The cement sheath mainly serves to support the borehole casing and seal the 
annulus to flow along the axis of the well. Especially geothermal wells require a 
high-quality cement sheath because they are subject to strong mechanical 
stress resulting from high temperature changes. Moreover expansion of 
trapped fluid behind the casing can lead to unintended fracturing of the 
formation or casing collapse. Temperature logs have traditionally been used to 
determine the top of cement, while more recently acoustic and nuclear 
measurements have been added to the methods used for cement sheath 
evaluation. Using distributed temperature sensing (DTS) continuous 
temperature profiles can be recorded with high temporal and spatial resolution. 
In contrast to conventional wireline logging, the complete evolution of the well 
temperature profile over time can be monitored. The fiber-optic sensor cables 
can be permanently installed behind the borehole casing allowing for 
continuous monitoring during operation and production without well 
intervention. Here we report on a set of DTS measurements performed during a 
stinger cementation in an 800m deep well which was drilled in a saline aquifer 
in the Northeast-German basin within the framework of the CO2SINK project. 
From the evolution of the well temperature profile over time the position and 
quality of the cemented sections was determined. Apart from information during 
construction and completion, important data for the operation of a well and for 
monitoring of processes inside the reservoir causing temperature changes can 
be collected using the installed DTS cable.

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Reykjavik,
Iceland