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Abstract:
Common failure mechanisms in high-temperature geothermal wells are casing collapse and tensile joint rupture. For medium- to high-enthalpy geothermal wells, thermal cycling has the potential to severely deteriorate the integrity of the cemented annulus. Additionally, for higher enthalpy wells, yielding of casings becomes a structural concern. A recently innovated patented solution, flexible couplings, aim to reduce thermal strains by allowing displacement from thermally expanding casing segments at ~12 m intervals (API Range 3 casings). In the GeConnect project, a full-scale surface experiment composed of a 9⅝′′ casing equipped with a flexible coupling cemented into a 13⅜′′ casing is constructed and installed on a wellpad of an existing high-temperature geothermal well in Iceland. The aim is to investigate effects of thermal cycling on well integrity and to test the function of cemented-in flexible couplings. Along with testing the flexible coupling, cement sheath integrity and the cement-casing boundary behavior will be evaluated atmoderate to high temperatures. Structural models are used to analyze casing-cement interactions and to evaluate prospects and potential improvements of well integrity by using flexible couplings on experimental up to field scale.
