ReSalt

ReSalt

PhD thesis D. Gottron

Reactive reservoir systems – solution and precipitation of salts and the impact on hydraulic and mechanical rock mass properties

The geothermal energy production process can lead to the precipitation of minerals in the existing fracture network by reinjection of the reservoir fluids (Reservoirscaling). As a result, the hydraulic and mechanical properties of the rock mass will change. Within the joint research project ReSalt, funded by the BMWi, the work of the Department of Engineering Geology is focused on the characterization of reservoir analogs (Fig. 1) with respect to the geometry of the fracture network, the determination of the rock mechanical properties of sedimentary rocks and fractures as well as the upscaling from laboratory to reservoir scale.

Figure 1: Sandstone reservoir analog Remlingen. (Picture: Philipp Zuber)
Figure 1: Sandstone reservoir analog Remlingen. (Picture: Philipp Zuber)

The geological mapping and sampling of two quarries, which act as geological analogs, is performed using a terrestrial laser scanner and drill cores. The focus concentrates in particular on the characterization of the fracture network and fracture parameters. The rock mechanical properties of the rocks and fractures are investigated with uniaxial and triaxial tests as well as direct shear tests in the laboratory. The upscaling to the reservoir scale is based firstly on conventional rock classifications (RMR, Q-system) for the mechanical properties. An alternative approach are upscaling concepts based on the Discrete Fracture Network (DFN) method which allows an upscaling of hydraulic and mechanical parameters. Based on a deterministic-stochastic fracture model, a spatially variable and anisotropic rock mass E-module and a rock mass permeability is computed, respectively. In addition, these DFN models will be connected with synthetic rock mass (SRM) models.

The aim of the ReSalt research project is the application of upscaling concepts and the development of new concepts for the transfer of hydromechanical parameters, which are determined in the field and in the laboratory, to the reservoir scale.

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