A production impairment that can occur when the formationmatrix in the near-wellbore area becomes water-saturated, thereby decreasing the relative permeability to hydrocarbons. Water block may result from the invasion of water-base drilling or completion fluids or from fingering or coning of formation waters.The most extreme cases of water block occur in low-pressure, low-permeability gas formations, where alcoholic acid systems are recommended because they promote water vaporization in the produced gas.Alcoholic acid formulations are a mixture of acid and alcohol. The acids normally employed are usually either hydrochloric acid [HCl], mud acid [HF-HCl or HF-organic acid (formic or acetic)]. The alcohol is either methyl or isopropyl. Alcohol lowers the surface tension of acid and allows deeper penetration of the acid into the matrix of the rock. Alcohol is somewhat soluble in both acid and water, and penetration of low-surface-tension volatile alcohol into a water block will aid in its removal.

Related Terms:

water-base drilling fluid