APPLICATION OF MICRO-FOAM DRILLING FLUID AND COARSE-FOAM PLUGGING FLUID IN TBK GASFIELD

TBK Gasfield is located at an elevation of 1125 m, with its surface formation mainly consisted of fractured carbonate, and the hole size is ?914.4 mm. The main troubles encountered during drilling were severe lost circulation and poor cleaning in large hole, and when clay drilling fluid, MMH fluid and clean water were used no fluid returned up to the surface, while pipe sticking often took place when drilling was continued. Micro-foam drilling fluid drops borehole hydraulic pressure and at the same time forms a resorting layer similar to a fluid casing in the near wellbore area, thus it exhibits very good lost circulation prevention during drilling. Coarse foam plugging technology involves mixing certain amount of micro-foam drilling fluid into recyclable foam drilling fluid of higher density and minor stability, aiming at shortening the foam stabilization time and letting foam fluid entering into the fractures. In the condition of low flow velocity or static, the micro-foam then turn into cell like foam gel of high structure strength, and forms gas block and gel sealing to the lost circulation communications, and this in turn prevents cementing slurry from losing. Field applications showed that the micro-foam drilling fluid has such advantages as lower density, higher visco-shearing, recyclable, low cost, minimum equipment requirements, and good cuttings transportation; while coarse foam plugging technology is easy to operate and conduct, and it produces good plugging results and cementing quality.