Thermal maturity and paleogeotemperature reconstruction of organic matter in the Jeju Basin, Korea

초록

This study investigated the thermal maturity of organic matter (Tmax and vitrinite reflectance, Ro) in mudstone and coal fragments from the J5 well in the Jeju Basin. Tmax and Ro ranged from 430 to 535 degrees C and 0.5-1.8%, respectively. Considering the thermal maturity of organic matter, the oil window is estimated to begin at a depth of approximately 2,500 m, while the gas window is reached at around 3,400 m. Based on Tmax and Ro measurements, a Jeju Basin optimized correlation equation (Ro = 0.0123 & times; Tmax - 4.5769) was established. Using this equation, the reconstructed paleogeotemperatures indicate values predominantly above 170 degrees C in the early Oligocene interval, mostly within 120-170 degrees C in the late Oligocene interval, and gradually decreasing to 108-120 degrees C in the Miocene interval. Geothermal gradients derived from these paleogeotemperatures show a decreasing trend from the Oligocene to the Miocene, which is consistent with the progressive evolution of the rift basin. Discrepancies among previously published Tmax-Ro correlations were attributed to the lack of overmature samples. By incorporating overmature samples from the Jeju Basin with previous data, this study proposes an improved, internationally applicable Tmax-Ro correlation (Ro = 0.01 & times; Tmax - 3.5854).

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