Abstract
The Wichian Buri sub-basin is located in the southern Phetchabun basin, Thailand. It is reported to have significant recoverable hydrocarbons from relatively shallow fractured igneous rock reservoirs, but until now no detailed research has been done on the effect of the igneous intrusion on thermal enhancement of maturity of the source rocks and their hydrocarbon generation. The particular feature of the petroleum system in this basin is that the igneous intrusions of 11–16 Ma and 18–24 Ma played a dual role. On the one hand, they increased maturity of the source rock, and on the other hand, they became shallow fractured igneous rock reservoirs. In this study, well logging analysis and 1D petroleum system modeling (1D PSM) were integrated to evaluate the source rock of the Wichian Buri sub-basin based on the data from public domain of the petroleum industry of Thailand, including vertical well sections, well logs, regional geological sections, base maps, and geochemical data. The results of well log analysis found intervals of fractured igneous rock reservoirs with typical low gamma ray of 20 to 30 API and average porosity around 8 to 12%. The well log data were used to determine the total organic carbon (TOC) by the ΔlogR technique that was further used in 1D petroleum system modeling (1D PSM) with consideration of the effect of igneous intrusion on enhancing source rock maturity. Vitrine reflectance (Ro) and hydrogen index (HI) of the source rock in this study were found as 0.62% and 222 mgHC/gTOC, respectively. As a result of 1D PSM, hydrocarbon generation was found to have started in the Permo-Triassic Nam Duk Formation and ended in the late Miocene basalt and Miocene source rock. For an original hydrogen index (HI0) of 600 mgHC/gTOC, the hydrocarbons generated, retained, and expulsed in/from the source rock were estimated as 3178.6, 2823.0, and 355.5 MMSTB, respectively. By correcting HCexp for petroleum system efficiency (PSeff), which was chosen as 5, 8, and 15% in this study, one can obtain the charge volume of hydrocarbons that could be trapped as HCIIP, which is 53.33 MMSTB with PSeff of 15%, indicating a good hydrocarbon potential for further exploration in the Wichian Buri sub-basin.
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