Validation of Produced Gas Rate Modelling in an Oil Reservoir with Very High CO2 Through Matching of Live Oil Coreflood

Abstract

Fatehgarh reservoirs in Aishwariya field, located in Barmer Basin of Rajasthan India, have very high CO2 content in reservoir fluid. A procedure was developed earlier to model the impact of reservoir CO2 on waterflood, polymer flood and ASP flood (Mishra and Pandey 2017, 2018) in this field. Another observation is that in such a system with very high amount of CO2, produced gas rate does not follow conventional trend. Conventionally, gas is dissolved in oil and produced gas is the gas released out from the oil. However, in a system like Aishwariya with very high amount of CO2 in dissolved gas, produced gas is the cumulative of gas released out from both liquid streams i.e., oil and water. Interestingly, gas can continue to produce even after no more oil is being produced from the system. A live oil coreflood was carried out to generate produced gas rate profile under Aishwariya reservoir conditions. The objective of this work was to validate the modelling procedure developed to predict the produced gas rate in such a system with very high amount of CO2 in reservoir fluid. A live oil coreflood experiment was carried out using 12 inches long Bentheimer core under Aishwariya reservoir pressure and temperature conditions. After saturating the core with live oil, the core was water flooded with brine for ~3.7 pore volumes. Produced gas volume was measured at different times so as to generate gas production profile. Two different simulation techniques were used to simulate the experiment and match the gas production profile. First technique was using a compositional simulator with EOS based PVT while the other technique was using an "advanced processes simulator" modeling the component distributions based on partitioning coefficients. Both methods could successfully capture the production of gas from both liquid streams; oil and water and a reasonable match for the produced gas could be obtained. The approach developed to simulate impact of CO2 on different aqueous based flooding processes in Aishwariya field was validated by matching the coreflood experiment carried out under actual Aishwariya reservoir conditions. It helped to confirm confidence in performance prediction of aqueous based flooding mechanisms planned in Aishwariya field despite the presence of significant amount of CO2. The paper presents history match of unconventional produced gas profile of a coreflood carried out under Aishwariya field conditions with very high amount of dissolved CO2. The proposed method can be applied to estimate produced gas rate in other fields with very high amount of CO2 in reservoir fluid.