester through which the hoist lines pass is connected with each hoist to move with the platform during vertical motions thereof and selectively engage the hoist lines to allow only downward movement of the platform arrester relative to the hoist lines. A motorized tether tensioning tool connected to each hoist line has a lock-down nut at its lower which releasably connects to the upper end of each tether such that the nut is vertically movable on the tether. The upper ends of the tethers are positioned on the porches and nominal constant tension is applied to the tethers while the platform arresters allow only downward movement relative to the hoist line until platform trim is within predetermined limits. The tensioning tools then run the nuts down on the tethers to engage them on the porches and apply tension in the tethers between the porches and foundation and are thereafter removed whereby tension loading in each tether is transmitted to the platform such that the total platforn tension load is equally distributed between the whole tether complement.

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Houston, TX, United States of America

David N Dunlop