Hydrocarbon Generation Potentials of Cenozoic Lacustrine Source Rocks: Gulf of Thailand, Southeast Asia

Abstract

Several hydrocarbon-rich Cenozoic basins are scattered across Southeast Asia and they present excellent opportunity to examine these rich but under-explored basins. These near-shore basins have petroleum potentials that are associated with the Oligocene-Miocene fluvio-lacustrine multipetroleum systems but are largely underexplored. This study evaluates the petroleum source potentials of some selected Cenozoic basins via maturation modelling analysis, burial and heat flow histories. ZetaWare's Genesis modelling software was used for the study with burial history and thermal history parameters (vitrinite, TOC and HI). The maximum transformation of kerogen to hydrocarbon for source rocks in these basins may be as high as 80-100%. Analyses showed that threshold maturity for maximum hydrocarbon expulsion is around 1.0% vitrinite reflectance (Ro). Thermal maturation is accentuated with depth-especially southward and offshore. Source rocks in the Western (central) and Hua Hin (north) Basins are the most prolific (with up to 400 mgHC/gtoc); least prolific sources are in the Western (north and south) Basin with 96-120 mgHC/gtoc and 40-50 mgHC/gtoc respectively. These sources have expelled only secondary amount of gas (11-80mg/gtoc) because they are oil prone sources. Oil to gas expulsion ratio of 7:1 is estimated. Hydrocarbon expulsion started in the Late Miocene after the emplacement of all necessary traps. Deeply buried sources show good prospects for possible residual hydrocarbon generation. Moreover, all the modelled wells displayed source rocks that expelled significant quantity of hydrocarbon. All these basins show strong correlation with Pattani Basin, the most prolific hydrocarbon-bearing basin in the Gulf of Thailand.