An investigation of the effectiveness of anhydrous mud acid to remove damage in sandstone formations

Abstract

The goal of this experimental research was to determine the reactivity of anhydrous mud acid with clay minerals present in sandstone formations and its ability to remove damage in sandstone acidizing. Berea core flood experiments were conducted with a mixture of carbon dioxide, hydrogen chloride and hydrogen fluoride. These tests were carried out with oven dried cores and cores at irreducible water saturation. Anhydrous mud acid appears to be reactive with all the cores tested. However, it does not have the ability to reduce damage as hoped. The aqueous phase is required to transport the products of the reaction. To confirm this, other tests with a mixture of 75% C02 and 25% aqueous acid by volume were done and again found to be reactive with the cores tested but were unable to remove the products of the reactions. Salt water afterflushes were done on these cores and the dissolved material was able to be transported out of the core. Therefore, it appears aqueous acid is required in an amount greater than 25% by volume to remove damage effectively in sandstone mud acidizing treatments utilizing C02 as a conjugate fluid.