Abstract This describes the results of extensive phase behavior and slim-tube analyses for CO2 EOR study in a Middle Eastern offshore reservoir. The objectives of this study are to evaluate the effectiveness of CO2 injection to the target reservoir and to reduce uncertainties based on laboratory and simulation studies. This study is focused on solubility and slim-tube tests in the laboratory studies, and its analyses using an equation of state (EOS) model that reproduces the majority of conventional PVT and solubility swelling results for an associated hydrocarbon gas and oil system.
We performed conventional PVT and solubility swelling tests for a CO2-Oil system successfully. With the results of solubility tests, an EOS model was established and tuned for predicting the solubility behavior in the mixing fluid between CO2 and the target reservoir oil within sufficiently acceptable ranges. In addition, we conducted a series of slim-tube tests with CO2 and a synthetic hydrocarbon gas, which is similar compositions to the associated hydrocarbon gas, at some pressure levels. In comparison between CO2 and the synthetic hydrocarbon gas injection, there is a significant difference of oil recovery at relatively low pressure, indicating that CO2 injection is more effective than the synthetic hydrocarbon gas injection. Results of slim-tube tests with CO2 show that the oil recovery reaches greater than 90% at any pressure level, but the displacements of oil at the outlet of slim-tube by the visual cell observations appear in different manners.
We simulated slim-tube tests with the adequate EOS model for CO2 injection under carefully arranged simulation conditions. As a result, we confirmed that simulated gas saturation and k-value profiles are consistent with the visual cell observations, and this displacement of oil by CO2 is characterized as condensing/vaporizing drive. These results confirm the effectiveness of CO2 injection to the target reservoir and lessen the uncertainties of fluid interaction at the laboratory scale.