Innovative design of high temperature geothermal wells Ingolfur Thorbjornsson Head of Geothermal Engineering Iceland GeoSurvey

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1 Innovative design of high temperature geothermal wells Ingolfur Thorbjornsson Head of Geothermal Engineering Iceland GeoSurvey The GeoWell project has received funding from the European Union s Horizon 2020 research and innovation programme under grant agreement No The DEEPEGS project has received funding from the European Union s Horizon 2020 research and innovation programme under grant agreement No

2 Reaching deeper higher temperatures harsh chemistry Simplified model of high temperature system with two feed zones

3 Temperature rise - thermal expansion Mitigation of thermal expansion in surface equipment by using thermal expansion loops is common practice in geothermal fields Designed to prevent damages and displacement of the pipes Photo: Gunnar S. Kaldal Geothermal Well reaching 2-4 km down is drilled and cemented in place no compensation for thermal expansion?? Same physics applies for materials on surface as downhole

4 High Temperature - Thermal expansion damages of Casing during warm up Photo: ISOR HS-ORKA Photo: Thorbjornsson Due to high axial load, the constrained casing either collapse bulge, or deform locally

5 And if the need for cooling the well down! Photo: ISOR-IDDP1 Photo: ISOR-IDDP1 Coupling failures due to high tensile load during cooling from deformed casing segment

6 Mitigation Flexible couplings Allow displacement that compensate for thermal expansion of the casing Stress in the casings will be within the elastic range No plastic strains are therefore generated If wells need to be shut-in or quenched with cold water for maintenance, no axial tension is generated if the well cools down again

7 Mitigation Flexible couplings The Flexible Coupling is designed according to applicable standards, API (American Petroleum Institute) and ISO standards Designed with conventional API BTC threads Made of L80 material (for K55 and L80 casings) Allows clearance for cementing

8 Flexible couplings function Casings with Flexible coupling are run in hole with same procedure as normally done The couplings remain in their open position during casing installation The gap length L T is fixed for design temperatures in each case When the casing warms up it expands and the Flexible couplings close without generating plastic strains in the casing L T ~12m

9 Flexible couplings Designed and tested Main load cases of couplings Installation: make-up torque axial tension (self weight) Operational: axial compression due to thermal expansion axial tension due to cooling burst and collapse pressures (radial and hoop loads) additional bending The Flexible Coupling is designed so that when the casing expands thermally it reaches 70-80% of casing material yield strength without generating plastic deformations -σ b σ th σ w σ b σ th

10 Testing of Flexible Couplings Photo: Thorbjornsson Testing results: Tight up to 110 bar (with pressurized water, open position) Can hold load up to 3000 KN (as build) Sliding not affected by bending Sliding force constant with repeatable sliding. In total 4 full size 9,5/8 Flexible Couplings tested Photo: Thorbjornsson

11 Conclusion Current design standards for casing design do not prevent plastic deformation of casings due to thermal expansion Flexible Couplings for high-temperature geothermal wells aim to eliminate these forces by allowing displacement of every casing segment (~12m) Flexible Couplings have been in development in the EU funded H2020 project GeoWell (and further developed in H2020 project DEEPEGS) It is our hope that the new solution, Flexible Couplings, can in part solve problems involved in designing and drilling for geothermal wells, conventional as well as high temperatures Photo: Gunnar S. Kaldal

12 THANK YOU