Effect of absorption boundary layer on nonlinear flow in low permeability porous media

Taking low permeability cores of Daqing oilfield for example, the flow characteristics at low velocity were studied with the self-designed micro-flux measuring instrument. Considering the throat distribution and capillary model, the thickness of fluid boundary layer under different pressure gradients was calculated, and the mechanism and influencing factors of nonlinear percolation were discussed. The results show that the percolation curve of ultra-low rocks is nonlinear, and apparent permeability is not a constant which increases with pressure gradient. The absorption boundary layer decreases with the increase of pressure gradient, and changes significantly especially in low pressure gradient, which is the essence of nonlinear percolation. The absorption boundary layer is also found to be impacted by the surface property of rocks.