复合/滑动钻井钻头与页岩气难钻地层岩石相互作用关系OA

The southern Sichuan Basin is characterized by complex geological structure,ancient formations,and deeply buried target horizons.Especially in hard-to-drill formations such as the Middle Cambrian Douposi Formation,Lower Cambrian Longwangmiao Formation,and Lower Cambrian Canglangpu Formation,the rock compressive strength exceeds 145 MPa,resulting in poor drillability.In the build-up sections,the steerable drilling assembly yields low build-up rate,leading to a rate of penetration(ROP)of only 0.96 m/h during build-up drilling.To enhance the ROP and reduce the drilling period,rock mechanics and drillability experiments were conducted targeting core samples and field outcrops.Furthermore,the force distribution characteristics of PDC bits and the rock properties were analyzed by modeling.The following results are obtained.(i)The established rock-breaking dynamics simulation model of PDC bit provides optimization guidance for cutter layout to achieve high cutting efficiency.(ii)The developed discrete element numerical model clarifies the fragmentation mechanism of anisotropic rocks under PDC cutting.It is revealed that weight on bit(WOB)is the most influential factor on cutting force,followed by rotation speed,front rake angle,and flow rate.(iii)The evaluation on effect index for interaction between rock anisotropy and bit cutting force shows that the lateral cutting force in composite drilling is lower than that in slide drilling,resulting in higher rock-breaking efficiency.It is concluded that:(1)the optimized design combining axe-shaped cutters with triangular prism/axe-shaped hybrid cutter arrangements,maintaining a height difference≤1 mm between front and rear rows,significantly enhances ROP in hard-to-drill formations;(2)in terms of drilling parameters,WOB control,in conjunction with small front rake angle and medium rotation speed,helps improve build-up efficiency;and(3)field applications of the optimized 6-blade hybrid cutter bit demonstrates a 70%improvement in ROP.