Corrected DTS measurements based on Raman-Stokes signals
AssigneeWeatherford/Lamb, Inc.
InventorsDomino Taverner, Trevor MacDougall
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Abstract
Methods and apparatus allowing distributed temperature sensing (DTS) measurements to be compensated for differential and/or varying loss between Raman Stokes and anti-Stokes signals are provided. By irradiating an optical waveguide with signals at wavelengths at or near the Raman Stokes and anti-Stokes bands, a distributed loss profile for the waveguide may be generated. This distributed loss profile may be used to adjust the amplitudes or amplitude ratios of Raman Stokes and anti-Stokes signals used in DTS measurements, which may lead to more accurate DTS profiles.
Claims20
A method of generating a distributed temperature sensing (DTS) profile for an optical waveguide, comprising:
- irradiating the waveguide with a first light signal at a first frequency such that the waveguide generates Raman Stokes and Raman anti-Stokes signals in response;
- irradiating the waveguide with second and third light signals at second and third frequencies, respectively;
- calculating a differential loss between the second and third frequencies at different points along the waveguide, based on reflected signals generated in response to the second and third light signals;
- and
- calculating a distributed temperature sensor (DTS) profile for the waveguide based on amplitudes of the Raman Stokes and Raman anti-Stokes signals and the distributed loss calculations.
An apparatus for sensing temperature along an optical waveguide, comprising:
- at least a first light transmitter for irradiating the waveguide with a first light signal at a first frequency, a second light signal at a second frequency, and a third light signal at a third frequency;
- and
- processing circuitry configured to calculate a distributed temperature sensor (DTS) profile based on backscattered Raman Stokes and anti-Stokes signals generated in response to the first light signal and to compensate the DTS profile based on backscattered signals generated in response to the second and third light signals.
A system for measuring temperature in a wellbore, comprising:
- an optical waveguide disposed in the wellbore;
- means for irradiating the waveguide with a first light signal having a first frequency suitable to cause backscattered Raman Stokes and anti-Stokes signals;
- means for irradiating the waveguide with a second light signal having a second frequency at or near a frequency band of the Raman Stokes signals;
- means for irradiating the waveguide with a third light signal having a third frequency at or near a frequency band of the Raman anti-Stokes signals;
- and
- processing circuitry configured to calculate a temperature at one or more positions along the wellbore based on the backscattered Raman Stokes and anti-Stokes signals generated in response to the first light signal and backscattered signals generated in response to the second and third light signals.
Dependencies are inferred from the claim text.