关键词: 页岩气, 保存条件, 富集模式, 五峰组—龙马溪组

Abstract: In addressing the challenge of unclear understanding of the dynamic evolution history and enrichment patterns of shale gas in strongly reformed syncline-type structures in northern Guizhou, the burial history, hydrocarbon generation history, and dynamic accumulation process of the Wufeng-Longmaxi shale in the Anchang Syncline were reconstructed based on testing data, drilling data, and geophysical data. The results indicate that the Wufeng-Longmaxi shale in the Anchang Syncline generally exhibited the characteristics of "continuous hydrocarbon generation, overall gas enrichment, formation overpressure" before the Indosinian period, and experienced a process of "slow hydrocarbon generation, differential enrichment, uplift and pressure release" after the Indosinian period, with shale maturity ranging from 2.8% to 3.0%; the evolution of shale gas content shows a trend of stable increase during the Indosinian-Early Yanshanian period and gradual decrease during the Yanshanian-Himalayan period; the pressure system underwent an evolution process of "normal pressure - hydrocarbon generation pressurization - overpressure - pressure release", and is currently at normal formation pressure; the gas content structure indicates that adsorbed hydrocarbon was dominant in the early stage, free hydrocarbon gradually increased after the Hercynian period, and both adsorbed and free hydrocarbons generally decreased after the Yanshanian period. Currently, free hydrocarbon is dominant, with a free-to-adsorbed hydrocarbon ratio of 1.50-1.80. Shale gas enrichment in syncline structures shows good correlation with formation dip angle, burial depth, and distance to outcrop areas; Class I and II faults damage shale gas reservoirs, while shale gas is locally enriched near Class III and IV faults. The Anchang Syncline structure develops five shale gas enrichment patterns: core long-term gas accumulation type, gentle wing slow accumulation type, small fault lateral sealing type, steep wing-through-going fault type, and late-stage erosion dissipation type. Among them, the core long-term gas accumulation type is the most favorable shale gas enrichment pattern. The research results provide a typical case for shale gas resource evaluation in strongly reformed areas of northern Guizhou.

Key words: shale gas, preservation conditions, enrichment patterns, Wufeng-Longmaxi Formation