Microbial induced mineral precipitations caused by nitrate treatment for souring control during microbial enhanced oil recovery (MEOR)

Microbiologically active environments, like oil reservoirs, can suffer different a range of problems due to the presence of sulfate-reducing microorganisms. These includeing, but are not limited to: H2S formation, souring and corrosion caused mainly by sulfate-reducing microorganisms. To prevent biogenic sulfate reduction, nitrate can be used as an environmentally friendly alternative to biocides. However, side effects of nitrate injection are sometimes observed but not well understood. In our study, we used original water from an onshore reservoir, where a microbial enhanced oil recovery (MEOR) application is planned, and investigated the effects of nitrate addition on H2S generation, mineral precipitation and microbiology. We observed that nitrate did inhibit H2S formation in most, but not all cases while available in the medium. During nitrate reduction, iron and calcite minerals precipitated over short- and long-term (10 or 160 days) incubations. This was caused by a nitrate-reducing group of bacteria belonging to the family Deferribacteraceae. Using dynamic sandpack setups and numerical modeling approaches with the simulator TOUGHREACT, we observed significant reduction in permeabilities (~44x) suggesting injectivity issues over time in case nitrate is continuously added to the reservoir. Our study shows that nitrate-dependent processes, which were described separately for pure-cultures before, are also valid for natural mixed communities present in oil fields and underlines the complex interplay of microbial metabolisms associated with those communities.

微生物活性环境，例如油田，由于硫酸盐还原微生物的存在，可能遭受多种问题。这些问题包括但不限于：由硫酸盐还原微生物主要引起的硫化氢生成、酸化和腐蚀。为防止生物成因的硫酸盐还原，硝酸盐可作为生物杀灭剂的环境友好替代品。然而，硝酸盐注入的副作用有时被观察到，但尚未得到充分理解。在我们的研究中，我们使用了陆上储层的水样，该储层计划实施微生物增强油采收（MEOR）应用，并研究了硝酸盐添加对硫化氢生成、矿物沉淀和微生物学的影响。我们发现，硝酸盐在大多数情况下但并非全部情况下抑制了硫化氢的形成，条件是在培养基中存在硝酸盐。在硝酸盐还原过程中，铁和方解石矿物在短期（10天）和长期（160天）的孵化期间沉淀。这是由于属于Deferribacteraceae科的硝酸盐还原菌所致。利用动态沙包装置和数值模拟方法，结合TOUGHREACT模拟器，我们观察到渗透率显著降低（约44倍），表明如果持续向储层添加硝酸盐，则可能随着时间的推移出现注入性问题。我们的研究表明，之前针对纯培养体描述的硝酸盐依赖性过程，同样适用于油田中存在的自然混合群落，并突出了与这些群落相关的微生物代谢的复杂相互作用。