Triaxial testing and hydraulic–mechanical modeling of sandstone reservoir rock in the Upper Rhine Graben

Abstract

Background The determination of the subsurface conditions and reservoir properties is indispensable for exploration and exploitation of a geothermal field. It includes the expected geological structures as well as the hydraulic, thermal, chemical and mechanical parameters of the target horizon which should be favorable for geothermal utilization. Most essential is a high permeability to supply sufficient flow rates and high temperatures (Stober and Bucher 2012). An area in Germany which fulfills the criteria is the Upper Rhine Graben with a unique geothermal potential (Agemar et al. 2014). Local temperature anomalies with elevated temperatures up to 165 °C are expected at a depth of 2500 m, while the average geothermal gradient of the URG is above 40K km −1 (Agemar et al. 2013). Especially the sedimentary formation of the Triassic, Buntsandstein and Muschelkalk shows high permeabilities, which are necessary to provide high flow rates (Stober and Bucher 2014).

Spatial Characterization of Channeling in Sheared Rough‐Walled Fractures in the Transition to Nonlinear Fluid Flow

“…In the geothermal context, freshly fractured surfaces with well‐connected void space and good hydraulic conductivity are of interest. These voids are created when initially well‐mated fracture surfaces are sheared against each other under natural or artificially induced tectonical stresses (Egert et al., 2018). To introduce this shearing into the numerical models, the rough surface is doubled.…”

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

“…Up-scaling of hydraulic parameters (porosity and permeability) and geomechanical behavior (rock strength, compressibility, stress sensitivity) can be very challenging in carbonate reservoirs due to depositional and diagenetic heterogeneity (Menke et al 2021). While large-scale karst and fault structures can be spatially interpreted from geophysical data (seismic surveys, downhole logging), small-scale heterogeneities are almost unresolvable (Egert et al 2018). However, by defining common parameter ranges for different rock and facies types of the Malm carbonates by laboratory tests, as done in this study and in the studies of Bohnsack et al (2020) and Potten (2020), heterogeneity can be controlled even in a coarser modeling grid of numerical simulations (e.g., THM models) by up-scaling these value ranges for different lithologies (Settari et al 2013).…”