Reservoir And Cap Rock Characteristics Of Yanchang Formation In Triassic And Its Effect On The Oil Accumulation At The North Of Zhifang-shunning Block Of The Ordos Basin

The north of Zhifang-Shunning Block located in central Shaanxi slope in Ordos basin,formation is a pour sloping in the west as a whole,develop some low amplitude nose fold structures.The paper aim at YanChang formation in Triassic,used theory of sedimentology,oil geology,and reservoir geology and logging,with drill,and logging,rock logging,and well test and producing test data,and combination with multiple test method and the analysis means,researched formation,structure,characteristic of reservoir with type and distribution of micro-facies.The research shows that YanChang formationis delta front deposition that divided into facies of distributary channel,shunt Bay,mouth bar and sheet sand.The research indicates that lithology of reservoirs are mainly powder to finegrain,fine grain arcose sandstone with low compositional maturity and higher texturalmaturity.YanChang reservoirs experience strong diagenesis that included machinery compactionpressure solution,cementation,filling,and dissolution,metasomatosis and deposition of authigenic clay mineral,are typical reservoir with low-porosity and ultra low permeability.Pore type main with residual intergranular pore,dissolved pore,intercrystalline pore,and microfissure.YanChang reservoirs are classified and evaluated by the above data.Cap Rock is mudstone seal,the mainly sealing mechanism is capillary sealing.The oil-bearing factors of reservoirs are mainly controlled by the sand-body distribution of the sedimentary facies and thickness of sand bodies,as well as reservoir physical property and cap rock.