A coupled reactive-chemo-mechanical model for acidizing assisted hydraulic fracturing in carbonates

Abstract

Since the development of horizontal drilling, the technique of hydraulic fracturing has been widely applied in the oil and gas industry and enhanced geothermal systems (EGS). For low-permeability, tight, unconventional reservoirs, acidizing treatment is often incorporated to soften the rock and promote crack connectivity. This technique is proven effective for carbonate-rich reservoirs. However, the complex interplay between evolution of the stress field, deformation, hydraulic properties and chemical processes (e.g. mineral dissolution) in the geomaterial during the stimulation and maintenance phase demands a more sophisticated understanding. In particular, how to model a single crack/fracture propagating into a stressed medium subject to fluid pressurization acting on the crack surface and meanwhile being affected by the mineral mass removal due to chemical dissolution, is still an open question. In this short paper, we present a coupled reactive-chemo-mechanical model considering the effect of micro-fracturing enhanced chemical shrinkage in both the elastic and plastic domain of rock behavior as well as a chemical ductilization effect post-yield. Reactive transport of minerals and hydrogen is coupled with the deformation process of the solid matrix via a dependence of dissolution rate on the specific surface area. The formulated reactive-chemo-mechanical framework is implemented and numerical investigations are conducted in an open-source Finite Element simulator based on the Multiphysics Object Oriented Simulation Environment (MOOSE). The effect of micro-fracturation enhancement and that of microstructural heterogeneity on the material behaviour are presented.