Effect of Closure Stress, Mineralogy, and Temperature on Acid-Etched Fracture Patterns in Fractured Carbonate Rocks

Summary

Acid fracturing is widely applied to enhance production from oil, gas, and geothermal reservoirs in fractured carbonate formations. Because acid preferentially flows along natural fractures, accurate prediction of acid-etched fracture behavior is essential. However, existing acid-etching models fail to account for fracture deformation under in-situ conditions, particularly the thermal effects prevalent at depth. To bridge this gap in this study, we develop a new model that can simulate the spatiotemporal evolution of contact asperities on fracture walls under coupled thermal-hydrological-mechanical-chemical conditions. The model is validated against acid coreflooding experiments, and the results show that closure stress compacts fractures, forms closed regions, and hinders acid transport, yet ramified, channel, and uniform dissolution patterns still develop. The closure area evolves in two stages: an initial dissolution-driven decrease followed by a deformation-driven increase, whereas uniform dissolution remains stable in the later stage. A higher injection rate enhances acid transport but narrows fracture width; higher closure stress strengthens deformation and reduces transport, with uniform dissolution being the most sensitive and ramified dissolution being the least. In multimineral fractures, quartz and dolomite mitigate closure-stress-induced fracture width loss and increase the effective acid-penetration distance. Compared with uniform dissolution, ramified and channel dissolution are less sensitive to temperature in their final etching patterns. This study advances acid-etching modeling for fractured carbonate rocks, provides insights into reactive flow in narrow fractures, and supports the efficient development of subsurface energy resources.