Studies On Low Permeability Reservoir Characteristics Of The Chang4+5 In Hujianshan Area,the Ordos Basin

Ordos basin is one of the largest continental sedimentary basin in Mesozoic of the central regin in China,Yanchang formation of Upper Triassic in Ordos basin is a major oil and gas department. Hujianshan area locates in the middle east of Shanbei Slope Belt in Ordos basin, and chang4+5 is a mainly oil-bearing segment of Yanchang formation. However, the complexity of its geological features, the varity of its diagenism and the unclear main controling factor of the Reservoir distribution have brought enormous difficulties to the oil development. Based on the information of core, logging data,analysis and production test,etc,This paper Anaysis the distributed characteristics and controling facters of reservoir from the structure,sedimentary facies, reservoir character and diagenism,etc,Aim at clearing the low permeability Reservoir Characteristics and dividing reservoir rang of profitability,to provide technical support to exploration and development.Based on the petrology,sedimentary structures,paleontology and well logging, the sedimentary systems of chang4+5 had braided river delta system, it develops delta plain facies and delta front facies, and then this paper analysis sedimentary microfacies characteristics of the single well and flat. The direction of the river is NE-SW. To sum up, the distributary channel and distributary channel under water are the higt quality sedimentary microfacies.According to a large number of rock cores and rock flakes,we think that the reservoir lithology of Hujianshan area mainly were fine-medium grained lithic feldspathic sandstone and feldspathic sandstone,The main diagenesis of the study area were compaction,pressure solution,cementation,dissolution and metasomatism,the diagenesis had reached late diagenesis A period.Though the analysis of physical property and pore structure,the criteria of reservoir zonation has been established,and reservoir predication has been finished.The study area of Chang4+5 main types of rock porosity were primary intergranular porosity and dissolution porosity,The reservoir porosity was all below 12%,the composition type of pore throat mainly were fine hole micro throat.the porosity and permeability are controlled by sedimentary facies, diagenesis,types of rock and so on,the evaluation criterion of the reservoir heterogeneity is established based on the analysis of permeability heterogeneity,and the reservoir of the study area is high heterogeneous.According to the sendimentary facies, petrology, physical property, heterogeneity and diagenesis,we initially inquire the oil/gas enrichment and distribution of Hujianshan area.We examine the geological analysis above, this paper established the evaluation criterion of reservoir range of profitability,and offer some optimum area of Chang4+5₁ and Chang4+5₂ ,These above provide evidencies for further exploration and exploitation.