An armored, 1/4" cabled, temperature sensor array was developed for oil and gas down-hole applications using Bragg
gratings written into large diameter, single-mode cane waveguides to provide strain-isolated temperature sensor
elements. The temperature sensor array was deployed and evaluated in a test-well. A measured temperature 1-σ
deviation of better than 0.002°C and an overnight stability range of 0.02°C were demonstrated.
A new class of Bragg grating components based on large diameter cylindrical waveguides has been commercially released. Unique properties of the waveguide including grating fabrication, low loss splicing to optical fibers, and specialized machining for optimization in sensor applications are reported. The waveguide structure enables packaging of Bragg gratings that overcomes attachment, mechanical creep, and hermeticity problems commonly associated with fiber Bragg gratings. This enables exceptionally robust Bragg grating sensor transducers well suited for the high temperature, corrosive downhole environment of oil and gas. Sensor transducers have been demonstrated showing no measurable drift or error after over 4-year aging tests at 150°C. More than 50 pressure/temperature installations have been successfully completed and are operational, delivering real-time data cumulatively over 500,000 operation hours. These systems integrate a range of support components specific to in-well oil and gas applications, such as downhole cables, interconnects, and platform instruments. This optical sensing platform, coupled with other optical techniques, has been extended beyond optical pressure/temperature measurements to distributed temperature measurements, multiphase flow, and in-well seismic sensing. These systems have been successfully deployed in multi-zonal, multi-parameter system architectures. This sensing technology is integrated with in-well controls, data acquisition and interpretation, and reservoir modeling. This systems approach is required to close the value loop of intelligent completions in oil and gas production.
Bragg Gratings are waveguides, typically single-mode optical fibers, into which a periodic refractive index modulation has been imprinted by a patterned UV exposure. Fiber Bragg Gratings separate telecom frequency bands or compensate for optical dispersion in long-haul fiber networks, and also serve as strain sensors for civil engineering or geophysical studies and oil, gas or mining exploitation. A Bragg Grating writer is an interferometer for generating the UV exposure pattern. It is one of the unusual cases where an interferometer is a production tool, rather than a metrology instrument. In this paper, we review the most common Bragg Grating writing geometry and propose an opto-mechanical structure having minimal adjustment and very high mechanical stability.
A detailed overview of the design of an optical current sensor implemented with all fiber optic components is presented. Laboratory and field data representing stability with time and temperature is included. Fundamental limits and their relationship to product specifications are also discussed.
Conference Committee Involvement (1)
20th International Conference on Optical Fibre Sensors