oa Carbon Dioxide Distribution and Origins in North Malay Basin, Gulf of Thailand

Carbon dioxide (CO2) is a key component in gas reservoirs of the North Malay Basin, with concentrations varying across formations, depths, and structural settings. Although CO2 content generally increases with depth, some stratigraphic units exhibit anomalously high or low levels, prompting further investigation into its origins and controlling mechanisms. Based on CO2 content and stable carbon isotopes, four primary sources are identified: mantle-derived, carbonate thermal alteration, organic, and mixed origins. High CO2 concentrations (40–90%) are commonly linked to mantle or carbonate sources and are spatially associated with structural highs and deep-seated faults. In contrast, organic and mixed-origin CO2 tends to occur near basin depocenters, where hydrocarbons display high thermal maturity.

An integrated analysis of gas composition, isotopic data, and geological context reveals that CO2 accumulation results from a complex interplay of source mechanisms, structural features, and reservoir conditions. Notably, some deep zones exhibit unexpectedly low CO2 levels, contradicting the typical depth-related trend. If verified, these findings could reveal new deep exploration potential. Ongoing work focuses on further evaluating CO2 distribution in relation to geological factors such as depth, faulting, reservoir pressure-temperature conditions, hydrocarbon column height, and basement lithology.