塔里木盆地克拉苏构造带巴西改组地层在钻井过程中井壁失稳现象频发,严重影响钻井效率。以巴西改组岩石为研究对象,开展了矿物组成测试、阳离子交换实验等理化性能测试,以及三轴压缩试验等力学测试,研究了巴西改组砂岩与泥岩理化性能、力学特性差异以及钻井液浸泡对力学性能的影响。研究结果表明,巴西改组泥岩的黏土矿物含量较高,阳离子交换容量约为砂岩的3倍,并发育大量微裂缝,水化膨胀能力明显强于砂岩,在溶液浸泡作用下更容易发生结构损伤。同时,由于油基钻井液的润滑作用,导致强度降低,且泥岩强度降低量约为砂岩的1.5倍。在相同围压状态下,巴西改组泥岩与砂岩的强度、临界破坏点处对应的轴向、径向应变以及岩石破坏模式均存在差异,且钻井液浸泡对泥岩强度影响大于砂岩。通过分析巴西改组地层岩石力学特性,对弄清该地层井壁失稳机理、制定井壁失稳防控措施具有重要意义。

During the drilling process, the wellbore instability frequently occurres in Baxigai Formation in the Kelasu structural belt of the Tarim Basin, which seriously affects the drilling efficiency. In order to study the physic-chemical and mechanical mechanical properties properties, differences of physical and pechanical characteristics and influence of drilling fluid immersion on the mechanical properties of the sandstone and mudstone in Baxigai Formation, the physic-chemical characteristic tests （such as mineral composition test and cation exchange experiment）, and mechanical test （such as triaxial compression test） have been carried out. The research results show that the clay minerals content of mudstone in Baxigai Formation is high, and the cation exchange capacity is about three times that of sandstone. The mudstone here also has a large number of micro-cracks, and the hydration swelling is obviously stronger than that of sandstone. All these things make it m ore prone to be damaged. At the same time, the strength decreases under the immersion and lubricating effects of oil-based drilling fluid. The strength decrease of mudstone is about 1.5 times that of sandstone. Under the same confining pressure, the mudstone and sandstone strength, the corresponding axial and radial strain at the critical failure point, and the rock damage mode of mudstone and sandstone in Baxigai Formation are different. The damage to mudstone structure caused by drilling fluid immersion is greater than that of sandstone. The analysis of the mechanical properties of the rock in Baxigai Formation is of great significance to clarify the mechanism of wellbore instability in this formation and formulate prevention and control measures for wellbore instability.