An Unexpected Thermal Event in the Khaleej Al Bahrain Basin, Arabian Plate

Abstract A recent study investigating Upper Jurassic source rocks in Southwest Bahrain (Khaleej al Bahrain basin) reveals that subsurface temperatures were once significantly higher – by around 20-40°C – than they are today. This discrepancy suggests a previously undocumented "past thermal event," which may hold major implications for understanding the regional petroleum system and could influence future hydrocarbon exploration efforts. To uncover evidence of this thermal anomaly, the research team employed a suite of advanced geochemical techniques. These included organic petrography (bitumen reflectance), thermal Rock-Eval® (Shale Play™ method), bulk kinetic analysis using extracted kerogen, fluid inclusion studies, and oil and biomarker analysis of both rock extracts and crude oil samples. Additionally, a comprehensive 3D basin model (TemisFlow®) was created and calibrated using pressure and temperature data from wells to integrate these findings into the geological context. Key results indicate that thermal maturity levels exceed 0.8 to 0.9% VRoeq (peak oil window) at a burial depth of 7,500 feet, despite current temperatures at this depth being only 95–100°C – insufficient to cause such maturity. Fluid inclusion data show past temperatures of 135°C at the same depth. At 10,000 feet, current maturity levels between 1.15% and 1.3% VRoeq cannot be explained by the present thermal gradient (~30°C/km). The basin model, coupled with a lithospheric model, makes it possible to test hypotheses about the nature of "past thermal event" that could explain the observed anomalies. One possible explanation is the Arabian Plate's movement over the Afar Hotspot, which may have led to localized thermal anomalies. An alternative explanation could be a significant erosion of over 4,000 feet of the Dammam Formation during the Oligocene, which is considered unlikely and less supported by data. This proposed thermal event has not been previously documented and warrants further investigation. If validated, it could reshape current geological models of Bahrain and surrounding areas, challenging the notion of thermal stability in similar sedimentary basins and offering new perspectives for exploring unconventional hydrocarbon plays.