Naprzemienne zatłaczanie wody i gazu (WAG) wspomagane pianą (FAWAG) jako efektywna metoda EOR w złożach szczelinowatych i heterogenicznych

Gas injection in enhanced oil recovery (EOR) processes is associated with the occurrence of an unfavourable mobility factor. It often leads to the destabilisation of displacement front, viscous fingering and the early breakthrough of the injected fluids into extraction wells. One of the most interesting methods for effective controlling of gas mobility is water alternating gas injection (WAG). It combines the advantages of increased volumetric sweep efficiency (macro-scale) by water injection and improved efficiency of pore-scale oil displacement by gas injection. The largest domestic crude oil accumulations are located in carbonate formations which represent problematic features for EOR processes such as strong heterogeneity and fracturing. Field experience shows that in such cases a conventional WAG process may not be capable to counteract unfavourable (for displacement efficiency) phenomena occurring during the flow of injected fluids. Therefore, suitable chemicals are used to produce foam to enhance the WAG process efficiency. It significantly reduces the mobility of gas and equalises the flow velocity between the rock matrix and fractures. The foam system allows the flow of injected fluids to be directed out of the permeable zones, thus increasing the effectiveness of oil displacement in the rock matrix. In this review paper, detailed principles of the Foam Assisted WAG (FAWAG) process as well as its position among other WAG variants are presented. The application of foam is discussed. The properties of the foam are characterised in detail, and the issues of its stability in the porous medium are presented. The mechanisms responsible for the foam formation in a porous medium are also discussed. Finally, the chemical agents used in EOR processes are briefly characterised, and the examples of FAWAG reservoir scale implementation are presented.