Exploring the preservation of greigite in hydrocarbon reservoirs using thermodynamic modelling

Previously, thermodynamic modelling has been used to predict the magnetic phases favoured under varying geochemical conditions at hydrocarbon seepage zones. Although greigite (Fe3S4) has been identified by magnetic experiments in the North Sea and Wytch Farm oilfields, it was not included in previous thermodynamic models. Multiple studies have outlined the conditions required for greigite preservation in nature: sulphur supply needs to be enough to form greigite but limited as to not proceed to form pyrite; total organic carbon content needs to be low as it can produce sulphides; there needs to be a high availability of reactive iron. This study uses thermodynamic modelling to help constrain the following: What is the optimum level of sulphur? How much available iron is required? At what temperatures is greigite stable? Answering these questions is the first step in determining how greigite can exist in hydrocarbon environments.