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Simulation of nano-pore structure of shale formations for flow analysis

Simulation and modeling of flow in ultra-tight formations such as shale formation is of great research interest. Flow regimes in shale formation are due to slip flow and Knudsen diffusion and are different from viscous type flow regimes found in other geo-materials such as soils and porous rock. The apparent permeability model is widely adopted to simulate nanoscale pore flow properties. In this research a 3 dimensional nanoscale pore network was used to simulate dynamic gas flow and to determine transient properties of flow regimes. Instead of constant coordination number for each pore, a variable pore sizes and coordination numbers were used that obeyed the normal distribution, and average values are based on real shale reservoir data. The simulated pore network model reflected the low connectivity and anisotropy of shale formations. The simulated gas flow regimes from extracted pore network backbone showed reasonable in real gas flows with many isolated pores in the shale matrix. Results also showed that considering slip flow and Knudsen diffusion regimes, gas mass flux rate significantly increased, especially at lower reservoir pressures. With the decrease of reservoir pressure, slip flow weakened and Knudsen diffusion gradually became dominant flow regime, causing dynamic apparent permeability ratio to increase. The pore throat size directly influenced the Knudsen number based on different pore throat size simulations for mass flux rates for sensitivity analysis where the fingering phenomenon occurred.

Author(s):

Pengwei Zhang    
Tsinghua University
China

Liming Hu    
Tsinghua University
China

Jay Meegoda    
New Jersey Institute of Technology
United States