Abstract

As the geothermal industry continues to drill wells at higher temperatures to increase energy production, including recent activities to develop supercritical geothermal systems, the potential for casing structural and serviceability failures related to thermally-induced plastic deformation and cyclic thermal loading increases. Accordingly, selection of casing materials and connection designs suitable for the extreme temperature variations expected throughout the life of geothermal well is critical for maintaining well integrity and optimizing project economics.

Current well design practices employed in the thermal enhanced oil recovery (EOR) operations of Western Canada, where operating temperatures can reach up to 350°C, have been suggested as a basis for the evaluation of geothermal well designs. Specifically, by combining established thermal casing connection evaluation approaches using Finite Element Analysis (FEA) developed for thermal well applications with recently developed connection sealability criteria, an integrated analytical approach can be developed for casing connection evaluation in such high-temperature applications. This proposed approach provides a cost-effective means for screening suitable casing connection designs with adequate structural integrity and sealability under high-temperature geothermal operating conditions.

This paper provides a review of existing protocols with procedures for FEA evaluation and full-scale experimental testing to evaluate casing connections. An analytical sealability criterion suitable for premium casing connections subjected to geothermal operating conditions is introduced, and an integrated analytical evaluation approach is proposed for geothermal applications, which in many cases may be both cost-effective and appropriate for the level of risk. Examples of premium casing connection designs subjected to cyclic thermal load conditions and curvature loading are analyzed and presented in this paper to demonstrate the use of the proposed integrated approach.