Heyangshan Oil Area,Wuqi Oilfield,Ordos Basin Study On Characteristics And Evaluation Of Chang 4+5 Reservoir Of Triassic Yanchang Formation

Reservoir is an important factor to control the distribution and enrichment of oil and gas reservoirs.Reservoir evaluation is an important link in oil and gas exploration.The results of reservoir evaluation will directly affect the effect of oil and gas reservoir development.Heyangshan oil area in Wuqi oilfield is located in the middle and western part of Yishan slope.Chang 4+5 reservoir is one of the reservoirs with great development potential in the study area.With the deepening of Chang 4+5 reservoir exploration,there is a lack of comprehensive understanding of reservoirs in the study area.Therefore,it is necessary to further analyze and study the reservoir characteristics and reservoir evaluation of Chang 4+5 reservoir in this area,so as to provide reference for further exploration and development of Chang 4+5 reservoir in this area.Guided by the disciplines of petroleum geology,sedimentology,and petrology,the paper analyzes well logs,core observations,and physical properties,and combines common thin slices,prayer slices,scanning electron microscopy,and X-ray diffraction to analyze the test.The sand body,sedimentary facies,reservoir physical properties,reservoir microscopic characteristics and diagenesis of the 4+5 interval are studied,and the influencing factors of the reservoir are analyzed.Finally,the 4+5 reservoirs in the study area are comprehensively evaluated.The structure of Chang 4+5 reservoir in the study area is basically similar to that of northern Ordos.It is a gentle westward inclined monoclinic structure with a nasal structure formed by differential compaction.The Chang 4+5 reservoir in Heyangshan oil area of Wuqi develops delta front subfacies,in which the underwater distributary channel develops from northeast to southwest,which is the main reservoir sand body in the study area.The lithology of Chang 4+5 reservoir group is dominated by feldspar sandstone,quartz and feldspar account for a large proportion of the clastic composition,chlorite and calcite are the main components of the fillings,and pore cementation is the main form of cementation.The Chang 4+5 reservoir in the study area mainly develops intergranular pore,feldspar solution pore and intragranular solution pore.Chang 4+5 reservoir has a porosity of3.9%¹6.3%and permeability of 0.02¹4.54×10^-3um²,which generally belongs to low-porosity,ultra-low-porosity and ultra-low-permeability reservoirs.Chang 4+5 reservoir has strong heterogeneity.The main diagenesis in the study area includes compaction,cementation,metasomatism and dissolution.The main influencing factors of Chang 4+5 reservoir in the study area include sedimentary environment and diagenesis.In the reservoir,the physical properties of sand body are controlled by sedimentary facies,and the content of fillings is negatively correlated with physical properties.The average particle size of clastic particles is positively correlated with physical properties.The occurrence of dissolution plays a positive role in reservoir physical properties.Based on the analysis of reservoir controlling factors and combined with the parameters of reservoir sedimentary facies,reservoir lithology,reservoir physical properties and diagenesis,the reservoirs in the study area are comprehensively evaluated.The reservoirs of type II and III are mainly developed in Chang 4+5 reservoir,and type I reservoirs are developed in the underwater distributary channels in the northwest and east of the study area.