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

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.