Evaluation of Flow-Log Data From Crystalline Rocks With Steady-State Pumping and Ambient Flow

Abstract

Alternative evaluation methods are assessed by numerical modeling of pumping tests in three-dimensional fracture networks. Network scale heterogeneity, fracture-to-fracture scale heterogeneity, and individual fracture scale heterogeneity (fracture roughness) are considered as representative of multi-scale hydraulic and structural heterogeneity of crystalline rocks. The results show that ambient hydraulic gradient has a negligible effect on transmissivity inference of sparsely fractured rocks using flow logs. Consequently, the common dual pumping method used to account for the ambient flow can be simplified to a single pumping. This could potentially reduce the site characterization effort in typical applications such as nuclear waste disposal. The transmissivity inference method based on the Thiem solution provides representative median transmissivity. It, however, underestimates relatively high transmissivities due to its inability to account for the impact of fracture roughness. These findings have important implications regarding pumping test schemes and data interpretation methods in the hydrogeological characterization of sparsely fractured rocks using flow-log data.