Carbonate reservoirs have been recognized as very heterogeneous formations due to complex depositional environments, which complicate application of Alkaline/ Surfactant/Polymer (ASP) process.

The main objectives of this study are to (1) present progress of screening criteria for chemical EOR processes, (2) investigate the feasibility of Polymer flood (P), Alkaline/Polymer (AP), Surfactant/Polymer (SP), and Alkaline/Surfactant/Polymer(ASP) processes in low permeability carbonate reservoirs, (3) study the effect of using high concentration of surfactant in the ASP slug on oil viscosity and attained recovery, and (4) study the effect of initial oil saturation at the start of the ASP process on the oil recovery. Actual crude oil, formation brine, and low permeability carbonate reservoir samples are used to undertake this experimental study. Viscosity, pH, and Interfacial tension (IFT) for oil-water, and different chemical systems are measured. Additionally, eight core flood experiments are carried out to test different formulated chemical slug volumes and concentrations on oil recovery.

The results indicated real progress in screening criteria of polymer EOR processes and thier successful applications in lower permeability reservoir (> 10 md). This study proved that ASP process is successfully applied as an enhanced oil recovery in carbonate reservoir having permeability less than 5 millidarcy (md). Moreover, addition of sodium hydroxide (NaOH), or surfactant (F75N) in polymer constituting a single slug has important effects on viscosity and pH of the different chemical slugs applied.

The results also pointed out that the application of ASP process at higher mobile oil saturation leads to higher oil recovery than when applied at later stages of water flooded low permeability carbonate reservoirs. In addition, Alkaline/ Surfactant/Polymer (ASP) process has successfully recovered the highest recovery in comparison to other chemical processes. The application of the attained results develops a new window for more applications of chemical EOR processes in lower permeability carbonate reservoirs.

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