水平井PDC钻头井下颗粒流数值模拟研究

Numerical Simulation of Downhole Particle Flow in Horizontal Well with PDC Bit

针对深层页岩气水平井钻探过程中,岩屑运移效率低导致钻头泥包的问题,采用CFD-DEM耦合方法,对水平井PDC钻头井底流场进行数值模拟。研究了不同条件下井底流场岩屑运移情况,提出用岩屑滞留量和岩屑运移比来评价PDC钻头井底流场的携岩性能。研究结果表明:在井底PDC钻头区域,钻井液排量越小,岩屑在钻头心部区域的窜流越明显;钻井液的窜流与流量大小无关,主要与钻头水力结构有关;在环空区域,钻井液排量越小,重力作用越明显,重力是井底出现岩屑床的主要因素;旋转体力可使岩屑从低速流层跃迁到高速流层,从而获取轴向运移动能,随高速钻井液排向出口;钻井液排量和旋转均会影响岩屑滞留量和岩屑运移比。研究结果可为后续水平井PDC钻头携岩问题研究提供参考。

In the deep shale gas horizontal well drilling,the low cutting carrying efficiency often lead to the problem of bit ball.To address the problem,the CFD-DEM coupling method is used to simulate the horizontal well flow field between PDC bit and bottomhole.The cutting movements in the bottomhole flow field under different conditions are studied.It is proposed to evaluate the cutting carrying performance of the flow field between PDC bit and bottomhole by using the cutting retention volume and cutting carrying ratio.The results show that in the bottomhole near PDC bit,smaller drilling fluid flow rate results in greater cutting channeling in the core area of PDC bit.The channeling of drilling fluid is mainly related to the hydraulic structure of the drill bit,but has nothing to do with the flow rate.In the annular,smaller drilling fluid flow rate leads to more dominant gravity effect.Gravity is the main factor of cutting bed forming at the bottomhole.The force by the rotating body can bring the cuttings from the low velocity flow layer to the high velocity flow layer,thus gives the cuttings the axial movement energy,which was carried to the wellhead with high-velocity drilling fluid.The drilling fluid flow rate and rotation will affect the cutting retention volume and cuttings carrying ratio.The study results can provide references for the study of cutting carrying near PDC bit in horizontal wells.