Summary Roughness characteristics significantly influence flow and reactive transport processes within fractures. A comprehensive understanding of the fundamental control mechanisms exerted by fracture roughness on these processes is crucial for accurately comprehending the hydrodynamic formation and evolution of acid fracturing. In this study, rough-walled fractures are generated using the spectral density function method. Their multiscale roughness is decomposed via Gaussian low-pass filtering, and an acid flow and reactive transport model is established to simulate acid-etching processes. The results indicate that the macroscopic large-scale roughness primarily dictates the fundamental direction and specific pathways of acid flow and reactive transport processes, serving as the predominant factor governing the morphology of acid-etched fractures. Moderate roughness focuses the acid flow through preferential channels, thereby enhancing local flow velocity and the efficiency of mass transfer by diffusion, which ultimately leads to a deeper penetration of acid etching. Mesoscopic small-scale roughness can influence the detailed morphological characteristics of acid etching by perturbing local acid flow and mass transfer by diffusion processes. An increase in mesoscopic small-scale roughness tends to inhibit the transport of acid deeper into the fractures, reduce the effective penetration distance of the acid, and consequently impair the overall acid-etching outcome. The preferential flow paths, established by the initial rough morphology of the fractures, form the foundational framework for the final acid-etched fracture morphology. Our results indicate that the acid-etching process primarily serves to enhance pre-existing dominant channels and connects potential regions, rather than significantly inducing the formation of new preferential flow paths. The processes of flow and reactive transport are largely incapable of fundamentally altering the development patterns of acid etching, underscoring the dominant control exerted by the original multiscale rough morphology of fractures on the ultimate morphology of acid-etched fractures. The static initial aperture distribution exerts a far more dominant control over the acid-etched fractures morphology than the dynamic adjustment of acid injection rate. Attempting to create new preferential flow channels by regulating the acid injection rate is difficult to achieve.
Zeng et al. (Sun,) studied this question.