Mapping 3D Pore Scale Fluid Distributions: How Rock Resistivity is Influenced by Wettability and Saturation History

Abstract

Complexities in pore scale structure, rock-fluid and fluid-fluid interactions have a profound effect on the estimation of reserves, recovery and productivity in reservoir rocks. These complexities determine the pore scale distribution of fluids within the pore space. An example is the estimation of water saturation via resistivity measurements. Default saturation exponents (n=2) are often used in estimating saturations despite experimental laboratory results which show a wide range; 0.9<n<6. Understanding the resistivity response of reservoir rocks requires an ability to accurately map the pore scale structure and fluid distributions in 3D within core samples under variable wettability states and with different saturation histories. This can be done using an image registration technique which overlays 3D tomographic images at varying saturation states. This permits the analysis of two-phase fluid distributions within reservoir core material at the pore scale. Multiple experiments on the same core comparing the fluid distributions at the pore scale allows the analysis of the roles of rock structure, rock type, wettability and saturation history on the resistivity response. The wide range of saturation exponents can be explained from the direct visualization of pore scale fluid distributions. This understanding can lead to more accurate predictions of insitu fluid saturations within reservoirs.