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井壁稳定性是页岩气勘探开发关键技术的核心问题之一。针对页岩井壁稳定问题,以四川盆地龙马溪组页岩为研究对象,结合实际钻井情况,开展了不同围压、加卸载模式、取芯角度、流体浸泡等一系列岩石力学实验,为页岩气的勘探和开发提供基础数据。研究表明:四川盆地龙马溪组页岩单轴抗压强度较高,脆性较强;卸载作用造成岩样破坏更加剧烈,破坏模式更加复杂;取芯方向与层理面夹角为15°时,岩样的抗压强度和内聚力最低,夹角为45°时,岩样的破坏最剧烈;流体浸泡使岩样的强度和内聚力大幅下降,岩样以剪切破坏为主,浸泡过油基钻井液的岩样的强度和内聚力损失最小;随浸泡时间的增长,岩样的内聚力和内摩擦角先快速降低后趋于平缓。
Wellbore stability is one of the core issues in shale gas exploration and development. Aimed at the shale wellbore stability, a series of rock mechanics experiments with different confining pressure, loading and unloading mode, coring angle and fluid immersion were carried out based on the actual situation of Longmaxi shale in Sichuan Basin. Gas exploration and development to provide the basic data. The results show that the uniaxial compressive strength and brittleness of the Longmaxi Formation in the Sichuan Basin are higher than that of the bedding layer. The unloading causes the rock specimen to be damaged more and the failure mode to be more complicated. When the angle between the core direction and bedding plane is 15 °, The compressive strength and cohesion of the rock samples are the lowest. When the included angle is 45 °, the rock samples are most destructed. The fluid immersion greatly decreases the strength and cohesiveness of the samples, and the rock samples are mainly shear failure. The strength and cohesive loss of the rock samples are the smallest. With the increase of immersion time, the cohesion and internal friction angle of the rock samples decrease rapidly and then tend to be gentle.