Abstract
High-resolution 3D geological models are crucial for underground development projects and corresponding numerical simulations with applications in e.g., tunneling, hydrocarbon exploration, geothermal exploitation and mining. Most geological models are based on sparse geological data sampled pointwise or along lines (e.g., boreholes), leading to oversimplified model geometries. In the framework of a hydraulic stimulation experiment in crystalline rock at the Grimsel Test Site, we collected geological data in 15 boreholes using a variety of methods to characterize a decameter-scale rock volume. The experiment aims to identify and understand relevant thermo-hydro-mechanical-seismic coupled rock mass responses during high-pressure fluid injections. Prior to fluid injections, we characterized the rock mass using geological, hydraulic and geophysical prospecting. The combination of methods allowed for compilation of a deterministic 3D geological analog that includes five shear zones, fracture density information and fracture locations. The model may serve as a decameter-scale analog of crystalline basement rocks, which are often targeted for enhanced geothermal systems. In this contribution, we summarize the geological data and the resulting geological interpretation.
Highlights
Background & SummaryThree-dimensional geological models are of foremost importance for many geo-mechanical investigations, related numerical simulations, and interpretation of complex 3D monitoring data
The Grimsel Test Site (GTS) is operated by Nagra and hosted approximately 480 m below surface in the crystalline rocks of the Central Aar Granite and Grimsel Granodiorite
We present a 3D visualization of our geological interpretation of the test volume, including the geological architecture, which can be expanded towards a discrete fracture network, or implemented in hydrogeological, mechanical, hydro-mechanical or THMS-coupled numerical models
Summary
Three-dimensional geological models are of foremost importance for many geo-mechanical investigations (e.g., tunneling, hydropower infrastructure, geothermal energy, groundwater), related numerical simulations (e.g., modeling of hydraulic stimulations), and interpretation of complex 3D monitoring data. There is a lack of observations of detailed geological information at the intermediate scale and of the non-linear scaling relationships between rock mechanical parameters Reducing this data gap might lead to a better understanding of THMS-coupled processes (e.g., onset of hydraulic shearing and fracturing, aseismic vs seismic slip displacement, pressure diffusion, etc.) and more accurate corresponding numerical models. The GTS is operated by Nagra and hosted approximately 480 m below surface in the crystalline rocks of the Central Aar Granite and Grimsel Granodiorite These rocks are assumed to represent a suitable analogue for the deep crystalline basement, which is the target of several deep geothermal boreholes in Switzerland and elsewhere. We present a 3D visualization of our geological interpretation of the test volume, including the geological architecture (i.e., structures and their properties), which can be expanded towards a discrete fracture network, or implemented in hydrogeological, mechanical, hydro-mechanical or THMS-coupled numerical models. The published geological dataset and visualization can be used to study various hydro-mechanical or THMS-coupled processes in a decameterscale crystalline rock mass independent of a fixed geographic location, thereby advancing research of THMS-coupled processes
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