Modes of Shale-Gas Enrichment Controlled by Tectonic Evolution

The typical characteristics of shale gas and the enrichment differences show that some shale gases are insufficiently explained by the existing continuous enrichment mode. These shale gases include the Wufeng-Longmaxi shale gas in the Jiaoshiba and Youyang Blocks, the Lewis shale gas in the San Juan Basin. Further analysis reveals three static subsystems (hydrocarbon source rock, gas reservoirs and seal formations) and four dynamic subsystems (tectonic evolution, sedimentary sequence, diagenetic evolution and hydrocarbon-generation history) in shale- gas enrichment systems. Tectonic evolution drives the dynamic operation of the whole shale-gas enrichment system. The shale-gas enrichment modes controlled by tectonic evolution are classifiable into three groups and six subgroups. Group I modes are characterized by tectonically controlled hydrocarbon source rock, and include continuous in-situ biogenic shale gas (I-1) and continuous in-situ thermogenic shale gas (I-2). Group II modes are characterized by tectonically controlled gas reservoirs, and include anticline-controlled reservoir enrichment (II1) and fracture-controlled reservoir enrichment (II2). Group III modes possess tectonically controlled seal formations, and include faulted leakage enrichment (III1) and eroded residual enrichment (III2). In terms of quantity and exploitation potential, I-1 and I-2 are the best shale-gas enrichment modes, followed by II1 and II2. The least effective modes are III1 and III2. The categorization provides a different perspective for deep shale-gas exploration.