Laboratory evaluation of different mode of supercritical CO₂ miscible flooding for carbonate rocks

Field application of supercritical CO₂ (sc-CO₂) miscible flooding continues to grow. Optimization of sc-CO₂ injection during miscible flooding modes represents one of the dominant factors affecting its performance in carbonate oil reservoirs. The main objective of this study was to investigate the impact of different modes of sc-CO₂ miscible injection on oil recovery and injectivity in carbonate rocks. Several modes of sc-CO₂ injection modes were investigated including continuous CO₂ miscible flooding, water-alternating-gas (WAG), and tapered WAG injection. Five coreflooding experiments were conducted to evaluate oil recovery for different modes of CO₂ injection under reservoir conditions. Composite cores of 25 cm length from a specific, producing carbonate reservoir were used in the study. Both horizontal and vertical coreflooding experiments of continuous CO₂ injection mode were carried out to compare oil recovery and injectivity during CO₂ flooding. Horizontal core flooding experiments under WAG mode was performed at pore pressures of 3,200 psi and 3,800 psi. The experimental results indicate that tertiary oil recovery was influenced significantly by different CO₂ injection modes and the direction of displacement. 18.4% and 26.74% of original oil in cores were recovered for horizontal and vertical experiments of continuous CO₂ injection modes, respectively. In horizontal WAG experiments with different pore pressures, higher oil recovery was observed at a pore pressure of 3,800 psi compared to 3,200 psi. The marginal increase in incremental oil recovery indicates that pressure increase beyond 3,200 psi will not have a significant impact. The injectivity of different CO₂ injection modes is reported in this paper.