Foam processes in naturally fractured carbonate oil-wet reservoirs: Technical and economic analysis and optimization

Abstract

In the recent years, foam process has shown a growing potential in producing naturally fractured reservoirs. While much effort was devoted to fractured reservoir characterization and laboratory design of foaming chemicals, decision-making for field development goes through reservoir simulation. This work assesses foam flooding performance through dual-media reservoir simulations, to optimize injection strategy and foam key features such as stability, mobility reduction, adsorption and interfacial tension (IFT) reduction.Foam flooding may improve significantly oil recovery in fractured oil-wet reservoirs through a better fluid mobility control and an increase in viscous forces in fractures, improving the sweep efficiency. Additionally, foaming chemicals can lead to low to ultra-low interfacial tension between oil and water, and thus enhance oil mobilization. This study evaluates the sensitivity of foam flooding performances to foam properties and injection strategy at pilot-scale.This sensitivity analysis is based on the variance decomposition (Sobol indexes) of the response model (such as oil production), while a surrogate model is built to limit the number of simulations required to evaluate the objective function. Optimizations are performed to constrain the process to be more efficient than gas and/or water injection.The foam process optimum is a trade-off between oil recovery maximization and costs minimization, which corresponds to a rise in viscous forces that force out the oil from the matrix while respecting the fracture pressure and limiting the amount of injected chemicals.This sensitivity assessment brings new insights for pre-feasibility studies, in particular for the foaming formulation design. Specifically, as foam flooding recovery mechanisms interplay, impacts of chemicals adsorption, injection strategy and optimization parameters will strongly differ whether foaming chemicals achieve or not low interfacial tension. The foam process efficiency mainly depends on viscous forces developed in the fracture network whereas the ”low-IFT” effect mainly relies on the penetration of aqueous chemicals in the matrix. The proposed optimization workflow demonstrates its ability to evaluate and to guide the selection of the most appropriate process at pilot scale, according to the reservoir specificities.