Biochar Surfactants in High-Salinity EOR: A Comparative Study of Stability and Performance Over 20 Days

Chemical enhanced oil recovery (EOR) methods, particularly surfactant flooding, are essential for mobilizing residual oil trapped in reservoir pores. However, synthetic surfactants are expensive, toxic, and sensitive to high salinity and temperature. This study investigates five biochars derived from spirulina algae (S1), fertilizer (S2), corn (S3), plantain (S4), and lawn (S5) as eco-friendly surfactant candidates for EOR. Biochar samples (0.1 g) were dissolved in 20 mL of sugarcane water at 5000 ppm, diluted to 70 ppm, and mixed with 50% formation water to simulate high-salinity conditions. Stability and performance were monitored over 20 days at 80°C via visual inspection and pH measurements. S1 and S5 exhibited superior solubility and short-term stability with no precipitation at Days 1 and 3. S3 and S4 showed no precipitation at Day 1 but began to precipitate by Day 3 (10%). S2 exhibited precipitation from Day 1 (15%). After 20 days, all samples showed visible precipitation, ranging from 40% (S1) to 80% (S2), with none reaching complete settling. pH values ranged from 7.05 to 7.39, confirming precipitation was primarily salinity-driven. S1 proved the most promising candidate due to its protein-rich structure and amphiphilic functional groups. However, none of the biochars were stable enough for long-term field injection without modification. This study provides comparative data for screening biochar-based surfactants and highlights the need for chemical modification or polymer combination to enhance stability in high-salinity reservoirs, contributing to sustainable, cost-effective alternatives to conventional synthetic surfactants.