Subcritical crack propagation enhanced by chemical injection

Abstract

This paper studies the conditions of crack propagation in a subcritically stressed rock subject to chemically aggressive environment, which is often encountered in technologies of oil/gas extraction from low-permeability reservoirs. Frequently, matrix acidizing is employed, upon which mineral mass is dissolved and washed away by fracturing fluids. Such a mineral mass removal weakens the material mechanically and causes crack propagation and, eventually, permeability changes in the medium. The crack process zone is modeled mathematically using a recently developed chemo-plasticity coupling model. The coupling is established between mineral dissolution and a yield limit of rock matrix via chemo-plastic softening function. The rate of dissolution is a function of a rate constant and variable internal specific surface area which is, in turn, affected by the initial void ratio as well as dilatant micro-cracking induced by irreversible damage (treated as a plastic strain). Numerical simulations for such a coupled system are performed under simplified boundary conditions. © 2014 American Society of Civil Engineers.