A new approach of pressure profile and oil recovery during dual and single core flooding of seawater and CO₂ injection process for carbonate reservoir

Sweep efficiency during waterflooding and CO₂ miscible injection can be challenging because of channeling and bypassing of injected 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 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, and two composite plugs with different permeabilities. Two composite coreplugs, high permeable core plug (HPCP) and low perbeable core plug (LPCP) were placed in parallel in a coreflood apparatus. No crossflow of fluids occurred between high and low permeable plugs. Different injection schemes were completed, which included seawater flooding, initial CO₂ injection, gel slug injection for conformance control and a second CO₂ injection. In addition, two experiments of seawater and continuous CO₂ injection were completed at the same experimental conditions in a single coreflood for comparison with dual core flooding experiments. The results indicate that 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 single core continuous CO₂ process (horizontal and vertical injection) are discussed in this paper.