中扬子区海相天然气勘探层系及突破方向

EXPLORATION STRATA AND BREAKTHROUGH ORIENTATION OF MARINE FACIES NATURAL GAS IN THE MIDDLE YANGTZE REGION

中扬子海相地层在地质发展史中经历了加里东期、海西—早印支期、晚印支—早燕山期以及晚燕山—喜山期4次大的旋回,大体形成了浅海、前陆坳陷、陆相断陷3大类型的盆地。多期盆地沉积充填、叠加改造,奠定了油气成藏聚集的物质基础。受不同时期海平面升降变化的影响,在沉积古地理环境和表生溶蚀作用控制下,形成了上震旦统灯影组、下寒武统石龙洞组、中石炭统黄龙组及中二叠统茅口组等古岩溶型储层。中扬子区晚二叠、早三叠世沉积期具备台地边缘礁、滩的沉积背景,同时区内还发育台内礁、滩。此外,志留纪前陆盆地发展阶段广泛发育的砂岩储层,应成为南方古生界勘探的重要领域。这些不同的油气聚集空间,显示区内勘探领域广阔。开展储层沉积相和高精度地震预测攻关研究,弄清不同储层发育的地球物理响应及其分布规律是勘探突破的关键。勘探对策应该立足于寻找大型天然气藏,坚持上、中、下组合并举和多领域勘探兼顾,优选有利勘探区块,实施重点突破。

Marine facies strata in the middle Yangtze region have experienced 4 big cycles including Caledonian,Hercynian-early Indosinian,late Indosinian-early Yanshanian,and late Yanshanian-Himalayan during geological evolutions,giving birth to 3 types of basin: shallow-sea facies,foreland depression and rift-subsidence.Sedimentary packing and deformation of stages of basin have formed foundation for petroleum accumulation.Influenced by eustacy,controlled by sedimentary palaeogeologic environment and surface corrosion,different types of reserve such as Dengying Formation of Upper Sinian,Shilongdong Formation of Lower Cambrian,Huanglong Formation of Middle Carboniferous and Maokou Formation of Middle Permian are formed.The middle Yangtze region is set in platform edge reef bank background during late Permian and early Triassic,generating reef and bank in platform.On the other hand,sandstone reserves generated widely during Silurian foreland basin evolution should be the focus for Paleozoic exploration in South China.Different types of reserve prove large fields for exploration in the region.Study of reserve sedimentary facies,precise seismic prediction,as well as geophysical respond and distribution rules of different types of reserve is the key for exploration breakthrough.Large gas fields should be paid attention to.The upper,middle,lower strata and multifields should be taken into consideration.Breakthrough can be made in favorable areas.