The pore structure and mineral composition play a crucial role in controlling the water flow behaviors of low-permeability media, which is characterized by threshold pressure gradient (TPG) and nonlinear flow curve. To figure out the coupling effects of these two factors on pre-Darcy flow regimes, water flow experiments were conducted on four tight sandstones, three shales and one fractured shale. The results indicate that both the TPG and pseudo threshold pressure gradient (PTPG) decrease with an increase in total porosity and macropores porosity. The variation of the nonlinear exponent (n) with total porosity and macropore porosity can be described by an exponential function with three parameters. The clay minerals and brittle minerals exert completely opposite influence on the variation of pre-Darcy flow parameters (PTPG, TPG and n). Both TPG/PTPG and n increase with increasing clay content while reduce with increase in the brittle minerals content. Theoretical analyses based on the disjoining pressure demonstrate that immovable water and electro-viscous effect are mainly responsible for water flow deviating from Darcy's law in tight sandstone and shale. Calculation results show that the proportion of immovable water of intact samples ranges from 23.46% to 89.73%, the movable water content ranges from 10.27%–76.54%. The pre-Darcy flow parameters exponentially increase with increase in immovable water content while exponentially decrease with increasing proportion of movable water. For the shale sample used in this work, the immovable water and electro-viscous effect contributing to the pre-Darcy flow account for 81.11%–90.35% and 9.58%–18.51%, respectively. The different flow regimes are controlled by the pore diameter and the thickness of water with shear fluidity. If the diameter of interconnected pores is larger than 10 μm, the Darcy flow regime dominates. When the diameter of minor pore throat of the flow channels are less than 33.82 nm for sandstones and 37.68 nm for shales, the movement of water in this flow channel would generate the TPG.

孔隙结构和矿物成分对控制低渗透介质的水流动行为具有至关重要的作用，其特点是启动压力梯度（TPG）和非线性流动曲线。为了弄清楚这两个因素对前达西流态的耦合影响，对四种致密砂岩、三种页岩和一种裂缝页岩进行了水流实验。结果表明，TPG 和拟启动压力梯度（PTPG）均随着总孔隙度和大孔孔隙度的增加而降低。非线性指数的变化 ( n) 具有总孔隙度和大孔孔隙度可以用具有三个参数的指数函数来描述。粘土矿物和脆性矿物对前达西流动参数（PTPG、TPG和n）的变化产生完全相反的影响。TPG/PTPG 和n随着粘土含量的增加而增加，而随着脆性矿物含量的增加而减少。基于分离压力的理论分析表明，致密砂岩和页岩中水流偏离达西定律的主要原因是不流动的水和电粘性效应。计算结果表明，完整样品的可动水比例为23.46%~89.73%，可动水含量为10.27%~76.54%。前达西流参数随着不可动水含量的增加呈指数增加，而随着可动水比例的增加呈指数减少。对于本工作所使用的页岩样品，对前达西流的贡献率分别为 81.11%~90.35% 和 9.58%~18.51%。不同的流态由具有剪切流动性的水的孔径和厚度控制。如果互连孔隙的直径大于 10 μm，则达西流态占主导地位。当流道的小孔喉直径对于砂岩小于 33.82 nm，对于页岩小于 37.68 nm 时，水在该流道中的运动会产生 TPG。