Laboratory work on the response of reservoir rocks from the Los Humeros geothermal field, Puebla, Mexico, with acid solutions

Abstract

Rock matrix stimulation is a methodology used to enhance well productivity in oil systems. Some years ago this methodology began to be applied in geothermal systems. In order to investigate the behavior of altered volcanic rocks interacting with an acid solution, experiments were carried out using rock samples from Los Humeros geothermal reservoir. Two acid solutions, 10% HCl and a mixture of 10% HCL-5% HF, were used to investigate rock dissolution at atmospheric pressure and 150 degrees C. Chemistry, mineralogy and permeability of rocks were determined before and after the reaction with acid solutions. Mineral dissolution depends on the mineral reactivity with acids. Calcite in veins and micro fractures reacts immediately with the acid solution. Calc silicates react by dissolution of minerals in contact while leaving the rock matrix untreated. Preliminary experimental data indicate that both solutions are effective dissolution agents. Dissolution capacity increases with time. No precipitation of secondary minerals was detected.