Discussion on Safe Drilling Technology for Heterogeneous, Ultra-Thick and Active Bitumen Zone

During development of Y Oilfield,several wells were drilled through Kazhdumi Formation which contains ultra-thick active bitumen.Those heterogeneous and scatterly-distributed formations brought severe challenges to drilling operation.In particular,drilling fluid contamination,simultaneous mud loss and well kick,escaping H2S and other complexities have caused abandonment of several wells and tampered with the overall progress of Y Oilfield development.Based on actual drilling data,the active bitumen zone is investigated in respect to formation pressure,connecting channel,bitumen feature and its distribution,and treatment difficulties are also analyzed.Then,the technical solution is proposed for further study on the distribution of bitumen and optimize casing program and managed pressure drilling(MPD)along with bitumen hardening process.The results show that the pressure of active bitumen is 1.58-1.65 g/cm3 and the long open hole where bitumen zone is encountered in current casing program is a bottleneck in the treatment of active bitumen.However,bitumen hardening agent YHJ-6 can increase the softening point of bitumen by over 60℃.Field test shows that this agent can effectively reduce the volume of bitumen invading into wellbore and enhance the sealing of leaking channel in bitumen environment.