Objectives: The aim of WP3 is to measure axial and hoop strain development within a casing equipped with a flexible coupling under varying thermal and mechanical load conditions and thereby demonstrate the capability of the flexible coupling to operate under harsh downhole conditions (from TRL 4 testing in GeoWell to TRL 6 in GeConnect). The test, performed in situ at a high temperature geothermal field will reveal the main function of the Flexible Coupling, its tightness and behavior during thermal loading. Therefore, a full-scale 9⅝″ casing equipped with a flexible coupling will be cemented into a 13⅜″ casing and equipped with monitoring equipment. The test rig will be installed at the surface and geothermal fluid will be diverted through the inner casing. To test the performance of the flexible coupling at temperatures typical for medium enthalpy geothermal wells in Europa as well as high enthalpy geothermal wells like in Iceland or Italy, the test will be split into two parts. Thermal cycling experiments will be performed at temperatures up to 150°C and in a later step at high-temperature geothermal conditions of more than 250°C. Thermal and mechanical stresses and strains will be calculated (from temperature/pressure information) and strain in axial and tangential direction along the 9⅝″ casing will be measured. Therefore, an optical fiber cable will be attached to the casing and fiber optic distributed sensing technologies will be used to access temperature and strain variations with a high spatial and temporal resolution. Strain data will be used to analyze the casing cement interface as well as the displacement within the Flexible Coupling. Data will also be used to determine the threshold when the casing loses mechanical connection to the surrounding cement and starts to elongate due to its thermal expansion.
- Task 3.1 Site selection and preparation of surface test (ISOR, LV, HS, GFZ) In the task, the surface experiment will be designed and prepared. The surface experiment will be performed on a convenient well pad near to a flowing geothermal well. Site selection is based on availability on site where 100°C to 300°C media can be connected to the experimental setup. A full-scale casing (9⅝″) and length of 12 m with attached Flexible Coupling will be installed at the surface and cemented within an outer casing (13⅜″) to simulate annular clearance and real downhole conditions. The inner casing will be fitted with a flexible coupling, where approximately 12 m of casing will have the capability to expand into the flexible coupling. The test piece, made of the inner and outer casings, will be integrated into a steel/concrete support frame and bypass a surface flow line from an operating high temperature geothermal well. Along the casing, an optical fiber will be installed to measure the strain of the casing during thermal load changes. In addition, a window will be cut into the outer casing at the position of the coupling to visually observe the movement of the casing pipe into the coupling. To monitor the acoustic noise during the movement, an acoustic acquisition system will be attached as well.
- Task 3.2 Set-up experimental facility and demonstration In the task, the experimental setup will be assembled and installed at pre-selected location, where the surface test will then be executed. In order to simulate the thermal load onto the flexible coupling under in-situ conditions, geothermal fluid at different temperature levels is diverted through the casing. Starting with fluid at about 100-150°C to resemble medium-enthalpy geothermal reservoir conditions, with heating and cooling cycles performed and strain evolution along the casing measured. In a second step, the temperature will slowly be increased to higher temperatures to observe the performance as well as the cement integrity evolution at temperatures typical for high enthalpy geothermal environments.
- Task 3.3 Data analysis (and system calibration) In the task, data gathered from the surface experiment will be analyzed and acoustic data will be calibrated. Data from strain sensing will be used to demonstrate and quantify the movement of the flexible coupling as well as the strain of the casing during load changes. A characteristic noise that is generated when the flexible coupling closes will be monitored by acoustic sensors placed on the casing. Data from the fiber optic measurement shall be used to calibrate the acoustic data.