加载途径对深部孔隙性砂岩力学特性的影响

EFFECT OF LOADING PATHS ON MECHANICAL PROPERTIES OF DEEP POROUS SANDSTONE

深部孔隙性砂岩具有压实程度高、岩石较致密、孔隙度较低、且孔隙中一般含有油/气或水、孔隙流体具有压力的特点。已有的理论研究表明,多孔介质孔隙流体压力对岩石的变形和破坏存在一定影响,不同岩石其影响程度不同。从孔隙流体压力为正常静水压力、实际地层孔隙压力和大气压3个方面,通过实验研究由于孔隙内压改变而引起的加载途径变化对岩石变形和破坏的影响。研究结果表明:孔隙流体压力的存在使岩石的塑性增强,即模拟砂岩实际地层孔隙压力和围压得到的三轴抗压强度、轴向应变、径向应变和泊松比大于其他两个条件下相应的值,弹性模量则小于其他两个条件下的岩石弹性模量;对深部孔隙性地层岩石,要表述岩石的力学特性,应考虑孔隙压力的存在和影响,应尽量模拟岩石在深部埋藏条件下所受到的实际上覆岩石压力、实际地层孔隙压力测试岩石的应力–应变特性。

The deep porous sandstone has many unique features, such as high consolidation level, high compactability, lower porosity, oil/gas/water-included pore, pore fluid with pressure holding and so on. The existing studies have shown that the pore fluid pressure of porous media has some effects on the deformation and damage of rock, and the influential level is distinct to different rock masses. Based on the pore fluid pressure which is composed of regular hydrostatic pressure, actual formation pore pressure and atmospheric pressure, the experimental study has been carried out to analyze the effect of different loading paths owing to the change of internal pore pressure on the deformation and damage of rock samples. The results have shown that the existence of pore fluid pressure enhances the plasticity of rock sample. This means that the triaxial compressive strength, the axial strain, the radial strain; and the Poisson＇s ratio obtained by simulating the actual pore pressure and confining pressure are greater than those obtained under the other two conditions, while the elastic modulus is less than that obtained under the other two conditions. In order to declare the mechanical behavior of the deep porous sandstone, the existence and influence of pore fluid pressure should be considered. If possible, the actual overlying pressure of deep embedded rock and the actual formation pore pressure should be simulated to test the stress-strain characters of rock samples.