Unjacketed bulk compressibility of sandstone in laboratory experiments

The unjacketed bulk modulus of sandstone, Ks', is often considered to be equal to the bulk modulus of quartz, the main mineral which forms it. However, preliminary tests and some other works show that for Berea sandstone this assumption might be violated. Three different types of laboratory experiments were performed on the rock to measure Ks' and Biot's coefficient α: unjacketed plane strain compression, drained compression with water collection, and jacketed/unjacketed hydrostatic compression. The values of these parameters are reported at 5 MPa mean Terzaghi effective stress; α is found to be in the range of 0.64 - 0.74 and Ks' = 27.2 - 30.9 GPa. The latter value is significantly smaller than the measured bulk modulus of quartz, Kquartz = 37.0 GPa. It can be explained by the presence of clays or the existence of non-connected pore space in the rock.