Initial Assessment of Biological and Thermal Increases in H2S Production at Chichimene Field

Summary Oilfield souring is a global concern aimed at ensuring efficient and sustainable crude oil production, environmental protection, reduced operational costs, and the mitigation of the occupational risks during oil and gas production. For these reasons, identifying the origin and production mechanisms of H2S in the reservoir enables us to design effective strategies for monitoring and controlling sulfur gas emissions in oil fields. In this context, this study aimed to complement the information about the microbiological Chichimene (CH) oilfield conditions with the physicochemical characterization in 26 producer wells and the sulfur isotopic analysis through mass spectrometry isotope ratio (δ34S). Our results showed that in the CH center and south zones, approximately 60% of wells could produce H2S composed of the heavier isotope, showing isotopic sulfur ratio (δ34S) values between 9 and 12.7‰. It was the first evidence in the hypothesis that H2S could originate from the thermochemical sulfate reduction (TSR) process. Additionally, we found ions like Ca2+ and Mg2+ in CH PW (produced water), which, according to literature, could act as a promoter in both inorganic and organic compounds’ thermal sulfur reduction. Alternatively, the concentration values of sulfate-reducing bacteria (SRB) were associated with H2S production. Then, SRB microorganisms were found in analyzed oil producer wells where lower isotopic sulfur ratio (δ34S) values (between 3.1 and 9‰) were obtained, which could indicate more input of an H2S biogenic production. In consequence, these preliminary results obtained in the CH oil field suggest that H2S originates from both thermal and biogenic reduction of sulfur compounds, indicating a hybrid strategy using biocides and H2S scavengers to control souring conditions.