Method for measuring and calibrating measurments using optical fiber distributed sensor

Abstract

Methods for calibrating and making measurements using fiber optic sensors are disclosed using backscattered wavelengths and independent sensors. The disclosure sets outs methods applicable with fiber optic sensors either in a deployed in a loop and in a linear configuration and useful for measurements including temperature.

1 . A method of determining temperature using a fiber optic distributed temperature sensor, comprising: 
 a) providing optical energy at the Stokes wavelength to a fiber optic distributed temperature sensor;    b) receiving backscattered signal at Stokes wavelength and measuring its intensity;    c) providing optical energy at the anti-Stokes wavelength to said fiber optic distributed temperature sensor;    d) receiving backscattering signal at anti-Stokes wavelength and measuring its intensity;    e) calculating the attenuation ratio between the backscattered signal at Stokes and anti-Stokes wavelengths at selected positions along the optical fiber;    f) repeating steps a through e at a different time;    g) calculating the change in the attenuation ratio with time of the Stokes and anti-Stokes wavelengths;    h) calculating a corrected SAR by multiplying the measured SAR and said change in attenuation ratio with time; and    h) using the corrected SAR to adjust temperatures measured by said fiber optic distributed temperature sensor.    
   
   
       2 . The method as claimed in  claim 1 , wherein a tunable light source provides said optical energy at Stokes wavelength and said optical energy at anti-Stokes wavelength.  
   
   
       3 . The method as claimed in  claim 1 , wherein said fiber optic distributed temperature sensor is deployed in a borehole.  
   
   
       4 . A method of calibrating fiber optic distributed temperature sensor measurements comprising: 
 a) providing optical energy at the Stokes wavelength to a fiber optic distributed temperature sensor;    b) receiving backscattered signal at Stokes wavelength and measuring its intensity;    c) providing optical energy at the anti-Stokes wavelength to said fiber optic distributed temperature sensor;    d) receiving backscattering signal at anti-Stokes wavelength and measuring its intensity;    e) calculating the attenuation ratio between the backscattered signal at Stokes and anti-Stokes wavelengths at selected positions along the optical fiber;    f) repeating steps a through e at a different time;    g) calculating the change in the attenuation ratio with time of the Stokes and anti-Stokes wavelengths;    h) measuring temperature using the fiber optic distributed temperature sensor; and    i) calculating a corrected SAR by multiplying the measured SAR and said change in attenuation ratio with time.    
   
   
       5 . The method as claimed in  claim 4 , wherein a tunable light source provides said optical energy at Stokes wavelength and said optical energy at anti-Stokes wavelength.  
   
   
       6 . The method as claimed in  claim 4 , wherein said fiber optic distributed temperature sensor is deployed in a borehole.  
   
   
       7 . A method of determining temperature along a fiber optic distributed temperature sensor, comprising the steps of: 
 a) measuring temperature using a fiber optic distributed temperature sensor;    b) measuring temperature using an independent temperature sensor located along said fiber optic distributed temperature sensor;    c) calculating the difference in temperature ΔT 1  between the temperature measured by said independent temperature sensor and the temperature measured by said fiber optic distributed temperature sensor at the location of said independent temperature sensor; and    d) using ΔT 1  to adjust temperatures measured by the fiber optic distributed temperature sensor.    
   
   
       8 . The method as claimed in  claim 7 , wherein said fiber optic distributed temperature sensor is deployed in a borehole.  
   
   
       9 . The method as claimed in  claim 7 , wherein said fiber optic distributed temperature sensor further comprises a fiber Bragg grating.  
   
   
       10 . A method of calibrating fiber optic distributed sensor measurements, comprising the steps of: 
 a) measuring a parameter of interest along a fiber optic distributed sensor;    b) measuring said parameter of interest by an independent sensor;    c) determining the difference ΔT 1  between said parameter of interest measured by said independent sensor and said parameter of interest measured by said fiber optic distributed sensor at the location of said independent sensor;    d) using ΔT 1  to adjust said parameter of interest as measured by said optical fiber distributed sensor.    
   
   
       11 . The method as claimed in  claim 10 , wherein said fiber optic distributed sensor is deployed in a borehole.  
   
   
       12 . The method as claimed in  claim 10 , wherein said fiber optic distributed sensor further comprises a fiber Bragg grating.  
   
   
       13 . The method as claimed in  claim 10 , wherein said parameter of interest is temperature.  
   
   
       14 . The method as claimed in  claim 10 , wherein said parameter of interest is pressure.  
   
   
       15 . The method as claimed in  claim 11  wherein the independent sensor is placed at a location of particular interest in said borehole.  
   
   
       16 . A calibrated fiber optic distributed temperature sensor deployed in a borehole, comprising a fiber optic distributed temperature sensor comprising at least one fiber Bragg grating and a least one independent temperature sensor deployed in said borehole.  
   
