Petroleum Technology Digest: Reverse circulation drilling avoids damage to low pressure gas reservoirs ///

PressSol Ltd. of Calgary has adapted reverse-circulation, center-discharge drilling (RCCD) for oil and gas drilling. Because RCCD drilling returns cuttings through the ID of the inner portion of double-wall drill pipe, it does not expose the formation to possible damage from drilling fluid and, thus, is particularly well suited for drilling low-pressure reservoirs. K2 Energy of Calgary has applied RCCD to successfully drill and test gas wells in the low-pressure (formation pressure estimated at 150 psi) Bow Island formation on the Blackfeet Indian Reservation in northern Montana, US. As of February 1, 2003, the system has been used to drill 11 Bow Island wells on the reservation and an additional five wells in the Thrust Belt. Drilling cost is competitive with mud or air drilling in that area; $15/ft for surface string to 600 ft and $10/ft for a long string to 2,500 ft. The system can be adapted to any rig with the addition of a dual-wall drillstring.

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