Estimating the Hydraulic Conductivity of Deep Fractured Rock Strata from High-pressure Injection Tests

Deep coal mining in the Yanzhou coalfield is threatened by a confined Ordovician limestone aquifer where water pressure exceeds 10 MPa. High-pressure injection tests are widely used to characterize the hydraulic properties of water-resisting fractured rock strata under such conditions, although estimating hydraulic conductivity remains an issue. This paper presents an approach to estimate it, using data from several high-pressure injection tests by accounting for the flow conditions. Typical P-Q curves obtained from the injection tests were summarized and divided into Darcian and non-Darcian flow phases, and an equation was proposed to estimate the hydraulic conductivity of fractured rocks. The hydraulic conductivity is pressure dependent and increased by injection pressure in the non-Darcian flow phase, due to hydraulic fracturing. As one would expect, the hydraulic conductivity estimated using the new equation was much greater than that estimated using Darcy's law.