Direct and indirect laboratory measurements of poroelastic properties of two consolidated sandstones

• Direct and indirect measurements of the poroelastic Biot coefficient, Skempton coefficient and porosity.
• Estimation of unjacketed pore compressibility.
• Application of fibre optic sensors during undrained laboratory experiments.

Experimental measurements to derive the drained bulk C and the solid bulk Csu compressibility, the poroelastic Biot coefficient αα, Skempton coefficient B   as well as porosity ϕϕ were performed under drained, undrained and unjacketed pore pressure conditions. The experiments were conducted for two different kinds of sandstones, Bentheimer and Flechtinger. During all experiments, the confining hydrostatic pressure was continuously increased up to 85 MPa. To measure the undrained pore pressure response within the interior of the sample, a novel fibre optic sensors technique was applied. Subsequently, we compared the direct measurement of αdirαdir, Bdir and ϕdirϕdir to indirect calculated values using C and Csu. For low effective pressure, it showed that all parameters display a non-linear decrease with increasing effective pressure. At high effective pressure the decrease of all poroelastic coefficients is almost linear with increasing effective pressure. In accordance with Terzaghi's effective stress concept, the comparison between direct and indirect methods showed a good to excellent agreement for all calculated parameters. Differences between the direct and indirect methods were used to quantify drained and unjacketed pore compressibilities, as well as jacket effects during the experiment.