切削和侵入作用下层理岩层破碎机理浅析

层理岩层是石油钻井中经常遇到的一类地层,特别是在页岩气开采过程中,所钻页岩属于典型的层理岩层。研究层理岩层在钻齿作用下的破碎机理对于控制井眼轨迹、优化钻进参数、提高钻进效率都有很大指导作用。在以往岩石破碎机理研究中,一般多假设岩石介质为各向同性;但是对于层理岩层,由于其表现出强烈的强度各向异性特征,各项同性假设不再适用。本文利用离散单元方法(PFC2D)建立了钻齿与层理岩层相互作用模型。研究了层理岩层在钻齿切削和侵入过程中的破碎情况、裂纹的扩展情况以及钻齿受力情况。研究表明:切削力根据层理倾角分为高切削力区和低切削力区;液柱压力的存在对裂纹扩展有抑制作用,增大切削力;在岩石侵入过程中,层理的存在改变了裂纹的走向,当主裂纹扩展至层理处时,裂纹不再向岩石内部扩展,而是朝着层理的方向扩展。

Investigation on the Mechanism of Laminated Rock Fragmentation under the Action of Cutting and Indenting

Laminated rock formations are frequently met in oil&gas drilling, especially in shale gas drilling. The fragmentation mechanism of the laminated rock plays a significant role in well trajectory control, drilling parameters optimization and drilling efficiency improvement. In the past researches, the rock mass is simply treated as isotropic material; this method may be acceptable for shallow formations, but for the deep formations, with the increase of drilling depth the anisotropic properties of rock mass become stronger due to the existence of weakness plane for fracture plane. Therefore, the tool-rock interaction model is established by the PFC(2D), the cutting process and indentation process and the development of fractures are studied. The results show that, the joints have a significant effect on cutting force. The laminated dip can be divided into high cutting force area and low cutting force area. The cutting force increases with mud drilling pressure. In the indentation process, the existence of joints can change the propagation direction of vertical crack, leading it towards to the joints.