HOUSTON – Rigless subsea intervention is a growing technology for the offshore oil and gas industry. Attendees of the Deep Offshore Technology conference were given a presentation by Bill Siersdorfer about Schlumberger’s developments in the area.
The objective of rigless subsea well intervention is to reduce the cost of a subsea well through-tubing intervention. Cost savings are achieved by selecting an optimal intervention cost to capability ratio.
The paper describes a novel rigless subsea intervention system that optimizes capability through the use of two complementary subsea intervention methodologies: Open Water Wireline (OWWL) and the Spoolable Compliant Guide (SCG). The system enables rigless coiled tubing, electric line, and slickline through-tubing services in subsea wells in water depths to 3,000 m (9,842 ft). OWWL is the method of running electric line and slickline services through the water column down to the well control package on top of the christmas tree and into the well.
The Spoolable Compliant Guide is the method that, in addition to electric or slick line, allows the addition of coiled tubing via a compliant guide to connect the vessel to the christmas tree. Both methods achieve their intervention objectives without bringing hydrocarbons back to the vessel, allowing the use of simpler, cost-effective marine support.
The presentation reviewed the enabling methodologies (OWWL and SCG), the components of the system including the subsea well control package, required marine support, risk assessment analysis, enabled services, and discussion of optimal capability. Included was a summary of some challenges encountered, and solutions that evolved to meet those challenges in developing a system that extends the water depth range of open water wireline from 500 m to 3,000 m, and adds coiled tubing to the services offered for rigless subsea intervention.
The Open Water Wireline technique uses a subsea well control package that in turn is connected to the subsea well. The electric line and/or slickline string, in addition to the upper dynamic well seal components, are run from the vessel, through the water column, and on to the well intervention package. The well seal remains on top of the lubricator while the toolstring is run into the well. Vessel motion is not decoupled from the subsea well, so heave compensation is required. This enables slickline and/or electric line to services to be run from the vessel.