Hydrocarbon Resource Evaluation and Favorable Area Screening of Khorat Plateau Basin, Thailand

Abstract

In this paper, with the study focus on the progressive controlling roles of tectonic evolution, sedimentation filling and hydrocarbon accumulation on hydrocarbon play, we have divided the sequence interfaces and identified the hydrocarbon plays in Khorat Plateau Basin. With subjective probability method, we have calculated the undiscovered reserves, and predicated the favorable exploration areas. The study results show that Sunda Block was the earliest shaped tectonically in the area of Southeast Asia, and was spliced by sub-continental blocks including Indo-China, Mid Myanmar and West Myanmar. In terms of tectonic location, Khorat Plateau Basin is located in Indo-China sub-continental block, which is affiliated to Sunda continental Block, being a large-scale intracontinental craton basin (Fig.1). Since the Late Devonian, the basin has experienced two tectonic stages, including the drifting of Paleo-Tethys Ocean during Neopaleozoic and splicing of Sunda Block during Mesozoic. Controlled by the regional tectonic deposition, the sedimentary sequence of the basin can be divided into two mega-sequences of TS1 and TS2 (Fig. 2), of which TS1 is marine sedimentary sequence, filled with the deposits of the shallow marine shoreland, the continental shelve and carbonate tableland. In TS1 sequence, the major reservoir is the Permian Pha Nok Khao Formation, and the regional Seals are Permian Pha Nok Khao Formation mudstone and Permian Upper Clastic Formation. The major source rocks are Permian Saraburi Group mudstones, which had entered into gas generation stage during the Middle to Late Cretaceous. The TS2 sequence is Mesozoic continental deposits, filled with continental alluvial fan, river and lacustrine deposits, in which the Triassic secondary reservoir of fluvio-lacustrine sandstones are well developed, the regional seal of Maha Sarakham Formation and the internal seal of Huai Hinlat Formation are also developed. According to the definition of hydrocarbon play, two Class I hydrocarbon plays (the proved Permian play and prospective Triassic play) and four Class II hydrocarbon plays have been identified. The distribution range of hydrocarbon plays has been determined with multi-factor superposition method. In Permian, the undiscovered reserves in Class I hydrocarbon play are 124 million barrels, and the undiscovered natural gas reserves are 2 trillion cubic feet, which are mainly distributed in the middle of Phu Phan Uplift and its peripheries. In Triassic, the undiscovered reserves in Class I hydrocarbon play are 444 million barrels, and the undiscovered natural gas reserves are 91 trillion cubic feet, which are mainly distributed in the north of Khorat Subbasin and the west of Sakhon-Nakhon Subbasin.