1. n. 
A treatment designed to treat the near-wellbore reservoir formation rather than other areas of the production conduit, such as the casing across the production interval, production tubulars or the perforations. Matrix stimulation treatments include acid, solvent and chemical treatments to improve the permeability of the near-wellbore formation, enhancing the productivity of a well. Matrix stimulation is a process of injecting a fluid into the formation, either an acid or solvent at pressures below the fracturing pressure, to improve the production or injection flow capacity of a well. The goal of a matrix treatment is different in sandstones than in carbonates. In sandstones, matrix treatments restore or improve the natural formation permeability around the wellbore by removing formation damage, by dissolving material plugging the pores or by enlarging the pore spaces. In carbonates, matrix stimulation creates new, highly conductive channels (wormholes) that bypass damage. Because of these differences, the selection criteria for the treating fluid are also distinct. For sandstone treatments, knowledge of the extent, type of damage, location, origin, reservoir mineralogy (petrographic study) and compatibility of the treating fluid with the formation are especially important. In carbonate treatments, reservoir temperature, pumping rate and fluid type become more significant because these parameters directly affect the reactivity of the treating fluid with the reservoir rock. A sandstone matrix stimulation treatment is generally composed of a hydrochloric acid [HCl] preflush, a main treating fluid (HCl-HF mixtures) and an overflush (weak acid solution or brine). The treating fluid is maintained under pressure inside the reservoir for a period of time, after which the well is swabbed and returned to production. In carbonate reservoirs, HCl is the most common fluid used. Organic acids such as formic and acetic acid are used in either sandstone or carbonate acidizing, mainly in retarded-acid systems or in high-temperature applications. Matrix stimulation is also called matrix treatment or matrix acidizing.