非线性应力作用下裂缝砂岩应力敏感性特征

为了实现和评价变围压应力敏感实验关系转换为变内压应力敏感实验的等效关系，进而获取储层岩石渗透率与地层压力的关系，采用室内实验的方法，针对含微裂缝和人造裂缝的致密砂岩开展了变围压应力敏感实验、变内压应力敏感实验和特殊应力敏感实验；基于变围压实验数据，结合有效应力方程计算得到了实验岩样的渗透率随地层压力的变化关系，并与实验测定结果进行了对比分析。结果表明，计算得到的渗透率大于实验直接测定的渗透率，这种差异源于气体滑脱效应；基于Terzaghi有效应力方程计算的无因次渗透率小于对应变内压实验测定的无因次渗透率；基于非线性有效应力方程计算的无因次渗透率与对应变内压实验的无因次渗透率一致。有效应力和气体滑脱效应影响地层条件下渗透率的确定。

Effect of Nonlinear Effective Pressure on Stress Sensitivity in Fracture Sandstones

To implement the transformation of the relationships between permeability and confining pressures in changing-confining-pressure stress sensitivity experiments into the ones in changing-pore-pressure stress sensitivity experiments, and obtain the relationships between permeability and pore pressure, changing- confining -pressure stress sensitivity experiments and special stress sensitive experiments in tight sandstones with microfractures and artificial fractures are carried out. At the same time, based on the experimental data in changing-confining-pressure stress sensitivity experiments and the effective stress equations, the relationships between permeability and pore pressure are calculated, and are compared with the results in changing-pore-pressure stress sensitivity experiments. The results indicate that calculated permeabilities are larger than those measured directly, which is caused by the Klinkenberg effect, dimensionless permeabilities measured directly are equal to those calculated with the nonlinear effective principle, while larger than those calculated with Terzaghi effective principle. Both effective stress and slippage effect affect the determination of permeability in situ.