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

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.