Effect of Rock Surface Cleaning on Acid Dissolution Behavior in Carbonate Reservoirs

Abstract The interaction between acidic fluids and carbonate rocks is central to reactive flow processes, especially in acidizing operations. While carbonate reactivity has been widely studied, the effect of pre-experimental cleaning protocols remains underexplored. Cleaning can alter rock surface properties, influencing dissolution behavior and experimental reproducibility. This study investigates how alternative cleaning methods affect the acid dissolution response of carbonates with different permeabilities and mineralogical compositions. Two permeability ranges were examined: low (~2 mD) and high (~100 mD). Following API RP 40 guidelines, mini-plugs (0.80 × 1.0 cm) were prepared and subjected to Soxhlet extraction using organic solvents: (i) toluene/acetone (TA) and (ii) chloroform (C). Uncleaned samples (NC) served as controls. All specimens underwent static dissolution tests in 1 mol/L of HCl under ambient conditions. Dissolution kinetics were assessed through t50, the time to achieve 50% mass loss, with measurements taken at four-time intervals (¼, ½, ¾, and full t50). Results demonstrate that cleaning protocols influence dissolution behavior differently depending on mineralogy. Calcite-rich samples exhibited relatively consistent dissolution trends across cleaning conditions and permeability appears to influence reaction intensity under the experimental conditions adopted. In contrast, dolomitic samples displayed strong sensitivity to both cleaning procedures and textural heterogeneity. Chloroform cleaning enhanced dissolution rates, indicating more effective removal of organic barriers and improved exposure of reactive surfaces. Additionally, low-permeability dolomite samples exhibited greater overall mass loss than high-permeability samples, suggesting that localized macropores acted as preferential acid attack sites, promoting selective dissolution and mechanical disintegration of the matrix. Comparison between mass loss and ion-based reaction rates indicates that mass removal does not necessarily represent purely chemical dissolution, particularly in dolomitic systems where fragment detachment may contribute to total mass reduction. Micro-CT analyses confirmed that dissolution patterns are governed by the coupled effects of mineralogy, pore architecture, and surface conditioning. These results stress the need to consider sample preparation in laboratory studies of carbonate reactivity and provide valuable implications for subsurface engineering applications, including acid stimulation and CO2 storage. Future research should extend this framework to additional lithologies and reservoir-relevant conditions of pressure and temperature, enhancing predictive models of fluid–rock interactions.