中上扬子地区寒武系页岩气富集条件及有利区优选

Enrichment conditions and favorable prospecting targets of Cambrian shale gas in Middle-Upper Yangtze

为查明寒武系海相页岩气富集机理及有利勘探区带,通过页岩沉积、烃源、储集特征及典型页岩气井综合解剖与对比,明确寒武系页岩气发育的地质条件及富集主控因素,评价优选出了页岩气有利勘探区带。研究结果表明:寒武系页岩整体具有厚度大、有机质丰度高、热演化程度高、保存条件差及含气性差的地质特点,页岩气富集受沉积相带、储集性能及保存条件3个因素控制,表现为深水陆棚相优质页岩的发育是页岩气“成烃”的物质基础,页岩储集性能好是页岩气“聚集成藏”的关键因素,良好的保存条件是决定页岩气“富集程度”的关键保障;采用单因素分析—多因素叠合评价的方法,在建造条件方面以深水陆棚相带及其控制下的优质页岩厚度为核心参数,在改造条件方面强调构造上“动中找静”、热演化程度“高中找低”、埋藏深度适中的评价原则,提出川西南井研—犍为—威远—资阳、川北南江及中扬子宜昌地区为页岩气勘探最有利地区,长宁—资阳—南江一线的深层地区、隶属于湘、鄂、黔等省份的志留系、奥陶系开孔的向斜区是值得关注的潜在领域。

Enrichment mechanism and favorable prospecting targets of Cambrian marine shale gas in MiddleUpper Yangtze were investigated.Geological enrichment conditions and primary controlling factors of shale reservoirs were clarified through integrating deposition environment,source rock property and reservoir quality as well as drilling data from typical shale gas wells.Favorable shale gas exploration targets were subsequently evaluated and optimized.The results show that Cambrian shale in Middle-Upper Yangtze is characterized by large thickness,high organic matter abundance,high thermal maturity,poor preservation conditions and poor gas bearing property.Shale gas enrichment is controlled by three primary factors:sedimentary facies,reservoir performance and preservation conditions.High-quality shale from deep-water shelf provides solid foundation for hydrocarbon generation,high reservoir quality is the key for shale gas accumulation,and good preservation conditions determine gas content at shale reservoir.Prospecting targets are determined through superposing multiple factors after analyzing and mapping each factor.Organic-rich shale thickness associated with deep-water shelf facies is emphasized for construction conditions.Evaluation principles,e.g.,stable structure zones in unstable structure units,low-mature shale among high thermal-maturity regions and moderate burial depth are proposed for reconstruction conditions.Consequently,the most favorable zones evaluated are mainly distributed in the Jingyan-Qianwei-Weiyuan-Ziyang in Southwest Sichuan Basin,the Nanjiang in North Sichuan Basin and the Yichang in the Middle Yangtze.Deep-buried Cambrian shale reservoirs along Ziyang-Changning-Nanjiang within Sichuan Basin and shale reservoirs at synclines outside Sichuan Basin with Silurian system or Ordovician system exposed,e.g.,at Guizhou province,at Hubei province,at Hunan province,etc.,are potential exploration targets in the future.