Experimental Investigation of Liquid, Supercritical CO2, CH4, and CO2/CH4 Mixture to Improve Oil Recovery

Abstract

Abstract This study investigates the efficiency of injecting CO2 and CH4 in improving oil production from black oil reservoirs. While prior research highlights the effectiveness of these gases in enhancing oil recovery factors, comparing their performance in bulk interaction to their performance in the porous medium is scarce. Furthermore, the impact of the physical state of the injected CO2—liquid, gas, or supercritical— on oil extraction mechanisms still needs to be explored. Hence, our study aims to bridge this gap through a comprehensive experimental analysis of gas-oil interactions in the bulk phase and within porous media. The bulk gas-oil interactions were investigated using a visual Pressure Volume Temperature (PVT) cell. In contrast, the gas-oil interaction within the porous media was investigated using a coreflooding experimental approach. The proposed investigation is designed to evaluate the influence of the permeability on the gas-oil interactions and the effect of the physical state of the injected fluid —liquid, gas, or supercritical — on the gas miscibility in oil. Since viscosity reduction and oil swelling are the primary mechanisms for miscible gas Enhanced Oil Recovery (EOR), this study focuses on the efficiency of different injected gases and the physical state of CO2 on the swelling factor, saturation pressure alternation, and viscosity reduction. The swelling factor and saturation pressure curves were measured when different molecular percentages of gas above the minimum miscible pressure were mixed with oil. The viscosity reduction effect was calculated by comparing the viscosity of the oil produced from the coreflooding experiment to the viscosity of the original oil. The oil minimum miscible pressure (MMP) of each considered gas in the oil sample was determined based on the oil composition determined by Gas Chromatography (GC) analysis. The results showed that the CO2/CH4 mixture outperformed CO2 liquid, supercritical, and CH4 in coreflooding experiments. Additionally, the coreflooding experiments proved liquid CO2 (Cold) performed better in improving oil recovery than supercritical CO2. However, the bulk PVT analysis revealed a higher swelling factor for supercritical than liquid CO2, which suggests supercritical CO2 outperforms other gases, including cold CO2. In contrast, the viscosity of the produced oil when supercritical CO2 was injected was lower than that of all other gases. The observed variation in CO2 performance indicates the significant role of CO2 physical state of CO2 in the oil extraction mechanism. The conclusion of this study provides a better understanding of the performance of different gas injection strategies in conventional reservoirs, which brings insights into optimizing gas injection into depleted oil reservoirs that contain dead oil.