Research On Sedimentary Environment And Reservoir Characteristics Of The Late Triassic Nanshuangyashan Formation In Sanjiang Region

The Sanjiang region is located in the eastern Heilongjiang province,and its geotectonic setting is specific.This region belongs to the eastern Jiamusi Block,and it is also located in the southeastern Central Asian Orogenic Belt;it is an important component of northwest Pacific Ocean continental margin tectonic domain as well.In this thesis,sedimentary microfacies of Nanshuangyashan Formation had been divided and lithofacies of the Late Triassic in the Sanjiang region was recovered simply based on microscopic observation and field reconnaissance.At the same time,this dissertation also analyzed the source nature and direction of Nanshuangyashan Formation using detrital zircon U-Pb dating,element geochemical analysis and sandstone modal analysis.Finally,physical properties of reservoir from the Nanshuangyashan Formation were analyzed.This dissertation has got the following conclusions.1.The lithology of the Nanshuangyashan Formation mainly comprises coarse sandstone,medium sandstone,fine sandstone,siltstone,argillaceous siltstone,mudstone,silty mudstone,tufaceous coarse sandstones,basalt and siliceous rock.2.The lithofacies of the Nanshuangyashan Formation consists of delta facies,littoral facies,and abyssal facies.Overall,the Fujin-Baoqing-Mishan developed marine-terrigenous facies.On the west of this area,fluvial deposits were widely developed,and the abyssal facies was developed on the east of the Fujin-Mishan area.There exists dramatic change of facies between the west and the east of the study and that means the marine-terrigenous facies is in direct contact with the abysmal facies,suggesting that there were structural changes and stratigraphic erosion near the Fujin-Baoqing-Mishan area.3.The weighted mean age of youngest cluster of 3 zircons ages overlapping in age at 1?(YC1?)from the Nanshuangyashan Formation is 206.8±4.6 Ma(MWSD=0.17),indicate that the maximum depositional age of the Nanshuangyashan Formation was between the Norian and Rhaetian.Sandstone detrital modal analysis indicated the main source area of the Nanshuangyashan Formation was the the recycled orogen source area,and both stable continental blocks and magmatic arcs might provide sediment sources for the Nanshuangyashan Formation.Mudstone geochemistry suggest the Nanshuangyashan Formation samples were mainly derived from the felsic igneous and quartzose sedimentary provenance areas and a few samples might be influenced by rocks from the andesitic arc and the upper crust.The results indicated the western part of the Fujin city is a key area of exploring excellent reservoir.4.13 reservoir rocks from the Nanshuangyashan Formation were analyzed.Results showed that the porosity is between 0.051% and 2.988%,indicating these rocks are ultra-low porosity reservoir.Permeability is between 0.001 Md and 0.006 Md,meaning that rocks are ultra-low permeability reservoir.In conclusion,the reservoir rocks of the Nanshuangyashan Formation are ultra-low porosity and ultra-low permeability reservoir.5.The development characteristics of reservoir from the Nanshuangyashan Formation were affected by many factors,such as sedimentation,provenance,and diagenesis.Compaction,pressure solution,cementation,and recrystallization can reduce porosity and damage the reservoir,and dissolution played an important role in reservoir construction.