Reservoir Characteristics And Petroleum Accumulation Of Permian Longtan Fomation In Xiqiao Tectonic Belt Of Huangqiao Region, Lower Yangtze Basin

The Tectonic belt of Huangqiao area is located in Subei Slopes of Lower Yangtze region, under the Nanjing Depression of Yangtze Basin. Permian, from bottom to top, is composed by Qixia, Gufeng, Longtan and Dalong Formation. Longtan Formation sedimentary period, the water depth decreases, more adequate supply of source material, sediments appear as a coarsening upward sedimentary cycles, followed by deposition of a shallow sea shore, delta front and delta plain sediments. Lower Yangtze Huangqiao region has gone through smooth motion long before the Indo-down, Indo late--mid-Yanshan extrusion pushover, Yanshan late-early Himalayan extensional rift and late Himalayan uplift and erosion of the four tectonic stages, resulting in formation in the region repeatedly settlement-burial uplifting history feature.Based on mud logging, electric logging, core analysis data and the former studies, the sedimentary facies fo the study area mainly includes delta plain branch rivers, swamps, underwater distributary channel and delta front Meanwhile Bay, as well as shore shallow mud deposition. Overall, during the deposition of Longtan Formation performance from the bottom up as regressive, as the transition from marine deltaic.Through rock flakes, cast thin, X-ray diffraction analysis, electron microprobe analysis, scanning electron microscopy and spectroscopy analysis, detailed study about reservoir petrology, diagenesis reservoir space and reservoir properties, etc. feature Huangqiao Permian Longtan Formation show that reservoir lithology in the area of the main target layer lithic feldspathic quartz sandstone and lithic sandstone, detrital components is quartz, debris, feldspar and mica-based, with calciμm-based cements containing a small amount of clay, siliceous and iron, the mainly clay minerals is illite/mixed layer, illite, and show some kaolinite and chlorite see Diagenesis main types of compaction, cementation, metasomatism and dissolution and so on. Longtan Formation of study area depth larger, with diagenesis deeper level, leads a greater impact on reservoir properties of the reservoir, resulting in lower porosity and permeability. Compaction and cementation is the strongest of diagenesis, which is the main cause of deterioration of reservoir properties. On diagenesis phasing, Longtan Formation reservoir in the study area is in diagenetic B phases. Reservoir space is based on secondary porosity, the main types include micro-pores, micro-cracks, intergranular dissolved pores and intragranular dissolved pores, poor thing, is extremely low porosity-ultra-low permeability reservoirs, where the physical properties of Xi1well is slightly better than Xi2well.The widely developed fluid inclusions of Permian Longtan Formation reservoir in Lower Yangtze Huangqiao region, which are main aqueous and oil inclusions, distribute in quartz crack and quartz secondary enlargement edge, and are small individually. Oil inclusions show green-yellowish and blue-and-white respectively with blueray and ultraviolet excitation, thus indicating that the oil in Longtan Formation in the researched area is primarily in middle mature stage.Through microscopic temperature measurement of inclusions, combined with the burial history-thermal history, tectonic evolution and diagenetic evolution model research, We speculate that the oil in Longtan Formation in Tectonic belt of Huangqiao area experiences three major oil and gas filling period:the first period for73-70Ma (late Cretaceous), the second period for58-52Ma (Paleogene), the third period45-38Ma(Paleogene), predominately the second and the third period.