Characteristics of Chang-8 Oil Reservoir and Distribution of Oil Reservoirs in Maling Oilfield,Ordos Basin

Chang-8 member of upper Triassic Yanchang Formation in the Maling oilfield of Ordos basin is an important supplementary target for oil exploration and exploitation in the future.The top of Chang-8 oil reservoirs with low permeability and porosity is mainly composed of sandstones,considered as low and ultra-low permeability reservoir.The reservoir is largely distributed in the sites of underwater distributary channel development.During diagenesis process,the dissolution improved obviously the physical property of reservoir.Chang-8 oil reservoirs are mainly distributed in the underwater distributary channels or their flank having sandstone development,with relatively good physical property of reservoir.Meanwhile,there is a positive correlation between saturation and solution pore of reservoir,indicating that the formation of Chang-8 oil reservoir would be closely related with distribution and property of sandstone reservoirs.Sand body of underwater distributary channel of delta front is near the oil source rocks and surrounded by both sides of mudstone.Thus,the underwater distributary channel is the favorable facies belt for oil accumualtion.