A case study of underbalanced and managed pressure drilling process

Managed pressure drilling is recently developed as a new technology at abroad,which provides a new solution to safe drilling especially in complicated formations.However,such studies have just started in China so we can not find good experience to learn from.In view of this,this paper makes a systematic analysis of the differences between underbalanced drilling(UBD) and managed pressure drilling(MPD),and compares the features of managed over-balanced process,managed near-balanced process,and UBD process.On the basis of this,a set of methods are proposed to realize the underbalanced and managed pressure drilling process,including the MPD procedures adopted under different conditions such as circulation,tripping and pipe connection.Through a case study of the well Penglai-9 in the central Sichuan Basin,the developed UBD and MPD drilling process not only achieved the controlled flow drilling,but realized a smooth pressure convergence during circulation,tripping,and pipe connection with the pressure error of about 0.2 MPa during drilling and about 0.5 MPa during tripping and pipe connection.To summarize,this drilling process can ensure downhole safety and ROP improvement,meanwhile realize effective discovery of pay zones.