Low adsorbing CO2 soluble surfactants and their deployment strategy for commercially viable CO2 foam EOR Technology

Abstract: Several aqueous-foam-based gas conformance enhancement field pilots for enhanced oil recovery (EOR) have been conducted in the last 30 years. While these pilots were technically successful, commercial viability of this technology was challenged due to multiple factors. These pilots were implemented with water-soluble foaming surfactants impacted by in-situ gas-water segregation and adsorption losses up to 90% of the injected surfactant. Novel low-adsorbing and CO2-soluble surfactants were developed that can be injected and carried with the gas phase to the thief zones faster and deeper with relatively lower adsorption loss to the rock surface. While these novel surfactants resulted in improved conformance enhancement in the field pilots, the incremental oil remained uneconomical.

Detailed core-flood foaming experiments were performed to measure foam rheology and its dependency on variables such as surfactant concentration, fluid saturation and shear, and rock permeability. Leveraging modeling and simulations, empirical foam modeling methodology was corrected by incorporating gas partitioning fraction of the injected surfactant to confirm advantages of gas-soluble foaming surfactants. Unlike laboratory experiments where foam generation in porous medium is studied at constant injection rate, field operations deploy constant pressure injection. A 3D 5-spot reservoir simulation model was created that simplistically captured vertical conformance problem in a CO2 flood. The simulation results highlighted that with constant surface pressure and a baseline injection strategy, foam generation results in loss of injected gas throughput, limiting oil recovery despite improved conformance. Therefore, a novel injection strategy was developed, and field proven in our latest CO2-foam field pilot which turned out to be the longest running economically successful CO2 foam pilot. Methodology and results pertaining to this development will be discussed.