Role of Heterogeneity on the Apparent Thermal Properties of Sandstones: Insights for Remote Measurements and Monitoring?

Abstract

Understanding the thermal properties in reservoir rocks and how one can accurately measure and/or infer it at both laboratory and field scale is a long-standing issue. At the field scale, precise measuring techniques are still sought to assess thermal conductivity and diffusivity at depths, and cored rock samples are usually retrieved and measured in the laboratory. At the laboratory scale, the samples from cored logs are measured using different techniques, which sometimes are affected by the interplay between rock heterogeneity and measuring techniques. Using laboratory experiments, we test if and how the thermal properties are affected by apparently invisible heterogeneities in rocks. First, we measure the effective thermal conductivity and diffusivity of homogeneous rocks, under dry and water-saturated conditions. We then create an internal heterogeneity by drilling cylinders of 30mm and 40mm inside the samples, and measure again the apparently intact sample under both dry and water-saturated conditions. We show that, depending on the rock type and the heterogeneity characteristic size and distance to the measured face, extreme variations in apparent thermal properties could be observed. Using the different measurements, we investigate the relevant rocks’ intrinsic properties responsible for “observing” the effect of an internal heterogeneity. By introducing foreign sandstone samples, either dry or water-saturated, within the 40mm diameter drilled region, we then investigate whether one might be able to attain the thermal properties of this foreign object across the measured interface.