Influence of Mineralogical Heterogeneity on Acid–Rock Interaction in Dolomitized Carbonates from the Parnaíba Basin, Northeastern Brazil: Implications for Reservoir Matrix Acid Stimulation

High Resolution Image Download MS PowerPoint Slide In matrix acid stimulation of carbonate rocks, understanding acid–rock interaction is essential to optimize wormhole formation and overall treatment efficiency, since heterogeneity can lead to distinct dissolution patterns. Mineralogical heterogeneity significantly affects this process due to the different dissolution kinetics of calcite and dolomite; however, it remains unclear how grain size, crystal defects, and mineral distribution influence this interaction. To investigate these factors, five highly dolomitized carbonate samples from the Piauí Formation (Parnaíba Basin) were characterized by petrography, X-ray diffraction, X-ray fluorescence, scanning electron microscopy, and porosity measurements, and subjected to static dissolution in 1 M HCl with evaluation of mass loss and quantification of calcium and magnesium ions. The results showed that texture and mineralogical composition play a fundamental role in dissolution: larger crystals generated wider cavities due to detachment during acid attack; samples with higher Ca and Mg contents relative to Si exhibited higher dissolution rates, whereas increasing quartz content reduced reactivity. Most samples showed an early predominance of Ca 2+ release followed by increasing Mg 2+ concentrations, reflecting preferential calcite dissolution and progressive dolomite contribution. Well-developed crystals with fewer structural defects exhibited lower reactivity. Postdissolution peak broadening in XRD patterns suggests structural modification of the minerals. Overall, mineralogical heterogeneity controls acid–rock reactivity across multiple scales, highlighting the importance of integrated mineralogical and textural characterization to improve prediction and optimization of acid stimulation in heterogeneous carbonate reservoirs.