Investigation of Acid-Etching Evolution in Natural Fractures of Carbonate Reservoirs Under High Closure Stress

Summary The acid-etching evolution of local natural fractures in high-stress carbonate rocks is a complex, multifield coupled phenomenon, governed primarily by closure stress loading, acid flow, and mass transfer reaction. To unravel the characteristics of this evolution and the impact of closure stress and acid injection rate on acid-etching effectiveness, a set of numerical models that integrate fluid flow, chemical reaction, and mechanical deformation within local natural fractures is established, and numerical simulations of fracture deformation and fracture acid-etching are conducted. The results show that continuous closure stress loading fosters the emergence of dominant flow channels by means of acid flow and acid-rock reaction. These channels guide most of the acid flow, continuously dissolving and etching the fracture walls, ultimately forming channelized acid-etching fractures. When closure stress ranges between 10 MPa and 15 MPa, a coupling balance between high closure stress and flow reaction enables the acid-etching fractures to attain greater widths and flow channels, significantly enhancing their long-term conductivity and deformation resistance. As the acid injection rate increases, the dominant flow channels merge into a single channelized acid-etching fracture due to competitive propagation and preferential dissolution. The dominant flow channel expands both vertically and horizontally under the scouring effect of high injection rates, leading to an increase in both the width of the channelized acid-etching fracture channel and the overall acid-etching fracture width.