Coupled optimization of enhanced gas recovery and carbon dioxide sequestration in natural gas reservoirs: Case study in a real gas field in the south of Iran

Since the beginning of industrial age the atmospheric concentration of greenhouse gases has been increased significantly due to excessive use of fossil fuels. An effective way for decreasing emission of greenhouse gases is injection of CO2 in geological formations. Moreover, from the reservoir engineering point of view, CO2 injection has been considered as a method of enhancing oil and gas recovery. While using CO2 for enhanced oil recovery (EOR) has been the subject of several studies in the past decades, enhanced gas recovery (EGR) has not been fully studied in the gas reservoirs, mainly because of high recovery factor of gas reservoirs and mixing of the reservoir gas and CO2. In this work, the effective parameters on the EGR and CO2 storage in a real gas reservoir in south of Iran have been studied and optimized using genetic algorithm. All economic investigations have been performed with and without Clean Development Mechanism (CDM) consideration. Finally the effect of CO2 solubility in the reservoir connate water has been investigated. This study shows that in addition to the production of residual gas, injecting CO2 in the gas reservoirs at optimized conditions results in the permanent storage of considerable amount of CO2 and therefore preventing it from being emitted to the atmosphere. Although this process increases NPV due to revenue of EGR, considering the certified emission reduction (CER) has additional positive effect on NPV. Finally this study shows that dissolution of CO2 in reservoir connate water can delay breakthrough of CO2 in production well effectively.