Evaluation of Cenozoic source rock potential from drill cuttings in the northern Jeju Basin, offshore southern Korea

초록

Uncertainties associated with mixed drill cuttings have limited quantitative assessments of hydrocarbon generation and the contribution of coal-bearing source rocks in the Jeju Basin. This study evaluated the source rock potential of the Jeju Basin by separating mudstone and coal fragments from the drill cuttings of the O well and integrating their proportions with the organic matter characteristics. Three mudstone-dominated source rocks (OM1, OM2, and OM3) and two coal-bearing source rocks (OC1 and OC2) were identified within the late Eocene and Oligocene sequences. Although coal fragments comprised less than 10% of the coal-bearing source rocks, their hydrocarbon generation potential (fair to good) is comparable to that of the mudstone-dominated source rocks. OM2 and OM3, characterized by high hydrogen index (HI) and the preservation of liptinite, are interpreted as oil-prone source rocks, whereas OM1 is oil/gas-prone. The coal-bearing source rocks, dominated by vitrinite (>90%) and relatively low HI values, were initially considered gas-prone. However, re-evaluated maximum HI values and abundant detrovitrinite indicate the potential for both oil and gas generation. The lower part of the late Eocene sequence, where OM1 and OC1 co-occur, exhibits the highest hydrocarbon generation potential. Considering both generation potential and source rock thickness, the late Eocene intervals (OM1 + OC1 and OM2) are expected to yield more hydrocarbons than the Oligocene intervals (OM3 and OC2). These results clarify the contribution of coal-bearing source rocks and refine understanding of the Jeju Basin petroleum system.

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