Patent number:US2008232425 Publication date: 2008-09-25 Inventor:HALL TRAVIS S (US); CHILDERS BROOKS A (US) Applicant:BAKER HUGHES INC (US)  

BACKGROUND
A common problem with distributed temperature sensing systems (DTS) involves difficulties in making calibrated temperature measurements. Calibrations have very limited benefit if the spectral dependent loss is non-linear (location dependent). In the case of non-linear spectral attenuation, one accepted solution is to deploy a DTS sensing fiber in a dual-ended configuration, which, when interrogated from both directions by a DTS system on the surface, can be used to correct for errors due to non-linear spectral attenuation. To date, a primary technique to achieve a dual-ended DTS configuration has been to use control line tubing (which may be, e.g., around [1/4] inch in outer diameter) and a U-tube at the distal end of the system that connects the tubing, and then to pump an optical fiber along the entire length of the tubing (in the case of downhole applications, from the surface to bottom hole and back to the surface).

Prior art procedures for calibrating DTS data include averaging entire sections of temperature data along a fiber's length. Due to various inconsistencies in the temperature data generated from these procedures, such procedures are often unreliable. Unreliability often comes in the form of temperature value spikes and other inconsistencies at various locations along the fiber's length. Such current DTS calibration procedures result in significant inaccuracies in temperature data, such as spikes at various locations along the fiber's length and/or sections of temperature data forming slopes or gradients along sections of the fiber's length.

SUMMARY
A method for calibrating distributed temperature sensing (DTS) systems includes: receiving temperature data associated with one or more locations along a length of an optical fiber; calculating a set of unique calibration coefficients specific to each of the one or more locations along the fiber length; and applying the set of calibration coefficients specific to each of the one or more locations along the fiber length to the temperature data for calibrated correction thereof.

A system for calibrating DTS data includes: an optical fiber having one or more sensing locations along a fiber length; and a DTS unit for receiving temperature data associated with one or more locations along a length of the optical fiber. The DTS unit includes: a receiver for receiving temperature dependent signals and generating the temperature data therefrom; and a processor for calculating a set of unique calibration coefficients specific to each of the one or more locations along the fiber length, and applying the set of calibration coefficients specific to the one or more locations along the fiber length to the temperature data for calibrated correction thereof.

A wellbore for providing calibrated DTS data includes: an optical fiber having one or more sensing locations along a fiber length; and a DTS unit for receiving temperature data associated with one or more locations along a length of the optical fiber. The DTS unit includes: a receiver for receiving temperature dependent signals and generating the temperature data therefrom; and a processor for calculating a set of unique calibration coefficients specific to each of the one or more locations along the fiber length, and applying the set of calibration coefficients specific to the one or more locations along the fiber length to the temperature data for calibrated correction thereof.

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