高渗压条件下基于非达西流的裂隙岩体渗透特性研究

PERMEABILITY OF NON-DARCIAN FLOW IN FRACTURED ROCK MASS UNDER HIGH SEEPAGE PRESSURE

钻孔高压压水试验是评估高水头条件下岩体渗透特性的主要手段。目前,高水压条件下岩体的渗透特性估算多借鉴基于Darcy流假定的钻孔常规压水试验行业规程推荐公式,尚缺乏成熟、有效的计算方法。基于非线性Izbash定律,建立高渗压条件下岩体渗透系数的估算公式,并将高压压水试验P-Q曲线分为线性段、非线性段和水力劈裂扩展段。提出的公式应用简便,各压水试验段岩体渗透系数的确定只需稳态下的流量和水头,并且表征水流流态的系数m可通过曲线拟合得到。通过对琼中抽水蓄能电站高岔区钻孔高压压水试验数据的研究表明,岩体的渗透特性不受水流流态的影响,在高压压水试验的线性段和非线性段基本保持一致;岩体发生水力劈裂后,岩体的渗透特性将急剧增大。建立的公式可为高渗压条件下岩体的渗透特性取值提供一种有效的途径。

High pressure packer test（HPPT） is an important field technique for estimating the permeability of rocks subjected to high seepage pressure. Up to now,no effective method has been proposed to estimate the permeability of rocks subjected to high seepage pressure and the estimation is still commonly performed based on the Darcy′s law as assumed in the constant head packer tests（CPTs）. A formula for estimating the permeability of rocks through single borehole HPPTs was established based on Izbash′s empirical nonlinear equation between the apparent velocity and the hydraulic gradient. The P-Q curve obtained from HPPTs was divided into a linear,a nonlinear and a hydraulic fracturing stage correspondingly,where P is seepage pressure,and Q is seepage quantity. The proposed formula was validated against the in-situ measured data obtained in HPPTs performed to the surrounding rocks of the underground bifurcated pipe at Qiongzhong pumped storage power station. It was discovered that the permeability of rocks was not influenced by the flow pattern,and the estimated permeabilities in the linear and nonlinear stages basically had the same values. As the hydraulic fracturing occurred,however,the permeability increased drastically. The proposed formula provides an effective method for permeability estimation in rocks subjected to high seepage pressure.