Fluvial Sedimentary Characteristics And Evolution Of The Middle And Upper Jurassic,Southern Jungger Basin

Junggar basin is one of the large oil and gas bearing basins in China.According to the third time national oil and gas evaluation the geological resource of Junggar basin is 10.68 billion tons with a OIP of 2.09 billion tons.As part of Tianshan tectonic belt South Junggar basin was close to oil production area,and the fracture development and migration condition was good in there,multiple rows of large anticline developed,so the southern margin of Junggar basin is a key area of oil and gas exploration.Fine descriptions of the outcrop could provide the most direct and reliable understanding of geological evidence for the South Junggar basin.Guided by clastic reservoir sedimentology,this paper combined outcrop measurements and descriptions with comprehensive indoor study based on recognition and description of sedimentary characteristics.The study was done on the basis of the explanation to genetic sand-body and the summary to the body of reservoir structure;the core was to determine sedimentary system types and establish sedimentary evolution model;this paper set up geological knowledge of different fluvial facies sedimentary characteristics of reservoir sand body;it compared different fluvial facies reservior attributes under different A/S conditions;it clarified the sedimentary evolution law of river sedimentary system in the middle-late Jurassic in the southern margin of Junggar basin.Main results and understandings are as follows:1?There are two groups of fluvial sedimentary system developed in Mid-UpperJurassic Ershi in the Southern Jungger basin.The Toutunhe formation developed a set of gray-green?gray-yellow?magenta fluvial-lacustrine glutenite,fine-siltstone and mudstone facies interactive fluvial-lacustrine strata,Qigu formation developed a set of coal-free fine-grained sediments mainly brick red strata,mainly distributed in the west of Sangong River of the Southern Juggar basin,the majority of areas suffered from erosion or incomplete deposition.2?Measurement and quantitive analysis show that:different ratios of A/S were contributed to significant sedimentary characteristics differences of sections in the Qigu formation.A/S was smallest in the Hutubi section,sand/shale ratio was 0.37,width-thickness ratio of sand body was between 16.0 and 50.0;A/S became bigger in the Honggou section,sand/shale ratio was 0.22,width-thickness ratio of sand body was between 26.0 to 80.0;A/S was biggest in the Hongmogou section,sand/shale ratio was 0.14,width-thickness ratio of sand body was between 28.5 and 75.0.In the Toutunhe formation A/S was smallest in the Toutunhe section,sand/shale ratio was 0.92,width-thickness ratio of sand body was between 25.5 and 51.7;A/S became bigger in the Honggou section,sand/shale ratio was 0.34,width-thickness ratio of sand body was between 23.4 and 51.0;A/S was biggest in the Hongmogou section,sand/shale ratio was 0.23,width-thickness ratio of sand body was between 23.9 and 61.7.3?By the explained sand body from outcrops explained,this paper summarized the law of superposed sand body from braided river to the meandering river,it also summed up the response to fluvial of a cycle period.Based on detailed outcrop measurement and indoor analysis,this paper compared the sedimentary characteristics in different parts of the South Junggar basin,it established the geological knowledge database from braided river to the meandering river,it clarified the rule of fluvial evolution in the Southern Junggar.All of these studies provided the reference for the prediction to the exploration of lithology reservoirs in the study region.