Apparatus and method for analyzing fluids

• US 6,507,401 B1
• Filed: 12/02/1999
• Issued: 01/14/2003
• Est. Priority Date: 12/02/1999
• Status: Expired due to Term

• Current Assignee: APS Technology Inc, Old Dominion University Research Foundation
• Original Assignee: APS Technology Inc, Old Dominion University Research Foundation
• Inventors: Biglin, Denis P. Jr., Cooper, John B., Aust, Jeffrey F., Turner, William Edward
• Primary Examiner(s): Rosenberger, Richard A.
• Application Number:
  US09/453,003
• Time in Patent Office: 1,139 Days
• Field of Search: 356/70, 356/317, 356/417
• US Class Current: 356/436
• CPC Class Codes: E21B 47/113 using electrical indications; using light radiations
• CPC Class Codes: E21B 47/114 using light radiation
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction
• CPC Class Codes: G01N 21/31 Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry G01N21/72 takes precedence
• CPC Class Codes: G01N 21/64 Fluorescence; Phosphorescence
• CPC Class Codes: G01N 21/8507 Probe photometers, i.e. with optical measuring part dipped into fluid sample
• CPC Class Codes: G01N 2201/084 Fibres for remote transmission
• CPC Class Codes: G01N 33/2823 Raw oil, drilling fluid or polyphasic mixtures

Abstract

A method and apparatus for determining the concentration of a constituent in a fluid by directing a beam of light into the fluid and sensing the intensity of components of the light emerging from the fluid at various wavelengths. The light emerging from the fluid can be light that has been attenuated by absorption or induced by fluorescent radiation. The effect of scattering on the light is minimized by normalizing the component intensities, which are then applied to an algorithm incorporating weighting factors that weighs the influence that the intensity at each wavelength has on the determination of the concentration of the constituent for which the algorithm was developed. The algorithm is developed by a regression analysis based upon a plurality of known mixtures containing various concentrations of the constituent of interest.

Claims

1. A method of determining the concentration of at least one predetermined constituent in a fluid flowing through a downhole portion a well, comprising the steps of:

a) generating a beam of light;

b) directing said beam of light into said fluid flowing through said downhole portion of said well so as to cause one portion of said light to be absorbed by said fluid and another portion of said light to travel through said fluid and emerge from said fluid, said emerging light having been scattered by said fluid and comprised of a plurality components each of which has a different wavelength;

c) transmitting at least a portion of said light that traveled through said fluid and emerged therefrom to a location proximate to the surface of the earth;

d) measuring the intensity of each of at least a portion of said components of said transmitted light, each of said light components in said portion of light components having a wavelength falling within a predetermined range of wavelengths, said light component intensity measurements being conducted at said location proximate said surface;

e) normalizing at least those of said measured light component intensities having selected wavelengths by dividing said intensities by a characteristic derived from said measured component intensities so as to reduce the effect of said scattering of said light components;

f) raising each of said normalized light component intensities at said selected wavelengths by a respective exponent, said exponents being any non-zero numbers;

g) multiplying each of said exponentially raised normalized light component intensities at said selected wavelengths by a predetermined weighting factor based upon its respective wavelength so as to obtain a weighted and normalized light component intensity at each of said selected wavelengths; and

h) combining said weighted and normalized light component intensities at said selected wavelengths so as to calculate said concentration of said constituent.

2. The method according to claim 1, wherein said characteristic by which said measured components intensities are normalized is derived from all of said measured component intensities at all wavelengths at which said component intensities are measured.

3. The method according to claim 2, wherein the step of normalizing said component intensities comprises dividing each of said component intensities at said selected wavelengths by the vector length of said measured component intensities.

4. The method according to claim 3, wherein said vector length is calculated from the equation:

$f=\sqrt{\underset{i=1}{\overset{m}{\sum <br><br>}}<br><br>I_i^2}$

where;

f=the vector length,

i=represents the wavelength of each of said light components whose intensity is measured,

I_i=the measured intensity of the light component having wavelength

m=the total number of components whose intensities are measured.

5. The method according to claim 2, wherein the step of normalizing said component intensities comprises dividing each of said component intensities at said selected wavelengths by f, where:

$f=\underset{i=1}{\overset{m}{\sum <br><br>}}<br><br><br><br>I_i<br><br>$

where;

i=represents the wavelength of each of said light components whose intensity is measured,

I_i=the measured intensity of the light component having wavelength i,

m=the total number of components whose intensities are measured.

6. The method according to claim 2, wherein the step of normalizing said component intensities comprises dividing each of said component intensities at said selected wavelengths by the maximum measured intensity of said light components.

