Sedimentary System Research Of Yanchang Formation In South Ordos Basin

In order to clear depositional system types and sedimentary facies characteristics of Yanchang Group in the south of the Ordos basin, summarize its sedimentary evolution, and analysis the main controlling factors and resource potential, based on sedimentary principle and integrated use of the theory and methods of geophysics, geochemistry, basin analysis, through a comprehensive analysis of the outcrop, drilling, logging data, we research the provenance characteristics, sedimentary facies types and their distribution rules of Upper Triassic Yanchang Group in the south of the Ordos basin.To classification and correlate the stratum, through the way of flag layer control and cycle contrast, we found5main marker beds and an auxiliary one distributed stably on regional, combined with the thickness principle, we divide Yanchang Group in research area to10reservoir groups bottom-up from Chang10to Chang1. Due to serious denudation in the middle-late formation of Yanchang Group in research area, in stratigraphic division, we identified the unconformity at the top of the Yanchang Group by the coal beds at the top of Yan8and Yan9. Simultaneously, combining with the standard wells and isochronoustratigraphic correlation standard section across the study area, we compared and regulated the division results vertically, finally we divided the stratigraphic of target layer of more than300wells in the study area.Through the study of paleocurrent, light and heavy minerals, rock debris and enrichment patterns of lanthanides, we think the study area mainly affected by the northeast and southern provenance, and locally influenced by the southwestern source. We speculate that northeast provenance was from archaeozoic metamorphite of Yinshan Mountains and Daqingshan Mountains, southern provenance was from Qinling orogenic belt, and southeast provenance was from Longxi old land.Based the collection of sedimentary structural, textural, paleontological and other facies indicators in core drilling and observation of outcrops, combined with rock types, single well facies analysis and well sections contrast, we identified that Upper Triassic Series Yanchang Group mainly developed lakes and delta deposional systems in study area, which can be divided into adeep lake, shallow lake, delta plain and delta front four types of sub-facies, which can be further divided into ten categories of micro-phase.