空气锤钻具防斜机理研究

Mechanism for Deviation Control of Drilling Assembly with Air Hammer

空气锤在提高气体钻井机械钻速的同时可以有效控制井斜。通过对井底应力及空气锤破岩过程的研究,利用摩尔-库伦准则建立了考虑岩石本身以及周围压力的各向异性指数计算公式。结合空气锤的破岩特性得出空气锤钻具的防斜机理为:空气锤钻具的破岩力主要来自于内部冲击力,较小的钻压使钻具变形较小;空气锤的半圆形牙齿以及巨大冲击载荷使待破碎岩石的局部各向异性指数变小;空气锤低转速条件下的高频冲击有利于克服岩石的各向异性而实现平衡破碎。

Air hammer can control well deviation while enhance ROP. According to Mohr-Coulomb criteria,an anisotropy index of formation based on intrinsic features and confining pressures by studying the process of rock failure by air hammer. Combined with the features of air hammer, this paper presents three reasons for that air hammer can control deflection. Because WOB is smaller and the deformation of drill string becomes smaller. The huge impact force make the anisotropy index of formation being smaller. The air hammer works in low rotation speed and high frequent impact, this kind of character can generate balance failure of anisotropy rock.