Application of French Downhole Temperature Measurement Optical Cable

Downhole temperature measurement optical cables use fiber-optic technology to provide continuous, high-resolution temperature profiles along the wellbore, enabling real-time monitoring of reservoir and well performance.

Overview of Technology

Downhole optical cables for temperature measurement rely on Distributed Temperature Sensing (DTS), which uses Raman scattering in optical fibers to detect temperature changes along the cable length . A laser pulse is sent through the fiber, and the backscattered light is analyzed to determine temperature at multiple points, providing a continuous thermal profile. DTS systems can detect temperature changes as small as 0.01°C, allowing precise identification of fluid movement, leaks, or thermal anomalies in the wellbore .

Cable Design and Construction

Permanent downhole fiber-optic cables are engineered to withstand extreme downhole conditions, including high pressure, elevated temperatures, mechanical shock, and corrosive fluids . Key design features include:

• Fiber-in-Metal Tube (FIMT): Optical fibers are hermetically sealed in stainless steel or INCONEL® tubes, protecting against chemical ingress and microbending .
• Multi-mode and single-mode fibers: Multi-mode fibers are typically used for DTS, while single-mode fibers support acoustic sensing (DAS) and communication .
• Protective layers: Filling gels, extruded polymer belts, and outer encapsulation provide mechanical buffering, centralization, and additional protection during deployment .
• Prestressing: Controlled overstressing during fabrication ensures fibers remain strain-free, minimizing optical degradation during operation . Cables can be customized for fiber type, quantity, armor, and encapsulation to meet specific well requirements.

Deployment and Applications

Downhole optical cables are deployed on tubing or behind casing, often clamped and coupled mechanically to ensure accurate temperature measurement . They are used in:

• Reservoir monitoring: Detecting fluid movement, thermal fronts, and injection patterns.
• Well integrity: Identifying leaks, casing or tubing anomalies, and temperature anomalies caused by production issues .
• Enhanced completion design: Combined with DAS, DTS data helps optimize fracture mapping, cluster spacing, and inflow control valves in horizontal wells .

Advantages

• Continuous monitoring: Unlike point sensors, optical fibers provide a distributed measurement along the entire wellbore.
• High spatial and temporal resolution: Down to <1 meter spatial resolution and sub-second temporal resolution .
• Durability: Designed for long-term operation in harsh downhole environments.
• Integration: Can be combined with DAS and strain sensing (DSS) for comprehensive well monitoring . In summary, French downhole temperature measurement optical cables are robust, fiber-optic-based systems that provide real-time, high-resolution temperature data along the wellbore, supporting reservoir management, well integrity, and optimized production operations.