Supporting the completion process of boreholes using combined fiber-optic monitoring technologies

Efficient, safe and sustainable utilization of geothermal reservoirs depends on reliable well completion and monitoring technologies. Conventional borehole measurement methods can only be used after the completion process and usually show snapshots of the borehole conditions at discrete points in time. Therefore, the successful borehole completion is a risky process and mainly relies on the experience of the driller. By using distributed fiber-optic sensing technologies, it is possible to monitor all along the cable with dense spatial sampling and continuous in real-time.

In this presentation, we give insights into our newest case study in Berlin. A 450 m deep exploration well for an Aquifer Thermal Energy Storage was completed. We installed a fiber optic sensor cable along the whole production tubing, that contained several single-mode and multi-mode fibers in loose tube and tight buffered configuration. This cable allows to simultaneously measure distributed temperature (DTS), distributed acoustics (DAS) and distributed strain (DSS/DTSS) for the entire completion process.

Particularly with a combined analysis and interpretation of the different fiber-optic technologies, conventionally untraceable processes can be visualized. We are able to show changes of subsurface flow paths due to blockages. Processes to be prevented, like caving or bridging can be detected and the proper rise of gravel or cement can be surveyed. Provided to the driller in real time, subsurface uncertainties can be significantly reduced.

Monitoring geothermal wells with a fiber-optic sensing infrastructure is not only a powerful tool to reduce risks during well completion, which can lead to compromised well integrity. The installed equipment and technology can also be used to assess the well integrity over the whole cycle of the well, to ensure a longest possible lifespan.