Drag reduction technology for ultra-long horizontal drilling in the Changqing tight gas reservoir

For the purposes of protecting the ecological environment and increasing single-well production, the Changqing gas field deploys multiple wells with horizontal wells exceeding 3000 m. Given the ultra-long horizontal openhole well and the excessive drag and torque, the S135-steel grade drill string and the cutting-removal drillpipe drag reduction tool were adopted; the rotary steerable system was used for trajectory control; the drilling parameters were optimized. Specifically, the optimal annular circulation rate of drilling fluids is 1.20–1.30 m/s; the minimum drill string rotation speed is 60 r/min; the potassium chlorite, limestone and high-performance lubricant are used to improve the lubricant performance of drilling fluids and formed mud cake, control the content of unwanted solids in drilling fluids, and raise the ratio of yield point to plastic viscosity to 0.5Pa/(mPa · s). The above measures jointly form the drag reduction technology for ultra-long horizontal wells in the Changqing tight gas field. It has been applied to Well Jing 51-X with a 5256 m long horizontal well. The average dogleg severity of the horizontal well was 0.74 (°)/30 m; the maximum solid content of drilling fluids was 16%; the maximum drag of tripping out after completion of drilling is 380 kN; the maximum drag of tripping in was 280 kN. Such an application to ultra-long horizontal drilling demonstrates the excellent drag reduction performance of the presented technology.