Coiled Tubing Injection String for Geothermal Wells

Abstract

Abstract Geothermal wells are constantly producing extremely hightemperature steam and endogenous fluids containing corrosive substances.1 These corrosive substances are detrimental to completion, surface, and processingplant materials. In addition, geothermal wells contain high percentages of dangerous gasses, such as hydrogen sulfide (H2S), requiring operators to take special safety precautions. When coiled tubing (CT) injection strings are used to complete such wells, equipment and surfaceplant damage caused by corrosive geothermal fluids can be significantly reduced. Conventional methods require well cleanup operations at regular intervals, but CT provides a permanent installation that allows corrosioninhibiting fluids to be injected continually, thus neutralizing the chlorides produced from the steam. Consequently, operational costs are reduced, lost production time is avoided, and the need for workover interventions is decreased. In addition, because CT is continuous pipe without joints, it provides operators with a greater degree of safety when they work on wells under pressure. This paper discusses the techniques, wellhead equipment, and bottomhole assembly (BHA) used to install CT injection strings in several geothermal wells in Italy. The technical aspects of some of the 15 wells already completed by this method are also discussed. In addition, ideas for improving future geothermal well completions are presented.