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查明煤层气井排采过程中动水孔隙度的变化规律能为产水量准确预测、排采工作制度合理制定提供依据。借助复变函数理论和弹塑性力学理论,构建了原始状态不同裂隙展布下储层应力分布的数理模型;结合损伤理论、有效应力原理以及结构变形理论,构建了排采过程中应力与结构的损伤动态演化模型;基于水运移平衡条件以及储层孔裂隙展布规律,耦合应力、结构变形损伤作用,构建了单相水流阶段动水孔隙度的数理模型。以沁水盆地樊庄区块为例,计算得出:当裂隙宽度为0.1μm左右时,裂隙周围应力、结构损伤加剧,相关研究佐证了这一结论。随着排采的进行,储层压力的降低,动水孔隙度呈指数形式减小并最终趋于稳定。随孔隙度的增大呈线性增大;随尺寸较小的裂隙比例增大呈线性降低。
It can provide the basis for the accurate prediction of water production and the reasonable drafting of discharge working system by ascertaining the variation law of dynamic water porosity in the process of CBM well drainage. With the help of the theory of complex functions and the theory of elasto-plastic mechanics, the mathematical model of the reservoir stress distribution under different fractures in the original state is constructed. Combined with the damage theory, the effective stress principle and the theory of structural deformation, the stress and structural damage Dynamic evolution model. Based on the equilibrium conditions of water migration as well as the fracture distribution of reservoir pores, coupled stress and structural deformation damage, a mathematical model of dynamic water porosity in single-phase water flow stage was constructed. Taking Fanzhuang block in Qinshui Basin as an example, it is calculated that the stress and structural damage around crack are aggravated when the crack width is about 0.1μm, which is proved by relevant research. With the progress of extraction and reservoir pressure reduction, the dynamic water porosity decreases exponentially and eventually stabilizes. It increases linearly with the increase of porosity, and decreases linearly with the increase of porosity with smaller size.