Experimental measurement on the hydraulic conductivity of deep low-permeability rock

Hydraulic conductivity is an important hydrogeological parameter and is difficultly measured by laboratory experiments. In order to obtain the effective hydraulic conductivity of deep low-permeability rock and to study the water flow behavior within the rocks, in situ water injection experiments were employed in a deep underground tunnel. The applicability of Darcy's law is discussed as well. The study results show that Darcy's law may still be applicable for the initial determination of hydraulic conductivity for a partial transitional flow of water injection experiments, which retains linear relationship between pressure and flow rate. Water flow behavior in the rock experiences the initial stable phase, the increase phase, and the late stable phase in general but also has distinct flow properties due to the different characters of rocks. Hydraulic conductivity change with differential injection pressure can be divided into two phases, i.e., approximated constant hydraulic conductivity values which can be considered as the hydraulic conductivity of the rock in the initial flow phase and its effective value jump in the flow mutation phase caused by hydraulic fracturing.