   
       17 . A method for accurately determining a borehole parameter comprising: 
 a) deploying a fiber optic distributed sensor in a borehole;    b) providing an independent sensor in said borehole along said fiber optic distributed sensor;    c) measuring a borehole parameter using said fiber optic distributed sensor;    d) measuring said borehole parameter using said independent sensor, wherein said independent sensor provides a more accurate measurement than said fiber optic distributed sensor;    e) calculating the difference between the borehole parameter measurement made by the independent sensor and the borehole parameter measurement made using the fiber optic distributed sensor at the location of the independent sensor; and    f) adjusting the borehole parameter measurements made using the fiber optic distributed sensor by said difference.    
   
   
       18 . The method as claimed in  claim 17 , wherein said borehole parameter is temperature.  
   
   
       19 . The method as claimed in  claim 17 , wherein said borehole parameter is pressure.  
   
   
       20 . The method as claimed in  claim 17 , wherein said fiber optic distributed sensor further comprises FBG.  
   
   
       21 . A method of determining a parameter of interest along an optical fiber distributed sensor, comprising the steps of: 
 a) providing optical energy to a fiber optic distributed sensor;    b) measuring a parameter of interest using said fiber optic distributed sensor;    c) measuring said parameter of interest using at least one fiber Bragg grating in the optical fiber distributed sensor;    d) determining the difference in said parameter of interest ΔT 2j  between the parameter of interest measurement by the at least one fiber Bragg grating and the parameter of interest measured using said fiber optic distributed sensor at the location of the at least one fiber Bragg grating reference, wherein j is the number of fiber Bragg gratings; and    e) using ΔT 2j  to adjust parameter of interest measurements made using the optical fiber distributed sensor.    
   
   
       22 . The method as claimed in  claim 21 , wherein said fiber optic distributed sensor is deployed in a borehole.  
   
   
       23 . The method as claimed in  claim 21 , wherein said borehole parameter is temperature.  
   
   
       24 . The method as claimed in  claim 21 , wherein said borehole parameter is pressure.  
   
   
       25 . The method as claimed in  claim 21 , wherein said fiber optic distributed sensor is a single mode fiber.  
   
   
       26 . The method as claimed in  claim 21 , wherein said fiber optic distributed sensor is a multimode fiber.  
   
   
       27 . The method as claimed in  claim 21 , wherein said fiber optic distributed sensor is a combination of single mode and multimode fibers.  
   
   
       28 . A method of determining temperature along an optical fiber distributed temperature sensor, comprising the steps of: 
 a) providing optical energy to a fiber optic distributed temperature sensor;    b) measuring temperature using said fiber optic distributed temperature sensor;    c) measuring temperature using at least one independent temperature sensor located along said fiber optic distributed temperature sensor;    d) measuring temperature using at least one fiber Bragg grating temperature in the optical fiber distributed temperature sensor,    e) determining the difference in temperature ΔT 1i  between said at least one independent temperature sensor and the temperature measured by said fiber optic distributed temperature sensor at the location of said at least one independent temperature sensor, wherein i is the number of independent temperature sensors;    f) determining the difference in temperature ΔT 2j  between the temperature measured by said at least one fiber Bragg grating and the temperature measured by said distributed temperature sensor at the location of said at least one fiber Bragg grating reference, wherein j is the number of fiber Bragg gratings, and    g) using ΔT 1i  and ΔT 2j  to adjust temperatures measured by said optical fiber distributed temperature sensor.    
   
   
       29 . The method as claimed in  claim 28 , wherein adjustments to temperatures measured by the optic fiber distributed sensor are made between the locations of the i independent temperature sensors and the location of the j fiber Bragg gratings.  
   
   
       30 . The method as claimed in  claim 28 , wherein said fiber optic distributed temperature sensor is deployed in a borehole.  
   
   
       31 . The method as claimed in  claim 28 , wherein said adjustment to temperatures measured by the optic fiber distributed sensor varies spatially along the fiber optic distributed temperature sensor.  
   
   
       32 . The method as claimed in  claim 31 , wherein the adjustment is spatially varied based on the location of known features of the fiber optic distributed temperature sensor.  
   
   
       33 . A method of calibrating optical fiber distributed temperature sensor measurements, comprising the steps of: 
 a) providing optical energy to a fiber optic distributed temperature sensor;    b) measuring temperature using at least one independent temperature sensor located along said fiber optic distributed temperature sensor;    c) measuring temperature using at least one fiber Bragg grating in said optical fiber distributed temperature sensor; and    d) using the temperature measured by the at least one independent temperature sensor and the temperature measured by the at least one fiber Bragg grating to adjust the temperature measured by said fiber optic distributed temperature sensor.    
   
   
       34 . The method as claimed in  claim 33 , wherein said fiber optic distributed sensor is deployed in a borehole.  
   
