Application of Monitoring Formation Pressure while Drilling in Western Sichuan Basin

Without a uniform pressure system or even with abnormal high pressure,gas reservoirs in western Sichuan Basin are characterized by a deep burial depth and a few gas layers existing in longitudinal.In addition,some accidents such as blowout,leakage and drill pipe sticking may occur if drilling-fluid density is designed unreasonably.Based on the principles of both dc index and Sigma methods,monitoring formation pressure while drilling has been carried through at drilling site.The results show that these two methods can be applied to the monitoring in western Sichuan Basin.Dc index method is suitable for roller bit and Sigma method for PDC bit,respectively.Both of them can provide some guidance for predicting abnormal formation pressure and designing drilling-fluid density in order to avoid accidents occurring.