Biot coefficient
α is basically a function of the quotient of the drained bulk modulus Kb and the bulk modulus of solid grain only Kg:
α = 1 - Kb/Kg 0 ≤ α ≤ 1 (Biot 1962).
Incorporation of the Biot coefficient considers the pore pressure influence on the effective stress: A solid rock without pore space such as a quartzite has an α » 0 and shows consequently no pore pressure influence. Weak and porous rocks have α » 1 and display, therefore, the maximum pore pressure influence (Zoback 2007).
Bulk modulus
K describes the stiffness of a rock in hydrostatic compression (Zoback 2007). It is expressed as the change of the confining pressure acting on a rock specimen dP in relation to the thereby caused volume change dV/C:
K = (dP/dV)*V.
The compressibility is the reciprocal bulk modulus K-1.
Capillary threshold pressure
Pcc is the pressure difference between the injected gas phase and the water phase in the caprock. This pressure is needed to overcome the capillary forces to initiate a flow into the caprock (Egermann et al. 2006).
Coefficient of internal friction
µ is the tangent of the angle of (internal) friction φ
µ = tanφ
and to this effect a material constant which describes the break angle with the main principle (compressive) stress σ1 in response to its (diagenetic) compaction, grain size and mineralogical composition. As a rule of thumb applies: loose and/or fine grained rocks which consist mainly of platy minerals (poorly consolidated sandstone, clay- and siltstone, shale and schist) have a lower µ (generally in the range of 0.25, φ » 15°) than hard, coarse grained rocks composed of subangular to well-rounded grains (e.g. a silica cemented, coarse grained, mature sandstone with µ approximately 0.6, φ » 30°).
Cohesion
σ0 is the shear strength of a rock at the absence of normal stress (σn = 0 MPa) caused by the adhesive forces of the mineral grains.
News
With the recent acquisition of the state-of-the-art DIL 502 Expedis® Select thermal dilatometer from Netzsch, we are expanding our capabilities for the precise analysis of the thermal properties of rocks and mineral materials. We are now able to determine the coefficient of thermal expansion in accordance with DIN EN 14581:2004, ASTM D4535-13e1. (2013) or using a measurement program specifically tailored to the customer’s needs (for more information, see Thermal Dilatometer).
The project, which was funded by the Free State of Thuringia, was co-financed by the European Union through the European Regional Development Fund (EFRE).
This year’s EAGE GET Conference and Exhibition is taking place in Germany:
Gesteinslabor Dr. Eberhard Jahns will again be taking part as an exhibitor this year. From 2 to 6 November 2026, you can find us at Stand 31 at the HCC in Hannover.
We would be delighted to welcome you to our stand.
Gesteinslabor Dr. Eberhard Jahns is project and research partner within the HENRI (Hydrogen Energy Reservoir) project.
Our main focus is on determining the impact of H2 on the cap rock. Besides other parameters, we measure the capillary threshold pressure using various gases and gas mixtures of hydrogen and methane.
Results were presented at the third HENRI conference in Bratislava in September 2025
We are pleased to be part of the Dutch subsurface research for geothermal heat SCAN.
Further information can be found on the official homepage:
https://scanaardwarmte.nl/english/
