Investigation of relative permeability characteristics for supercritical CO₂ displacing water and remaining oil after seawater flooding in carbonate rocks at reservoir conditions

Supercritical CO₂ (sc-CO₂) miscible flooding has been successfully used as an enhanced oil recovery (EOR) method in both sandstone and carbonate reservoirs. The sc-CO₂ is miscible with the remaining oil left after water flooding at injection pressures above MMP to achieve higher recoveries. During the process of the sc-CO₂ injection after water flooding, there are two phases in the formation, a water phase and a miscible phase (sc-CO₂dissolve into oil). To describe the flow characteristics and performance of these phase, the water (K_rw) and miscible phase (K_rm) relative permeability curves are needed in reservoir numerical simulation during sc-CO₂ miscible injection. Surprisingly, publications of experimental data that include water and miscible phase are relatively rare due to the lack of proper experimental methods used. Usually, researchers use water and sc-CO₂ relative permeability curves instead of water and miscible phase relative permeability to describe the flow characteristics when sc-CO₂ displaces water and remaining oil. In this paper, we propose a modified method based on Corey's model to describe water and miscible phase relative permeability using end point values of water and sc-CO₂ miscible flooding. To obtain the end point values from water and sc-CO₂ miscible flooding, four core flooding experiments were carried out on carbonate composite cores using live oil at reservoir conditions. These included two short core and two long cores. The Corey's model was used directly to predict oil/water relative permeability in the carbonate composite cores. A modified Corey model (proposed in this paper) was used to calculate water and miscible phase relative permeability and describe the flow behavior of sc-CO₂. The effect of the Corey's exponents, N_w and N_m, were evaluated on relative permeability characteristics in the carbonate composite cores during sc-CO₂miscible flooding. Modified Corey model paramaters include the maximum water saturation, S_w(max), remaining oil saturation S_orw and K_rw at S_orw from water flooding process, residual water and oil saturations and the maximum sc-CO₂saturation from sc-CO₂ injection process. The relationship between relative permeability to water and miscible phase vs. miscible saturation has been developed when the water saturation is decreasing during sc-CO₂ miscible injection process. In addition, it is an obvious influence of water and miscible phase relative permeability when the Corey exponents, N_w and N_m are changed.