上扬子区页岩气甜点分布控制因素探讨——以上奥陶统五峰组—下志留统龙马溪组为例

上扬子区作为中国南方海相地层最稳定的地区,发育多套海相页岩。为研究控制该区页岩气甜点分布的主要因素,以上奥陶统五峰组—下志留统龙马溪组页岩为研究对象,依据上扬子区域地质事件及盆地结构特征,从构造控源控藏的角度对该区构造格局、高产井分布与气藏控制因素进行了分析,指出四川盆地东南及边缘发育的达州—利川、涪陵—彭水、南川—遵义、永川—习水、富顺—盐津、威远—犍为6大构造转换与调节带,其页岩具有弱变形与弱改造特征,是盆内最有利的页岩气赋存与保存区。结论认为:(1)受高热演化、强改造因素影响,上扬子区海相页岩以构造转换带与调节带变形最弱,具有页岩气多源汇聚与复合成藏的有利条件,且天然缝网与圈闭最为匹配,是盆内最有利的页岩气赋存与保存区,页岩气资源量最为丰富;(2)四川盆地东北部达州—利川及东南永川—习水构造转换带与调节带应引起下一步页岩气选区评价与勘探工作的高度重视。

Controlling factors for shale gas sweet spots distribution in the Upper Yangtze region: A case study of the Upper Ordovician Wufeng Fm–Lower Silurian ongmaxi Fm,Sichuan Basin

In The Upper Yangtze region, the most stable region for the development of marine strata in South China, multiple sets of marine shale has developed. The Upper Ordovician Wufeng Fm–Lower Silurian Longmaxi Fm shale was taken as the study object to study the key factors controlling the sweet spots distribution of shale gas in this region. According to the geological events in the Upper Yangtze region and basinal structural characteristics and from the perspective of structural control on the source and accumulation, the regional tectonic framework, distribution of high-yield wells, and gas reservoir controlling factors were analyzed. It is indicated that the six major structural transformation and adjustment belts of the Dazhou–Lichuan, Fuling–Pengshui, Nanchuan–Zunyi,Yongchuan–Xishui, Fushun–Yanjin, and Weiyuan–Qianwei developed in SE Sichuan Basin and its margin show weak deformation and weak alteration features for shale, being the most favorable zone for the occurrence and preservation of shale gas. It is concluded that: (1) affected by high thermal evolution and intensive alteration, marine shales in the Upper Yangtze region have the weakest deformation in the structural transformation zone and adjustment zone, demonstrating a favorable condition of multisource convergence and composite accumulation. And the natural fracture networks are well matched with the traps, being the most favorable zone for the occurrence and preservation of shale gas and showing the most abundant shale gas resources; (2) great importance should be attached to the structural transformation zone and adjustment zone of the Dazhou–Lichuan in the NE Sichuan Basin and of the Yongchuan–Xishui in the SE Sichuan Basin in the further target optimization and exploration work for shale gas.