Work

Geological, geochemical and oil content characteristics of alkaline lacustrine shale: Fengcheng formation in Mahu Sag, Junggar Basin

Year: 2026

Type: article

Abstract: The Fengcheng Formation(P 1 f) in the Mahu Sag of the Junggar Basin is a typical alkaline lake deposit rich in shale oil. The strong heterogeneity poses significant challenges for oil-bearing evaluation, severely restricting exploration decision-making and favourable interval prediction. Therefore, the 283 m shale sedimentary sequence in the P 1 f section of Well Maye one was studied. Source rocks of the P 1 f geological and geochemical characteristics, hydrocarbon-generating source materials, and sedimentary paleoenvironment were investigated using extensive organic and inorganic geochemical analyses. An improved three-dimensional(3D) oil content evaluation model based on pyrolysis parameters and oil saturation index (OSI) was used to classify the oil content of different types of organic matter and predict the shale dessert section in P 1 f. The source rock in P 1 f is developed in the saline and anoxic environment of sedimentary water stratification. The overall characteristics of the source composition of parent material are that the abundance of bacteria and algae is higher than that of terrestrial plants, and the abundance of bacteria is higher than that of algae, and cyanobacteria account for a certain proportion. The hydrocarbon generation potential index of P 1 f decreases with the transition of kerogen type from I to III, and the OSI value shows a trend of first increasing and then decreasing from Type I to Type II 1 and then to Type III. The shale oil resources in the P 1 f shale were classified into four categories: enriched, moderately enriched, less efficient, and invalid resources. The enriched and moderately enriched resources are mainly Type II 1 kerogen. Six favorable shale intervals were predicted vertically in the P 1 f of Well Maye 1. The 3D model used in this study can more accurately evaluate the quality of shale oil reservoirs in Mahu Sag. The research results provide favorable guidance for exploring and developing strongly heterogeneous alkaline shale oil in Mahu Sag and other regions in the world.

Source: Frontiers in Earth Science

DOI: 10.3389/feart.2026.1866539