We have successfully performed bacterial reduction of an iron-containing outcrop sand sample under static conditions using Shewanella genus bacteria. Adsorption of an anionic (alkyl benzyl sulfonate) surfactant was around 7-times lower on treated outcrop samples. Most of this reduction (~3X) occurs over the first 3-4 days of incubation, contemporaneously with iron dissolution and limited biofilm formation. Continued incubation after this point attends the formation of significant biofilm, as well as a continued decrease in surfactant adsorption. Non-iron-reducing bacteria also formed biofilm on outcrop samples, yielding a significant (though smaller) decrease in surfactant adsorption. Microscopy demonstrates preferential attachment of biofilm to iron minerals in a heterogenous outrop sample. Repeated rinsing results in a removal of biofilm formed by iron-reducing or bacteria and a corresponding increase in surfactant adsorption to about 1/3 to 1/2 of original levels.

This proof of concept for a bacterial core restoration method using iron-reducing bacteria is considered successful, with the caveat that care must be taken to minimize and/or remove biofilm in order to avoid biofilm-related artifacts. Implications of these results for the determination of reservoir rock-fluid properties in biologically-active reservoirs are also discussed.

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