Optimization And Application Of High Performance Water-based Drilling Fluid For Shale Gas Wells In South Sichuan

Based on the investigation and analysis of the development of water-based drilling fluids in shale gas wells at home and abroad,the mineral composition,microstructure and physical and chemical properties of the Longmaxi Formation shale in Weiyuan are tested,and the mechanism of shale sidewall instability is analyzed.A large number of laboratory experiments have been carried out to optimize the high performance water-based drilling fluid treatment agent and formulation for shale gas wells,and its performance has been evaluated in laboratory.Field tests of the optimized high performance water-based drilling fluid were carried out in shale gas horizontal wells in Weiyuan area.The following main understandings were obtained:(1)The total amount of clay minerals in the Longmaxi shale of Weiyuan is less than 40%,mainly illite,with a small amount of chlorite and the interlayer between illite and mongolia.The micro-fractures are well developed,and the specific surface area and cation exchange capacity are not high.Shale hydration capacity is not strong,but the problem of shaft wall instability caused by micro cracks is more prominent.(2)The shale high-performance water-based drilling fluid was optimized by experiments,and the main treatment,namely,fluid loss agent,inhibitor and lubricant of PAC-LV+SPNH+SMP-II,NR-1,PEG and interior lubricant emulsion preparation.By the process performance evaluation,the system meets the requirements of shale gas for drilling fluid.(3)Through the borehole stability of indoor experiment and push the hardness test and triaxial compressive strength experiment,the experimental results show that the research and development of high-performance water-based drilling fluid has good shale borehole stability,including good sealing and inhibition.(4)Through in WEI A well and WEI B well field application,shale high-performance water-based drilling fluid system showed good sealing ability and the inhibition ability,has the very good sidewall stability collapse prevention ability.In addition,it has greatly reduced the processing cost and the environmental protection requirement in the use.