Advancing hydraulic conductivity estimation in the Permo-Triassic Sherwood Sandstone Group using borehole NMR logging

Abstract The Permo-Triassic Sherwood Sandstone Group is an important aquifer in the United Kingdom (UK) for groundwater and geothermal energy applications. Hydraulic conductivity ( K ) is essential for understanding groundwater movement, contaminant and heat transport in aquifers. Pumping test and borehole nuclear magnetic resonance logging (BNMR) were conducted in three boreholes drilled into the Sherwood Sandstone to determine K . BNMR provides information on the water-filled porosity and pore space geometry, and compared to conventional methods, it is an effective way to estimate K at a high vertical resolution. Schlumberger-Doll Research (SDR) and Timur-Coates (T-C) were used to estimate K using the standard empirical constants initially developed for petroleum reservoir applications. K SDR and K T-C were upscaled to the larger volume represented by K pumping for comparison. Both the standard SDR and T-C equations underestimated K by at least two orders of magnitude because of the limited transferability of their empirical constants to shallow groundwater systems, as they were derived for petroleum reservoir rocks rather than near-surface materials. The fits between the K SDR , K T-C and K pumping were optimised using a semi-constrained least-squares approach to obtain a set of site-specific parameters for the Sherwood Sandstone Group. The new K SDR and K T-C estimates, based on site-specific parameters, are within an order of magnitude of the K pumping . This study presents the first reported SDR and T-C constants for the Sherwood Sandstone Group, which may be used to estimate a more reliable NMR-derived high-resolution hydraulic conductivity in other locations where this formation is present.