Hydrocarbon Generation, Migration, and Accumulation in the Eocene Niubao Formation in the Lunpola Basin, Tibet, China: Insights from Basin Modeling and Fluid Inclusion Analysis

Abstract

The Eocene Niubao Formation is the primary research target of oil exploration in the Lunpola Basin. Crude oil was extracted from Well Z1 on the northern margin of the basin in 1993. In this study, an integrated evaluation of the source rock, geothermal, and maturity histories and the fluid inclusion and fluid potential distributions was performed to aid in predicting areas of hydrocarbon accumulation. Due to the abundance of organic matter, the kerogen types, maturity, and oil-sources correlate with the geochemical data. The middle submember of the second member of the Niubao Formation (E₂ n ^2-2) is the most favorable source rock based on the amount of oil produced from the E₂ n ^2-3 and E₂ n ^3-1 reservoirs. One- and two-dimensional basin modeling, using BasinMod software, shows that the E₂ n ^2-2 source rock started to generate hydrocarbon at 35-30 Ma, reached a maturity of R0=0.7% at 25-20 Ma, and at present, it has reached the peak oil generation stage with a thermal maturity of R0=0.8% to less than R0=1.0%. By using fluid inclusion petrography, fluorescence spectroscopy, and microthermometry, two major periods of oil charging have been revealed at 26.1-17.5 and 32.4-24.6 Ma. The oil accumulation modeling results, conducted by using the Trinity software, show a good fit of the oil shows in the wells and predict that the structural highs and lithologic transitions within the Jiangriaco and Paco sags are potential oil traps.

Keywords

Niubao Formation / Lunpola Basin / source rocks / basin modeling / fluid inclusions / hydrocarbon migration and accumulation / petroleum geology

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