After most operators quit using Pin connector, Riser and Diverter for safety reasons, when drilling the tophole section of subsea wells, the use of seawater and sacrificial mud with return to seafloor has to date been the only available practical method.
The development of AGR's Riserless Mud Recovery System (RMR) enables drilling the tophole section using weighted inhibited drilling mud. Hence, a number of benefits, such as: Improved hole stability, reduced wash outs, improved well control both with regard to shallow gas and shallow water flow are obtained. Also clay and sand deposits from the boreholes on subsea production templates are prevented.
A Demo 2000 project to qualify the RMR System was therefore approved and a Joint Industry project (JIP) was established funded by the Norwegian Research Counsel, Hydro, Statoil and AGR. The JIP was established to qualify the RMR technology for use in 450 meters of water depth.
The Demo 2000 project objective was to enable drilling tophole sections collecting returns subsea, and returning to surface in a closed system. A Suction Module with a low pressure rotating control head was installed on the template. This Suction Module collected and diverted the well return into a subsea mud pump lifting the stream of mud and cuttings to the rig processing system.
The RMR spread was run through the moon pool on a single derrick rig, and guided and stabilized by a heave compensated guide wire extending to a subsea anchor. Ref. System Schematic, Fig 1.
The equipment was engineered and manufactured within an 8-month period, and the field trial took place in December 2004.
The paper also discusses the fluid system used, the operational benefits and limitations by applying the RMR technology.
Most operators have abandoned the use of Pin Connector, Riser and Diverter when drilling surface holes for both safety and operational reasons. Especially when drilling deep-water wells, using seawater and gel sweeps being dumped on the seafloor has to date been the only viable solution. In production drilling this has led to the use of Cutting Transport Systems (CTS) or subsea ejector pumps to remove the well returns to a distance from the subsea templates.
To allow the use of weighted and inhibited mud for improved bore hole stability, well control and preventing the drill cuttings and cement returns to be dumped on the subsea template and or seafloor, AGR developed a Tophole Drilling Package named RMR - Riserless Mud Recovery System.
A Pre- Engineering phase was completed in 2002. This served as basis for establishing the design basis and defining the scope of work when applying for Demo 2000 funding in 2003, to demonstrate and qualify The RMR system for 450 meter water depth by offshore field testing.
At the same time as the RMR Demo 2000 project was initiated, AGR was requested to design and build a Riserless Mud Recovery System for BP to be tested on the West Azeri field in The Caspian Sea.