High-temperature fiber-optic logging systems enable precise, distributed temperature measurements in harsh environments, offering real-time monitoring and long-term reliability beyond traditional sensors.

Overview

High-temperature logging fiber-optic systems are designed to measure temperature profiles in extreme conditions, such as deep wells, geothermal reservoirs, and industrial furnaces, where temperatures can exceed 300 °C and even reach above 1000 °C in specialized applications . These systems use optical fibers as linear sensors, allowing distributed temperature sensing (DTS) along the entire length of the fiber, often spanning several kilometers . Unlike conventional thermocouples, fiber-optic systems are immune to electromagnetic interference, can be multiplexed, and support remote monitoring .

Measurement Principles

The system typically relies on Raman or Brillouin optical scattering. A laser pulse is sent through the fiber, and the backscattered light is analyzed. In Raman-based DTS, the Stokes and anti-Stokes components are measured, and their intensity ratio is used to calculate the local temperature along the fiber . The position of each temperature reading is determined using Optical Time Domain Reflectometry (OTDR), which calculates the distance based on the time delay of the returning light . Some systems also use Optical Frequency Domain Reflectometry (OFDR) for high-resolution measurements over shorter distances.

Applications

These systems are widely used in downhole logging for oil, gas, and geothermal wells, where they provide continuous temperature profiles along the wellbore . They can be permanently installed behind casing or deployed temporarily for surveys. Key applications include:

• Production monitoring: Identifying gas and liquid influx, evaluating cluster efficiency, and assessing stage uniformity in horizontal wells .
• Geothermal and CO₂ injection monitoring: Measuring temperature changes to evaluate thermal conductivity and reservoir behavior .
• Industrial high-temperature monitoring: Tracking combustion efficiency in furnaces, turbines, and boilers .

Advantages

• Distributed sensing: Provides continuous temperature data along the entire fiber length, unlike point sensors.
• High spatial resolution: Typically down to 1 meter, enabling precise detection of thermal anomalies .
• Harsh environment tolerance: Can operate under high temperatures, pressures, and electromagnetic interference.
• Integration with other measurements: Can be combined with distributed acoustic sensing (DAS) and distributed strain sensing (DSS) for comprehensive downhole monitoring .
• Real-time monitoring: Supports automated workflows for production optimization, leak detection, and reservoir management .

Deployment Considerations

The fiber type, cable design, and installation method must be carefully selected based on temperature range, well depth, and environmental conditions . Permanent installations behind casing are common for long-term monitoring, while temporary deployments are used for surveys or testing. Advanced systems may include code-correlation OTDR to enhance signal-to-noise ratio and extend measurement range . In summary, Dutch high-temperature logging fiber-optic systems leverage distributed optical sensing technologies to provide reliable, high-resolution temperature monitoring in extreme environments, offering significant advantages over traditional electronic sensors in terms of durability, spatial coverage, and real-time operational insights .