Experimental and Theoretical Investigation of Nonlinear Flow in Low Permeability Reservoir

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