SOLUBILITY OF PETROLEUM IN OIL-FIELD WATERS AS A FUNCTION OF THE OXIDATION-STATE OF THE SYSTEM

Aqueous solubilities of liquid nonane (C9H20[liq]) with activities ran ging from 1.0 in pure nonane to 0.1 and 0.01 in crude oil have been ca lculated at approximately 120-degrees-C and 400 bar as a function of o xygen fugacity (f(o2)(g), where g stands for gas) in a generic oil-fie ld water containing representative concentrations of NaCl, CaCl2, MgCl 2, and FeCl2 in equilibrium with minerals in the system CaO-MgO-FeO-CO 2-O2-H2O. The calculations indicate that in the presence of calcite, t he oxidative solubilities resulting from the formation of aqueous CO2, n-carboxylic acids, and other oxidized organic aqueous species from n -alkanes in crude oil are several orders of magnitude greater than the ir stoichiometric counterparts. For example, the oxidative solubility in the aqueous phase of nonane with an activity of 0.1 in crude oil co existing with calcite at the oil-water interface increases dramaticall y with increasing logf(o2)(g) at approximately 120-degrees-C and 400 b ar from a stoichiometric solubility of approximately 0.26 ppm to an ox idative solubility of approximately 320 ppm at log f(o2)(g) = -56, whi ch is typical of the fugacity of oxygen in hydrocarbon reservoirs at a pproximately 120-degrees-C and 400 bar. Because oil-field waters are g enerally acidic, production of carbonic acid by the oxidative dissolut ion of crude oil in hydrocarbon reservoirs favors generation of second ary porosity at the oil-water interface, which may be mediated by hype rthermobarophilic microbes.