Enhanced oil recovery by flooding with aqueous surfactant solution : a model study and comparison with theory

The aim of the work within this thesis is to elucidate the details of enhanced oil recovery by surfactant solution flooding. This was achieved by determining the detailed surface chemistry and flow behaviour of model systems consisting of a packed column of calcium carbonate particles as the porous rock with interstices filled with a pure oil, and aqueous solutions of three different surfactants (an anionic, cationic and nonionic) as the displacing phase. Each three phase system is characterised in detail in terms of its surface chemistry properties, including; water-rock adsorption, water-oil interfacial tensions, water-oil-rock contact angles, aqueous phase behaviour, microemulsion phase behaviour and water-oil partitioning.Two models are derived to enable modelling of the oil recovery performance of the aqueous surfactant solutions being pumped through the powder packed columns with interstices filled with the oil. The first model enables the concentration of free surfactant, [surf]free, present within the packed columns during flooding to be calculated from the initial concentration pumped in, [surf]init. This allows a direct comparison between surface chemistry characterisation results (which relate to [surf]free) and %oil recovery results (which relate to [surf]init). The second two-part model shows how, based on the hypothesis that the residual oil is trapped in the form of liquid bridges between contacting calcite particles, the measured %oil recovery variation with surfactant concentration can be understood and predicted for concentrations of surfactant both below and above the cμc in terms of the characterisation results.It was found that, for surfactant concentrations cμc, additional oil is recovered by a solubilisation plus emulsification mechanism. Experimental results were in reasonable agreement with those predicted from the model

A model study of enhanced oil recovery by flooding with aqueous surfactant solution and comparison with theory

With the aim of elucidating the details of enhanced oil recovery by surfactant solution flooding, we have determined the detailed behavior of model systems consisting of a packed column of calcium carbonate particles as the porous rock, n-decane as the trapped oil, and aqueous solutions of the anionic surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT). The AOT concentration was varied from zero to above the critical aggregation concentration (cac). The salt content of the aqueous solutions was varied to give systems of widely different, post-cac oil–water interfacial tensions. The systems were characterized in detail by measuring the permeability behavior of the packed columns, the adsorption isotherms of AOT from the water to the oil–water interface and to the water–calcium carbonate interface, and oil–water–calcium carbonate contact angles. Measurements of the percent oil recovery by pumping surfactant solutions into calcium carbonate-packed columns initially filled with oil were analyzed in terms of the characterization results. We show that the measured contact angles as a function of AOT concentration are in reasonable agreement with those calculated from values of the surface energy of the calcium carbonate–air surface plus the measured adsorption isotherms. Surfactant adsorption onto the calcium carbonate–water interface causes depletion of its aqueous-phase concentration, and we derive equations which enable the concentration of nonadsorbed surfactant within the packed column to be estimated from measured parameters. The percent oil recovery as a function of the surfactant concentration is determined solely by the oil–water–calcium carbonate contact angle for nonadsorbed surfactant concentrations less than the cac. For surfactant concentrations greater than the cac, additional oil removal occurs by a combination of solubilization and emulsification plus oil mobilization due to the low oil–water interfacial tension and a pumping pressure increase

Model Study of Enhanced Oil Recovery by Flooding with Aqueous Solutions of Different Surfactants: How the Surface Chemical Properties of the Surfactants Relate to the Amount of Oil Recovered

© 2016 American Chemical Society. The main aim of this work is to establish how the fraction of oil recovered from an oil-filled calcite powder packed column by injection of aqueous surfactant solution depends on the phase behavior and surface chemical properties of the surfactant system. We have measured the phase behavior, the adsorption of surfactant to the oil-water, calcite-water, and calcite-oil interfaces, tensions, and contact angles for anionic, cationic, and nonionic surfactant/oil/aqueous phase systems. We show how the measured surface chemical properties can be used to approximately predict the fraction of oil recovered as a function of the volume and concentration of the surfactant solutions injected into the column. Measured and calculated plots of %oil recovery versus surfactant concentration show reasonably good agreement for the different surfactant systems. The experimentally validated model for oil recovery provides a sound basis for the rational selection of surfactant type and concentration to achieve maximum oil recovery based on laboratory measurements of the surface chemical properties of candidate surfactants