Sedimentary Characteristics Study On Lower Cretaceous Of Saihantala Sag, Erlian Basin

In order to enlarge the exploration field and improve the exploration success rate in Erlian Basin, this thesis used Saihantala Depression of Erlian Basin as a study area. In current thesis, the stratum, source, distribution of sand bodies of Saihantala depression were emphatically studied, then the sedimentary facies and distribution rules were analyzed by collecting and analyzing basic geological data, logging, logging maps, seismic data, single well facies and profile facies comparison under the guidance of sedimentology and petroleum geology, etc. finally, the sedimentary facies of key layers were determined based on frontal results. The results of this thesis will provide certain foundation of oil and gas exploration for the next step.Stratigraphic correlation section showed that Aershan group and Tenggeer group were thicker in east and thiner in west, Due to strong tectonic activity and rapid subsidence of Xilin rupture of boundary fault, very thick Aershan group and Tenggeer group mudstone were deposited, it laid a solid foundation for the source rocks of this depression. At the same time, the thrown side fault deposited multiple waistband-like underwater fan and sublacustrine fan from east, plus plenty sediment source during sedimentary period of Tengger group and Saihantala groupk, It provided a favorable condition for oil and gas reservoir.Sedimentary facies analysis shows that fan-delta plain subfacies, fan-delta front subfacies, front fan-delta subfacies, lacustrine fan, lacustrine facies and braided delta plain subfacies were developed in the research area.During Aershan depositional period, the lake range was rather smaller and shore-shallow lake facies is the main characteristic. At the late phase of Aershan period, the Northwest uplift provided a large number of sedimentary sources for the studied region and the braided river delta was the preferential depositional system, along the north-south long axis trend, mainly developed delta facies, otherwise at the short direction of east-west, underwater fan and fan delta sedimentaries were abroadly deposited. In this period, both at the lake and the east steep shore, it deposited thick dark shale deposition, as the first set of source rocks depression of the depression.During Teng 1 episode, a great thichness of lake mudstone was yielded, at the east Sai 4 trough, forming the large-scale fan delta front deposits of the eastern provence, thickness keep stability through research region and easy-to-oil and gas accumulation. As The long axis of the lake, north to south, donimated by delta deposits.Within Teng 2 episode, large scale fan-delta deposits was formed in the west gentle slope zone, and the steep eastern shore mainly formed subaqueous fan and lacustrine fan.Sandstone body of the lacustrine fan and submarine fan around the east Steep slope closed to the source rock, which easy to form subtle trap and has significant meaning for the oil and gas exploration.