Characteristics Of The Chang 8 And Chang 9 Reservoirs In The Pengyang-Hudong Area Of The Ordos Basin

Panyang-Hudong area is located in the southwestern part of Ordos Basin and is rich in oil and gas resources.The complex spreading and poor physical properties of the sand bodies in the Chang 8-Chang 9 reservoir have led to its low development degree.In this paper,we take the Chang 8 and Chang 9 reservoirs in this area as the object of study,based on the theories of sedimentary petrology and petroleum geology,and carry out stratigraphic delineation and comparison of the Chang 8 and Chang9 reservoirs by various methods such as core observation,cast thin section,scanning electron microscopy and mercury-pressure experiment,and systematically study the sedimentary characteristics,lithological characteristics,diagenesis and pore structure of the Chang8 and Chang 9 reservoirs in the Panyang-Hudong area.The results show that:the reservoir quality is influenced by the lithological characteristics,pore structure,etc.,and the comprehensive classification and evaluation of the reservoir is carried out to provide a theoretical basis for the subsequent development of the Chang 8-Chang 9 formation in the Panyang-Hu Dong area.The results show that:（1）The Chang 8 and Chang 9 reservoirs in the study area are shallow water deltaic deposits,divided into delta plain and delta front sedimentary phases,containing sedimentary micro-phases such as divergent channels,submerged divergent channels,estuarine dams and inter-divergent bays.（2）The study area mainly develops rock chip feldspathic sandstone,feldspathic sandstone and feldspathic rock chip sandstone,and the rock particles are mainly gray-green and gray medium to fine sandstone,and the sandstone particles are medium to good rounding.The fillings are mainly chlorite,iron calcite and hydromica,the average content of fillings in the Chang 8 reservoir is about 11.74%,and the content of fillings in the Chang 9 reservoir is less,9.27%.The pore type is mainly intergranular pores,followed by feldspathic pores and rock chip pores.Its average porosity is 8.89%and 13.53%respectively,and its average permeability is 0.245×10^-3μm²and 0.8×10^-3μm².The physical properties of the Chang 9reservoir are better than those of the Chang 8.The pore structure is mainly mesopore-microthroat,and its discharge pressure is small,median pressure is large and median radius is small.（3）Compaction and cementation are the main reasons for the physical deterioration of the reservoir in the study area,and the dissolution pore space produced by dissolution improves the reservoir storage performance.The reservoirs of Chang 8 and Chang 9 in the study area are considered to be in the middle-formation A-B stage,based on the criteria of rock formation stage classification.Combining the sand body spreading characteristics,lithological characteristics and physical characteristics,the Chang 8 and Chang 9 reservoirs in the study area are divided intoⅠ,Ⅱ,ⅢandⅣcategories,among which the Chang 9 section is dominated byⅠandⅡcategory reservoirs and the Chang 8 section is dominated byⅡandⅢcategory reservoirs.The physical properties ofⅠandⅡcategory reservoirs are better,with the average porosity greater than 8%and the average permeability greater than 0.5×10^-3μm²,while the physical properties ofⅢandⅣcategory reservoirs are worse.