多孔介质内流体扩散系数的计算方法

Calculation of Fluid Diffusion Coefficient in Porous Medium

岩心内流体的扩散系数可由传质扩散方程推出解析解,但其需要实验提供一定数量的质量浓度值(关键的基础参数)。由于常规实验获取到的流体量较少,使扩散系数的计算受到制约。建立了传质扩散的一维数学模型,提出了数值模拟和实验相结合的方法,只需一次测量较多体积的流体的平均质量浓度,通过调整拟合即可求出扩散系数。模拟结果表明,扩散系数受流体质量浓度、类型、流速和岩石渗透率等因素的影响。对于溶液而言,扩散系数在一定范围内的变化对流体质量浓度分布影响很小,故通常可假设扩散系数为常数。

The fluid diffusion coefficient in core can be deduced from the mass diffusion equation, but some mass concentration as a key basic parameter of fluid should be obtained in core lab. The calculation of fluid diffusion coefficient is restricted for little volume of the fluid by conventional core test, so one-dimensional mathematical model of mass transfer diffusion is developed, and method of combining numerical simulation with experimental result is put forward. With this method, just one-time measurement of the average mass concentration of high volume of fluid is conducted, followed by tuning and match, the diffusion coefficient is offered. The modeling result shows that the proper diffusion coefficient is influenced by mass concentration, type, flowing velocity of fluid and rock permeability, etc. But the limit-range change of a solution diffusion coefficient has little effect on the distribution of fluid mass concentration. For this reason, the diffusion coefficient is normally assumed to be a constant.