AGER推荐文章--网络模型基础上流体流变学特征和孔隙连通性对岩石渗透率的影响分析

vlambda
2020-04-06

AGER推荐文章--网络模型基础上流体流变学特征和孔隙连通性对岩石渗透率的影响分析

AGER

Advances in Geo-Energy Research

推荐文章

网络模型基础上流体流变学特征和孔隙连通性对岩石渗透率的影响分析

摘要

渗透率是地球物理学中一个重要的岩石属性。达西定律假定一个具有常值的稳定渗透率。然而，近年来的研究表明，流体粘度和孔隙几何形状对渗透率的影响不容忽视。

近日，清华大学孙卫涛副研究员团队考虑一个三维孔隙网络中受谐波振荡影响的的麦克斯韦流体。孔隙网络是通过Voronoi图创建的，具有更为真实的连接关系。文章模拟了聚乙烯氧化物(PEO)、十六烷基吡啶氯和水杨酸钠溶液(CPyCl/NaSal)的渗透率。结果表明，当频率小于几千赫兹时，渗透率是恒定的，当频率增长趋于无穷大时，渗透率迅速降低到极低值。在特定频率观察到了麦克斯韦流体的渗透率变化峰值。此外，我们发现流体在低频时主要在稀疏大孔隙网络中流动，而在高频时则以稠密小孔隙网络为主要通道。麦克斯韦流体的渗透率峰值与特定的平均配位数(MCN)相关，这表明存在最优的网络连接水平，在这种连接关系下流体流动变得更容易。这些结果对于理解天然储层岩石中的流体流动起到了关键作用。渗透率变化受频率、流体流变学属性和孔隙连通性的影响，能够反映储层流体性质和孔隙网络结构的关键信息。结果表明，达西静态渗透率能否应用于高频范围是值得怀疑的。

Effects of Fluid Rheology and Pore Connectivity on Rock Permeability Based on a Network Model

Fansheng Xiong, Weitao Sun, Jing Ba, Jose M. Carione

Abstract

Permeability is an important rock property in exploration geophysics. Darcy's law assumes a steady‐state regime and constant permeability. However, recent studies showed that the effects of fluid viscosity and pore geometry on permeability cannot be neglected. The periodic variation of pore fluid pressure gradient due to elastic wave propagation induces the oscillated fluid flow. We consider a Maxwell fluid in a 3‐D pore network subject to harmonic oscillations. The network is based on the Voronoi method, which provides a realistic connectivity. The permeability of polyethylene oxide and cetylpyridinium chloride and sodium salicylate solution have been simulated. The results show that permeability is constant at frequencies less than several kHz and rapidly decreases to extremely low values as frequency tends to infinite. In addition, we find that fluid mainly flows in sparse‐large pore networks at low frequencies and in dense‐small pore networks at high frequencies. The Maxwell fluid shows significant permeability peaks related to the mean coordination number, indicating that there exists an optimal network connectivity at which fluid flow is maximum. These results have been central to understand how fluid flows in natural reservoir rocks. The permeability variations versus frequency, fluid rheology, and pore connectivity provide key information of reservoir fluid properties and pore network structure. The results indicate that it is questionable whether Darcy static permeability can be applied at high frequencies.

AGER推荐文章--网络模型基础上流体流变学特征和孔隙连通性对岩石渗透率的影响分析

Figure 1. Equivalent random network with pore‐throat structure. The color from blue to red indicates a transition from small to large size/radius of the pore/throat.

Figure 12. Permeability as a function of MCN(z value) at different frequencies for a Maxwell fluid. The open circles are the numerical results, and the dashed line is a fitting curve of the power model (for a) and Gaussian model (for b to d). (a) At low frequencies (10 Hz), permeability decreases as z increases from a small value (sparse‐large‐pore network) to large z (dense‐small‐pore network). (b) At intermediate frequencies (9 kHz), permeability is comparable in networks with small and large z. Two peaks appear at MCN around 9.7 and 10.6. (c) Permeability in dense‐small‐pore network (large z) exceeds that of the sparse‐large‐pore network (small z) at 10 kHz. (d) At high frequencies (100 kHz), the permeability in dense‐small‐pore network becomes dominant (peak at z = 10.9), but the magnitude is much lower than that at low frequencies.