Two novel distinctly different laboratory apparatus have been developed to allow controlled, precise, repeatable and observable experimental simulations of hydraulic fracturing over a broad range of well-determined dominant parameters and practical geometries. One system avoids specimen preparation (by using predetermined interface separation), while the other most efficiently employs castable blocks with proper scaling of fracture toughness to correctly capture crack turning. These are based on a rigorous analysis of the physics and equations governing the hydrafrac process, which allow the extraction of the role played by each physical variable - so that these can be incorporated correctly in the scaling, e.g. from field operations to lab conditions. The experiments have already verified most of the primary features and results of the analysis: principal achievements include vindication of a characteristic time for the process, containing excess crack-opening pressure, material modulus and fluid rheology; general agreement with numerical results for actual growth rates of various fracture geometries; and verification of even more detailed predictions for evolution of cracks with mutual/tectonic interaction in various structural geometries and stress fields. Being perhaps the first stable, quasi-static and observable simulators, these apparatus promise to have a very broad range of applications in geophysics, resource extraction, structural analysis and geotechnical engineering.

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