Performance assessment of solvent-assisted low-salinity waterflooding in cyclic injection mode for Alaska heavy oil recovery

This work highlights the potential of CO₂-alternating-LSW as a more effective and environmentally favorable solution for heavy oil recovery. It provides valuable insights for reservoir engineers and researchers. These findings could impact strategies for sustainable hydrocarbon extraction in unconventional reservoirs. Key Highlights from the Results: • Cost-Effective and Sustainable Enhanced Oil Recovery: The study uses low-cost lean hydrocarbon gas and CO₂ from Alaska's North Slope to enhance heavy oil recovery in the Ugnu reservoir. This reduces gas flaring and greenhouse gas emissions. • Comparison of Solvent Effectiveness: Coreflood and interfacial tension experiments compare the effectiveness of lean hydrocarbon gas and CO₂ in low-salinity waterflooding (LSW). Each solvent's potential to enhance oil recovery is analyzed. • Superior Recovery with CO₂-Alternating LSW: Results show CO₂ alternating with LSW achieves the highest oil recovery. It recovers 91.9% of original oil in place (OOIP) after a 24-hour soaking period, compared to 68.4% OOIP with lean hydrocarbon gas. • Influence of Gas Composition on Recovery Efficiency: Lean gas composition contributes to its lower recovery performance compared to liquid CO₂. • Insights into Production Cycles: Initial oil recovery rates were promising, but later cycles experienced high water cuts. Cycle management is crucial for better recovery efficiency. The market price of lean hydrocarbon gas from Alaska North Slope has declined due to increased production from unconventional reservoirs in the U.S. Abundant CO 2 and hydrocarbon gas produced alongside the produced oil from light and viscous oil on the slope present a low-cost opportunity for enhanced heavy oil recovery while reducing greenhouse gas emissions through reinjection. Although experimental studies on solvent-alternating low-salinity waterflood (LSW) for Alaska's viscous oil resources show promise, little research exists on Ugnu heavy oil. This study investigates the feasibility of using lean gas and CO 2 alternating LSW for Ugnu heavy oil recovery via displacement experiments, equilibrium interfacial tension measurements, and simulation studies. Results indicate that lean gas alternating LSW has potential but performs lower (68.4% OOIP) than liquid CO 2 (91.9% OOIP) after a 24-hour soaking period, likely due to both injection gas and live oil compositions. Liquid CO 2 's superior recovery is attributed to its higher mass transfer into heavy oil under pressure. Oil production rates declined significantly after the first cycle due to high water cut. Overall, CO 2 -alternating-LSW proved more effective than lean gas for Ugnu heavy oil recovery. The simulation results closely match the experimental findings, identifying the optimal soaking time and CO₂ slug volume as 24 hours and 0.3 PV, respectively. This injection scheme (CO 2 ) for heavy oil recovery offers significant environmental benefits, as it reduces greenhouse gas emissions by utilizing CO 2 that would otherwise be flared or vented.