Experimental investigation of the influence of differential stress on permeability of a Lower Permian (Rotliegend) sandstone deformed in the brittle deformation field

A fine-grained (mean grain size 0,2 mm), low-porosity (6-9%) sandstone, wit h an unconfined compressive strength of 55 MPa (fluid-saturated) and an ini tial permeability in the order of 0.5 x 10(-1)5 m(2), was used to investiga te the influence of differential stress on permeability. A new technique of measuring permeability by a steady-state method, while continuously deform ing the rock specimen, has been developed. Permeability reduction due to hy drostatic loading was found to be similar to permeability reduction due to stress-induced compaction in the pre-failure region. This is considered as a first proof of the validity of the new method. Deformation experiments in the brittle field show that low-porosity sandsto nes have a permeability evolution in triaxial compression which is qualitat ively similar to crystalline rocks. In the pre-failure region permeability is strongly reduced by stress-induced compaction. After the onset of dilata ncy, permeability starts to increase; however, when the initial sample volu me is reached again, the permeability reduction is not recovered. (C) 2001 Elsevier Science Ltd. All rights reserved.