Carrier bed plays of the Cambrian Qiongzhusi Formation in the Sichuan Basin, China: Exploration practices and significance

In conventional petroleum systems, carrier beds are traditionally regarded as pathways for petroleum migration. However, petroleum geologists are increasingly recognizing the exploration significance of carrier beds as potential reservoirs, introducing the concept of the carrier bed play. Research on these plays remains in its early stages, and the controlling factors and accumulation models still require systematic investigation. The academic community also needs more representative examples to strengthen the theoretical understanding of carrier bed plays. This study focuses on the silty shale of the Qiongzhusi Formation in the Jingyan-Qianwei area in the southwestern Sichuan Basin. We identify four lithofacies in the silty shale, with sedimentary textures driving differences in physical properties. Among them, the laminated siliceous silty shale with relatively low total organic carbon (TOC) content in the middle member of the Qiongzhusi Formation functions as a carrier bed. Natural gas enrichment in this interval depends on six factors: favorable physical properties, high feldspar content (average >20%) with well-developed laminations, moderate TOC content (commonly <0.5 wt. %), sufficient natural gas supply, an effective seal–reservoir configuration, and the absence of migration pathways that connect with conventional reservoirs (e.g., faults). The successful breakthrough of carrier bed plays in the Qiongzhusi Formation of the Jingyan-Qianwei area demonstrates the broad exploration potential of shallow-water depositional systems in the southwestern and central Sichuan Basin. Future exploration should prioritize shallow-water settings with stable tectonics, limited large-scale faulting, and proximity to deep-water source rocks. A comparison with well-known North American carrier bed plays (Mancos Shale play) shows that although the accumulation mechanisms are broadly similar across different petroleum systems, each exhibits unique characteristics. More studies are therefore needed to advance systematic knowledge of carrier bed play accumulation mechanisms.