Energy Reports (Dec 2023)
Literary review: Permeability alterations in sandstone after acidizing
Abstract
Sandstone acidizing, overall, increases permeability, though damage may occur during pre-, main-, or post-flush. For example, hydrochloric acid pre-flush can increase permeability by 80%–90%. However, reactions with clays and oils may decrease permeability. Organic and sulfamic acids can be used instead of hydrochloric acid to minimize damage.In low permeability rocks, the mud acid main-flush is unlikely to remove the pre-flush-induced damage. The main-flush induced damage may be overlooked if the length of the core is less than 20-30cm.Formulations based on ammonium bifluoride can increase oil production rate in 2 times. In high temperature and high clay content reservoirs fluoroboric acid can be used as an alternative to mud acid to avoid damage. Emulsified acids and hydrochloric-fluosilicic acid have been claimed to provide deeper stimulation than regular mud acid. Pre-flushing with surfactants helps to increase mud acid penetration distance. Also, citric-hydrofluoric acid was proven to be an effective alternative to regular mud acid.Hydrochloric acid post-flush may cause additional damage. On the contrary, fluoroboric acid post-flush increases permeability, as evidenced in reservoirs with fines migration.The presented analysis show that, besides other factors, the results of core acidizing are affected by the presence of oil phase, direction in which permeability is measured, core length, and whether or not the core was pre-damaged.
