Laboratory Measurement of High-Porosity, Low-Permeability Rock Deformation with Pore Water Movement

Deformation of rock masses and fluid flow through reservoirs are important when designing sites for geological nuclear waste disposal, carbon dioxide capture and storage, and an enhanced geothermal system. To estimate the behavior of the rock and pore fluid, the poroelastic and hydraulic parameters of high-porosity, low-permeability sedimentary rocks were evaluated simultaneously from triaxial compression tests with instantaneous change of axial stress, confining pressure, or pore pressure. The experimental results of the fluid discharges from the specimen during the tests were used in theoretical interpretations. Thus, besides analyzing the behavior of the pore water, the transient response of the rock deformation corresponding to the pore water movement can be analytically evaluated. Accordingly, the hydraulic constants can be evaluated from the transient strain data of the triaxial compression tests with instantaneous change of stress or pore pressure. The hydraulic constants obtained from the triaxial compression tests agreed well with those from the transient pulse permeability tests. Furthermore, a simple coupling model introduced in this study provided a good representation of the time-dependent rock deformation with pore water movement.