Reservoir Characteristics of Member 4+5 & 6 of Yangchang Formation from Upper Triassic in Hujianshan Area,Ordos Basin and Their Relationship with Oil Accumulation

From the reservoir geological characteristics,rock composition and diagenesis,physical properties,pore types and so on,this paper analyzes the particularity of sandstone reservoirs in the member 6 to the member 4+5 of the upper Triassic Yanchang Formation from the Hujianshan area of Ordos basin,and discusses the reservoir characteristics and their relationship with oil accumulation.The sand body with strong heterogeneity develops in submarine distributary channel of delta front.The sandstones are mainly feldspathic lithic fine sandstone with strong diagenesis and low physical property values as a whole.Most of the reservoirs are low porosity and low permeability-tight and the effective pore types are mainly intergranular pore,dissolution pore and intracrystalline pore.Oil accumulates in the reservoir layers with different physical properties and many aquifers have high porosity and permeability.So reservoir characteristics itself can not afford a decisive role in the petroleum gathering.There must have a good assemblage of higher physical property value reservoir,conduct pathway and oil surce can form oil pool.