Abstract
To investigate the gas flow characteristics in tight porous media, a microscale lattice Boltzmann (LB) model with the regularization procedure is firstly adopted to simulate gas flow in three-dimensional (3D) digital rocks. A shale digital rock and a sandstone digital rock are reconstructed to study the effects of pressure, temperature and pore size on microscale gas flow. The simulation results show that because of the microscale effect in tight porous media, the apparent permeability is always higher than the intrinsic permeability, and with the decrease of pressure or pore size, or with the increase of temperature, the difference between apparent permeability and intrinsic permeability increases. In addition, the Knudsen numbers under different conditions are calculated and the results show that gas flow characteristics in the digital rocks under different Knudsen numbers are quite different. With the increase of Knudsen number, gas flow in the digital rocks becomes more uniform and the effect of heterogeneity of the porous media on gas flow decreases. Finally, two commonly used apparent permeability calculation models are evaluated by the simulation results and the Klinkenberg model shows better accuracy. In addition, a better proportionality factor in Klinkenberg model is proposed according to the simulation results.
Highlights
With the development of advanced techniques such as horizontal drilling and multi-stage hydraulic fracturing, unconventional oil and gas resources are drawing more and more attention all over the world
The shale digital rock is reconstructed by Markov Chain Monte Carlo (MCMC) method based on the scanning electron microscope (SEM) scanning image shown in Fig. 1(a) and it is adopted to study the effect of pressure and temperature on microscale gas flow
As this work mainly focuses on the microscale gas flow characteristics in tight porous media, the effect of kerogen is not taken into account here
Summary
With the development of advanced techniques such as horizontal drilling and multi-stage hydraulic fracturing, unconventional oil and gas resources are drawing more and more attention all over the world. Some other researchers adopted LBM to simulate gas flow in microscale porous media[28,29,30], the geometries of their physical models are simple compared with the real rocks They didn’t take the regularization procedure into account in their models. They simulated the viscous flow and Knudsen diffusion separately with different LB models and the total mass flux can be considered as a combined result of viscous flow and Knudsen diffusion This model can be used to simulate microscale gas flow in real digital rocks under any Knudsen numbers, it is not based on the kinetic theory and it could not obtain the detailed velocity distributions in the porous media. As this work mainly focuses on the gas flow characteristics in microscale porous media, the common microscale LB model is adopted here
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