| The fine-grained sandstone of Shanxi formation in Ordos Basin is the tackling experimental target and risk exploration target of Upper Paleozoic natural gas exploration.The exploration and prediction of fine-grained sandstone reservoirs are severely restricted by the characteristics of various petrological characteristics,lithologic combination types,remarkable differences in pore-throat structure,poor reservoir physical property and complex gas-water relationship.Taking the fine-grained sandstone reservoir of Shanxi formation in Zizhou area of northern Shaanxi as the study object,this dissertation carried out petrological,pore-throat structure characteristics,porous media flow mechanism in the reservoir,reservoir cause-control and reservoir evaluation study.The following main results and insights were achieved:The lithological characteristics of the fine-grained sandstone reservoir in Shanxi formation were studied,the depositional control mode of the fine-grained sandstone reservoir was clearly explored,and the source-storage combination mode of the reservoir in Shanxi formation was summarized.The fine-grained sandstone rock type is quartz arenite-sublitharenite-litharenite,and the rock fragment type is mainly shallow metamorphic soft rock fragments and volcanic rock fragments.The cement is mainly siliceous,clay and carbonate.The fine-grained sandstone reservoir is most strongly modified by compaction and cementation.The source reservoir combination types are: coal-sandstone,coal-mudstone-sandstone and sandstone-mudstone.The pore-throat combination types of the Shanxi formation fine-grained sandstone are delineated,and the sedimentary and diagenetic control mechanism of the porethroat structure of the Shanxi formation fine-grained sandstone were explained.According to the types of pore-throat assemblages,the residual intergranular poreintergranular pore-lamellar throat assemblage(type I),intergranular pore-lamellar throat-tubular throat assemblage(type II)and intergranular pore-tubular throat assemblage(type III)were classified.The content of soft rock fragments in underwater divergent channel fine-grained sandstone is higher than that in divergent channel finegrained sandstone,which influences the pore-throat combination type;rock-forming compaction-collagenases controls the difference of the rock pore-throat combination type,and the soft rock fragments are subject to strong compaction and claycollagenases to form a large number of tube-bound throat channels.The dissertation reveals the binary structure characteristics of fine-grained sandstone pores.The physical properties of fine-grained sandstone reservoir rocks are mainly controlled by the number of small pores and connectivity.The relative bounded fluid output process and geological control mechanism of the fine-grained sandstone reservoir were revealed,and the porous media flow of the fine-grained sandstone reservoir with different pore-throat combinations was evaluated.The movable fluid saturation of sandstone of type I-III pore-throat combination decreases,the average co-infiltration range decreases,the clay mineral content affects the movable fluid content and co-infiltration interval,and the wettability of fine-grained sandstone reservoir is hydrophilic-weakly hydrophilic,which is controlled by quartz and clay mineral content.In the process of effective stress reduction,movable fluids are mainly stored in large pores,and relatively bounded water in small pores is transformed into movable water by effective stress perturbation.The pore-throat combination type from Type I to Type III reservoir decreases the content of movable fluid and the gas water extraction ability becomes poorer.A reservoir evaluation system integrating geological control mechanism and reservoir evaluation parameters is established,and the selection of favorable zones for exploration and development of fine-grained sandstone reservoirs is proposed.Phase control analysis concluded that the distribution of fine-grained sandstone sand body,rock fragment type and lithology combination is controlled by the sedimentary microphase,and can control the physical properties of fine-grained sandstone reservoir,the physical properties of fine-grained sandstone of the diversion channel phase is better than that of the submerged diversion channel and submerged natural dike microphase.Lithologic combination controls the gas content of fine-grained sandstone reservoir,coal-sandstone combination has the best gas content,mudstone-sandstone combination having poor gas content.Through the analytic hierarchy process combined with the ratio scale method to calculate the geological control index and the weight coefficient of reservoir parameters,and the reservoir rating index is obtained.The comprehensive evaluation standard of fine-grained sandstone reservoir in Shanxi formation is established,and the distribution of high-quality reservoir is predicted.This dissertation has 95 figures,21 tables and 175 references... |
