Ordos Basin,Low Permeability Reservoir Characteristics And Productivity Analysis

With the penetration of hydrocarbon exploration in Jiyuan Oil Field, the proportion of low-permeability reservoir has shown an increasing trend. However, the confusion of the microscopic geological conditions, the oil reservoir distribution laws, the reservoir heterogeneity, the way how water and oil distributed, the relatively high permeability zone, the injection-production pressure and reservoir pressure has influenced the path, effectivity and technical skill of the water-oil replacement, which could limit the stable and high production. Fine reservoir description in Yuan 214 region Chang 213 was carried out in order to meet the need of the enterprise and society. The profound study of the reservoir comprehensive characteristics has compared with the production performance, additionally, the coupling relations among the influencing factors of reservoir micropore features has been characterized qualitatively and quantitatively in order to improve the development effect as well as recovery efficiency, and to provide a reliable theory and technic support which the oil field could depend on in future development. The results of this study which are from the understanding of geological characteristics and micro geological features can be expressed as follows.1. The main lithology of Jiyuan Oil Field Chang 213 tight sandstone reservoir is arkoses, locally can see lithic feldspar sandstone. The composition maturity is low with a high content of feldspar and a low content of quartz. The main cement are kaolinite and chlorite while siliceous cement and carbonate cement account for only a small amount in the study area. The average porosity and permeability are 14.5%,5.7×10-3?m2 respectively?2. Jiyuan Oil Field Chang 213 reservoir has developed a variety of diagenetic facies. The diagenesis types and strength have the decisive effect to the reservoir property. The compaction and pressure solution are the main process which caused the reservoir become vertical tight. Diagenetic stage of Chang 213 reservoir should be A stage. The 4% surface porosity was used as the diagenetic facies naming boundary, combined with pore types and cement content to give five diagenetic combination types.3. The pore structure types are mostly large pore, medium to fine throat. Diagenesis has controlled the reserving capability and seepage ability by controlling the development of the pore and throat. The minimum radius of pore and throat for flowing is 0.052?m. Different diagenetic facies will cause different pore structure complexities.4. The high pressure mercury experiment has indicated that there are 4 types of the pore structures in the study area. Pore types in different pore structures are different. Chlorite cementation and residual intergranular pore has largely occupied the type ?. The type ? and ?capillary pressure curves also can be observed in the study area. Type ? is invalid reservoir.5. According to the constant-rate mercury injection experiment there are 3 oil-water occurrence area, a). Throat-dominated (water rich zone), b). Both controlled (oil and water coexistence zone), c). pore-dominated (oil rich zone). The difference of the permeability contribution in oil and water coexistence zone is the main reason for oil-water differential degree inconsistency in different reservoir.6. On the basis of reservoir structure and diagenesis facies, the porosity and permeability of oil layers, oil and water layers are over 11%,0.4× 10-3 ?m2 respectively. Oil saturation in oil layers is over 45%, it is from 36% to 45% in oil and water layers and less than 36% in water layers. The electrical resistivity of oil layers and oil and water layers are over RT=-0.067*AC+23.33. But it still can meet the exploit need when the AC is higher than 245?s/m and RT is higher than 3.3?·m.7. The reservoir had been classified into four types using custering methodology. Reference sequence was associated and characteristic parameter was selected, besides, the test oil yield was also taken into consideration. Type I sand was well developed and have a large effective thickness. This kind of reservoir possesses high quality parameters so that the physical property as well as oil-bearing strata performs well, but the area of it is very limit. Type ? and ? have a medium developed sand and medium physical property and it getting worse successively, the effective thickness is medium. Type ? and ? have account for a large amount of the whole area. Type IV has the worst sand connectivity, porosity and permeability, the area of this type is the smallest.