Key technology of second-spud one-trip drilling for tight gas horizontal wells in Tianfu gasfield
The Tianfu gasfield in Sichuan Basin is rich in tight gas resources,which are mainly recovered by horizontal wells.During the well drilling,there exists problems including low rate of penetration(ROP),multiple trips in second spud,large operating friction torque,and frequent occurrence of complex accidents such as sticking.Therefore,targeted at the tight gas reservoirs in the Jurassic Shaximiao Formation of Tianfu gasfield,optimization research and technical study were carried out in the aspects of drill bit type,rotary steering tools,drilling tool sets,drilling parameters,and drilling fluid performance,to formulate key technical measures.And then,an optimized and fast drilling technology for horizontal wells was developed based on"second-spud casing program+3D tra-jectory profile+efficient PDC bit+oil-based drilling fluid+rotary steering".The research results show that,(i)by optimizing the cutting tooth arrangement of PDC bit and enhancing the bit aggressivity,the bit adaptability to heterogeneous strata can be effectively improved,and thereby the ROP is increased;(ii)by optimizing drilling tool sets and drilling parameters,a drilling tool set suitable for the home-made CG STEER rotary geological steering drilling system is developed,which ensures the rock breaking ability and reduces the sticking risk;and(iii)the design of oil-based drilling fluid performance and density is optimized by the wellbore stability evaluation based on the Mohr-Coulomb criterion,further reducing the sticking risk.This drilling technology has been successfully ap-plied to 8 wells in the field,achieving the excellent"one-trip"drilling for second spud in Ø215.9 mm wellbore.The application results show that,(i)compared with the wells to which this technology has not been applied,the average ROP of second spud for the 8 wells is increased by 30.7%(from 17.75 m/h to 23.20 m/h),the average drilling period of second spud is shortened by 23.4%(from 12.00 d to 9.19 d),and the average of the whole drilling period is shortened by 30.5%(from 16.10 d to 11.19 d),exhibiting the good applica-tion effect;and(ii)Well JQ12-8-H2 has the best performance among the 8 wells:the ROP is as high as 40.62 m/h,the drilling period of second spud is only 6.15 d,breaking the records of the fastest ROP and the shortest drilling period of tight gas horizontal wells in Tianfu gasfield,achieving the significant improvement in ROP.The research and application of this drilling technology strongly sup-port the rapid production of tight gas in the Sichuan Basin.
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