Characteristics of petroleum source rock and basin modelling of Mergui Basin, Andaman Sea, Thailand

Abstract

Exploration in the Mergui Basin, located in the Andaman Sea offshore Southern Thailand, has so far been unsuccessful. There were no commercial hydrocarbons found in this basin. Previous study has focused on structure and trap but had overlooked source rock study. It was deemed necessary to study the geochemical and basin modeling in order to understand the petroleum system of this basin. Source rock cutting samples from 7 wells (Kra Buri-1, Kantang-1A, Thalang-1, W9-A-1, Mergui-1, W9-D-1 and W9-E-1) were geochemically analyzed including Total Organic Carbon content (TOC), Rock-Eval pyrolysis and vitrinite reflectance to determine their source rock potential, organic matter type and thermal maturity. Geochemical interpretations are made based on results from this study and from previous studies by oil companies. Source potential of the analyzed sediments are generally poor to fair. Organic-rich beds representing good or very good potential source rocks were discovered but are rather thin. Organic matter type within the sample sediments is predominantly gas-prone (type III) kerogen or mixed oil/gas-prone (type II/III-Type III SEA kerogen). The basin modeling of Kra Buri-1, W9-E-1 and Thalang-1 wells shows depth of petroleum generation at about 9,500-10,000 feet and had been started since 7 Ma in the shallow part of the basin (Kra Buri-1 well) and 17 Ma in the deeper part of the basin (W9-E-1 well).