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WP5 – Well monitoring

Leader: GFZ

Other partners involved: ISOR, TNO, HS ORKA

Objectives

In order to increase the lifetime of a geothermal well and to allow for a safe operation throughout its lifetime, the structural integrity of casing and cement will be analysed. In geothermal wells, especially large temperature and pressure changes during production/injection as well as shut-in periods lead to strong variations of the thermal and mechanical load onto the subsurface construction. To study the performance of casing and cement during varying load conditions as well as to identify processes influencing the integrity of casing and cement, this workpackage focuses on real-time well monitoring technologies. Therefore, distributed fiber optic sensing technologies shall be developed and tested to simultaneously measure temperature, strain and acoustic noise within the cemented annulus of a geothermal well. Data shall be compared to conventional well logging procedures and used to evaluate the casing/cement performance as well as optimize the monitoring strategy for future wells.

Description of work

In order to monitor the response of a casing to changing load conditions, temperature, strain and noise will be measured within the annulus of a geothermal well at the onset of a production/injection test applying a combination of different distributed fibre optic sensing technologies. These include the distributed temperature sensing (DTS) technology as well as the cutting edge distributed strain and distributed acoustic/vibration sensing (DAS/DVS). In order to allow for a simplified and more accurate detection of strain as well as acoustic noise, an improved fibre optic interrogation unit will be developed and tested within this WP.

Within this work package the combined measurement of temperature and strain behind casing of a geothermal well, preferably IDDP2, during cementation shall be performed. The data will be compared to temperature data acquired within wells HE-53 (HiTI project) and RN-34 (IMAGE project) in order to evaluate the current cementation practice for geothermal wells, optimize cement placement and pumping procedures and quantitatively analyse the cement quality along the casing. Apart from the cementation practice, the installation shall also be used to analyse the behaviour of the subsurface installation during changing thermal load conditions. The thermal and mechanical load exerted onto the subsurface installation shall be measured in real-time and compared to the measured cement quality behind casing. Furthermore, DAS measurements shall be performed simultaneously to evaluate vibrations induced by the fluid flow onto the subsurface installation as well as to investigate the integrity of the cemented annulus in response to the applied mechanical and thermal load.

In order to test the combined measurement of temperature and strain, laboratory experiments are planned for testing various fibre optic cable installation techniques under controlled temperature conditions. An oven and a climate chamber can be used for these systematic studies. Partial and full cemented test samples will be subjected to different simulated wellbore strain conditions. Appropriate data filtering and pre-processing techniques will be tested and selected for the required strain quantification. To monitor the properties of the casing and cement properties in WPs 3 and 4, a combined experiment shall be performed in a laboratory environment.

In a second step, a preliminary field test will be conducted at the Ketzin pilot site where there are three wellbores equipped with fibre optic cables which can be deployed for temperature and strain measurements. During site specific technical operations, some strain producing activities will take place and these will be accompanied by a combined distributed temperature and strain measurement technique.

The results of the measurements will provide information to review current cementation and completion practices and monitor the load cycles on subsurface components (casing/cement).

Dernière mise à jour le 31.05.2016