Lithofacies paleogeography during the depositional period of the Nanhua System Datangpo Formation and its indications for hydrocarbon accumulation in the Middle and Upper Yangtze Region, South China

This paper is the result of oil and gas exploration engineering.

Objective The marine black manganese−bearing carbonaceous shale of the Datangpo Formation, widely distributed in the mid−Neoproterozoic Nanhua strata of the Middle−Upper Yangtze Region, South China, has been extensively studied as a manganese deposit but remains poorly investigated regarding its petroleum geological characteristics. This study systematically analyzes the lithofacies paleogeography of the Datangpo Formation and evaluates its implications for hydrocaron accumulation, providing critical insights for guiding petroleum exploration in the southern China.

Methods Through field surveys and comprehensive data synthesis of the Datangpo Formation, we systematically evaluated hydrocarbon conditions, source rock geochemistry, and reservoir−caprock assemblage, especially lithofacies and paleogeography. This integrated approach combined individual well log interpretation, multi−well correlation analysis, and lithofacies paleogeographic with advanced analytical techniques including organic geochemical testing, petrophysical characterization, and reservoir evaluation.

Results The Datangpo Formation developed during an interglacial period, with its depositional architecture constrained by extensional riftdynamics. Sedimentary facies within the formationare classified into two principal types, seven subcategories and multiple microfacies. The sequence comprises a complete transgressive−highstand−regressive cycle. Hydrocarbon−prospective facies are limited shelf subfacies and lagoon subfacies, predominantly occurring in the first member. These intervals exhibitfavorableorganic geochemical index, and constitute potential source rock horizons.

Conclusions The first member of the Datangpo Formation exhibits significant hydrocarbon−generation potential and viable shale gas prospects. Strategic areas including Songtao, Huayuan, Xiushan, Xiangtan and Hefeng, located at the confluence of Hunan, Chongqing and Guizhou Province, demonstrate favorable geological conditions for shale gas exploitation. This unit serves as a competent source rock capable of forming multiple prospective hydrocarbon reservoir assemblages. Notably, The Xiushan−Songtao−Huayuan sector along the tri−province boundary of Chongqing, Guizhou, and Hunan exhibits optimal source−reservoir coupling configuration, indicating promising targets for conventional petroleum exploration.