Enhanced Oil Recovery in Heterogeneous Carbonate Rocks Using a Gemini Surfactant under Harsh Conditions

Carbonate reservoirs contribute over 50% of global oil production but present challenges due to their high heterogeneity, oil-wet nature, and natural fractures, which limit efficient oil recovery. Surfactant flooding has shown potential to enhance oil recovery by reducing water–oil interfacial tension and altering rock wettability. However, many surfactants fail under the harsh conditions typical of carbonate reservoirs. This study evaluates a locally developed cationic Gemini surfactant for improving oil recovery in challenging carbonate formations using local outcrop rocks. The study involved collecting, preparing, and characterizing the rocks as well as conducting contact angle measurements, static adsorption tests, and coreflooding experiments. Coreflooding was performed under reservoir-mimicking conditions: a temperature of 100 °C, pressures above 3000 psi, and water salinities resembling connate water and seawater, exceeding 213,000 and 57,000 ppm, respectively. The process included continuous flooding with seawater, followed by a surfactant solution in seawater at 2500 ppm concentration. Seawater flooding recovered approximately 55% of the oil, while subsequent surfactant flooding yielded an additional 17% recovery, highlighting the surfactant’s efficiency in enhancing oil recovery. Analysis of the effluent collected during the coreflooding test revealed a dynamic retention of 0.51 mg/g of rock, within acceptable limits for surfactant retention. Contact angle measurements demonstrated the surfactant’s ability to modify rock wettability toward a water-wet state, a key factor in improved recovery. Static adsorption tests showed a positive correlation between surfactant concentration and adsorption levels. These findings underscore the promise of the tested cationic Gemini surfactant for enhanced oil recovery (EOR) in carbonate reservoirs. This work demonstrates the surfactant’s potential and establishes a robust framework for conducting EOR studies under challenging reservoir conditions, providing valuable insights into optimizing oil recovery strategies for complex carbonate formations.