Sweep efficiency during waterflooding and CO2 miscible injection can be challenging because of channeling and bypassing of injecting fluids. Some of these factors include reservoir heterogeneity, permeability contrast and gravity override. These factors contribute to reduced volumetric sweep efficiency in both sandstone and carbonate reservoirs. To study the effect of reservoir heterogeneity on pressure profile and oil recovery, and accurately describe the displacement mechanisms during seawater and CO2 flooding, an effective experimental methodology including the laboratory set-up and procedures are proposed in this paper. Dual core flooding experiments were conducted at reservoir conditions using live oil, seawater, supercritical CO2 (sc-CO2), and two composite plugs with different permeabilities. Two composite core plugs, a high permeable core plug (HPCP) and a low permeable core plug (LPCP), were placed in parallel in a coreflood apparatus. No crossflow of fluids occurred between the high and low permeable plugs. Different injection schemes were completed, which included seawater flooding, initial sc- CO2 injection, gel slug injection for conformance control and a second sc-CO2 injection. In addition, two experiments with seawater and continuous CO2 injection were completed with the same conditions in a single coreflood for comparison with the dual core flooding experiments.
The results indicate that the dual core flooding technique is an effective method to evaluate the performance of IOR and EOR processes, especially involving CO2 or gas injection. The profiles of differential pressure across both HPCP and LPCP show a demonstrable distinction. The differential pressure across LPCP is higher than that of HPCP for both seawater and supercritical CO2 (sc-CO2) injection before breakthrough, and drops to levels similar to that in HPCP after breakthrough. A substantial increase of differential pressure in HPCP (up to 200 psi) was observed during base gel slug injection, which indicates that in- situ CO2-emulsion was generated and was able to block the high permeable zone and resulted in displacing fluids into LPCP, therebyimproving sweep efficiency in the LPCP. The comparisons of oil recovery by seawater and sc-CO2 injection and the pressure profile between both dual core flooding and the single core continuous sc-CO2 process (horizontal and vertical injection) are discussed in this paper.