Characteristics and Controlling Factors of Hydrocarbon Expulsion and Retention in Typical Marine Sedimentary Basins of America

ABSTRACT With the proposal of the ‘whole petroleum system’ concept, conventional and unconventional resources should be assessed jointly; however, their allocation patterns remain unclear. This study analyses four US basins (i.e., Permian, Williston, Western Gulf and Denver Basins) using data from Energy Information Administration for the period 2007–2025 to clarify these patterns and provide insights for shale exploration in China. The results show that unconventional production (retention production) increased steadily across all basins, whereas conventional production (expulsion production) stabilized or declined. The expulsion‐to‐retention ratios stabilized at 0.11 in the Williston Basin and 0.35 in the Western Gulf Basin, indicating relatively mature development stages, with unconventional resources accounting for approximately 90% and 72.5% of total production, respectively. In contrast, the Permian and Denver Basins exhibit rapidly declining ratios, suggesting continued growth in unconventional production. The ratio is primarily controlled by thermal maturity (Ro), total organic carbon, brittle mineral content and the pressure coefficient, with Ro being the most influential factor. Among the four basins, the Permian Basin demonstrates the greatest potential for future growth. For the Chang 7 Member of China's Ordos Basin, estimated expulsion efficiency indicates unconventional resources are approximately one to two times the volume of conventional resources. Overall, the expulsion‐to‐retention ratio proves a valuable proxy for evaluating exploration maturity and resource potential and offers practical guidance for the assessment of complex continental shale petroleum systems in China.