Early-middle Jurassic sedimentary facies and its relationship with the hydrocarbon migration and accumulation in Baihe area of Ordos basin

In Baihe area of Ordos basin,Yan'an formation is characterized by gentle stratum,undeveloped structure,small reservoir distribution range and high yield.Aiming at the characteristics,the research on early-middle Jurassic sedimentary facies and its relationship with the hydrocarbon migration and accumulation has been carried out.By using lithology and logging curves,the types of sedimentary facies,the microfacies have been identified and divided.The results indicate Fuxian formation and Yan-10 member belong to braided river sedimentary bodies and developed sedimentary microfacies such as channel sand dam,diara,flood land and river flood swamp.Yan-9 member belongs to delta plain sedimentary system and developed sedimentary microfacies such as distributary channel and distributary bay.At the same time,based on the residual strata thickness distribution of Chang-1 and Chang-2,the ancient landform characteristics of the Jurassic have been restored.Studies have shown that thick sand layer of Fuxian formation was pressure relief opening of lower overpressure and acted as migration channel.Mainly controlled by sedimentary facies,channel sand bodies of Yan-10 and Yan-9 reservoir are of favorable sedimentary facies belt for oil and gas enrichment,with delta plain coal swamp acting as its good cap rock.