Impact of common completion and workover activities on the effective costs of geothermal wells

The impacts of completion practices on production and maintenance costs are considered. To evaluate alternative completion and workover technologies, a simple model has been developed that compares total well cost to total production or injection. The model is discussed briefly and results from its application to different completion and workover strategies are emphasized. The model development project had three aspects: (1) the establishment of a data base for the cost and effectiveness of various geothermal completion and workover activities; (2) the development of a computer model to specific cases. The data collected include geothermal production characteristics; initial costs and completion practices for representatives wells; estimated costs and effectiveness of common workover equipment and operations; the frequencies of and times required to perform workovers; etc. The model facilitates comparisons of completion and workover alternatives. The results discussed include an analysis of the impact of variations in well lifetime. A comparison of mechanical descaling of geothermal wells to chemical scale inhibition indicates that for certain conditions chemical inhibition is more cost effective. Results of an analysis of injectivity decline are also presented, as are studies of original well cost, initial flow, and productivity decline for production wells. Other results involving underreaming, changing casing profiles, perforating, and hydraulic fracturing are also discussed.