Gullfaks A Subsea Well System: Developments Completion, and Production Startup
- Mads Grinrod (Statoil) | Olav Inderberg (Statoil) | Tor W. Knudsen (Statoil)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling Engineering
- Publication Date
- March 1989
- Document Type
- Journal Paper
- 71 - 76
- 1989. Society of Petroleum Engineers
- 2 Well Completion, 6.5.2 Water use, produced water discharge and disposal, 6.1.5 Human Resources, Competence and Training, 5.1.2 Faults and Fracture Characterisation, 5.5 Reservoir Simulation, 1.10 Drilling Equipment, 1.6 Drilling Operations, 7.2.3 Decision-making Processes, 3 Production and Well Operations, 4.5.10 Remotely Operated Vehicles, 4.3.4 Scale, 4.2.4 Risers, 4.1.2 Separation and Treating, 7.3.3 Project Management, 4.2.3 Materials and Corrosion, 4.5.7 Controls and Umbilicals, 4.1.5 Processing Equipment, 4.2 Pipelines, Flowlines and Risers
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This paper discusses the philosophy, development plan, technical and functional descriptions, and experiences in the various phases, including startup, of the Gullfaks A subsea production system. The wells are connected to the Gullfaks A platform, which is a processing, drilling, and living quarters platform. Subsea operations were accomplished.
The Gullfaks Field
The Gullfaks field is 140 km [87 miles] from the Norwegian mainland (Fig. 1). The field appraisal drilling showed that the reservoirs are heavily faulted with a main north/south fault through the whole field. Recoverable reserves of the Gullfaks field are assumed to be 210 x 10(6) m3 [1,320 x 10(6) bbl] of oil and 23x10(9) std m3 [812 x 10(9) scf] of gas. The water depth at the field ranges from 130 to 220 m [427 to 722 ft].
Gullfaks A: Subsea Development Plan
The main objectives for incorporating subsea wells as part of the field development are (1) to develop reservoirs outside the efficient reach of the platform wells (Fig. 2); (2) to accelerate production and improve economic returns; and (3) to gain information and experience for future field developments.
The scope of the subsea part of the Gullfaks A project has changed from five producers in Feb. 1984 to three producers and I water injector in April 1985 to four producers and one water injector in April 1986. These changes result from increased knowledge from subsea-well drilling and new reservoir simulations. One exploration well was drilled in May 1987 and tied in as a fifth producer in May 1988.
The subsea wells are of a wet satellite type and non-through-flow-line (non-TFL), but are wireline serviceable. The same Christmas tree is used for both production and water injection. Each well is connected to the platform with a separate flexible flowline, a hydraulic umbilical, and an electrical umbilical.
The system is designed to be diverless; i.e., all tools required for installation and workover are non-diver-assisted. The design life of the subsea production system is 10 years. Fig. 3 shows plans for the development, installation, and startup of the Gullfaks A subsea system.
Fig. 4 shows the main components of the satellite system, which comprises (1) a protective structure, wellhead, tubing hanger, and downhole equipment; (2) a Christmas tree system; (3) a satellite-control module (SCM); (4) a workover system; and (5) pull-in and connection systems. The Gullfaks A satellite system is a new development.
Protective Structure. The protective structure is an open-frame-type structure that allows remote-operated vehicle (ROV) access. It is designed to deflect fishing gear, with a high probability, and is piled to absorb 100-metric-ton [91-ton] anchor-dragging loads. A removable roof is fitted to the structure to provide overhead protection (see Fig. 5). Additional protection is installed in the pull-in areas after pull-in and connection.
Wellhead and Tubing Hanger. Before the start of drilling operations, the protective roof is removed by a guideline establishment tool. In a single run, the tool establishes guidelines to the four main guideposts and retrieves the protective roof.
A 48-cm, 69-MPa [18 3/4 -in., 10,000 psi] weight-set wellhead system is used in the subsea wells. A five-string casing program comprising 76-, 51-, 41-, 34-, and 27-cm [30-, 20-, 16-, 13 3/8-, and 10 3/4-in.] casing strings is used. The 27-cm [10 3/4-in.] production casing string crosses to 24 cm [9% in.] below the tubing-retrievable subsurface safety valve.
The tubing hanger system allows the tubing hanger to be run, oriented, tested, and locked in one trip.
Christmas Tree System. The Christmas tree system (Fig. 4) contains the Christmas tree, a Christmas tree cap, and the Christmas tree/tree-cap running tool.
The Christmas tree valve block is forged as a single block. The guide frame provides protection for the valve operators. The valves are fitted for ROV override through an extension shaft supported by the framework. The Christmas tree running tool is used to run or to retrieve either the Christmas tree or the Christmas tree cap. SCM. This unit (Fig. 4) contains all active components of the control system installed subsea. All hydraulic connections are through the bottom of the SCM. The electrical connectors are inductive couplers on the outboard side of the SCM.
Workover Control System. This system (Fig. 6) is used to run, to retrieve, and to operate the Christmas tree and tree cap, the tubing hanger, and the pull-in and connection tools. The control of Christmas tree valves is transferred from the Gullfaks A platform to the workover rig during well workover. This transfer is achieved after removal of the tree cap and rerunning of the Christmas tree running tool.
Pull-In and Connection System. Each satellite well has three lines (flowline, hydraulic umbilical, and electrical umbilical) to be pulled in and connected. Fig. 4 shows the pull-in and connection tools. The tools are run on drillpipe.
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