A reactive-chemo-mechanical model for acidizing assisted cavity expansion

Abstract

Hydraulic fracturing has been widely used for unconventional reservoirs especially after the technique of horizontal drilling was invented. Acidizing treatment is often incorporated as a propagation enhancement of fractures, in particular, for very tight, low-permeability carbonate-rich reservoirs. How an individual crack propagates into a stressed medium subject to fluid pressure acting on the crack surfaces and meanwhile being affected by the chemically aggressive environment is still an open question. While there are interweaved connections between cavitation and fracturing during chemical degradation processes, both being affected by a characteristic internal length-scale, e.g. the size of the cavity or roundness of the fracture tip, this abstract presents a reactive-chemo-mechanical model that investigates a fundamental problem of chemical reaction-diffusion coupled into cavity expansion processes considering both the elastic and plastic domain of the rock behaviour. Numerical experiments are conducted using a multi-physics high performance computing finite-element simulator, REDBACK, featuring dissipative feedbacks in rocks based on the MOOSE environment. Parametric studies on the controlling parameters of the feedback mechanisms between the coupled processes of cavity expansion, chemical softening by mineral mass removal, reaction diffusion, irreversible damage manifested as micro-cracking, etc. are presented. The reactive-damage zone is found to be localised in the near cavity region as a result of the coupling between enhanced chemical dissolution and material degradation. The dynamic evolution of the the elasto-plastic interface is identified as an exponential function of time.