海陆过渡相地层不同岩性岩石力学特性研究——以鄂尔多斯盆地东缘山西组为例

Study on rock mechanical properties of different lithologies in marine continental transitional formation:a case study of the Shanxi Formation in the eastern margin of Ordos Basin

以鄂尔多斯盆地东缘山西组海陆过渡相地层为研究对象,开展了单三轴压缩、抗张强度、断裂韧性等力学测试实验,研究了不同岩性岩样的岩石力学特性.研究结果表明:鄂尔多斯盆地东缘山西组不同岩性岩样的力学特性存在明显差异,其中粉砂质页岩抗压强度及弹性模量高而泊松比较小;不同岩性岩样的峰值应变差异较明显,且变形特征差异较大,岩样的破坏形态在单轴压缩条件下主要为劈裂破坏,表现出明显的脆性特征;随着围压增加,破坏形态由劈裂破坏转换为剪切破坏,岩样的脆性减弱,延性增加;粉砂质页岩在压缩条件下裂缝面密度和分形维数较大,有潜力形成复杂缝网.研究成果为后续井眼轨迹优化,压裂施工及增产方案提供参考.

Taking the Shanxi Formation in the eastern margin of the Ordos Basin as the research object,the mechanical tests such as single triaxial compression,tensile strength and fracture toughness were carried out,and then the mechanical properties of rocks with different lithology were studied.The results show that there are obvious differences in the mechanical properties of different lithologic rock samples in Shanxi Formation in the eastern margin of Ordos Basin.The compressive strength and elastic modulus of silty shale are high and Poisson's ratio is small.The peak strain of rocks in different lithology reservoirs is obviously different,and the deformation characteristics are quite different.The failure mode of rocks is mainly splitting failure under uniaxial compression,showing obvious brittle characteristics.With the increase of confining pressure,the failure mode changes from splitting failure to shear failure,the brittleness of rock decreases and the ductility increases.The fracture surface density and fractal dimension of silty shale are large under compression,which has the potential to form complex fracture network.The research results provide reference for subsequent wellbore trajectory optimization,fracturing construction and stimulation plan formulation.