Petroleum Geochemistry of Huai Hin Lat Formation, Northeastern Thailand

Petroleum exploration in the Khorat Plateau, northeast of Thailand, began in 1962. Up until now (2015), 55 exploration wells were drilled in this area. In the Khorat Plateau, only Nam Phong and Sin Phu Horm fields have successfully produced gas from the Permian carbonate reservoirs. Potential source rocks are believed to be the organic-rich Triassic shale of Huai Hin Lat Formation and Permian shale of Saraburi Group. This study investigates well cutting samples of Huai Hin Lat Formation in order to assess the thermal maturity, source-potential, organic matter type and palaeodepositional conditions. Twenty two cutting samples of Huai Hin Lat Formation from ten exploration wells in the Khorat Plateau were investigated by petroleum geochemical method, including total organic carbon determination, Rock-Eval pyrolysis, vitrinite reflectance, kerogen microscopy, gas chromatography, and gas chromatography/mass spectrometry of extractable hydrocarbon. Vitrinite reflectance and thermal alteration scale (TAS) indicate that the samples of Huai Hin Lat Formation are within late mature to post mature stage. Based on HI and OI values, Huai Hin Lat Formation was likely to initially contain kerogen type II, II/III and III, but converted to kerogen type IV during thermal maturity process. The original total organic carbon (TOCO) content of cutting sample are considered to be of very low to very high in organic richness (poor to excellent source rocks potential). Huai Hin Lat formation samples from Phu Phan Anticlinorium have more organic content than Chum Phae and Khon Kaen-Ubon Areas. Moreover, the north-central part of Phu Phan Anticlinorium has higher in organic richness than the eastern and western parts of Phu Phan Anitclinorium. Nonbiomarker and biomarker parameters suggest the Huai Hin Lat Formation samples contain organic sources between terrestrial and marine organic matters deposited in less reducing to reducing environmental conditions. Bimodal distribution of n-alkane chromatogram indicates greater terrestrial higher plant organic matter input than marine organic matter. Ternary diagram of C27-C28-C29 regular sterane suggests the Huai Hin Lat Formation was possibly deposited in estuarine and/or marine environment, supported by a presence of gammacerane in all samples.