Abstract

Aqueous solubilities of liquid nonane (C9H20 [liq]) with activities ranging from 1.0 in pure nonane to 0.1 and 0.01 in crude oil have been calculated at ∼120 °C and 400 bar as a function of oxygen fugacity (fO2(g), where g stands for gas) in a generic oil-field water containing representative concentrations of NaCl, CaCl2, MgCl2, and FeCl2 in equilibrium with minerals in the system CaO-MgO-FeO-CO2-O2-H2O. The calculations indicate that in the presence of calcite, the 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 their stoichiometric counterparts. For example, the oxidative solubility in the aqueous phase of nonane with an activity of 0.1 in crude oil coexisting with calcite at the oil-water interface increases dramatically with increasing log fO2,( g) at ∼120 °C and 400 bar from a stoichiometric solubility of ∼0.26 ppm to an oxidative solubility of ∼320 ppm at log fo2 (g)= -56, which is typical of the fugacity of oxygen in hydrocarbon reservoirs at ∼120 °C and 400 bar. Because oil-field waters are generally acidic, production of carbonic acid by the oxidative dissolution of crude oil in hydrocarbon reservoirs favors generation of secondary porosity at the oil-water interface, which may be mediated by hyperthermobarophilic microbes.

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