7. The method according to claim 1, wherein said constituent has at least one wavelength at which the absorption of light contacting said constituent peaks, and wherein said predetermined range of wavelengths within which the wavelengths of said measured components fall encompasses said absorption peak.

8. The method according to claim 1, wherein the step of transmitting at least a portion of said emerging light to said remote location comprises directing said portion of said emerging light through a fiber optic cable extending from said downhole location to said location proximate the surface of the earth.

9. The method according to claim 1, wherein the step of measuring said intensity of each of at least a portion of said components of said transmitted light is performed so that all of said intensities are measured simultaneously.

10. The method according to claim 1, wherein said selected wavelengths for which said component intensities are normalized in step (e) comprise a plurality of wavelengths selected based upon the extent to which the intensities of light components at said wavelengths are effected by variations in said concentration of said constituent.

11. The method according to claim 1, wherein said selected wavelengths for which said component intensities are normalized in step (e) comprise a plurality of wavelengths, and further comprising the step of selecting said plurality of wavelengths based upon the extent to which the intensities of light components at said wavelengths contribute to the prediction of said concentration of said constituent.

12. The method according to claim 11, wherein the step of selecting said plurality of wavelengths based upon the extent to which the intensities of light components at said wavelengths contribute to the prediction of said concentration of said constituent comprises the steps of:

i) directing a calibration beam of light into a plurality of fluid calibration mixtures so as to cause light to emerge from each of said calibration mixtures, each of said calibration mixtures containing predetermined varying concentrations of said constituent, said light emerging from said calibration mixtures comprised of components each of which has a different wavelength;

j) measuring the intensity of each of said components of said light emerging from said calibration mixtures having a wavelength falling within said predetermined range of wavelengths;

k) normalizing said measured intensities of said light components emerging from said calibration mixtures;

l) performing a regression analysis on said normalized intensities of said calibration mixtures.

13. The method according to claim 1, wherein at least a portion of said respective exponents by which said normalized light component intensities are raised in step (f) have a value that is not equal to 1.

14. The method according to claim 1, wherein each of said respective exponents by which said normalized light component intensities are raised in step (f) has a value equal to 1.

15. The method according to claim 1, wherein at least a portion of said of said weighting factors are negative.

16. The method according to claim 1, wherein said wavelengths at which said component intensities are measured in step (d) comprises each of said wavelengths within said predetermined range of wavelengths.

17. The method according to claim 16, wherein said predetermined range of wavelengths encompasses at least a portion of the near infrared range.

18. The method according to claim 17, wherein said selected wavelengths for which said component intensities are normalized in step (e) comprise every wavelength at which said component intensity is measured.

19. The method according to claim 17, wherein said selected wavelengths for which said component intensities are normalized in step (e) comprise less than every wavelength at which said component intensity is measured.

20. The method according to claim 18, wherein said selected wavelengths for which said component intensities are normalized in step (e) comprise at least two wavelengths.

21. The method according to claim 1, wherein said selected wavelengths for which said component intensities are normalized in step (e) comprise each wavelength at which said component intensity is measured.

22. The method according to claim 1, wherein said selected wavelengths for which said component intensities are normalized in step (e) comprise less than every wavelength at which said component intensity is measured.

23. The method according to claim 1, wherein said selected wavelengths for which said component intensities are normalized in step (e) comprise at least two wavelengths.

24. The method according to claim 1, further comprising the step of determining said weighting factors by:

i) directing a calibration beam of light into a plurality of fluid calibration mixtures so as to cause light to emerge from each of said calibration mixtures, each of said calibration mixtures containing predetermined varying concentrations of said constituent, said light emerging from said calibration mixtures comprised of components each of which has a different wavelength;

j) measuring the intensity of each of said components of said light emerging from said calibration mixtures having a wavelength falling within said predetermined range of wavelengths;

k) normalizing at least a selected portion of said measured intensities of said light components emerging from said calibration mixtures;

l) performing a regression analysis on said normalized intensities of said calibration mixtures so as to determine said weighting factors.

25. The method according to claim 1, wherein said constituent is oil.

26. The method according to claim 1, wherein said constituent is natural gas.

27. The method according to claim 1, wherein said constituent is water.

28. The method according to claim 1, wherein said beam of light directed into said fluid is comprised of at least one component having a wavelength in the near infrared range.

29. The method according to claim 1, wherein said beam of light directed into said fluid is comprised of components having wavelengths that encompass at least a portion of the near infrared range.

30. The method according to claim 1, wherein said predetermined range of wavelengths within which the wavelengths of said measured components fall comprises at least a portion of the near-infrared range.

