Comparison of Gas Reservoir Performance from Simulation and General Material Balance

Abstract

The study of comparing gas reservoir performance using two different methods, namely numerical simulation and general material balance was conducted. The Songo Songo dry gas field in Tanzania was used for this study. The objective of this study was to compare results from the two methods with actual data obtained from the field and determine which one best fits the performance of dry gas reservoir.To accomplish the objective of this study, geology of the Songo Songo field was studied and physics and principles underlying gas reservoir simulation and material balance were reviewed. These guided to set-up simulation procedures, designing flowchart for material balance analysis and gathering relevant data. The geological formations and stratigraphy gave guidelines to reveal factors affecting the performance of the Songo Songo reservoir.From this study, it was determined that, reservoir simulation and general material balance gave similar trends of the performance curves in the pR/Z plot. The analysis of variance at 95% confidence level indicated that the probability of no significant difference between the results of the two methods was equal to 0.927. It is early to specify that reservoir simulation or general material balance gives better performance of the Songo Songo dry gas reservoir because the history of the field is short and the pressure support in reservoir simulation model and in general material balance model is different. Both reservoir simulation and general material balance models are advised for modelling the performance of Songo Songo dry gas reservoir. Estimated initial gas in place of 44.65 BCM was obtained using general material balance analysis and associate water volume ratio (M) of 1.55 was determined.