Chemo-mechanical models for acidizing assisted hydro-fracturing

Abstract

The technique of hydro-fracturing, together with horizontal drilling, has been widely used in many countries for the extraction of subsurface energy in the form of e.g. hydrocarbon and heat. For unconventional tight carbonate reservoirs, characterized by ultralow intrinsic permeability, acidizing treatment is often incorporated as an enhancement of crack propagation. Acidizing assisted hydro-fracturing, during or after the treatment phase, is a highly nonlinear coupled dynamic process that involves several physical/chemical processes occurring concurrently and affecting each other. We are particularly interested in the modelling of crack propagation into a stressed medium subject to fluid pressurization and meanwhile being affected by the chemically aggressive environment. This presentation shows our unique approach of tackling this problem by considering the effect of micro-fracturation enhanced chemical shrinkage, in both the normally defined elastic and plastic domains of the rock behaviour. Local reactive diffusion processes are coupled with the mechanical degradation via upscaling to a representative elementary volume. To this end, a general framework of reactive chemo-elasto-plasticity is formulated, based on which, boundary value problems simulating typical scenarios encountered in hydraulic fracturing will be investigated, with an emphasis on the feedback mechanisms between the coupled processes and the evolution of permeability.