Injection of dense supercritical CO2 (sc-CO2) represents today more than half of the EOR projects carried out in USA. While sc-CO2 flooding is very effective in mobilizing trapped oil at the microscopic (pore-scale) level, this technology is usually limited by unfavorable mobility ratio and gravity segregation issues. In that context, use of dense CO2 foams (emulsions) may be one of the most robust methods for improving sc-CO2 flooding efficiency and maximizing oil recovery at reservoir scale. However, surfactant screening for dense CO2 foams has until now been extremely time consuming and limited to a few products due to strong technical constraints (high pressure equipments). Here, we report an original set of high throughput screening for optimizing dense CO2 foams formulations. The formulation yielding the best results is further characterized in corefloods experiments.
We use a proprietary high pressure jet-drop transition technique to screen interfacial properties of molecules at the dense CO2 / brine interface. The surfactants showing significant interfacial activities between aqueous solution and sc-CO2 are selected for the next steps. We use an autoclave to generate highly sheared foam with low cell sizes and study generated foam stability in a high pressure variable volume view cell. Structure/properties relationships are extracted from our numerous screening experiments and complement existing design rules for dense CO2 foam formulations.
A surfactant formulation yielding superior sc-CO2 foam stability is tested for mobility reduction in low-permeability carbonate cores. Using a CO2/aqueous solution co-injection scheme, we observe various flow regimes for different fractional flows. We confront these first results to the existing theories of foam flooding in porous media.