Does Core-Length Matter for Mobility Control Displacements in Core?

Optimal core length for enhanced oil recovery (EOR) core flood experiments lacks consensus. Shorter cores are commonly used, but assessing sweep efficiency in mobility control EOR methods, crucial for longer inter-well distances, remains a question. The adequacy of shorter cores in evaluating sweep efficiency in these EOR processes needs attention. Despite the recognized importance of core flood for enhanced oil recovery (EOR) applications, there is no consensus in the literature on the optimal core length to be used in displacement experiments. Therefore, it is important to address the key question “whether the shorter length cores are sufficient for proper sweep efficiency evaluation in mobility control-based EOR processes?”. The objective of this study is to investigate the effect of core length on the core-scale sweep efficiency and ultimate recovery for the displacement experiments carried out at different viscosity ratios between injected fluid and residing oil. Two identical core flooding experiments were conducted using cores that have similar porous media properties ensured through chromatography scan (CT) but have different lengths of 3 and 7 inches. Two different viscosity ratio conditions (10, 0.1) were imposed sequentially in each of the core flooding experiments by injecting water at 2 ft/day as a primary slug and then 2,000 ppm HPAM polymer solutions at 0.25 ft/day as the secondary slug. The results suggest that the use of shorter-length cores for displacement experiments under unfavourable viscosity ratio conditions would overestimate the early sweep effect by over 10%. In contrast, polymer flood conducted under favourable viscosity ratio conditions resulted in a higher-pressure gradient of 95 psi and showed only a marginal ∼ 2% difference in the incremental recovery factor between shorter and longer cores from ∼ 0.4 PV to 1.9 PV injections.