Impact of Pressure Depletion Amplitude and Coupling Strategies on CO2 Flooding for Enhanced Oil Recovery: Insights From Core-Scale Experiments

Abstract The G-block reservoir, characterized by low permeability and significant interlayer heterogeneity, faces challenges in carbon dioxide (CO2) flooding, where CO2 preferentially flows through high-permeability layers, leaving low-permeability zones poorly swept. This leads to reduced sweep efficiency and suboptimal oil recovery. Limited research has focused on improving CO2 sweep efficiency under injection–production coupling. CO2 flooding strategies for enhanced oil recovery (EOR) are investigated through lab experiments, examining the effects of varying pressure depletion amplitudes, injection–production coupling times, and permeability ratios using 2 mD and 10 mD long cores to represent heterogeneous reservoir conditions. Experimental results show that lower pressure depletion amplitudes (15 MPa) lead to higher cumulative oil recovery than higher depletions (35 MPa), due to enhanced CO2 mobility and reduced oil viscosity. Early coupling at a gas–oil ratio (GOR) of 100 m3/m3 significantly enhances oil recovery by mitigating gas channeling effects observed at higher GORs (5000 m3/m3). Analysis of varying permeability ratios (2, 3, and 5) reveals differences in recovery dynamics, with higher ratios amplifying recovery disparities between low- and high-permeability zones due to preferential CO2 flow. These findings highlight the critical role of reservoir heterogeneity and the timing of operations in optimizing CO2 flooding strategies for EOR.