Downhole temperature logging data can be utilized to identify productive intervals, monitor the current inflow profile, and detect cross-flows and leaks in the annular space. This method is particularly relevant for wells where steam is injected to produce heavy oil. Accurate, continuous, and prompt temperature monitoring allows for real-time control of the injection profile and management of the steam injection process. Fiber-optic sensors are immune to electromagnetic interference, have small dimensions, and can withstand extreme conditions such as high temperatures, pressure, and aggressive environments. This makes them ideal for permanent monitoring of temperature and pressure within a wellbore.
The operating principle is based on distributed fiber-optic temperature reflectometry, where the optical fiber itself serves as both the sensor and the signal transmission medium. According to the principle of Raman backscattering, a laser pulse propagating through the fiber generates backscattering when heated. The higher the ambient temperature at a given point, the more intense the backscattered glow. By analyzing the intensity of the scattered light, the temperature at the measurement point can be determined. Using the principle of Optical Time-Domain Reflectometry (OTDR), the distance to the scattering point is calculated based on the travel time of the light pulse from the injection point to the scattering point and back. In thermal recovery wells, high-temperature steam injection with temperatures up to 300 ℃ is required. Special high-temperature optical fiber is capable of functioning within a temperature range of −65 ℃ to 300 ℃.
