Estimation of the Performance and Prediction of the Decline Time of Reservoir: A Case study of Libwa field, Democratic Republic of Congo

Abstract

During oil exploitation, the amount of oil originally in place decreases and the pressure of the reservoir declines. So it is imperative to do a thorough study on the future behaviour of the reservoir in the face of the pressure drop and to predict its decline time. Knowing that the upper Pinda reservoir of the Libwa field produced by dissolved gas drainage mechanism, this allowed us to estimate the future performance of the same reservoir from the gas solubility. The gas solubility value is found from empirical orrelations using parameter values (Volume and Temperature) of the reservoir fluids. It was noticed that the value of the instantaneous gas-oil ratio of the Petrosky correlation was so close to that of the Libwa field therefore to 552 standard Cubic feet per stock tank Barrel (scf/Stb) and could predict the volume behaviour of the Libwa field. The evolution of the reservoir
performance was determined from the cumulative gas-oil ratio using the material balance equation, this gave us as a result of the
gas-oil ratio Cumulative at 5250 standard Cubic feet per stock tank Barrel (scf/Stb) and this latter, by extrapolation, determined
the current reservoir pressure at 1567 pound per square inch atmospheric. Referring to the different decline curves, the exponential decline curve predicted that the end of oil production in this field is expected in 2044. These results sufficiently show the interest that the operator company in the libwa field for the performance of the reservoir to resort to the so-called "Gas Repressering" method of enhanced recovery that would allow it to maintain the Gas-oil ration Cumulative as low as possible in order to postpone the time of decline of the field.