| Gas reservoir with less permeability and tight sandstone has low productivity in wells and strong sensitivity, which is caused by its complex micro-pore structure. The aim of this work is to study the micro-structue of the low permeability and tight sandstone and its impact on gas production. Based upon the analyzes and experimental results of gas-water displacement in microscopic model of real sandstone, gas-water relative permeability and sensitivity test, core observation, identification of casting tin sections, electron scan microscope (ESM), mercury injection in high pressure and controlled rate, four aspects contents, which conclude the characteristics of rock, influence factor of gas production, pore structure and the relationship between sensitivity and micro-pore texture, are studied in Low permeability sandstone and Tight gas reservoir of the Ordos Basin. And then following results are obtained:(1) Types and compositional maturity of low permeability tight sandstone gas reservoir rock is affected by provenance and depositional enviromental obviously. The compositional maturity and rate of quartz sandstone in Shan2 formation, which lies in high-energy and clear water enviroment, is higher than that in He8 & Shanl formation, which lies in turbid water and low-energy water enviroment. The rate of quartz and compositional is increasing along the flow direction, and that in the western part is higher than that in the eastern part of gas pool in basin.(2) For the type and structure of pore is affected by compositional maturity and diagenisis, so the pore type is variegated, especially the dissolution pore is the most important type. The characteristics of micro-pore structure are divided into four types, typeⅠtoⅣ, and each type has its own pore types and pore structure. From typeⅠtoⅢ, the pore texture became worse, with the similar radius of pores, but the radius of throats become thinner. While the distribution of pores and throats in type IV is different from the three types.(3) The fractal dimension and feature is variegated. Fractal dimension has a very good correlation with the separation factor and the maximum saturation of mercury invasion, while no significant correlation with the characteristic parameters of pore size is found. The distribution of pore throat, which is variegated also, can be used to evaluate the value of porosity and permeability qualitatively.(4) Reservoir’s sensitive degree of water and pressure is close tied up with micro-pore structure, and it becoming seriously with the pore structure becomes poor. The radius of main flow room and big pore throat room increasing after acidulations, and the best effect is proved by clay acid treatment.(5) The specific rule of gas-water percolation and potential damage factors are decided by micro-pore structure. For production model has an impact on gas well perforation, which becoming obviously with the pore structure goes poor, so specific production mode is drawn. The proper production pressure differential is about 5MPa in He8 & Shanl formation and less than lOMPa in Shan2 formation, which can remove water locking and prevent water breakthrough. To produce the gas trapped near wellbore area, the measures of recovery gas by discharge water should be adopted according to the type of micro pore structure. The strategy of well opening and shutting frequently, made the pressure-sensitive and water-blocking effect more serious, and made the seepage character and distribution of water-gas more complex, should be avoided. |
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