Quantitative Evaluation Of Ultra-low Permeability Tight Oil Reservoir

The Chang 6 reservoir in the Z area of the Ordos Basin is a typical tight oil reservoir.Based on the basic geological data,logging data,and experimental data such as casting thin sections,SEM and rock mechanical tests,we have studied the sedimentary characteristics,diagenesis characteristics,sandbodies distribution characteristics and reservoir characteristics of tight oil reservoirs in Z area.The causes of reservoir compaction are discussed.The results show that the Chang 6 reservoir in the study area mainly develops underwater distributary channels,subsea natural barrier,and interdistributary bay.Among them,the underwater distributary channel have better physical properties,and the interdistributary bay have the worst physical properties.The structure is complex,the seepage capacity is poor,and the permeability is mainly distributed in 0.25?3×10-3?m2.The compaction and cementation are strong,which is the main controlling factor of physical property of ultra-low permeability reservoir.Comparative development of the dissolution make physical properties of the reservoir are better.According to the characteristics of the tight oil reservoir in the study area,six quantitative evaluation parameters were selected:average throat radius,mobile fluid index,starting pressure gradient,reservoir brittleness index,formation pressure coefficient,and clay mineral content.According to the selected six ev.aluation parameters,the six-element classification coefficient method is selected,and six quantitative evaluation parameters are fitted to obtain quantitative comprehensive evaluation parameters.The reservoirs are divided into ?,? and ?reservoirs according to the classification evaluation limits.Among them,the first and second type reservoirs are reservoirs with development value,which are mainly developed in the Chang 61-2 and the Chang 62 layers and distributed in a sheet or spot shape.