四川盆地寒武系筇竹寺组页岩气“槽-隆”富集规律及勘探前景

Aulacogen-uplift enrichment pattern and exploration prospect of Cambrian Qiongzhusi Formation shale gas in Sichuan Basin,SW China

针对寒武系筇竹寺组页岩埋深大、成熟度高及页岩气富集规律认识不清的问题,通过德阳—安岳裂陷槽的精细刻画、沉积环境分析、乐山—龙女寺古隆起背景下页岩气成烃富集演化恢复,揭示了“槽-隆”富集规律。研究表明,德阳—安岳裂陷槽控制筇竹寺组沉积环境,裂陷槽内具有沉积相带优和地层厚度大的特点;此外,乐山—龙女寺古隆起控制筇竹寺组的页岩成熟度演化,古隆起位于高部位且热演化程度适中、电阻率高。“槽-隆”叠合区在沉积、生油、生气和油气调整阶段均有利于页岩气富集,共同控制储层发育,叠合区储层品质优、储层套数多、厚度大。根据“槽-隆”富集规律及槽-隆组合关系,优选4类页岩气有利区带,并建立筇竹寺组甜点区评价标准,优选8200 km^(2)的槽内甜点区勘探面积,进而指导资201井的部署,获得73.88×104 m^(3)/d的高产工业气流。“槽-隆”富集规律的地质新认识,为寒武系深层—超深层页岩气勘探和突破提供了重要理论依据,并揭示该领域具有良好的勘探前景。

The shale of the ancient Cambrian Qiongzhusi Formation in Sichuan Basin is characterized by large burial depth and high maturity,but the shale gas enrichment pattern is still unclear.Based on the detailed characterization of Deyang-Anyue aulacogen,analysis of its depositional environments,together with reconstruction of shale gas generation and enrichment evolution against the background of the Leshan-Longnüsi paleouplift,the enrichment patterns of aulacogen-uplift system have been elucidated.It is revealed that the Deyang-Anyue aulacogen controls the depositional environment of the Qiongzhusi Formation,where high-quality sedimentary facies and thick strata are observed.Meanwhile,the Leshan-Longnüsi paleouplift controls the maturity evolution of the shale in the Qiongzhusi Formation,with the uplift located in a high position and exhibiting a moderate degree of thermal evolution and a high resistivity.The aulacogen-uplift overlap area is conducive to the enrichment of shale gas during the deposition,oil generation,gas generation,and oil-gas adjustment stage,which also has a joint control on the development of reservoirs,resulting in multiple reservoirs of high quality and large thickness.Based on the aulacogen-uplift enrichment pattern and its combination relationship,four types of shale gas play are identified,and the sweet spot evaluation criteria for the Qiongzhusi Formation is established.Accordingly,a sweet spot area of 8200 km^(2) in the aulacogen is determined,successfully guiding the deployment of Well Zi 201 with a high-yield industrial gas flow of 73.88×10^(4) m^(3)/d.The new geological insights into the enrichment patterns of aulacogen-uplift system provide a significant theoretical basis for the exploration and breakthrough of deep to ultra-deep Cambrian shale gas,highlighting the promising exploration prospect in this domain.