Different Types of Organic-Rich Geological Markers in South Pailin Field, Pattani Basin, Gulf of Thailand

Abstract

Organic-rich sediments were recognized and differentiated by integrating conventional cores, wireline log characteristics, palynology, and petrographic data, in the South Pailin Field, southern part of Pattani Basin, Gulf of Thailand. The core study indicates three types of organic-rich sediments. Laminated burrowed muddy siltstone is interpreted as marginal marine shale, which has lowresistivity and moderate-high density log characteristics and is widely distributed. Coal with pyrite is interpreted as marginal marine coal, which has high gamma ray and spiky density and neutron curves and a wide distribution with a limited extent to the south. Mudstone with coal is interpreted as non-marine coaly mudstone; its wireline characteristics are indistinctive and cannot be correlated laterally with high certainty. The overall succession was deposited in fluvial/floodplain and marginal marine settings with two major marine transgressions that occurred during the late lower and middle Miocene. Marginal marine shale is the best geological marker in the South Pailin area and also potentially correlates regionally to other fields. This regional marker provides better understanding of stratigraphic correlation, depositional framework and marine influence, which is useful for developing and predicting reservoir character in the study area. In contrast, marginal marine and non-marine coals are not very useful for regional stratigraphic correlation due to their limited lateral extent.