oa Insights into the Santos Basin from Integration of Clumped Isotope Signatures of Methane with Gas Geochemistry and Petroleum Molecular Proxies

The study integrates clumped isotope data of methane with gas geochemistry and petroleum molecular proxies to investigate the Santos Basin’s petroleum systems. Located on Brazil’s southeastern margin, the Santos Basin spans 350,000 km² and is renowned for its pre-salt reservoirs. Despite its high productivity, questions persist about aspects related to its active petroleum systems. Six fields and 16 gas samples were analyzed for methane clumped isotopes and other geochemical parameters. Results showed thermogenic classification for all samples, consistent with clumped isotope-derived temperatures. However, samples from Fields 4 and 6 displayed unrealistically high temperatures, possibly due to analytical artifacts, mixing effects, or deeper methane sources. Oil geochemical analysis revealed no biodegradation, with varying maturities across fields. Field 5A and 5B oils showed the highest maturity, while Field 3A exhibited the lowest. An inconsistency was noted between Field 3A’s oil biomarker profile and gas geochemistry data, suggesting fluid mixing from rocks at different thermal regimes. Most fields demonstrated coherence between oil and gas data, except for at least one anomalie linked to sampling artifacts. The study provides insights into the formation temperatures and maturity of gases and oils, highlighting complexities in the Santos Basin’s petroleum systems.