Fig. 10From: Stress sensitivity of porosity and permeability under varying hydrostatic stress conditions for different carbonate rock types of the geothermal Malm reservoir in Southern GermanyEvolution of Eulerian porosity (a) and permeability (b) as a function of Terzaghi effective pressure in drained hydrostatic tests. Porosity was measured during a continuous compression test, while permeability was measured for each pressure level over an extended period of time—the error bars, therefore, represent a threshold for each pressure stage. During the loading phase, porosity and permeability decrease continuously as the effective pressure increases. The stress sensitivity coefficients \(c\) for porosity and \(b\) were determined by exponential regression. The unloading phase shows a relaxation hysteresis, an irreversible loss of pore volume, and a permanent loss of permeability (up to 20%) at the end of the test cycle. “Indiana limestone” data from Meng et al. (2019) were used to compare the results and show similar behaviorBack to article page