Formation damage assessment in carbonate reservoirs after removing hematite-water-based filter cake using HCl.

Effective removal of filter cakes is essential for restoring formation permeability and productivity, especially in open-hole completions. While hydrochloric acid (HCl) is commonly used to dissolve filter cakes, it may also introduce secondary formation damage, particularly through iron precipitation and pore plugging during fluid-rock interaction, in addition to the primary damage already caused by mud filtrate invasion and internal filter cake deposition during drilling. This study investigates the relative contributions of primary and secondary damage mechanisms associated with the removal of hematite-water-based filter cake in carbonate reservoirs using 10 wt% HCl under two operational strategies: squeeze and flowback. Core flooding experiments were conducted on Indiana limestone samples under downhole-representative conditions, and formation damage was evaluated through permeability, resistivity, CT imaging, and mechanical property measurements. Results indicated that primary damage alone caused up to 75% permeability reduction, while secondary damage developed during the removal stage, especially in the squeeze treatment where deeper acid invasion promoted iron precipitation in previously undisturbed zones, reducing far-zone permeability and increasing stiffness. In contrast, the flowback scenario improved permeability in the near-wellbore region and minimized secondary damage in the deeper zones, thereby preserving mechanical and petrophysical integrity. Resistivity decreased after both primary and secondary stages due to the intrusion of conductive hematite-rich filtrate and acid-induced by-products. Mechanical analysis confirmed that the squeeze scenario resulted in near-wellbore weakening and far-zone stiffening due to localized dissolution and precipitate deposition. This study is distinct in explicitly differentiating primary from secondary damage, demonstrating their relative impacts, and showing how operational strategy governs which mechanism dominates. Its focus on hematite-weighted filter cakes, direct comparison of squeeze and flowback strategies, and integration of mechanical property analysis alongside petrophysical evaluation provides a unique contribution toward understanding and mitigating formation damage in carbonate reservoirs.