Microbial Sulfate Reduction and Perchlorate Inhibition in a Novel Mesoscale Tank Experiment

Abstract

Microbial sulfate reduction occurs ubiquitously in natural environments. In oil and gas reservoirs, the generation of sulfide (also known as souring) can result in the corrosion of steel infrastructure and downgrading of oil quality, among other environmental and healthrelated concerns. The complex interplay between hydrological, geochemical, and biological processes during souring is poorly understood, preventing effective treatment and mitigation especially in naturally heterogeneous subsurfaces. In this work, three-dimensional flow tank experiments are utilized as a mesoscale experiment that links well-constrained batch and column experiments to field measurements. The mesoscale tank experiment investigating perchlorate treatment of souring is coupled with reactive transport modeling to understand the effects of heterogeneity on souring and effectiveness of perchlorate treatment. Tracer experiments were conducted at the start and end of the experiment to constrain flow pathways and heterogeneities. Isotopic, geochemical, and microbial data revealed that perchlorate effectively inhibited sulfidogenesis and the growth of dominant sulfate reducing Desulfobacteraceae. Perchlorate treatment enriched Desulfobulbaceae, a sulfur-oxidizing group of bacteria, and Sulfurimonas, a potential perchlorate reducer. More organisms, including sulfate reducing bacteria, were observed closer to the influent. Results from the three-dimensional reactive transport model indicate horizontal preferential flows, as a result of the permeability contrast, led to faster bacteria growth (sulfate reducing bacteria) and sulfate reduction in fast flow regions. This work highlights the control that spatial distributions of hydrologic characteristics exert over reservoir souring and treatment.

Biofilm Feedbacks Alter Hydrological Characteristics of Fractured Rock Impacting Sulfidogenesis and Treatment

“…Results from this study mirror observations from earlier experimental studies. 24,25 4.2. Effects of Flow on Development of Thermal Gradients and Biological Reaction Zone.…”

“…The microbial community was enriched from San Francisco bay mud with acetate as the electron donor following earlier studies. 24,25 After inoculation, the flow was paused for 11 days to allow the microbial community to establish. Flow was resumed on day 11.…”

Flow and Permeability Evolution during Microbial Sulfate Reduction and Inhibition in Fractured Rocks

“…To promote souring, microbes enriched from San Francisco Bay mud were used to inoculate the sandstone columns, similar to the microbial community introduced into offshore oil reservoirs during the secondary recovery. The inoculum community was similar to the ones used in earlier souring and treatment studies [26][27][28]30 and consisted of sulfate-reducing groups such as Desulfovibrionaceae, Desulfobacteraceae, and Desulfobulbaceae. Sulfate-rich seawater flooding was introduced via the injection of synthetic seawater made from Instant Ocean sea salt (Spectrum Brand, mean sulfate concentration of 25.6 mM and standard deviation of 2.0 mM).…”

“…Nitrate effectively inhibits souring through a few known microbial mechanisms: (1) direct inhibition of SRMs through nitrite, an intermediate of nitrate reduction, (2) competition between the heterotrophic nitrate reducers (hNRMs) and SRMs for electron donors that are often limited in the environment, and (3) sulfide oxidation through nitrate-reducing, sulfide-oxidizing microorganisms (NR-SOMs). Column studies have previously investigated the impacts of nitrate/nitrite amendment on sulfide production with different electron donors (e.g., lactate and VFAs). − These flow-through systems used high permeability homogeneous sand packs as matrix materials and restricted flow complexity to one-dimensional. − A more recent 3D tank experimental study revealed the control that spatial distributions of hydrologic characteristics exerted over reservoir souring and treatment …”

“…25−27 A more recent 3D tank experimental study revealed the control that spatial distributions of hydrologic characteristics exerted over reservoir souring and treatment. 28 In oil-bearing subsurface systems, biofilm studies have been geared toward selective bioclogging in microbial-enhanced hydrocarbon recovery 29 in which oil-depleted high permeability zones are clogged selectively, allowing water to be diverted to oil-rich, low-permeable regions. To our knowledge, aside from a recently completed 2D fractured flow cell experiment, 30 no other bench-scale study investigating the role of a biofilm in influencing sulfidogensis and nitrate treatment efficacy in fractured rocks exists.…”