TX 75083-3836 U.S.A., fax 1.972.952.9435. Abstract:A riserless mud recovery system enables dual gradient subsea drilling operations to take place with the well open at the seabed. There are no pressure containment devices at the wellhead, but as with earlier systems developed for deep water drilling [1], mud and cuttings are returned to the rig by means of a subsea pumping system, fluid recovery hose and umbilical. The system was field tested as part of the Norwegian DEMO2000 project [2]. Subsequently, it has seen operational service in a multi-well drilling campaign in the Caspian Sea. This paper describes how the system was implemented in a remote area exploration drilling operation off Sakhalin Island. Following experience in 2004 and 2005 [3] a clear business case emerged with the underlying drivers of limited weather window, shallow gas and stringent discharge regulations. Accordingly a formal project was established and a number of critical risk reduction studies were carried out in relation to shallow gas and integrity of the return hose under high current conditions. Correct interfacing onboard the rig required careful choice of location, power supply, wellhead and remotely operated subsea vehicle. There changes were verified by means of a formal hazard and operability review. A significant part of the effort involved gaining certification of the equipment for use in the Russian Federation in parallel with the fabrication, acceptance testing, mobilisation, offshore installation and commissioning of the system. The paper concludes with a review of the operational experience from the 2006 drilling season along with the associated lessons learned and forward plan.
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