Tungstate Control of Microbial Sulfidogenesis and Souring of the Engineered Environment

Sulfide accumulation in oil reservoir fluids (souring) from the activity of sulfate-reducing microorganisms (SRM) is of grave concern because of the associated health and facility failure risks. Here, we present an assessment of tungstate as a selective and potent inhibitor of SRM. Dose-response inhibitor experiments were conducted with a number of SRM isolates and enrichments at 30-80 °C and an increase in the effectiveness of tungstate treatment at higher temperatures was observed. To explore mixed inhibitor treatment modes, we tested synergy or antagonism between several inhibitors with tungstate, and found synergism between WO₄^2- and NO₂^-, while additive effects were observed with ClO₄^- and NO₃^-. We also evaluated SRM inhibition by tungstate in advective upflow oil-sand-packed columns. Although 2 mM tungstate was initially sufficient to inhibit sulfidogenesis, subsequent temporal CaWO₄ precipitation resulted in loss of the bioavailable inhibitor from solution and a concurrent increase in effluent sulfide. Mixing 4 mM sodium carbonate with the 2 mM tungstate was enough to promote tungstate solubility to reach inhibitory concentrations, without precipitation, and completely inhibit SRM activity. Overall, we demonstrate the effectiveness of tungstate as a potent SRM inhibitor, particularly at higher temperatures, and propose a novel carbonate-tungstate formulation for application to soured oil reservoirs.