锦州25-1油田沙河街组地层井壁失稳严重,为解决该油田的井壁失稳问题,对该油田的泥页岩矿物组分进行了分析,开展了泥页岩的力学及水化特性实验,分析了锦州25-1油田沙河街组泥页岩的岩石力学特性和井壁失稳机制.研究发现,沙河街组地层层理性泥页岩和水敏性泥页岩共同发育;层理性泥页岩具有显著的各向异性,易发生沿层理面的剪切滑移,造成井壁失稳;水敏性泥页岩在钻井液作用下会发生水化膨胀,导致井周地层的力学性质和应力状态发生变化,表现为坍塌压力随井眼钻开时间的改变而改变;两种地层相互影响造成油田复杂事故频发.结合室内实验结果,建立了合理钻井液密度的确定方法,研究了锦州25-1油田层理性泥页岩坍塌压力随井眼轨迹的分布规律和水敏性泥页岩的水化坍塌周期,给出了保证安全钻进的工程对策,该油田的井壁失稳问题必须在优化井眼轨迹和选择合理钻井液密度基础上,并增强钻井液的封堵性和抑制性才能解决.

The wellbore instability of Jinzhou 25-1 oil field is quite serious. In order to decrease wellbore instability of the oil field, the clay mineral of shale is identified by the X-ray diffractometer. Laboratory experiments involving the rock mechanics and hydration characteristics of shale are conducted to study their rock mechanical characters and wellbore instability mechanism. Shale in Shahejie Formation has two types: they are bedding shale and water-sensitive shale. Strength of bedding shale is anisotropy, and is prone to shear failure along the bedding plane and causes wellbore instability. Water-sensitive shale would be hydration swelling under the action with drilling fluid, resulting in the change of mechanical properties around the well, showing a changed collapse pressure with the time. Based on the experimental results, the methods to determine collapse pressure are developed, which is applied to determine collapse pressure of Jinzhou 25-1 oil field, and engineering strategies for ensuring safe drilling are given. Based on optimized well trajectory and proper drilling fluid density, the problem involving the wellbore instability of the oil field is able to solve by increasing the plugging and inhibitory of drilling fluid.