Injection Improvements in Low Permeability and Negative Skin Wells, Using Mechanical Cleanout and Chemical Stimulation, Berlin Geothermal Field, El Salvador

Abstract

The primary resource challenge in maintaining the full output of the 56 MW Berlin geothermal power plant has to inject all the produced fluid. The injection wells at Berlin all encountered low permeability formations with small fractures that can be relatively easily plugged with scale or particles. Silica scaling from a saturated liquid, along with silica particles from the production wells and the gathering and injection systems have repeatedly reduced the injectivity of the low permeability injection wells. Successful mechanical cleanouts and acid chemical stimulations in injection wells TR10, TR7, and TR1B have been very important in maintaining adequate injectivity for the power plant by restoring injectivity from 30 to 60%. Pressure transient tests and analysis of the data have quantified the amount of improvement from most of the cleanouts and stimulations. The reduction of the skin factors to more negative values suggests the stimulations not only influenced the matrix of the formation but extended and modified the permeability inside the walls of the micro fractures. To reduce or eliminate the need for future cleanouts and stimulations, filters are being installed on the injection wells, the injectate will be acidified and high volume high pressure pumps are being installed on the injection system.