Abstract Souring induced by sulfate reducing microorganisms (SRM) represents a severe problem in the petroleum industry. In addition to conventional biocides and nitrate, alternative SRM inhibitors such as molybdate have been proposed recently for controlling microbial souring. We used oilfield-derived microbial consortia, rock and fluids to test molybdate as a specific SRM inhibitor for a microbial enhanced oil recovery (MEOR) application where souring might occur as a side effect. SRM cells were quantified and dissolved molybdate, sulfate and gaseous hydrogen sulfide were measured under different dynamic conditions in sandpacks with and without residual oil. In batch experiments, 0.5 mM molybdate inhibited SRM growth whereas hydrogen sulfide and mineral precipitations were observed in bottles amended with 100 mM nitrate. However, significant molybdate adsorption onto reservoir rock occurred and maximum Langmuir saturation was estimated to be ≥ 34 μmol g−1. Residual oil allowed a further propagation of molybdate into sandpacks, but a pH 11 μMH2S aq limited the efficiency of molybdate due to rapid adsorption. Under favorable souring conditions, we also observed the localized formation of macroscopic iron sulfide precipitations. These resulted in a four-fold permeability decrease after the injection of SRM substrates for 40 days and a calculated mean sulfate reduction rate of 52 μM h−1. However, delayed sulfate reduction in molybdate-preflushed sandpacks suggests an inhibitory effect even if molybdate is partially adsorbed. Sulfate reduction was not detected when molybdate was continuously injected with MEOR nutrients into sandpacks demonstrating its inhibitory efficiency in case it is applied in early phases of field operations with a potential risk of souring.

中文翻译：

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钼酸盐抑制微生物酸化及其在储层条件下的应用

摘要 硫酸盐还原微生物 (SRM) 引起的酸化是石油工业中的一个严重问题。除了传统的杀菌剂和硝酸盐之外，最近还提出了替代 SRM 抑制剂，例如钼酸盐，用于控制微生物酸化。我们使用油田衍生的微生物群落、岩石和流体来测试钼酸盐作为微生物提高采收率 (MEOR) 应用的特定 SRM 抑制剂，其中可能会发生酸化作为副作用。对 SRM 电池进行量化，并在不同动态条件下在有残油和无残油的沙堆中测量溶解的钼酸盐、硫酸盐和气态硫化氢。在批量实验中，0.5 mM 钼酸盐抑制 SRM 生长，而在用 100 mM 硝酸盐修正的瓶子中观察到硫化氢和矿物沉淀。然而，发生显着的钼酸盐吸附到储层岩石上，估计最大朗缪尔饱和度≥ 34 μmol g-1。残油允许钼酸盐进一步传播到沙包中，但由于快速吸附，pH 11 μMH2S 水溶液限制了钼酸盐的效率。在有利的酸化条件下，我们还观察到宏观硫化铁沉淀的局部形成。这些导致在注入 SRM 底物 40 天后渗透率下降四倍，计算的平均硫酸盐还原率为 52 μM h-1。然而，即使钼酸盐被部分吸附，钼酸盐预冲洗沙包中的硫酸盐延迟还原也表明存在抑制作用。