Hydrocarbon generation potential of deeply buried shales within the Jurassic transitional Badaowan Formation, central Junggar Basin

Abstract: [Objective] The deeply buried transitional shales within the Jurassic Badaowan Formation in the central Junggar Basin have become a frontier target for unconventional hydrocarbon exploration in recent years, yet their petroleum-generation potential remains to be fully constrained. Recent exploration wells in the Fukang and Dongdaohaizi depressions have encountered shale sequences within the Badaowan Formation at burial depths exceeding 5000 m, offering a valuable opportunity to assess hydrocarbon potential of deeply buried shales in this area. [Methods] This study evaluated the hydrocarbon generation potential of the deeply buried shales of Badaowan Formation in the central Junggar Basin by integrating organic geochemistry, microscopic component analysis, hydrous pyrolysis experiments, numerical modeling, and biomarker analysis. [Results] In this study, the deeply buried shales of Badaowan Formation in the Fukang and Dongdaohaizi depressions were selected as research target, and following outcomes are obtained: (1) shales exhibit relatively high organic matter abundances, with TOC values ranging from 0.75% to 5.06% and 0.81% to 5.27%, respectively, and kerogen is dominated by types II and III, (2) maturation parameters (R_o=0.70%–0.82% and 0.51%–0.80%, respectively) indicate that the shales are currently in the main oil generation window, (3) thermal history reconstruction shows that hydrocarbon generation began in the Late Jurassic, passed the main oil generation threshold in the Late Cretaceous, and has continued for approximately 150 million years, (4)hydrous pyrolysis results show that total hydrocarbon yields of the shales are 380–500 mg/g·TOC, (5) biomarker data reveal a transitional depositional environment of frequent redox fluctuations, with organic inputs from both aquatic organisms and higher terrestrial plants. [Conclusion] Consequently, deeply buried shales of Badaowan Formation in the central Junggar Basin possess substantial hydrocarbon generation capacity and constitute a promising exploration target for shale oil and gas.