Characterizing the hydraulic conductivity of rock formations between deep coal and aquifers using injection tests

The hydraulic behavior of the rock formations under coal floor is an important factor to evaluate the risk of floor water inrush, which is difficultly obtained exactly by laboratory hydraulic tests. For the purpose of obtaining the hydraulic conductivity of the rock formations between deep coal and aquifers and further evaluating the risk of floor water inrush, water injection tests are carried out at Baodian coal mine. Through drilling four boreholes, three water injection tests of three rock formations are carried out and the hydraulic conductivity of the rock formations is calculated. Experimental results analysis shows that the three test rock formations are low-permeability. The hydraulic conductivity propagation with injection pressure can be divided into two phases that include stable change phase and increase phase due to hydraulic fracturing. In addition, the crack connections and propagations model can be used to analyze the change process of hydraulic conductivity of rock formations under water pressure. It is a useful approach for obtaining the hydraulic conductivity of deep rock formation, evaluating the risk of floor water inrush, preventing water inrush and raising the coal mining efficiency in colliery.