PSI - Issue 64

Michael Iten et al. / Procedia Structural Integrity 64 (2024) 1642–1648 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

1645

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After the installation, the fiber optic sensors were connected to the readout unit and continuously measured with a temporal average over two minutes to monitor the cementation process and the subsequent setting process. As Raman based temperature monitoring can be performed in a single end setup, the intact sections of the cables that got damaged during installation could still be measured.

0 mTVD

0 mTVD

GES-F-1

GES-F-2

16"

200 mTVD 228 mTVD

239 mTVD

Surface casing

10 ¾"

Production casing

= Marl/clay = Sandstone = Quaternary

= Fibre-optics

V = “ Mini-Loop ” = Rupture

500 mTVD 477 mTVD

Fig. 2. Schematic of boreholes GES-F-1 and GES-F-2 with the fiber-optic instrumentation along the casings.

3. Results Fig. 3 and Fig. 4 show the temperature profiles measured during the cementation along the cable inside the annulus of the surface casing of GES-F-1 and GES-F-2, respectively. Please note that the plotted temperature ranges of the two presented boreholes are at a different absolute level due to the varying temperatures of the injection material. This was chosen purposely to better highlight the various effects, consciously accepting a trade-off in comparability between the boreholes. After applying a temperature matching approach to calibrate the differential attenuation along the fiber, the data shows a good correlation between the two strings of the looped cables. The temperature change of a few degrees Celsius induced by the rising grout level is clearly visible in the data. Activities above ground level (e.g. flushing the wellhead) can be observed, too. Temperature readings over a longer period of time after the cementation can be used to observe the setting of the cement. In Fig. 5 distributed temperature profiles over a 24 hour period at GES-F-1 are shown. It can be clearly seen that temperature changes are much higher over this period. At some locations, temperatures above 40°C are obtained. In addition, the time-dependent temperature curve can be easily recognized, reaching its peak around 14 hours after the start of cementation.