Acid stimulation of geothermal wells in Mexico, El Salvador and the Philippines

Abstract

Acid treatments are among the most common treatments used for increasing formation permeability in undamaged wells, as well as in removing formation damage. This is due to the acid’s ability to dissolve depositions of minerals that cause decreased mass flow rate or low injection capacity. One of the acid treatments is called matrix acidizing, which is a technique that involves the injection of acid into the formation through the well at a pressure below the pressure at which a fracture can be opened. In several countries such as Mexico, El Salvador and the Philippines, this stimulation technique has been used for several years, in both production and injection wells with successful results. Although the matrix acidizing technique applied in each country is based on the same treatment, there are differences between them. The main differences consist of the injected acid concentration and the volume used in each stage. Other variations include the omission of post-flush in the Philippines and also in some cases in El Salvador, and the use of fresh water for the over-flush in El Salvador and the Philippines while geothermal water is used in Mexico. Some wells in El Salvador and also in the Philippines have been treated with sandstone acid (RPHF) instead of hydrochloric acid (HCl), as is used in regular mud acid for the main flush, and that is probably the most important difference between the treatment design in Mexico and that in the other two countries.