digilib@itb.ac.id +62 812 2508 8800

The shift towards clean energy and the reduction of CO2 emissions from industries are essential for ensuring sustainable development. In this context, the utilization of Carbon Capture, Utilization, and Storage (CCUS) technologies, specifically through the injection of CO2 and CH4 mixtures, holds significant potential for effectively mitigating global warming and addressing climate change. Furthermore, the investigation of caprock sealing integrity is crucial to prevent any potential leakage of CO2.. With considerations to increase the breakthrough pressure, CH4 and CO2 gas injection, in immiscible condition, was conducted. The WAG technique is chosen to injected CO2 and CH4, it will improves macroscopic and microscopic sweep efficiency, maintains reservoir pressure, and reduces residual oil saturation. In this study, the author proposes the idea of modelling Water Alternating CH4-CO2 Gas Mixtures (WAG) Injection to investigated the effect of CO2 – CH4 injection upon the CCS-EOR mechanisms and performance with WAG ratio sensitivity on the optimum oil recovery and CO2 storage efficiency of the three main CO2 trapping mechanisms (structural, residual, and solubility) in the sandstone reservoir "B" Structure in "S" Field, South Sumatera Province, Indonesia. Reservoir simulations and production forecasts were done using CMG GEMTM 2021 Simulator during 16 year production period from January 2021 until January 2037. Simulators were forecasted 30 years after injection to study trapping mechanisms over the year of CO2. This study conducted a series of sensitivity analyses to identify the effects of operational parameters in modelling WAG injection and to determine the most optimum WAG injection scenario to be applied at "B" Structure in "S" Field to gain promising oil recovery and CO2 trapped using two injector wells. WAG ratio and gas composition were varied to observe those parameters' effects on oil recovery factor, CO2 trapped, plume migration, and caprock integrity. This study shows that highest co-optimization injection function (57%) using gas slug size 12.5%, WAG ratio 2, and 1 cycle/year. Furthermore, the resulting recovery factor and optimum CO2 trapped are higher when the water injection duration is longer than the gas mixture injection, in this case, with a 2:1 ratio of water-gas injection, which results in 57.11% of the oil recovery factor and 8.1 Kton CO2 and 1.72 Kton CH4 trapped. Therefore, Water Alternating CH4-CO2 Gas Mixtures Injection is suggested to be applied in the "B" Structure of "S" Ficld for further field development.