“…In a typical test, we found that the filter-cake formed in the formation damage test was looser than that formed in the filter-cake cleaning test and therefore easier to remove with a water flush, even at pH 10. The removal of the filter-cake likely improved the retained permeability of the core because the reservoir permeability, which influences well productivity, is related to the plugging of the rock matrix by poorly displaced oil mud and oil-wet filter-cake (Ali et al, 2006;Bailey et al, 2000;Khatib, 1994;Civan, 1994, 1996;Moajil, Nasr-El-Din, 2013). However, another question was proposed: why were low-pH conditions (pH 4-6) associated with easily removable filter-cake but unimproved retained permeability?…”