破碎颗粒堆积方式对渗透率应力敏感性的影响机制

Influence Mechanism of Broken Particle Accumulation Mode on Permeability Stress Sensitivity

颗粒堆积下的渗透性量化对采空区冒落带、断层破碎带阻水性能、低渗煤层应力敏感性评估具有重要意义。基于Hertz变形假设,构建了不同颗粒堆积方式的渗透率演化模型,分析了不同颗粒排列结构下应力敏感性及主控因素,探讨了本体变形与结构变形的应力敏感性作用机制。研究表明:若仅考虑本体变形,渗透率应力敏感性和组合颗粒数呈反比,颗粒弹性模量是加卸载试验中应力敏感性主导因素;颗粒发生结构变形的应力敏感性远高于本体变形,和结构变形程度呈正比(颗粒组合结构调整);颗粒结构应力敏感性是结构变形、等效弹模、结构调整综合作用的结果;数值验证了不同颗粒结构应力敏感性的合理性,不同位置渗透率的调整是导致孔压非均匀分布、渗透性变化的主要因素;研究结果表明低渗储层(煤层)存在强应力敏感性,与岩石、流体性质密切相关。

The quantification of permeability under particle accumulation is of great significance for evaluating the water resistance performance of goaf collapse zones,fault fracture zones,and reservoir stress sensitivity.A particle packing permeability evolution model was established,stress sensitivity and main controlling factors under different particle arrangement structures were analyzed and mechanism of stress sensitivity between body deformation and structural deformation is explored based on Hertz deformation.Results show that if only considering the deformation of the body,the stress sensitivity of permeability is inversely proportional to the number of combined particles,and the elastic modulus of particles is the dominant factor in stress sensitivity in loading and unloading tests.The stress sensitivity of particles undergoing structural deformation is much higher than that of the body deformation,and is directly proportional to the degree of structural deformation(particle combination structure adjustment).The stress sensitivity of granular structures is the result of the combined effects of structural deformation,equivalent elastic modulus,and structural adjustment.The rationality of stress sensitivity of different particle structures has been numerically verified,and the adjustment of permeability at different positions is the main factor leading to non-uniform distribution of pore pressure and changes in permeability.It is believed that low-permeability reservoirs(coal seams)have strong stress sensitivity and are closely related to rock and fluid properties.