Evaluation Of Reservoir Section 6^th Of Upper Triassic Yanchang Formation In Hujianshan Area, Ordos Basin

The reservoir in Ordos basin is a typical low–porosity and permeability one in our country,The chang 6 section of Yanchang Formation,Upper Triassic is the most important oil-bearing layer in Ordos basin. the sedimentary environment is delta deposit, and the sand bodies in the submerged delta frontier are very rich.This paper focus on the reservoir’s macrofeature and microscopic feature of the chang 6 section in Hujianshan area, Including the sand reservoir’s characteristics of petrology、diagenesis, the four characteristics of reservoir （lithologic、electric、physical and oil saturation）、pores type、pores textures and so on. We especially analysis the reservoir’s heterogeneity.At last we use both qualitative and quantitative methods to evaluate the reservoir.All that aims to supply reference for the study of oil and gas accumulation rules.Sand bodies develop from northeast to southwest. The plane distribution of shale content、porosity and permeability is the same with the sand distribution, generally, sand bodies are thick, and the physical properties are good in underwater distributary channel; the ones in the interchannel are contrary. On the basis of physical property reference , we include that porosity is from 7% to 17%,permeability is from 0.1×10^-3 to 1.5×10^-3 um².The porosity and permeability decrease from chang 6₁,chang 6₂ to chang 6₃.The reservoir’s plane heterogeneity is controlled by the sedimentary facies. The strong heterogeneity mainly distribute to the sandbody of underwater distributary channel, the heterogeneity of the channel margin is weak, and the heterogeneity of the interchannel is the weakest. On the low permeability reservoir background, the relative high permeability areas with thick sand bodies are sometimes the enriched oil sites.The chang 6 section of Hujianshan area mainly comprise feldspathic sandstone and partly litharenite sandstone. The psephicty is mianly subangular, the gradation is from mederate to good, the feldspathic weathering is moderate. The cementation types are mainly contaction and pores.The pores types are mainly intergranular pores ,the second is intercrystal pores、feldspathic dissolution pores、litharenite dissolution pores、laumontic dissolution pores and micropores. The devoloment of dissolution pores controls the second pores in Hujianshan area. The main diagenesis in this area include the compaction、cemetation、dissolution、metasomatosis and rejuvenation of crystals diagenetic satage is late-diagenesis.In this paper we select six parameters which have great influence to the reservoir to quantitatively evaluate the reservoir. At last ,we include that there are three types of reservoir formation.the type of I and II are the favorable ones ,type I mainly distributes in the southwest underwater distributary channel , type II mainly distributes in the channel margin.