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    1. Subsea

    SUBSEA PRODUCTION TECHNOLOGY Three exploration wells being tied back to Enserch's GB 388

    Dec. 1, 1995
    Ed Fisher Cooper Cameron The production riser for Enserch's GB 388 project, shown here with foam buoyancy and vortex-shedding strakes being lowered into position, was used previously on Placid Oil's Green Canyon project. Two of three previously drilled exploratory wells in the Gulf of Mexico Block 388 are now producing oil for Enserch. The third, primarily a gas-producer, will be tied back later. Three facets of the production system are unique: the subsea jumpers, the production
    12off33
    Ed Fisher
    Cooper Cameron
    12off33

    The production riser for Enserch's GB 388 project, shown here with foam buoyancy and vortex-shedding strakes being lowered into position, was used previously on Placid Oil's Green Canyon project.

    Two of three previously drilled exploratory wells in the Gulf of Mexico Block 388 are now producing oil for Enserch. The third, primarily a gas-producer, will be tied back later. Three facets of the production system are unique: the subsea jumpers, the production riser and titanium stress joint, and the trees.

    • Subsea jumpers: Cameron (a division of Houston-based Cooper Cameron) developed a jumper system using flexible, high-pressure lines capable of tying in satellite subsea wells to any of the 14 outside well bays in a 24-well template. A line may be connected directly to a standard well bay and does not require a dedicated flowline tie-in porch. Each jumper contains the flowline plus electrical/control lines for a single well and is completely independent and can be worked on without disturbing adjacent wells.

      Work is also underway to develop a similar system using rigid piping to reduce overall cost. In the meantime, Enserch has ordered six more of the existing and now proven flexible jumper systems. Plans call for use of the advanced rigid-pipe design on Enserch's Block 387 development.

    • Titanium riser: The production riser and its unique titanium stress joint was first designed and put into service for Placid's Green Canyon project in 1988. Enserch was a partner in this development. The riser was operational for just over two years. During this period, two hurricanes impacted the site. Also, rig instrumentation recorded water velocity from a loop current packing velocities in excess of 4 knots spun off from the Gulf Stream for over a week.

      When the reservoirs involved failed to produce as hoped and the field abandoned, the riser was removed. An examination showed it to be in excellent condition. The syntactic foam buoyancy had kept it in the desired position and the vortex-shedding strakes had performed their job successfully.

      Metallurgical examination of the titanium stress joint - a pioneering subsea application of titanium at the time - showed no indication of corrosion or fatigue-related damage even though stresses of 85 ksi had been recorded during the loop current event. The 85-ksi value is near the conservative design limit.

      A thorough metallurgical inspection showed no problems with the titanium-steel interfaces of either riser or stress joint, so they could be re-installed without modifications. The riser was extended from its original 1,500-ft length to about 2,100 ft for use on the GB 388 project. The plug and abandon lines were increased from 2-7/8-in. 7,500 lb WP to 3-1/2-in. 10,000 lb WP.

    • Christmas trees: Cameron SpoolTrees were placed on the previously drilled wells. All site integration and testing for the GB 388 development was based on use of these trees. The trees allow control of wellbore fluid, while providing vertical downhole communication for workover. Primary benefits to Enserch from their use are:

      1. The ability to complete a well with full BOP protection at all times

      2. The ability to retrieve a downhole completion without retrieving the tree or disturbing flowline connections

      3. Reduced equipment handling, for faster routine installation from conventional rigs using standard procedures.

      Trees may be configured for template or satellite installation. The design has been approved by the Mineral Management Services for US Gulf of Mexico use and the UK Health and Safety Executive for North Sea applications.

    Installation

    Installation started when the site's mooring system was placed in position. The DB 250 moved in to set the template. Then the Ocean Voyager moved in and set spool frees on the three existing discovery wells and connected their jumpers. The refurbished riser was run and fully populated with a total of about 94,000 feet of production tubing and left free standing. After the upper riser connector package was installed, testing confirmed all connections. The first two wells than started to produce oil.

    Copyright 1995 Offshore. All Rights Reserved.