Chemo-Hydro-Geomechanics in acidizing assisted hydraulic fracturing

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. This short paper investigates the fundamental coupled chemo-hydro-geomechanics as encountered in typical scenarios of hydraulic fracturing, with a specific focus on the role of acidizing treatment. The constitutive relations consisting of a reactive-chemo-elastic and a reactive-chemo-plastic formulation are presented, followed by the coupling with geochemical processes, namely reactive-diffusion equations. Numerical investigations of two representative cases within the chemo-elastically defined regime are presented, featuring a laboratory injection test and in-situ stress conditions of a deep geothermal reservoir, respectively. The results have demonstrated that the chemical dissolution process plays a critical role in the distribution of circumferential stress around the crack tip as well as the evolution of crack propagation, and that acidizing treatment may accelerate cracking exponentially after sufficient chemical exposure.