| The Linhe depression of Hetao basin is an important area for oil and gas exploration,which is concerned by the people all the time.There are 6 wells of 11 to be seen oil display in this district but no industrial value.Because of the early drilling wells mainly located in the southeast of the research area,which are used to study the characteristics of lithology,sedimentary facies,resource rocks,reservoir and cap of target intervals in this area,precision and accuracy is limited.In this paper,mainly based on the data of L1 well,which was drilled in 2014 and is located in in the middle of the study area,combining with the other wells'data and seismic data,applying to the techniques of core observation,analysis and determination of samples,ECS data lithology identification,paleo-structural restoration and comprehensive research,characteristics of Linhe formation lithology,lithofacies and source-reservoir-seal rocks in Linhe Depression are discussed in detail.The results are as follows:1.This text uses two lithological division methods to study characteristics of Linhe formation lithology in L1 well.First,using ECS data and new lithology interpretation method(by this method carbonate rocks can be identifyed effectively),which are based on the content of mineral composition,the results show that the Oligocene Linhe formation is mainly composed of quartz-clastic and complex,some of feldspar-clastic,carbonate and gypsiferous sedimentary rock.Second,according to traditional lithology divided(clastic rocks are based on particle size,carbonate rocks are based on the content of mineral).the results show that the Linhe formation is composed of mudstone,silty mudstone,gypsiferous mudstone,dolomitic mudstone,siltstone,fine sandstone,medium to coarse sandstone and fine gravel-bearing coarse sandstone.2.According to characteristics of pollen,trace element and lithology,the Linhe formation of L1 well were were generated in drought,semi-salty-salty and strong reducing sedimentary environment.Sedimentary facies of Linhe formation in Linhe depression mainly include semi-deep lake,shallow lake,shore shallow lake-delta plain facies and the existence of charcoal grey fine carbonate demonstates that there are a large range of semi-deep lake facies on the plane.From L1 well to its northwest district,the mudstone is more thickening and seismic reflector continuity is better,which reflect that it is deeper sedimentary facies in the northwest district of L1 well.3.The Linhe formation source rocks of L1 well are mainly charcoal grey,grey mudstones and based on the content of mineral composition,they are complex,clay,carbonate and fine quartz-clastic rocks.The total thickness of the Linhe formation source rocks is 235 m with the average and maximum single layer thickness of 2.43m and 12m,which is 25.74%of formation thickness.According to the geochemical analysis data of 56 oligocene source rocks in Ll well,the source rocks of Linhe formation are mainly in the range of type II and type I,with high abundance(organic carbon content up to 4.09%)and Ro between 0.76%and 1.06%.Combining with the characteristics of sedimentary facies and subsidence,it is indicated that the source rocks in the northwest district of L1 well have larger abundance of organic matter,better type,higher maturity and thicker layer.4.According to mechanical properties of rock,The change of Cenozoic sedimentary rocks of Linhe fornation in Linhe depression is divided into three stages of plastic compaction,elastic-plastic compression segment and rupture sectioa.Now the main body of Oligocene Linhe formation sedimentary rocks are in rupture section with medium-high permeability porosity sandstone reservoir,fractured mudstone reservoir and fracture-reconstruction mudstone cap.the main body of Miocene sedimentary rocks are in elastic-plastic compression segment with porosity sandstone reservoir and a large range of porosity mudstone cap.The main body of Pliocene sedimentary rocks are in plastic compaction with porosity sandstone reservoir and a few porosity mudstone cap.5.After comprehensive researching on source-reservoir-cap,structure and buried characteristics,it is concluded that the next exploration of Linhe depression should be around HangHou fault located in northwest of L1 well,which is next to favorable source area and can form two source-reservoir-seal assemblages of "self-generation and self-storage(Linhe formation-generation,Linhe formation-storage”and "lower-generation and upper storage(Linhe formation-generation,Miocene and Pliocene-storage)". |
PDF Full Text Request