Study On The Origin And Evolution Of Sedimentation Unit In Shallow Sand Rock Reservoir

As the area where the land contacts the sea,the coastal shallow sea area has always been one of the hot spots in the field of Geoscience.Discussing the origin and evolution of sedimentation unit has great significance for us to understand the evolution of the land and sea,and to find new oil and gas resources.This thesis takes Qinhuangdao Jiguanshan changlongshan formation of shallow sea sedimentary facies and Qinhuangdao Shandongpu and Beidaihe modern sandy coast as the research object,through the field reconnaissance and samples analysis,divides the coastal sedimentary,analyses their characteristics,as well as summarized the sedimentary model of sandy beach.The Changlongshan formation in Qinhuangdao Jiguanshan is mainly composed of gravel quartz sandstone,quartz sandstone and mudstone.They are generally characterized by high mineral maturity,good separation and high grinding roundness.The formation mainly developed trough cross-bedding,tabular cross-bedding,wavy cross-bedding,herringbone cross-bedding,swash cross-bedding,wave bedding and megaripples.According to their sedimentary characteristics,four facies belts are divided,including the backshore,the foreshore,the nearshore and the transition zone.And seven depositonal units are further divided,including the backshore beach ridge,the foreshore beach,the upper nearshore bar,the middle nearshore bar,the lower nearshore beach,the transition zone and the tidal channel.Because of the different water depth and hydrodynamic condition of each unit,they have different characteristics in mineral composition,distribution of size,sedimentary structure,thickness and sand body geometry characteristics.On the basis of the geomorphology,the depth of water and the mechanism of deposition,the modern sandy coastal environment of Qinhuangdao can be divided into four facies belts: aeolian dune,backshore,foreshore and nearshore.According to the topographic features,the foreshore zone can be divided into the upper foreshore and the lower foreshore,and the nearshore zone can be divided into the upper nearshore,the middle nearshore and the lower nearshore.Based on the analysis of grain-size and mineral components of the sand samples,Qinhuangdao modern sandy coastal sediments are generally characterized by coarse gralarity,good separation,high grinding roundness and high mineral maturity.Comprehensive ancient coastal shallow sea sedimentary facies and sedime ntary characteristics of modern sandy coast,established sedimentary model of coastal shallow sea based on the transgression model.And further analyse the relationship between the formation,reservoir and migration of oil and gas combined with relevant examples.Put forward the accumulation characteristics and exploration direction of the coastal shallow sea facies oil and gas reservoirs.