Successful Field Application in Continuous DTS Monitoring Under Harsh Environment of SAGD Wells Using Improved Optical Fiber Technology - Case Study from Canada

Kaura, Jiten D. (WellDynamics Inc.) | Sierra, Jose R. (WellDynamics Inc.)


The use of optical fibers in the oil and gas industry is becoming more viable for several permanent monitoring applications, such as distributed temperature sensing (DTS) and optical pressure transducers. However, long-term performance of fibers, especially at elevated temperatures, is still an issue yet to be fully resolved. This problem is critically important in steam-assisted gravity drainage (SAGD) applications, where wells operate in extreme conditions of high temperatures, often exceeding 250oC, as well as in high pressures within a hydrogen-rich environment.

Optical fiber performance is seriously affected by many factors, including:
        •     Hydrogen ingression
        •     Thermal resistance of the materials
        •     Mechanical resistance of the fiber

Exposure of optical fibers to hydrogen changes the performance of the fibers through what is referred to in the industry as "hydrogen aging?? or "hydrogen darkening.?? Hydrogen darkening is increased absorption or light loss due to various chemical species in the glass fiber resulting from the presence of hydrogen.

Value of DTS in SAGD Applications
It is known that temperature monitoring in SAGD wells is of significant importance because it provides a good understanding of the temperature distribution along the horizontal section. Conventionally, thermocouples have been used to measure and monitor the temperature along the horizontal section, and are typically installed at heel, middle and toe of the section. Since thermocouples (TC) inherently provide temperature data at these discrete points, temperature information between the TCs is
usually interpolated to understand the temperature distribution. As a result of this interpolation, there could be sections of the wellbore that would require more data from different sources for a detailed analysis instead of just being able to visualize the temperature behavior. Hence, there is a need for a tool that can provide temperature data along the entire length of the horizontal section. In addition, the installation must be simple in order to keep it safe and cost-effective. The optical fiberbased DTS technology has been applied in the past successfully and it is known that the optical fiber-based DTS technique provides temperature data along the entire length of the fiber. This temperature data provides information;, e.g., what sections of the lateral are operating at "sub cool,?? and enabling users to:

        •     Quickly identify anomalies
        •     Immediately implement corrective action
        •     Allow for better steam utilization