控压钻井过程中泥页岩井壁破坏分析

控压钻井过程中，控制井底压力与地层压力相当，可以减少井壁由于井底压力过小或过大引起的井壁坍塌或破裂问题。对于水敏性泥页岩地层，即使在压力平衡的情况下，由于水基钻井液和泥页岩之间的水化渗透作用，泥页岩井壁也有可能不稳定。为此，建立了控压钻井条件下泥页岩井壁稳定非线性流-固-化耦合新模型，考虑了离子扩散与岩石变形的全耦合以及流体流动和离子扩散过程的非线性；通过有限元分析泥页岩井壁周围孔隙压力场和应力场的变化，计算井壁周围地层破坏系数，检查井壁是否破坏。研究结果表明：①控制压力钻井与常规钻井相比，水化渗透引起的孔隙压力剖面变化较小，有利于泥页岩井壁稳定；②泥页岩井壁失稳主要有井壁破坏、井壁附近地层破坏两种方式且后者是有时间效应的；③现有模型与非线性全耦合模型相比，过大地预计了井周孔隙压力和总应力且其压力峰值传播较慢；④泥页岩井壁失稳后，新的泥页岩表面暴露在钻井液中继续进行水和溶质交换，井眼扩大到一定值后，发生进一步失稳的可能性较小。

Wellbore failures in shale wells during managed pressure drilling

During managed pressure drilling, the bottomhole pressure is controlled to be almost equivalent to the formation pressure,which can reduce wellbore collapse or fracture resulted from overly low or overly high bottomhole pressure. And for water sensitive shales, even under the balanced pressure conditions, the wellbore may be not stable because of osmotic hydration generated between shale and the water-based drilling fluid. In view of this, a nonlinear fluid-solid-chemical coupling model is developed for the...