Investigations into the opening of fractures during hydraulic testing using a hybrid-dimensional flow formulation
Steeb, Holger
Renner, Jörg
DOI: https://doi.org/10.1007/s12665-021-09767-4
Persistent URL: http://resolver.sub.uni-goettingen.de/purl?gldocs-11858/11316
Steeb, Holger; Stuttgart Center for Simulation Science (SC SimTech), University of Stuttgart, Stuttgart, Germany
Renner, Jörg; Institute of Geology, Mineralogy and Geophysics, Ruhr-Univerität Bochum, Bochum, Germany
Abstract
We applied a hybrid-dimensional flow model to pressure transients recorded during pumping experiments conducted at the Reiche Zeche underground research laboratory to study the opening behavior of fractures due to fluid injection. Two distinct types of pressure responses to flow-rate steps were identified that represent radial-symmetric and plane-axisymmetric flow regimes from a conventional pressure-diffusion perspective. We numerically modeled both using a radial-symmetric flow formulation for a fracture that comprises a non-linear constitutive relation for the contact mechanics governing reversible fracture surface interaction. The two types of pressure response can be modeled equally well. A sensitivity study revealed a positive correlation between fracture length and normal fracture stiffness that yield a match between field observations and numerical results. Decomposition of the acting normal stresses into stresses associated with the deformation state of the global fracture geometry and with the local contacts indicates that geometrically induced stresses contribute the more the lower the total effective normal stress and the shorter the fracture. Separating the contributions of the local contact mechanics and the overall fracture geometry to fracture normal stiffness indicates that the geometrical stiffness constitutes a lower bound for total stiffness; its relevance increases with decreasing fracture length. Our study demonstrates that non-linear hydro-mechanical coupling can lead to vastly different hydraulic responses and thus provides an alternative to conventional pressure-diffusion analysis that requires changes in flow regime to cover the full range of observations.
Subjects
Hydro-mechanics of fracturesHybrid-dimensional modeling
Fracture contact mechanics
Fracture stiffness
Hydraulic testing of fractures
Reiche Zeche underground research laboratory