- a tool for improved recovery.
The successful qualification of a second generation, riserless wireline intervention system gives Statoil a viable alternative for gaining quick and easy access to subsea wells
Occasionally wells have to be re-entered for maintenance and technical purposes (e.g. replacing and re-perforating tubing; replacing flow control devices; isolating production zones; monitoring production behaviour; and logging pressure, flow and temperature).
The procedure, which is known as well intervention, is difficult enough to do from conventional surface platforms let alone when wells are installed on the seafloor.
The normal subsea procedure is carried out from an anchored semi-submersible rig attached to the wells by risers (gas/fluid conduits linking subsea equipment to surface platforms).
Statoil, however, has already gained some experience of using a first generation riserless system, where the intervention equipment is lowered by means of a wire line paid out from a dynamically positioned monohull vessel.
As the operating conditions are somewhat limited, it was decided to test Prosafe Offshore’s latest Multi Service Vessel (MSV) Regalia system with its 7" riserless subsea wireline lubricator co-developed with FMC Kongsberg Subsea.
During late 2003, the company entered an all-inclusive contract with Prosafe to supply the services, equipment and procedures necessary to perform selected subsea well interventions at the Statfjord North, Visund and Åsgard fields.
Statoil was responsible for planning the individual downhole programmes, which involved a variety of light intervention tasks in water depths up to 390 metres.
Deemed a great success, the company now has the option to use this relatively inexpensive, second generation technology to gain quick and easy access to its subsea wells.
Furthermore, preliminary results from the operation suggest that intervention costs may be cut by as much as one third when compared with anchored rig and riser systems.