   
       35 . A method of determining temperature along a fiber optic distributed temperature sensor, comprising the steps of: 
 a) providing optical energy into one end of a fiber optic distributed temperature sensor and transmitting in the forward direction;    b) measuring the backscattered signal at Stokes wavelength;    c) determining the incremental loss in signal at Stokes wavelength at various points along the sensor from the optical energy input in the forward direction and populating an array;    d) measuring the backscattered signal at anti-Stokes wavelength;    e) determining the incremental loss in signal at anti-Stokes wavelength at various points along the sensor from the optical energy input in the forward direction and populating an array;    f) providing optical energy into the other end of said fiber optic distributed temperature sensor and transmitting in the reverse direction;    g) measuring the backscattered signal at Stokes wavelength;    h) determining the incremental loss in signal at Stokes wavelength at various points along said sensor from the optical energy input in the reverse direction and populating an array;    i) measuring the backscattered signal at anti-Stokes wavelength;    j) determining the incremental loss in signal at anti-Stokes wavelength at various points along said sensor from the optical energy input in the reverse direction and populating an array;    k) determining the difference between the measurement incremental loss variation in Stokes wavelength in the forward and the reverse directions for any given point along said sensor;    l) determining the difference between the measurement incremental loss variation in anti-Stokes wavelength in the forward and the reverse directions for any given point along said sensor;    m) correcting the measured Stokes wavelength at i by                S   i     =       S   ⁢           ⁢     f   i       -       ∑     j   =   0     i     ⁢       Δ   ⁢           ⁢     s   j       2           ;           n) correcting the measured anti-Stokes wavelength at i by                A   i     =       A   ⁢           ⁢     f   i       -       ∑     j   =   0     i     ⁢       Δ   ⁢           ⁢     a   j       2           ;           o) measuring temperature using said fiber optic distributed temperature sensor; and    p) adjusting measured temperature using corrected Stokes S i  and anti-Stokes A i  wavelengths.    
   
   
       36 . The method as claimed in  claim 35 , wherein a tunable light source provides said optical energy at Stokes wavelength and said optical energy at anti-Stokes wavelength.  
   
   
       37 . The method as claimed in  claim 35 , wherein said fiber optic distributed temperature sensor is deployed in a borehole.  
   
   
       38 . The method as claimed in  claim 35 , wherein said fiber optic distributed temperature sensor further comprises a fiber Bragg grating.  
   
   
       39 . A method of calibrating fiber optic distributed temperature sensor measurements, comprising the steps of: 
 a) providing optical energy into one end of a fiber optic distributed temperature sensor;    b) receiving backscattered signals at Stokes and anti-Stokes wavelengths at said one end and populating an array of signals at Stokes wavelengths and an array of signals at anti-Stokes wavelengths;    c) providing optical light into the opposite end of said fiber optic distributed temperature sensor;    d) receiving backscattered signals at Stokes wavelength and at anti-Stokes wavelength at said opposite end and populating an array of signals at Stokes wavelengths and an array of signals at anti-Stokes wavelengths;    e) correcting the measured signals received at Stokes wavelength backscattered at i by                S   i     =       S   ⁢           ⁢     f   i       -       ∑     j   =   0     i     ⁢       Δ   ⁢           ⁢     s   j       2           ;   and           f) correcting the measured signals received at anti-Stokes wavelength backscattered at i by              A   i     =       A   ⁢           ⁢     f   i       -       ∑     j   =   0     i     ⁢         Δ   ⁢           ⁢     a   j       2     .                 
   
   
       40 . A method of measuring a parameter of interest along a fiber optic distributed sensor, comprising the steps of: 
 a) providing optical energy into one end of a fiber optic distributed sensor and transmitting in the forward direction;    b) measuring the backscattered signal;    c) determining the incremental loss in signal from the optical energy input in the forward direction at various points along said sensor and populating an array;    d) providing optical energy into the other end of said fiber optic distributed sensor and transmitting in the reverse direction;    e) measuring the backscattered signal;    f) determining the incremental loss in signal from the optical energy input in the reverse direction at various points along the sensor and populating an array;    g) determining the average of the incremental loss in signal in the forward and the incremental loss in signal in the reverse directions for any given point along the fiber optic distributed sensor; and    h) adjusting parameter measurements made using the fiber optic distributed sensor by said average.    
   
   
       41 . The method as claimed in  claim 40 , wherein the backscattered signal is measured at the Stokes wavelength.  
   
   
       42 . The method as claimed in  claim 40 , wherein the backscattered signal is measured at the anti-Stokes wavelength.  
   
   
       43 . The method as claimed in  claim 40 , wherein the backscattered signal is measured at the Stokes wavelength and the anti-Stokes wavelength.  
   
   
       44 . The method as claimed in  claim 40 , wherein the backscattered signal is measured as the SAR.  
   
   
       45 . The method as claimed in  claim 40 , wherein a tunable light provides the optical energy.  
   
   
       46 . The method as claimed in  claim 40 , wherein said fiber optic distributed sensor is deployed in a borehole.  
   
   
       47 . The method as claimed in  claim 40 , wherein said fiber optic distributed sensor further comprises a fiber Bragg grating.  
   
   
       48 . The method as claimed in  claim 40 , wherein said fiber optic distributed sensor further comprises an independent sensor.