Managing the Need for Growing Re-injection Capacity at Hellisheiði Power Plant, Iceland

Abstract

Since the commissioning of Hellisheiði power plant, SW Iceland, in 2006 and subsequent increments in production until 2011, constant addition to the re-injection capacities of the power plant has been necessary. The reasons for the constant need of more re-injection capacities is a decrease in injection rates of injection wells and decline in average enthalpy of fluid produced from the geothermal field resulting in more brine at constant power production. Initially this decline in injection rates and the increase in geothermal brine for re-injection was met with converting wells, that initially were drilled for power production but as such were not successful, into injection wells. These wells are close to the production area and their use for re-injection into them had both positive and negative effects on nearby production wells. Injection into wells drilled into low-temperature formation were not successful as the decline in injection rate into these wells was rapid. These challenges called for a systematic approach identifying possible new re-injection area for the power plant. Analytical hierarchy process was used for evaluating possible new injection sites where each possible site was rated based on seven factors related to the feasibility of the site for re-injection. The result acted as a guide for a re-injection site selection and steps are being taken to move part of the re-injection of Hellisheiði power plant further away from the production field based on this approach.