Evaluation of Retrograde Condensate Dropout Phenomena in a Gas Condensate Reservoir

Abstract

Abstract The paper presents the result of an investigation of condensate drop-out phenomena through reservoir fluid characterization and well testing analysis to answer the condensate banking issue in an offshore gas field. Further evaluation via the Enhanced Gas Recovery (EGR) method has been conducted for condensate recovery optimization strategy. The fluid characterization through EOS modelling is performed to match the laboratory results. Having achieved a reasonable match of the EOS model, the Condensate Gas Ratio (CGR) variation over pressure depletion is established and compared with the actual CGR profile to understand the severity of the condensate drop-out in the reservoir. The investigation is continued in identifying the condensate banking behaviour. Multiple well testing data have been interpreted focusing on pressure derivative log-log plot matching, productivity index and skin factor changes. Interestingly, it is observed that the condensate banking issue is highly dependent on how the well completion and trajectory have been designed. A low deviated well has a higher tendency to experience severe condensate banking issues while the impact is reduced for a horizontal well. Subsequently, a compositional model is built by converting from an existing black oil model. It is used in the investigation of the EGR strategy by injecting different types of gas at different timings and rates. Based on the simulation results, better condensate recovery factor is expected with the incremental between 4 to 8%. The study can shed some light on the actual field experience and interesting lessons learned to be considered for a gas condensate reservoir development.