In-Place Volume Estimation: The Role of Down-Hole Temperature Data

Abstract The primary objective of this work was to leverage down-hole temperature measurements to enhance inverse modeling of the subsurface, particularly to enable more accurate estimations of fluid volumes in-place. This study examined nonisothermal closed reservoirs with impermeable boundaries, under the assumption of sufficiently high Peclet numbers where thermal diffusion is negligible. Considering an axisymmetric cylindrical domain, a dimensionless formulation was developed to simplify the analysis and to elucidate key parameters that govern the system's overall behavior. An analytical expression for temperature under a pseudosteady pressure regime was derived using the Method of Characteristics. The results were verified by comparing them with a commercial numerical thermal simulator. The application of the solution to reservoir parameter estimation was tested against a synthetic example for both sandface and wellbore data. The key question we wished to address was: What additional insights does temperature analysis offer that pressure analysis cannot? In conventional pressure analysis, estimating stock tank original oil-in-place (STOOIP) requires an assumed value for water saturation as input. This study leverages the full potential of temperature data—readily available and typically recorded alongside pressure at minimal cost—to directly estimate fluid saturations and reduce uncertainty in volumetric assessments. From an even more compelling perspective, our solution significantly enhances the accuracy of reservoir volume estimates, in scenarios involving hydraulic support systems such as aquifers. We present a real field case study featuring an active aquifer, which successfully demonstrated the effectiveness of our approach.