Abstract The purpose of this study was to estimate the original-gas-in-place (OGIP) of a water-drive reservoir using optimization algorithm for Port Arthur field, Texas, U.S.A. The properties of the associate aquifer were also obtained. The good agreement, between the results from this study and those from simulation study, would be demonstrated in this paper.
In this study, material balance equation for a gas reservoir and van Everdingen-Hurst model for an aquifer were solved simultaneously to calculate cumulative gas production. The result was then compared with cumulative gas production measured in the field that observed at each pressure. The following parameters were manually adjusted to obtain: OGIP, thickness of the aquifer, water encroachment angle, ratio of aquifer to reservoir radius, and aquifer's permeability. The procedure was then applied with simplex technique, an optimization algorithm, to adjust parameters automatically. When the difference between cumulative gas production calculated and observed was minimal, the parameters used in the model would be the results obtained.
A water-drive gas reservoir, "C" sand gas reservoir in Port Arthur field, which had produced for about 12 years, was analyzed successfully. The results showed that the OGIP of 60.6 BCF estimated in this study was favorably compared with 56.2 BCF obtained by a numerical simulator in other study. In addition, the aquifer properties that were unavailable from the conventional plotting method can be estimated from this study. The estimated aquifer properties from this study were compared favorably with the core data.
Introduction The original-gas-in-place of a water-drive gas reservoir was not easy to estimate by using analytical method because the complexity of water influx and aquifer properties involved. For a water-drive gas reservoir, the OGIP is an important parameter both for production performance and for feasibility study of converting a depleted gas reservoir to an underground storage.
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