UNDERBALANCED COILED-TUBING-DRILLED HORIZONTAL WELL IN THE NORTH-SEA

Maersk Olie & Gas A/S (Maersk Oil) has drilled a 3,309-ft-long near-ho rizontal drainhole with coiled tubing to a total measured depth (MD) o f 11,000 ft in the Danish sector of the North Sea. The well was comple ted in May 1994 as a 3 1/2-in. openhole producer in the Corm field cha lk reservoir. Part of the well was drilled at underbalanced conditions , and oil production rates of up to 1,100 STB/D were reached during dr illing. Conventional well-test equipment was used for handling returns . A nearby process facilities platform supplied lift gas and received the produced hydrocarbons during the drilling phase. Worth noting are the penetration of several chert layers, the fairly long reach, and th e application of geosteering. Indications were that the well productiv ity was significantly improved compared with that of a conventionally drilled well, but problems were experienced with borehole stability in a fractured region.