Experimental and modeling study on the acid-etching and conductivity of hydraulic fractures in carbonate rocks: A critical review

Acid fracturing is a pivotal technique for the exploitation of deep carbonate oil and gas, geothermal resources, and also an important injection technology for carbon capture, utilization and storage. The essence of acid fracturing lies in the process where acid non-uniformly etches hydraulic fracture to generate conductivity. Laboratory experiments and numerical simulations are two crucial means to replicate in-situ environment of acid fracturing, understand acid-rock reaction mechanism, and innovate on-site technologies. However, due to complex geological environment of ultra-deep carbonate formations and diverse on-site acid fracturing technologies, existing experimental methods and numerical simulation methods have struggled to fully characterize the emerging acid fracturing technology. Therefore, it is imperative to systematically review research progress on acid-etching and conductivity of acid-etched fractures while identifying gaps between experimental methods, numerical simulations, and on-site technologies, which holds immense significance in advancing theoretical research and technical development related to acid fracturing. Detailed reviews are provided on experimental equipment, models employed for acid etching analysis, as well as testing methods utilized for assessing both etching characteristics and conductivity. The current limitations of existing experimental techniques and numerical simulations are also presented. The proposed acid fracturing experiment and model researches, in conjunction with the engineering geological characteristics of deep and ultra-deep carbonate reservoirs over 10,000 m, not only offer valuable insights for future investigations into acid-etched fracture conductivity but also provide essential support for the advancement of acid fracturing engineering technology. Moreover, these findings can be applied to all the study on flow and reaction processes of reactive fluids within narrow channels.