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Effects of micro-fractures on gas flow in tight porous media
ZHAO Jianlin1, YAO Jun1, ZHANG Lei1, YANG Yongfei1, SUN Hai1, SUN Zhixue1, BAI Yuhu2
(1.School of Petroleum Engineering in China University of Petroleum, Qingdao 266580, China;2.CNOOC Research Institute, Beijing 100028, China)
Abstract:
In this paper, a microscale lattice Boltzmann (LB) model with a regularization procedure was adopted to investigate the effects of micro-fractures on gas flow in tight porous media. By adopting a diffuse reflection boundary condition and the regularization procedure, the microscale LB model was established, which is suitable to simulate gas flow in porous media with high Knudsen numbers. The mechanisms of gas flow in fractured tight porous media were also analyzed. Finally, a parallel slit pore model was established to investigate the influencing mechanisms of micro-fractures on gas flow in tight porous media.The simulation results show that the micro-fractures can significantly improve the permeability of the tight porous media and the effects of interconnected micro-fractures are more obvious. With the increase of pressure, the effects of micro-fractures increase, and the effects of micro-fractures tend to be stable at both high pressure and low pressure conditions. With the decrease of pressure, the difference of gas flow velocity in fractures and matrix becomes small, and the matrix contributes more to the permeability of the porous media. At relatively high pressures and low pressure conditions, the average velocity ratio in fractures and matrix also tends to be stable. The micro-fractures behave as high permeable channels parallel to the matrix in pressure decreasing directions, so they can significantly increase the permeability of the porous media.
Key words:  lattice Boltzmann method  tight porous media  micro-fractures  microscale effect