Verification of Coupled Hydraulic Fracturing Simulators Using Laboratory-Scale Experiments

Rock Mechanics and Rock Engineering, vol. 54, pp. 2881–2902

Abstract

Abstract 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.

Authors 6

1. Paromita Deb corresponding Aachen Institute for Applied Geophysics and Geothermal Energy

   RWTH Aachen University

   Affiliation as printed

   Institute for Applied Geophysics and Geothermal Energy, RWTH Aachen University, Aachen, Germany

2. Saeed Salimzadeh

   Commonwealth Scientific and Industrial Research Organisation

   Affiliation as printed

   Commonwealth Scientific and Industrial Research Organization, CSIRO, Clayton, Australia

3. Daniel Vogler

   ETH Zurich · Institute of Geophysics

   Affiliation as printed

   ETH Zurich , Geothermal Energy and Geofluids, Institute of Geophysics, Zurich, Switzerland

4. Stephan Düber Aachen Chair of Geotechnical Engineering

   RWTH Aachen University

   Affiliation as printed

   Chair of Geotechnical Engineering, RWTH Aachen University, Aachen, Germany

5. Christoph Clauser Aachen Institute for Applied Geophysics and Geothermal Energy

   RWTH Aachen University

   Affiliation as printed

   Institute for Applied Geophysics and Geothermal Energy, RWTH Aachen University, Aachen, Germany

6. Randolph R. Settgast

   Lawrence Livermore National Laboratory

   Affiliation as printed

   Lawrence Livermore National Laboratory, Atmospheric, Earth and Energy Division, Livermore, CA, USA