基于数字岩心技术的气体解析/扩散格子Boltzmann模拟

在页岩气和煤层气等非常规储层中普遍存在着气体解析/扩散现象,为了描述微观尺度下的流动模拟,通过在格子Boltzmann方法的演化方程中添加源汇项,模拟了多孔介质中的解析/扩散现象。并以Langmuir等温吸附定律为例进行模拟,模型计算结果与宏观扩散方程的有限差分结果基本一致,但有限差分方法对时间步长要求较高,计算量比格子Boltzmann方法大,格子Boltzmann方法在迭代次数上具有明显的优势。最后基于CT扫描的二维数字岩心,模拟了气体在复杂结构多孔介质中气体解析/扩散过程。这种处理方式避免了复杂的边界条件,计算量不会明显增加,并可以用来模拟具有复杂孔隙结构的真实岩心中的解析/扩散现象,同时可以根据不同储层中气体满足的解析/吸附规律来配置源汇项。

Lattice Boltzmann simulation of gas desorption and diffusion based on digital core technology

Gas desorption and diffusion phenomenon widely exists in unconventional reservoirs such as shale gas and coalbed methane. In order to describe the flow simulation on a micro-scale, a source-sink term is added to evolution equation of the lattice Boltzmann method, so as to simulate gas desorption and diffusion phenomenon in porous media. Meanwhile, Langmuir isothermal adsorption is taken as a case for simulation. The model calculation results are basically consistent with the finite difference results of macro diffusion equation. However, the finite difference method has a higher requirement for time step with more calculated amount than the lattice Boltzmann method. The latter method has a significant advantage in iterations. Finally, 2D digital core based on CT scanning was used to simulate gas desorption and diffusion process in porous media with complex structure. This processing method is able to avoid complex boundary conditions, and the calculated amount will not increase significantly, but can be used to simulate gas desorption and diffusion phenomenon in real cores with complex porous structure. In the meantime, a source-sink term can be configured according to gas desorption and diffusion laws in different reservoirs.