Coiled Tubing Acid Stimulation of Alasehir Geothermal Field, Turkey

Abstract

Alasehir geothermal field located in Gediz Graben, West Anatolia – Turkey is the current target for geothermal field development. Several wells drilled in Alasehir geothermal reservoir were below expectations. Static and dynamic pressure – temperature, pressure transient tests and a short term flow test were conducted to characterize the problem and to characterize the initial state of the permeable zones. It was observed that several of these wells had debris at the bottom of the well blocking permeable zones resulting in low injectivity indices obtained from the analyses of multi rate injectivity and pressure transient tests. Cleaning and acid treatments using a coiled tubing unit were designed and carried out to improve well performance of such wells. The criteria for the design of the acid treatment were type of rock formation, number and thickness of the permeable zones, extent of skin damage, and level of steam fraction. The acid treatment used 20% HCl that was placed at the target zones using coiled tubing. Post-acidizing production tests and well test analysis demonstrated that the cleaning and acid stimulation improved the permeability significantly, resulting in production increases more than twice of the initial values in some wells. It was concluded that the parameters such as volume of the fluid treatment, and the selection of additives and the operation parameters are very important to take into account in order to obtain excellent results.