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.