Effect of fluid injection on the fracture behavior of porous rock

Abstract

Abstract Laboratory triaxial tests on sandstone specimens under triaxial compression were conducted to investigate the influence of pore fluid pressure on the deformation and fracture behaviour of rock. The experiments were carried out under various constant initial axial displacements of the specimens in order to simulate actual field situations, where the tectonic stresses acting on a porous rock mass are mainly constant while the fluid pressure increases due to fluid injection or environmental changes. The experiments have shown that changes in the boundary stresses are produced by either expansion or contraction of the porous rock and that increase or decrease of boundary stresses will depend on whether the rock was initially deformed elastically or inelastically, respectively. The experiments determine the bulk modulus of the solid phase of the porous material as well as the coefficient of sliding friction along inclined crack surfaces. The experimental results may be applied to field situations and they demonstrate that the fluid pressure alone does not cause fracture instability of a porous rock mass. Instability is dependent rather on the stiffnesses of the rock masses involved.