玛湖凹陷百口泉组砂砾岩储集层岩石力学特征与裂缝扩展机理

摘要

以玛湖凹陷百口泉组砂砾岩储集层为研究对象,通过岩石力学实验,开展了不同岩性砂砾岩储集层的岩石力学特性和裂缝扩展机理研究.在此基础上,利用数值模拟方法构建含有真实砾石的二维模型,研究砂砾岩中裂缝扩展的过程,讨论了砾石强度对裂缝扩展机制的影响.研究结果表明:砂砾岩具有较强的非均质性,造成不同岩性的砂砾岩力学特性差异较明显,其中细砾岩的力学强度大于粗砾岩;岩石中砾石成分和基质成分间差异对砂砾岩力学特性的影响较大;单轴压缩中砂砾岩破坏模式主要以劈裂破坏为主,而三轴压缩中砂砾岩破坏模式包括劈裂破坏、单剪切破坏和双剪切破坏等;砾石颗粒对裂缝扩展存在屏蔽作用,砂砾岩的破裂过程中裂缝扩展形式主要分为穿砾、绕砾、嵌入止砾等;砾石与基质强度差异增大,砾石屏蔽作用增强,裂缝遇砾石受阻增强,将造成裂缝遇到砾石的扩展由穿砾形式变为绕砾形式.%Taking the rock of the sandy conglomerate reservoirs of Baikouquan formation in Mahu sag as the study objects,the mechanical characteristics and fracture propagation mechanism of the sandy conglomerate reservoirs with different lithologies are studied through various rock mechanical experiments.Based on which,a 2D model containing true gravels is established by using numerical modeling method,the dynamic process of fracture propagation in the sandy conglomerate are investigated,and the influence of gravel strength on fracture propagation mechanism is discussed.The results indicate that the sandy conglomerate are seriously heterogeneous,resulting in the obvious differences of mechanical characteristics in sandy conglomerates with different lithologies,among which the mechanical strength of fine conglomerate is higher than that of coarse conglomerate;the differences between gravel and matrix compositions have significant influence on rock mechanical characteristics of the sandy conglomerate;the failure mode of the sandy conglomerate is dominated by splitting failure in uniaxial compression and by splitting failure,single shear failure and dual shear failure etc.in triaxial compression;gravel particles have shielding effect on the extension of fractures and the fracture propagation during rock failure process in the sandy conglomerate mainly contains 3 types such as going-through gravel,bypassing gravel and embedded in gravel.The strength of gravels and the matrix reflects the mechanical properties of glutenite.The larger the strength difference between gravel and matrix is,the stronger the shielding effect of the gravels is,the stronger the received resistance of fracture will be,causing that the fracture propagation would transfer from going-through gravel to bypassing gravel.