Geothermal Well Costs and their Sensitivities to Changes in Drilling and Completion Operations

This paper presents a detailed analysis of the costs of drilling and completing geothermal wells. The basis for much of the analysis is a computer-simulation-based model which calculates and accrues operational costs involved in drilling and completing a well. Geothermal well costs are discussed in general, with special emphasis on variations among different geothermal areas in the United States, effects of escalation and inflation over the past few years, and comparisons of geothermal drilling costs with those for oil and gas wells. Cost differences between wells for direct use of geothermal energy and those for electric generation, are also indicated. In addition, a breakdown of total well cost into its components is presented. This provides an understanding of the relative contributions of different operations in drilling and completions. A major portion of the cost in many geothermal wells is from encountered troubles, such as lost circulation, cementing difficulties, and fishing. These trouble costs are considered through both specific examples and statistical treatment of drilling and completions problems. The sensitivities of well costs to variations in several drilling and completion parameters are presented. The mode1 makes it possible to easily vary parameters such as rates of penetration; bit lifetimes; bit rental, or rig costs; delay times; number of cement plugs; etc. are compared.