中文摘要：

空气钻井技术是以空气作为循环介质的欠平衡钻井技术，其钻头的破岩形式与常规泥浆钻井有很大的区别。在岩石力学和弹塑性力学的基础上，考虑岩石材料的各项异性、地层倾角、钻头与岩石间摩擦因数等影响因素，采用有限元方法建立空气钻井中全尺寸PDC钻头动态破岩的非线性动力学三维模型。通过对空气钻井中岩石的破坏机制和钻头动态破岩过程的研究以及对破岩后形成井眼、井壁和井底岩石应力应变的分析。结果表明：井底岩石受到较大拉应力的作用，使得空气钻井中破岩速度更快；干燥空气钻成的井眼井壁稳定性较好，但是一旦发生井壁不稳定性，井壁岩石将成块掉落。最后通过对钻头上随时间变化的位移分析，得到钻进各向异性地层岩石的井斜和方位的变化规律。本模型为空气钻井的破岩机制、井斜变化规律以及井壁稳定性研究提供一种新的方法，为钻头和钻具设备的研制、优化设计提供理论依据。

英文摘要：

Air drilling is a kind of under-balanced drilling technology with air, whose rock breaking form is different from conventional mud drilling. Based on rock mechanics and elastoplastic mechanics, a 3D non-linear dynamic model of dynamic rock breaking with full gauge PDC bit is established using finite element method （FEM）, in which anisotropy, strata dip and friction factor of drilling bit and rock are considered. The mechanism and process of dynamic rock breaking in air drilling are studied. And the stress and strain of borehole、 shaft wall and bottom hole after rock breaking are analyzed as well. It shows that the rate of rock breaking in air drilling is faster in bottom hole where the tensile stress is larger, and the shaft wall is quiet stable under dry air： however, it would collapse in blocks in case of instability. And the change law of hole deviation and azimuth in anisotropic formation in air drilling is obtained by investigating the displacement of drilling bit with time variation. The model provides a new method for the study of breaking mechanism, the change of deviation and stability of shaft wall, and it offers theoretical basis for the development and optimization of bit and drilling tool in air drilling.