Study On The Transporting Capability Of The Sandstone And Unconformity In The Shallow Of South Junggar Foreland Basin

Southern Junggar experienced twice superposition of foreland basin, Especially in the stage of intracontinental depression, formed the multiphase unconformity and the sandstone of facies changing quickly. All the unconformity and sandstone caused complexity of the passage system. Comprehensive variety of the latest technology is used to analyze the distribution of effective unconformity and sandstone during the key period, in order to further provide some information for oil and gas exploration.In this paper, based on sedimentary facies, from the sandstone’s thickness and diagenetic facies, macroscpic distribution characteristics was analyzed. Combined with the measurement of pore-throat by scanning electron microscopic and the image analysis in the casting thin sections, microscopic reservoir pore structure characteristics of sandstone was analyzed. And then, based on diagenesis researching and the determination of the key period, evolution of the porosity was analyzed and the porosity and permeability during the key period were recovered. The Storage Coefficient and Flow Coefficient were used to quantitatively calculate the transporting capability of the sandstone during the key period. Seismic data was used to analyze the macro structural style of the unconformity, and well-logging data was used to analyze the micro lithologic combination of the unconformity. Further, the transporting type of the unconformity was analyed. On this basis, the fluorescent display of logging and organic geochemical characteristics of homologous oil were used to analyze transporting characteristics of the unconformity. Combined with the hydrodynamic evolution and the surface of unconformity during the key period, the distribution of effective unconformity during the key period was determined. Finally, combining previous study of fault, the transporting mode was summarized during the key period.Studies have showed that the sandstone was controlled by delta-lacustrine facies on the macro, which the Qingshuihe group vertically stated on the pinchout line by fan-shaped and the Ziniquanzi group along the pinchout line extensioned to the inside basin by lobate-shaped. On the micro, main pores was the primary intergranular pore and the dissolved pore, the width of throat was the main influencing factor in the transporting capability of the sandstone. The Qingshuihe group belonged to A period of the mesogenetic stage, the Ziniquanzi group belonged to B period of the diagenetic stage and A period of the mesogenetic stage. The resorption of analcite mineral dominated the formation of secondary porosity, pores experienced decrease by the compaction, decrease by the cementation, increase by the resorption, mild increase by the rupture, mild increase by the precipitation in the later dissolution. According to the macro structural style and the micro lithologic combination of the unconformity, the unconformity was divided into vertical and lateral transporting type, lateral transporting type, trap type and non transporting type. During the key period, the ecffetive carrier bed of the Qingshuihe group distributed in middle of the fan by fan-shaped, and the Ziniquanzi group distributed parallel by Tianshan Mountains in the ribbon. The unconformity of K/J was a good migration pathway, in which oil and gas migrated from the Four-trees depression and Sawan depression to Chepaizi region. The unconformity of E/K was a good migration pathway in the Four-trees depression, but that was a little worse in Huo-Ma-Tu anticlinal zones, the area which could migrate hydrocarbon distributed along the pinchout line.