Unlocking Potential of CO2-Enhanced Recovery and Sequestration in a Waxy Oil Reservoir: A Phase Behavior Investigation

Abstract It is evident that the use of carbon dioxide (CO2) for enhanced oil recovery (CO2-EOR) and sequestration into reservoirs has the potential to not only enhance oil recovery but also contribute to reducing greenhouse gas emissions. This paper comprehensively evaluates the potential of CO2 to enhance recovery and sequestration in a waxy reservoir and focuses on phase behavior. The thermodynamics of CO2-hydrocarbon systems play a crucial role in determining the phase behavior of CO2 in the reservoir. Comprehensive fluid analysis laboratory experiments have been conducted such as compositional analysis, constant composition expansion (CCE), differential liberation (DLE), viscosity, and wax experiments, and swelling tests due to various CO2 injections. The dewaxing of crude oil was done as reference to investigate the influence of wax component to the phase behaviour. A PVT software was used to validate the laboratory data through PVT fluid characterization. Phase behavior of waxy crude oil the presence of various compositions of CO2 enrichment was studied. A thermodynamic EOS model was developed and characterized using PVT Software and fine-tuned to match the PVT experiments, including expansion and depletion studies, viscosity, solid content, and wax apparent temperature, including swelling tests over different enriched CO2 compositions. The swelling factor measurements indicate that the oil volume increases with pressure up to a certain point before decreasing. The comparison between laboratory measurements and model prediction of wax content also satisfactorily matches. The CO2 was found to change fluid properties which consequently increased bubble point pressure and other critical parameters. The presence of wax in crude oil has been identified to increase bubble point pressures can lead to require higher minimum miscibility pressure (MMP) because the oil is already closer to its gas liberation point, requiring more pressure to achieve miscibility with CO2. Higher MMP in CO2-EOR project can pose a challenge in CO2-EOR in waxy crude oil such as operational costs, safety risks, and technical challenges. It requires careful consideration of reservoir conditions, economic factors, and engineering solutions to ensure successful and efficient CO2-EOR method. This study demonstrates the importance of conducting extensive PVT experiments and analyses before deciding a CO2-EOR project, as this is crucial to understand the phase flow behaviour of fluids. Thermodynamic modeling is an effective approach for analysing advanced fluid behaviour.