The mechanism of capillaries hydraulic conductivity evolution under confining pressure: Experimental modelling using 3D-printing approach

The effect of confining pressure on the hydraulic conductivity of capillaries in cylindrical samples is examined. The three-dimensional-printed samples were made from photopolymer resin. Capillaries in the samples were modeled by grooves of various geometric shapes. The mechanism of capillary deformation in the samples under increasing confining pressure has been identified. The change in capillary conductivity depending on their location (central and lateral) and configuration (sinuous) has been revealed. Based on correction functions for the geometric dimensions of the capillaries, it has been mathematically confirmed that under confining pressure, a capillary deforms primarily along the contact plane due to the sliding of the sample’s halves against each other. The width of a capillary is more sensitive to confining pressure than its depth. It has been established that the exponent in the conductivity (permeability) equation of the samples under cyclic loading is determined by the hydraulic area of the capillary. The obtained values of the width and depth correction factors allow for predicting changes in the filtration resistances of capillaries in various materials. Capillary deformation manifests as a change in its geometric dimensions (height and width), i.e., the crushing of the capillary banks is observed, leading to a reduction in the capillary’s hydraulic area, which causes a decrease in sample conductivity with an incomplete hysteresis.