Abstract This study aims to explore the dual benefits of CO2 injection in Sabah Offshore depleted oil reservoir, focusing on both Carbon Capture and Storage (CCS) and Enhanced Oil Recovery (EOR). It examines the interaction between CO2 and residual oil properties with the aim is to optimize the oil recovery while advancing CCS initiatives. The study is structured into two core areas: (1) a detailed analysis of the effects of CO2 injection on residual oil properties under reservoir conditions, particularly focusing on how gas composition impacts the injection dynamics; and (2) an investigation on CO2 influencing the complex interaction between three fluid phases of gas-water-oil. These investigations are to assess the viability of CO2 injection as EOR method in the Sabah offshore reservoir. The methodology involves two critical components: fluid-fluid analysis and advanced fluid-rock analysis. The fluid-fluid analysis evaluates the impact of gas composition on key injection mechanisms, including Oil-Gas Interfacial Tension (IFT) reduction, oil swelling, and viscosity reduction. The study compares the effects of three different gases: CO2, Hydrocarbon, and Nitrogen, with Nitrogen used to represent the immiscible case. Viscosity reduction tests and Gas-Oil IFT reduction (miscibility) tests are conducted, alongside swelling simulations. In parallel, the fluid-rock analysis uses Unsteady-state (USS) Gas Injection coreflood method was carried out to evaluate three-phase gas-water-oil saturation and to assess the potential of CO2 as an EOR agent. All the tests are conducted under reservoir-specific high-pressure and high-temperature conditions using both live and crude oil. The study establishes a comparison between CO2, Hydrocarbon, and Nitrogen gases in terms of their effects on IFT and viscosity reduction mechanisms. CO2 gas consistently showed a higher miscibility and an increased potential to reduce viscosity, positioning it as the most effective gas for altering residual oil properties. The USS coreflood experiments quantifies CO2 storage potential, with the result indicating approximately 48% of rock pore volume occupied with CO2 gas. Additionally, the study of CO2 injection for EOR demonstrates a substantial improvement in oil recovery compared to immiscible gas injection underscoring its dual role as a storage medium and as an EOR enhancer. This study combines detailed fluid-fluid (miscibility effect study) and fluid-rock analyses to explore the dual benefits of CO2 injection in depleted oil reservoir. By thoroughly examining the influence of gas composition on residual oil properties, a valuable insight of the role of CO2 for CCS-EOR processes can be exploited to guide the future optimization process.
Affandi et al. (Mon,) studied this question.
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