Stress sensitivity of porosity and permeability under varying hydrostatic stress conditions for different carbonate rock types of the geothermal Malm reservoir in Southern Germany

Abstract In geothermal reservoir systems, changes in pore pressure due to production (depletion), injection or temperature result a displacement of the effective stresses acting on rock matrix aquifer. To compensate for these intrinsic stress changes, is subjected poroelastic deformation through and volume. This turn may induce network thus hydraulic properties Therefore, conception precise models long-term simulations, sensitivity porosity permeability required parametrization. Stress was measured hydrostatic compression tests 14 samples cores stemming from two boreholes Upper Jurassic Malm aquifer Bavarian Molasse Basin. account heterogeneity this carbonate sequence, typical facies types representing productive zones within thermal were used. Prior investigations, (effective porosity, permeability) geomechanical (rock strength, dynamic, static moduli) parameters as well microstructure (pore throat size) each sample studied thorough characterization. Subsequently, tested triaxial test setup with up 28 MPa (hydrostatic) simulate in-situ conditions depths 2000 m. It shown that comparably low, resulting relative reduction 0.7–2.1% at maximum stress. contrast, losses observed range 17.3–56.7% compared initial low stresses. coefficients derived characterization different types. For negative correlation strength positive observed. The probably controlled by more complex processes than where latter mainly compressibility space. depend compaction precedented flow paths geometry pores throats controlling connectivity matrix. general, limestone showed higher dolomitic dolostones, because dolomitization lead an increasing stiffness rock. Furthermore, related history burial diagenesis, during which (dissolution, precipitation, replacement minerals cements) microcrack formation occur. study, addition improving quality input hydraulic–mechanical modeling, shows largely characterized less stiff, porous limestones can deteriorate significantly