Thermochemical acid fracturing of tight and unconventional rocks: Experimental and modeling investigations

The exploitation of unconventional formations requires propped hydraulic fracturing treatments. Propped fracturing is an expensive process that usually suffers from operational challenges. In this study, a new technology is proposed which targets implementing thermochemical fluids to stimulate unconventional formations. These fluids release large pressure pulses upon a reaction that creates networks of cracks along the fracture. Triggering thermochemical fluids with acid creates differential etching along the fracture surfaces due to the acid/rock dissolution. The new technology was tested experimentally through coreflooding on Indiana limestone and Kentucky sandstone samples and through breakdown pressure experiments on Eagle Ford shale samples. The breakdown pressure of the Eagle Ford shale samples was reduced from 2400 to 900 pisa using thermochemical fluids triggered with acid. It was also observed that the acid triggered thermochemical fluids could maintain the permeability of the fractures at high closure stresses due to the acid/rock dissolution. A laboratory and field-scale models were also developed in this study to understand thermochemical reactions. The laboratory-scale model could capture the pressure pulses generated experimentally and the system temperature. The field-scale model was then used to understand the thermochemical reactive transport in a hydraulic fracture. The model showed that thermochemical concentration is the most significant parameter in controlling the temperature and pressure magnitudes in the field.