Thermal, mechanical and chemical influences on the performance of optical fibres for distributed temperature sensing in a hot geothermal well

Abstract

Structural wellbore integrity is an important issue for a sustainable provision of geothermal energy. Raman scattering based fiber optic distributed temperature sensing (DTS) can help to monitor the status of a well and therefore help to optimize expensive work-over activities. This study reports on the installation of a fibre optic cable in the cemented annulus behind the anchor casing in the high temperature geothermal well HE-53, Hellisheiði geothermal field, SW Iceland. Although the cable has been damaged during the installation, temperature data could be acquired during the entire length of installation down to 261.3 m. Temperature measurements were performed during the installation in spring 2009, during the onset of a flow test in summer 2009 and after a 8.5 month shut-in period in summer 2010. During the flow test, maximum temperatures of 230• C were measured after two weeks fluid production. Using optical time domain reflectometry (OTDR), attenuation measurements at 850 and 1300 nm enabled to identify mechanical, thermal, and chemical degradation along the optical fibre. The observed degradation led to erroneous temperature readings and limits, due to the optical budget of the DTS system, the accessible length of the fibre. The characteristics and the influence of the different degradation mechanisms on the accuracy of the DTS measurements are discussed and recommendations for an optimized installation are given.

Utilizing supercritical geothermal systems: a review of past ventures and ongoing research activities

“…The HiTI project (High Temperature Instruments for supercritical geothermal reservoir characterization and exploitation) focused on developing hightemperature tools and methods Sanjuan et al 2010). This work focused on the development and testing of a high-temperature distributed temperature sensing (DTS) cable (Reinsch and Henninges 2010;Reinsch et al 2013) and a wireline temperature tool, the MultiSensor memory tool that records temperature, pressure, fluid flow and casing collar locations, high-temperature borehole televiewer and resistivity logging tools, and new Na/Li geothermometers (Sanjuan et al 2010, and high-temperature tracers (Gadalia et al 2010;Juliusson et al 2015). The DESCRAMBLE project developed a slick-line temperature and pressure logging tool by SINTEF that can withstand downhole conditions of 450 °C and 450 bar for up to 8 h. The IMAGE (Integrated Methods for Advanced Geothermal Exploration) initiative led to the development of new seismic and electromagnetic investigation methods for characterizing supercritical systems (van Wees et al 2015), and these methods have been employed at the IDDP sites in Iceland.…”

Pressure, temperature and refractive index determination of fluids using a single fibre optic point sensor

“…However, for a long term application in hostile environments like downhole applications suitable strategies for the lead optical fiber as well as the sensor packaging have to be developed [26][27].…”

Well Integrity Analysis in a High Temperature Geothermal Well using Distributed Temperature Sensing Behind Casing

“…The results compare reasonably well with data from conventional acoustic CBL logging (Reinsch, 2012). During flow testing, DTS measurements were performed for a period of two weeks (Reinsch et al 2013). During this time the wellhead temperature increased to about 240°C, whereas maximum temperatures of 230°C were measured in the annulus.…”