Hydrocarbon Potential of the Late Permian and the Late Triassic Source Rocks from the Qamdo (Changdu) Basin, Eastern Tibet and Its Linkage with the Sea Level Change

Zhaolin Qi,Chengshan Wang,Yalin Li

doi:10.3389/feart.2021.778025

Zhaolin Qi, Chengshan Wang + Show 1 more

Open Access

https://doi.org/10.3389/feart.2021.778025

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Abstract

The Qamdo Basin in eastern Tibet has significant petroleum potential and previous studies indicate that the basin contains thick potential source rocks of the Late Permian and the Late Triassic ages. In this paper, the petroleum potential of samples from measured the Upper Permian and Upper Triassic outcrop sections were evaluated on the basis of sedimentological, organic petrographic and geochemical analyses. Initial evaluations of total organic carbon contents indicated that shale samples from the Upper Permian Tuoba Formation and the Upper Triassic Adula and Duogala Formations have major source rock potential, while carbonate rocks from the Upper Triassic Bolila Formation are comparatively lean in organic matter More detailed analyses of OM-rich shale samples from the Tuoba, Adula and Duogala Formations included Rock-eval, elemental analyses, gas chromatography and organic petrography. Maceral compositions and plots of atomic O/C versus H/C indicate that the organic matter present in the samples is primarily Type II with a mixed source. Analyses of acyclic isoprenoid biomarkers indicate the organic matter was deposited under reducing and sub-to anoxic conditions. Based on the high vitrinite reflectance (Ro&gt;1.3%) and Rock-eval data, the samples are classified as highly to over-mature, suggesting that the Tuoba, Adula and Duogaila Formation shales may generate thermogenic gas. Source rock intervals in the three formations are interpreted to have been deposited in marginal-marine environment during transgressions and under a warm and moist climatic condition.

Highlights

Tibet is located in the eastern part of the petroliferous Tethyan realm (Klemme and Ulmishek, 1991)
This study focuses on organic-rich shale strata in four formations in the Qamdo Basin and aims to evaluate their hydrocarbon potential
The total organic carbon (TOC) content of the eight Tuoba Formation samples from the TB section varies between 1.66 wt% and 3.01 wt%, with an average of 2.33 wt%

Summary

Introduction

Tibet is located in the eastern part of the petroliferous Tethyan realm (Klemme and Ulmishek, 1991). Compared to analogous areas to the west such as the Persian Gulf and the Caucasus, petroleum exploration in Tibet has not been successful due mainly to the complexity of the tectonic history (Yin and Harrison, 2000; DeCelles et al, 2002; Wang et al, 2014). Oil shows have been recorded in the Qiangtang Basin which is believed to have significant exploration potential (Fu et al, 2009; Yang et al, 2015). Shale Gas in Qamdo Basin outcrop and five potential petroleum systems have been identified within the Mesozoic succession (Tan et al, 2002; Wang et al, 2009; Zeng et al, 2013). The Tibetan Plateau is considered be an exploration Frontier with numerous under-explored marine and continental petroliferous basins (Taner and Meyerhoff, 1990a; Wang and Zhang, 1996; Wang et al, 2006)

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