Reservoir Characteristics Of The Frist Member Of Nantun Formation In Tanan Depression

Tanan depression is a subordinated structure unit located in the south of central rift zone in Hailer- Tamtsag Basin of the Mongolia part.For the last few years,the area had displayed good oil prospect in the formation,and became the dominated oil reservoir of the depression. For it's proximal deposit and complicated tectonic background,formation had hybrid sedimentation.That restrict the further prospection.The article made fully use of seismic date,such as logging information,core date,and so on,to study the lithologic character,diagenesis character.Using these results, we at last derived the horizontal distribution of the profitable areas of reservoir.The dominationg lithology of the formation was detrital rock and pyroclastic sedimentary rock.The formation had low compositional maturity.The detrital rock content feldspathic sandstone,feldspathic lithic sandstone,lithic sandstone,this made the precondition for corrosion.Secondary pore as the main reserving space of the formation,and the mercury intrusion data showed the structure of the reservoir pore was bad,medium and good only 23.51% .Low porosity and low permeability took main part of porosity-permeability distribution.Vertically the formation had two high porosity zones,and on the plane the higher porosity zone were centralized the west and middle structural belt;the west structural belt has bore the highest pore area.The permeability submited to the same regularity.In the target stratum, compaction,cementaction,metasomatism,corrosion were the most important diagenesis facters,the frist three lower the porosity and permeability of the formation called destructive diagenesis,but the last one extended the reserving space,called constructive diagenesis.The former deleloped in a wide range,but corrosion only concentrated around source rock.For the moment ,the formation in A period of middle diagenesis stage and small fraction in B. In the distribution of sedimentary facies,solutional phase distributed along braided delta plain and braided delta front.Aticle aggregate well logging,observed by microscope,geochemistry data,and acquired that the main controlling factors of high-quality reservoir distribution was hydrocarbon kitchen,sedimentary facies,organic content,antithetic fault and plane of unconformity.Combant the overall factors,found that the best sedimentary facies for high-quality reservoir were braided delta plain and braided delta front,tuffaceous corrasion and feldspar corrosion were common in high-quality reservoir.