Characteristics of Acid Reaction in Limestone Formations

A kinetic model for the reaction of hydrochloric acid with limestone has been determined. Reaction order and rate constant for this model were calculated from experiments where acid reacted with a single calcium carbonate plate. Experiments were performed so that acid flow past the plate and mass transfer rate to the rock surface could be calculated theoretically. The resulting model, therefore, accurately represents the acid reaction process at the rock surface and is independent of mass-transfer rate. Combination of this model with existing theory allows prediction of acid reaction during acid-fracturing operations. A model for acid reaction in wormholes created during matrix acidization treatments is presented along with data for reaction of hydrochloric, formic, and acetic acids in a wormhole. Factors limiting stimulation in acid fracturing or matrix acidizing treatments are discussed. (27 refs.)