Coupling of radial permeability and uniaxial loading of a saturated sandstone

Extensive testing and numerical analysis/modeling has been done by others on the coupling of normal stress and permeability associated with natural and man-made horizontal fractures. These researchers have shown that there is a decrease in permeability with increasing normal stress. However, there has been little published research into how permeability changes when loading non-horizontal fractures, and loading unfractured rock into the upper portion of the stress-strain curve. We have uniaxially loaded a sandstone through the upper stress-strain curve while measuring radial permeability. The test is very simple, but is providing very interesting results. We have shown that there are three stages in the permeability evolution. Initially, the permeability decreases, then remains constant in the lower and middle stress-strain curve. In the very upper portion of the stress-strain curve permeability increases markedly. The decrease in permeability is believed to be due to a reduction of pore space. The constant permeability is believed to be due to a subsequent tight packing of grains where the pore space cannot become smaller, yet the stress is not sufficient to initiate cracks. The increased permeability is believed to be due to the coalescence or localization of failure along vertical cracks.