不同围压下花岗岩渗透率及其渗透敏感性规律研究

Study on Permeability of Granite Under Different Confining Pressures and its Permeability Sensitivity

干热岩体渗透性对地热资源开发有着很大的影响。为进一步认识地热能开发中储层的渗流特性,采用脉冲法岩石三轴渗流仪,以花岗岩为研究对象,探究花岗岩在不同围压下渗透率和渗透敏感性的变化规律。结果表明:在加载和卸载围压过程中,花岗岩渗透率随围压的变化曲线都符合幂函数变化规律,同一围压下花岗岩加载过程的渗透率始终大于卸载过程的渗透率;花岗岩渗透率曲线在围压30 MPa时存在拐点,以围压30MPa为界渗透率曲线分为阶段A和阶段B。在A阶段,随着围压变大渗透率降幅较大、降速较快;在B阶段,随着围压变大渗透率降幅变小、降速明显变慢;定义渗透率敏感系数C_k反映岩石渗透率随围压的变化趋势,按照敏感系数值可将花岗岩渗透率敏感性分为高敏感、中敏感、低敏感3个阶段。

The permeability of dry and hot rock masses has a great impact on the development of geothermal resources.In order to further understand the seepage characteristics of reservoirs in the development of geothermal energy,the pulse method triaxial percolation instrument was used.Taking the granite as the research object,the variation of permeability and permeability sensitivity of granite under different confining pressures was explored.The results show that during the loading and unloading confining pressure,the variation curve of granite permeability with confining pressure conforms to the law of power function.Under the same confining pressure,the permeability of granite during loading is always greater than that during unloading.The granite permeability curve has an inflection point at the confining pressure of 30 MPa.The permeability curve is divided into stage A and stage B with a boundary confining pressure of 30 MPa.In stage A,with the confining pressure increasing,the decrease range of permeability decreases more rapidly and the decrease rate becomes faster.In the stage B,with the increase of confining pressure,the decrease range of permeability becomes smaller and the decrease rate becomes slower obviously.The permeability sensitivity coefficient C_k is defined to reflect the variation trend of rock permeability with confining pressure.According to the value of sensitivity coefficient,the permeability sensitivity of granite can be divided into three stages,including high sensitivity,medium sensitivity and low sensitivity.