Study On Sedimentary Facies Of The 8th Member Of The Shihezi Formation To The 1st Member Of Shanxi Formation In Daning-Jixian Area

The Ordos Basin is the second largest proliferous basin in China.It's in the binding site between the stability region of eastern and the active zone of western in China,and the Ordos Basin is a multi cycle composite basin.There are abundant mineral resources in the basin,and its petroleum exploration has a history of more than 60 years.Now it has become an important energy base in China.In recent years,the recognition of Ordos basins is going further resulting from huge amount of researches,explorations and developments on the southeastern part of the basin.It is discovered that upper Paleozoic layers in the southeast of the basin is rich in natural gas resources and have a great exploration potential,many large and medium-sized oil and gas fields have been found in the southeast of the basin.the main gas reservoirs are from the 1st member of Shanxi Formation and the 8th member of Shihezi Formation.In recent years,many previous researches have been conducted on the southeastern Ordos basin paleozoic stratigraphic sequence stratigraphy,deposition system,reservoir,reservoir etc.With the sharp increase in demand for oil and gas,the relative scarcity of oil and gas resources that is available for exploitation,the high-speed progress of oil exploration and development and the continue expansion of production and construction,the contradiction between the rapid development of oilfield and backup resources shortage is getting increasingly prominent.Key areas of this research are mainly located in Daning Jixian area located the southeast of Ordos basin,the key segment is the 1st member of Shanxi Formation and the 8th member of Shihezi Formation.Significant work has been done on this area which include:(1)a total of more than 80 pieces of thin sections were observed and analyzed in this paper through the analysis of the sample from 14 key wells in the area,and the main rock types in the study area were identified and summarized.(2)Find out the direction of material sources in the study area according to the well-logging data,core data,as well as field cross section and other information.(3)On the petrologic types and characters,single well section surface analysis,connected well section plane analysis,phase analysis system research is done to provide detailed geological information and favorable guidance for the next exploration.(4)Based on the core observation,sedimentary cycle,facies characteristics,sedimentary facies are determined based on the sedimentary characteristics of the study area.Through fine sedimentary facies research on single well and connected well,the distribution pattern of sedimentary facies unit in time and space and the establishment of sedimentary facies model can be determined.(5)The gas test data were collected and analyzed,and the gas test results and the main gas producing types of Shan 1 and He 8 section were summarized.the conclusions are as follows:(1)According to the results of thin core observation and microscopic analysis,the rock types in the area are mainly terrigenous clastic rocks,lithology types are mainly coarse sandstone,sandstone,fine sandstone and mudstone;sandstone is mainly quartz sandstone,detritus sandstone and detritus quartz sandstone,structural maturity of sandstones are medium to good and composition maturity of sandstones are medium to good.The good particle roundness reflects the sediments experienced relatively high degree of water flow energy transformation.The coarse and medium sandstone are mainly distributed in the south and the north of the research area.Fine grain sandstone and mudstone are mainly developed in the middle part of the study area.(2)Through the investigation of regional sedimentary background,paleocurrent analysis,light and heavy mineral assemblage analysis,the comprehensive research has make it clear that during the period of Shanxi and Shihezi Formation,there are both north and south directions of source in existence and in the middle of the study area they formed an intersection area.(3)The sedimentary microfacies of the 8th member of Shihezi Formation and the 1st member of Shanxi Formation in the study area are systematically divided.The research's target section layer developed lacustrine and braided river delta facies,they can be further divided into 3 subfacies: the delta front and the fore delta and shallow lake.In detail,the area contains 6 main kinds of microfacies: underwater distributary channel,inter channel,estuary sand bar,distal bar and fore delta mud,shallow lake mud etc.Underwater distributary channel,inter channel,estuary sand bar are the main sedimentary microfacies.(4)The braided river delta-lake depositional model is established in this paper,which is mainly composed of braided river delta front sub facies,fore delta sub facies and shallow lake sub facies.The underwater distributary channels extend from the north and south respectively in the study area,the distribution of these channels is in wide range,connectivity between each channel is medium.The microfacies of the inter river channel are distributed in the relatively depressed area between the underwater distributary channels.But because of the frequent migration of braided river,the microfacies may be altered by the underwater distributary channel or covered by the estuary sand bar.The estuary sand bar microfacies are developed at the front end of the underwater distributary channel,showing the distribution of inclusion-shape.The distal bar is located at the front of the estuary sand bar,and is modified by the lacustrine wave,developed at the periphery of the delta front.The fore delta and shallow lacustrine sand bars are developed in the middle of the study area.(5)Underwater distributary channel and estuary sand bar are the dominant facies belts in the study area and have good reservoir properties.