In this work, we aim to verify the predictions of the numerical simulators, which are used for designing field-scale hydraulic stimulation experiments. Although a strong theoretical understanding of this process has been gained over the past few decades, numerical predictions of fracture propagation in low-permeability rocks still remains a challenge. Against this background, we performed controlled laboratory-scale hydraulic fracturing experiments in granite samples, which not only provides high-quality experimental data but also a well-characterized experimental set-up. Using the experimental pressure responses and the final fracture sizes as benchmark, we compared the numerical predictions of two coupled hydraulic fracturing simulators—CSMP and GEOS. Both the simulators reproduced the experimental pressure behavior by implementing the physics of Linear Elastic Fracture Mechanics (LEFM) and lubrication theory within a reasonable degree of accuracy. The simulation results indicate that even in the very low-porosity (1–2 %) and low-permeability ($${10}^{-18}\ {\mathrm{m}}^{2}- {10}^{-19}\ {\mathrm{m}}^{2}$$ 10 - 18 m 2 - 10 - 19 m 2 ) crystalline rocks, which are usually the target of EGS, fluid-loss into the matrix and unsaturated flow impacts the formation breakdown pressure and the post-breakdown pressure trends. Therefore, underestimation of such parameters in numerical modeling can lead to significant underestimation of breakdown pressure. The simulation results also indicate the importance of implementing wellbore solvers for considering the effect of system compressibility and pressure drop due to friction in the injection line. The varying injection rate as a result of decompression at the instant of fracture initiation affects the fracture size, while the entry friction at the connection between the well and the initial notch may cause an increase in the measured breakdown pressure.

Against this background, a large-sample triaxial setup was developed at RWTH Aachen University under a project funded by BMWi (Federal Ministry of Economics and Technology). The planning and construction of the testing facility, including the analytical and numerical validation of the final experimental procedure, is thoroughly discussed in 2,3. The setup allows for experiments on rocks with size 30 cm × 30 cm × 45 cm under defined and controlled boundary conditions, yielding reproducible and repeatable datasets, well-suited for code benchmarking. In this paper we present hydraulic stimulation datasets from experiments where the borehole axis was parallel to the minimum horizontal stress direction and therefore the plane of crack propagation was parallel to the maximum horizontal stress direction. Investigated rock samples represent the reservoir rock types of a potential EGS site in Mexico. The datasets represent hydraulic stimulation responses in quasi-homogenous and extremely heterogeneous crystalline rock types, such as, a very fine-grained granite and a coarse-grained marble, respectively. Additionally, a dense network of 32 acoustic sensors, comprising of 28 GmuG standard ultrasonic sensors (http://www.gmugmbh.de/prod.html) and 4 Glaser amplitude-calibrated sensors 4,5 , was used to track the fracture propagation in real time. The validation dataset includes fluid injection rate, pressure in the injection interval, confining stresses, mechanical and petrophysical properties of the rock specimens, properties of the injection fluid, mechanical details of the experimental setup , and acoustic emission data. Additionally, we provide a Python-based code which can be used for processing the seismic data and visualizing of the experimental results. Methods The main components of the experimental setup , sample requirements and experimental protocol are described separately in the following subsections .

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