16.4 Calibrations

Two kinds of calibration are applied to DTS data. These are:

• Factors pertaining to the Instrument Box such as the oven reference temperature, the number of launches being stacked to get a temperature value at the required resolution.
• Factors related to the fiber, including the (practically linear) differential attenuation along the fiber, and the refractive index of the fiber.

Where the fiber may be installed in a well bore for several years, it is necessary to recalibrate these factors periodically in order to be able to compare reservoir temperatures over these periods.

The Optical Time Domain Reflectometry (OTDR) technique provides a routine means of examining the condition of the fiber. OTDR consists of observing the attenuation of backscattered light in the frequency band of the transmitted Rayleigh waves. An OTDR profile is illustrated in Figure 16.4-1 .

Figure 16.4-1 Optical Time Domain Reflectometry (OTDR) Profile.