Recovery from fractured, oil-wet/mixed-wet, carbonate reservoirs by waterflooding is poor. Dilute surfactant methods are being developed to improve oil recovery from fractured carbonates. This paper investigates the interactions of dilute alkaline anionic surfactant solutions with crude oil on carbonate mineral surfaces. Wettability, phase behavior, interfacial tension, and adsorption experiments have been conducted. Anionic surfactants have been identified that can change the wettability of the calcite surface to intermediate/water-wet condition as well or better than the cationic surfactant dodecyl trimethyl ammonium bromide (DTAB) with a west Texas crude oil. All the carbonate surfaces (lithographic limestone, marble, dolomite, and calcite) show similar behavior with respect to wettability alteration with an anionic surfactant. Anionic surfactants, which lower the interfacial tension with the crude oil to very low values (<10 -2 mN/m), have also been identified. The adsorption of the sulphonate surfactants can be suppressed significantly by the addition of Na 2 CO 3 , because the addition of carbonate can change the zeta potential of calcite to a negative value. Greater than 50% OOIP can be recovered from oil-wet carbonate cores by spontaneous imbibition of 0.05 wt% anionic surfactant solutions in the laboratory scale.

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Surfactant stabilized foams have been used in the past for vertical conformance and mobility control in gas enhanced oil recovery processes. Lack of stability of these foams often limits their application. The goal of this study is to investigate the synergistic effects of using a blend of silica nanoparticles (NP) and anionic surfactants on foam stability in both bulk and porous media. First, stability of static foams were studied using surfactants and surfactant-NP mixtures with and without the presence of a crude oil. Second, the foam drainage behavior and thickness of the foam lamella were studied by fluorescence microscopy. Third, mobility of foams were measured by co-injecting the surfactant or surfactant-NP solutions with nitrogen gas through a Berea sandstone core at a fixed foam quality (gas volume fraction). Finally, oil displacement experiments were conducted in Berea cores using these foams. Static foam tests indicate stabilization effect of nanoparticles on surfactant-nanoparticle stabilized foam in the absence of crude oil. Adding nanoparticles in low concentrations (0.3 wt%) improves the foam stability and increases the mobility reduction factor by a factor of two in the absence of oil. Fluorescence and confocal laser scanning microscopy elucidate the trapping of nanoparticles in plateau borders as well as lamellas which retards liquid drainage and bubble coalescence. The core floods with a reservoir crude oil show about 10% incremental oil recovery by an immiscible foam (with the surfactant-NP blend) over water flood. This study shows that nanoparticles have the potential to increase the stability of surfactant-stabilized foams in subsurface applications.

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A thermal, three-phase, one-dimensional numerical model is developed to simulate two regimes of gas production from sediments containing methane hydrates by depressurization: the dissociation-controlled regime and the flow-controlled regime. A parameter namely dissociation-flow time-scale ratio, R s , is defined and employed to identify the two regimes. The numerical model uses a finite-difference scheme; it is implicit in water and gas saturations, pressure and temperature, and explicit in hydrate saturation. The model shows that laboratory-scale experiments are often dissociation-controlled, but the field-scale processes are typically flow-controlled. Gas production from a linear reservoir is more sensitive to the heat transfer coefficient with the surrounding than the longitudinal heat conduction coefficient, in 1-D simulations. Gas production is not very sensitive to the well temperature boundary condition. This model can be used to fit laboratory-scale experimental data, but the dissociation rate constant, the multiphase flow parameters and the heat transfer parameters are uncertain and should be measured experimentally.