Study of the chemistry of soured and chemically treated reservoir fluids and potential impact on microbial influenced corrosion in oil and gas production facilities

Ibrahim, Abdulhaqq Ameen (2021) Study of the chemistry of soured and chemically treated reservoir fluids and potential impact on microbial influenced corrosion in oil and gas production facilities. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The chemical environment (e.g. soured produced water, oil, limited oxygen environments) plays an important role in microbial activities leading to microbiologically influenced corrosion (MIC). The major cause of reservoir souring and subsequent corrosion in oil and gas facilities is the increased concentration of H₂S in the system. Among the microbial groups associated with MIC, sulfate-reducing bacteria (SRB) produce H₂S as a metabolic product of sulfate reduction in anaerobic respiration to obtain energy. To mitigate the SRB activities, nitrate or nitrite is injected in the reservoir to displace SRB with nitrate reducers. H₂S and other sulfur (S) species, and nitrogen (N) species (nitrate/nitrite) present can impact the chemistry of the system and microbial activities leading to MIC. Also, the chemical–microbial interactions complicate the understanding of chemical species transformation and partitioning behavior in gas, water, and oil and the subsequent impact on corrosion. Hence, it is essential to assess the impact of the chemical environment on microbial activities with respect to the corrosion processes in the oil and gas facilities. Several studies by microbiologists and corrosion scientists focused on the understanding of MIC mechanisms independent of the surrounding chemical environment. However, little is known about the dynamic behavior of the chemical environment and the reactivity between S and N species under various conditions. This thesis advances the understanding of MIC in light of the surrounding chemical environment by identifying and analyzing different chemical species and transformations associated with MIC, resulting from biotic and abiotic processes. Microbial activities are found to overlap with chemical/electrochemical processes leading to corrosion. The chemical environment, environmental factors, and microbial processes were examined to further understand the interactions and contributory impact on MIC. This work also describes the behavior of chemical species in a sulfide-oxic-nitrite environment as a function of temperature, pressure, and concentrations using equilibrium, and kinetic model approaches. The equilibrium simulation predicted the formation of Sᴼ, FeS, FeO(OH), and Fe₂O₃ as the key products, the amount of which varied depending on the chemistry and operating conditions. The kinetic model of the sulfide-oxic reaction in seawater showed a similar trend with the laboratory experiment in PW. The wet-lab experiments were conducted to study the reactivity of sulfide with nitrite under a range of conditions and generate kinetic data. Experiments indicated that sulfide in produced water (PW), seawater, and water is oxidized by nitrite to yield polysulfide, Sᴼ, and NH₄⁺ under weakly acidic to weakly basic conditions. However, sulfide forms insoluble FeS in the presence of Fe²⁺ in PW, which removes the sulfide from the oxidative transformation pathway. The outcomes of this research provide a better understanding of the chemical environment impacting MIC. The understanding and information of S and N chemistry presented herein will provide insight into the chemical–microbial interactions in oil and gas operations under different conditions and inform further studies towards the development of robust MIC models.

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