Depletion Performance of Volumetric High-Pressured Gas Reservoirs

Abstract

Summary A method to predict the percent recovery of volumetric, high-pressured gas reservoirs from the initial pressure to the abandonment pressure with only initial reservoir data is presented. This method can also be used with early-life production data to predict the initial gas in place. The method is based on an incremental solution to the general material-balance equation. All parameters in the material balance are pressure-dependent and are recalculated for every 100-psi [690-kPa] drop in reservoir pressure. Procedures were developed to calculate these parameters with correlations and data available in the literature. PV compressibilities, formation-water compressibilities, and gas compressibility factors were determined for temperatures and pressures ranging up to 400°F and 20,000 psia [204°C and 137.9 MPa], respectively. The pressure dependency of the PV compressibility and the formation-water compressibility is a unique feature of this model. The reservoir depletion model presented here was applied to a field example, as were three published techniques for determining reserves in abnormally pressured reservoirs. When predictions of initial gas in place were compared, the reservoir depletion model yielded a more accurate value than the other techniques.