流道形状对PDC钻头携岩和冷却效率影响研究

Research on the effect of the shape of junk slot profile on cutting-carrying and cooling efficiency of PDC bits

在实际钻井过程中,PDC钻头的流道形状对钻头是否泥包有着重要影响。为了深入了解流道形状对PDC钻头携岩和冷却效率的影响规律,文中通过改变排屑槽轮廓平分线与切削轮廓平分线的夹角α值大小来调整PDC钻头模型的流道形状,并对各钻头模型进行破岩仿真获取各个切削齿的切削量、岩屑初始运动速度和方向;将具有一定质量流量、初始运动速度和方向的岩屑假设为从齿面生成进入流场的球状颗粒,采用拉格朗日粒子追踪法对岩屑颗粒运动进行追踪;把滞留岩屑量、流道排出岩屑匹配值均方差σ和切削齿散热量相对值作为钻头携岩和冷却效率的量化评价指标。数值结果表明:流道形状直接影响钻头的携岩和冷却效率,α值越大σ越小,井底的滞留岩屑量越小,钻头冷却效率越高。受PDC钻头结构设计限制,流道的形状设计存在一个最优值,且其最优夹角α值应在0°左右,正角最佳。

In the drilling process, the shape of junk slot profile of polycrystalline diamond compact（PDC） bits have an important impact on whether the bit balling. In order to further comprehend the effect of the shape of junk slot profile on cuttingcarrying and cooling efficiency of PDC bits, the shape of junk slot profile of PDC models was adjusted by changing the angle αof the bisector of the junk slot profile and cuttings trajectories. And a rock breaking simulation of PDC bits was worked out to obtain the stock removal of each cutter, the initial velocity and the direction of cuttings. Assuming the cuttings that with mass flow rate, initial migration velocity and direction as spherical particles that were generated from the surface of cutters and got into the flow field, and then the Lagrange particle tracking method was used to track the cuttings trajectories. The mass of retention cuttings in the bottom hole, the mean square deviation of cuttings matching value σ, and the relative value of the heat dissipating capacity of cutter were taken as an evaluation criterion of the cutting-carrying and cooling efficiency. The results show that the shape of junk slot profile directly affects the cutting-carrying and cooling efficiency of drill bits, the value of σ and the mass of retention cuttings in the bottom hole decrease with the increasing of the value of angle α, and the cooling efficiency of bits increase with the increasing of the value of angle α. Because of the constraints of PDC bits structure, there is an optimum value on the shape of junk slot profile, and the optimal angle value α should be positive and be nearly 0 degrees.