Improved oil recovery by miscible/near miscible CO2 gas injection : experimental and simulation approaches
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Miscible gas flooding has recently overtaken to be the most successful enhanced oil recovery technique. Carbon dioxide flooding is an integral part of miscible gas flooding. This thesis focuses on the feasibility of the implementation of miscible CO2 flooding and demonstrates the effects of different parameters, alongside alternative approaches to EOR which my result in more incremental oil production. To distinguish the miscibility of CO2 gas and oil, a key parameter of miscible CO2 flooding is the determination of the minimum miscibility pressure (MMP). MMP is the minimum pressure at which the oil and injected gas achieve miscibility so that previously trapped oil can be recovered. MMP can be determined in a variety of ways: through experimental, analytical, and computational methods, as well as through other empirical relationships. In common industry practice to define MMP, a series of carefully designed slim tube tests is required. However, since slim tube testing is time-consuming and costly, mathematical correlations are attractive, as they require few input parameters and little information regarding the fluids and are quick and easy to use. This thesis develops a more accurate MMP correlation for pure CO2 injection into high temperature reservoirs by applying a series of 17 new MMP slim tube experiments, with the assistance of a large database of slim tube MMPs that has been published in the literature. Gas/oil interfacial tension (IFT) is seen as one of the most critical fluid characteristic properties in oil reservoirs affecting gas injection production. Because IFT does not appear in the flow equations directly, it would be difficult for the current commercial reservoir simulator to capture its effect. Very few experimental data are available in the literature on displacement involving a low IFT. However, those data were based on synthetic oil not crude oil. This study evaluated the performance of miscible/near miscible gases as a displacing fluid. The study investigated the feasibility of near-miscible CO2 application and improve our understanding of the mechanisms of near-miscible CO2 flooding by conducting a series of two-phase CO2 gas/oil core flood experiments under reservoir condition in a carbonate core. Phase behaviour studies were carried out to characterize the near miscible conditions. Slim tube and swelling/extraction tests were performed to identify the near miscible range and eliminate mass transfer mechanisms to create phase equilibrium for the displaced fluid/fluid flow in porous media. The study's overall results indicate that near miscible could achieve the same ultimate oil recovery as miscible condition. This outcome will define a new strategy when applying CO2 gas injection hence economical in terms of compression costs. Reliable relative permeability curves of oil/gas systems are important for the successful simulation and modelling of gas injections, especially when the miscibility condition approaches. In this study, a series of relative permeability were obtained by history match the experiential data at different IFT level (immiscible, intermediate, and near miscible). To investigate the IFT scaling effect on gas/oil relative permeability. The results shows that the relative permeability of both gas and oil increase as the IFT decreases, but not equally. As the system moves from immiscible toward miscible conditions, the relative permeability increases, and its curvature reduces but does not achieve straight crossline. Finally in This thesis, will demonstrate the two different approaches in modeling miscible gas injection utilizing compositional and extended black oil model. Fully compositional model is complex and required a lot of information. Extended black oil simulation is an alternative approach to compositional simulation and provides an engineering tool to account for oil displacement by a miscible or immiscible fluid. the result shows that using EOS to obtain for MCM Miscible CO2 indicate that excellent prediction to experimental data at 1-D simulation. However, utilizing the ultra-low relative permeability for predicting the miscible displacement has shown promising results in terms of the ultimate oil recovery, this new approach would allow the performance of miscible displacement to by predicted utilizing the black oil model.