The Research Of Development Methods Optimization For Extra-low Permeability Reservoir

In China, extra-low permeability reservoirs account for nearly half of low permeability reservoirs, extra-low permeability reservoirs physical properties are poor and bring great difficulties for developing oil fields efficiently. With the development of national economy, the demand of crude oil is growing every year, international crude oil prices remain high and economic possibilities for developing extra-low permeability reservoirs come. Therefore, optimizing the extra-low permeability of reservoir development methods and achieving rational development have an important significance for the development of China's petroleum industry.On the base of researches for current status study of low permeability, through a combination of theoretical research and laboratory experiment, an effective extra-low permeability reservoir development method is summarized. Firstly, the main characteristics, the development measures and the status flow mechanism of low permeability reservoirs are introduced; secondly, through laboratory core flooding experiments, the development characteristics and effect of water, nitrogen and carbon dioxide flooding are analyzed; and then the mathematical models considering treshold pressure gradient are established, the influence of treshold pressure gradient on development characteristics is analyzed, the development characteristics between nitrogen and carbon dioxide injection are compared; combined with laboratory results, the relationship between injection pressure and permeability is calculated under different injection conditions using similar criteria; finally, the development methods under different development conditions are proposed.The results indicates that: during developing extra-low permeability reservoirs,there exists treshold pressure, the minimum threshold pressure and the pseudo threshold pressure increase as the permeability decreases, the presence of the threshold pressure makes displacement efficiency decrease. It can be seen from analysis of the different development methods for low permeability reservoir using laboratory experiments and theoretical calculations: nitrogen flooding injection pressure is greater than carbon dioxide flooding but less than water flooding, displacement efficiency is lower than carbon dioxide flooding but higher than water flooding; In a certain water injection rate pressure condition, there is a minimum permeability boundary for water flooding, the reservoir permeability below the boundary must choose the gas injection development. The research has theory direction for the reasonable development of extra-low permeability reservoir.