Alternative Deep Dual Circulation System
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The feasibility for a new drilling method called AD-DCS (alternative deep circulation system) has been studied. The AD-DCS method allows for two drilling fluids where the role between hydrostatic pressure and circulation is separated in the circulation system. An extra casing with smaller diamater than the last cemented casing is inserted down to the top of the reservoir and hung off. The drillstring is run through the extra casing. This creates two annuli, an annulus A between the casing and drillstring and an annulus B between the cemented casing and the hung off casing. The circulation fluid is transported through annulus A to the surface, whilst the annulus B contains a drilling fluid designed to provide hydrostatic pressure. The report explains how such a system could be implemented and compares the method to the conventional drilling method and MPD method with one circulation system. The preliminary results show promising in both improved hole cleaning, less choking of the return flow is required contra MPD with one circulation system. The method has lower circulation volumes, thus reducing the response time as well as reducing the time to displace the well to a hydrostatically stable mud.