Experimental Investigations of Spatial and Temporal Variations in Rock Thermal Properties as Necessary Stage in Thermal EOR

Abstract

Abstract More than 8,500 measurements of the rock thermal properties – thermal conductivity, thermal diffusivity and volumetric heat capacity – performed on samples of different rock types from 6 terrigenous and carbonaceous heavy oil reservoirs provided the vast experimental data base for 4D reservoir modeling of thermal EOR recovery methods. The experimental results describe the essential spatial variations (more than 100%) in the thermal properties, including thermal rock anisotropy and heterogeneity, within the reservoirs, and significant temporal variations (up to 100% in most cases) in rock thermal properties that are caused by significant changes in reservoir temperature (up to 250 0C) and fluid type (steam, oil and brine) in rock pore space during the heating of reservoirs and oil production. Wide ranges in all thermal properties were determined from the measurements and important information on the correlations between thermal and other petrophysical properties (porosity, elastic wave velocities, etc.) was found. The analyses demonstrate that such spatial-temporal (4D) variations in the thermal properties could not be obtained from the literature data and the existing data base. It was established also that the theoretical modeling of rock thermal properties in modern simulators leads to significant uncertainties in reservoir thermal properties estimation and could result in essential errors in oil production parameters evaluation. The importance of using accurate and representative experimental data on rock thermal properties in simulations of thermal EOR was illustrated by a simplified model of a SAGD process. In the cases simulated, serious influence (up to 50%) from uncertainties in each reservoir thermal properties (the thermal conductivity and volumetric heat capacity) on key outcome parameters – cumulative oil production and steam-to-oil ratio – was observed. Results demonstrated that different thermal properties influence on key production parameters in different ways. It was shown also that reliable data on the thermal properties of both pay zone and surrounding rocks are important for correct estimation of SAGD performance. In particular, the maximum influence of uncertainty in thermal properties of pay zone is established during first years while the influence of uncertainty in thermal properties of surrounding rocks increases with time monotonously. The parametric study showed that production predictions based on empirically derived thermal rock properties may significantly improve simulations and provide field operators with more realistic estimation of the project's economics. The results demonstrate the necessity of detailed experimental investigations of the thermal properties of reservoirs and surrounding rock for the heavy oil field under development to provide necessary reliability of hydrodynamic modeling results.