31. The method according to claim 1, wherein the step of combining said weighted and normalized light component intensities at said selected wavelengths so as to calculate said concentration of said constituent comprises summing each of said weighted and normalized light component intensities at said selected wavelengths.

32. A method of determining at a first location the concentration C of at least one predetermined constituent k in a fluid n located at a second location remote from the first location, comprising the steps of:

a) generating a beam of light proximate said first location;

b) transmitting said beam of light to said second location;

c) directing said beam of light into said fluid n at said second location so as to cause light to emerge from said fluid, said emerging light comprised of a plurality of components each of which has a different wavelength;

d) transmitting at least a portion of said emerging light to said first location;

e) measuring the intensity I of each of at least a portion of said components of said transmitted light at said first location, each of said light components having a wavelength falling within a predetermined range of wavelengths;

d) normalizing at least m measured light component intensities having selected wavelengths i so as to determine normalized light component intensities IN_in;

e) calculating said concentration C of said constituent k by inputting said normalized light component intensities into an equation of the form;

$C_{\mathrm{kn}}=\underset{i=1}{\overset{m}{\sum <br><br>}}<br><br>{\mathrm{\beta <br><br>}}_{\mathrm{ki}}<br><br>{\mathrm{IN}}_{i<br><br>\text{\hspace{1em}<br><br>}<br><br>n}^{{\mathrm{\alpha <br><br>}}_{\mathrm{ki}}}+b_k$

 

where;

β

_ki=Weighting factors for constituent k at wavelengths i

α

_ki=Exponents for constituent k at wavelengths i, at least a portion of said exponents being not equal to one, whereby said equation is non-linear

b_k=A constant for constituent k.

33. The method according to claim 32, wherein at least a portion of said weighting factors β

_i are equal to zero.

34. The method according to claim 32, wherein at least a portion of said exponents α

_i are equal to 1.

35. The method according to claim 32, wherein the step of normalizing said component intensities at said selected wavelengths i comprises dividing each of selected component intensities by the vector length f of said measured component intensities, said vector length being calculated from the equation:

$f=\sqrt{\underset{i=1}{\overset{m}{\sum <br><br>}}<br><br>I_i^2}$

where;

I_i=the intensity of the light component having wavelength i.

36. The method according to claim 32, wherein said constituent has at least one wavelength at which the absorption of light contacting said constituent peaks, and wherein said predetermined range of wavelengths within which the wavelengths of said measured components fall encompasses said absorption peak.

37. The method according to claim 32, wherein at least one of the components of said light directed to said fluid has a wavelength that causes said constituent to emit fluorescent radiation so that at least a portion of said light emerging from said fluid comprises fluorescent radiation emitted by said fluid.

38. The method according to claim 32, wherein said second location is downhole in a well and said first location is proximate the surface of the earth.

39. An apparatus for determining the concentration of a predetermined constituent in a fluid flowing through a downhole portion a well, comprising:

a) means for generating a beam of light;

b) a section of pipe for directing the flow of said fluid flowing in said well toward the surface of the earth;

c) a sensor incorporated in the wall of said section of pipe, said sensor having (i) means for directing said beam of light into said fluid flowing through said downhole portion of said well so as to cause light to emerge from said fluid, said emerging light comprised of a plurality of components each of which having a different wavelength, said light emerging from said fluid having been scattered by said fluid prior to emerging therefrom, and (ii) means for collecting at least a portion of said light emerging from said fluid;

d) a fiber optic cable for transmitting at least a portion of said light collected by said sensor to a location proximate the surface of the earth;

e) means for measuring the intensity of each of said components of said transmitted light having a wavelength falling within a predetermined range of wavelengths at said location proximate the surface of the earth;

f) normalizing means for reducing the effect of said scattering of said light by dividing at least a selected portion of said measured component intensities by a characteristic derived from said measured component intensities;

g) means for multiplying each of said normalized light component intensities by a predetermined weighting factor based upon the respective wavelength of said light component so as to obtain weighted and normalized light component intensities; and

h) means for determining said concentration of said constituent by combining said weighted and normalized selected light component intensities.

40. The apparatus according to claim 39, further comprising a mixer disposed in said well for mixing said fluid before said beam of light is directed into said fluid by said light beam directing means.

41. The apparatus according to claim 39, further comprising a diverter disposed in said well for diverting at least a portion of said fluid toward said means for measuring said component intensities.

43. The apparatus according to claim 39, wherein said means for multiplying said normalized selected light component intensities by said predetermined weighting factors and said means for determining said concentration of said constituent by combining said weighted and normalized selected light component intensities comprises software programed into a computer.

44. The apparatus according to claim 39, further comprising means for raising each of said normalized light component intensities by a respective exponent, at least a portion of said exponents not being equal to one.

42. The apparatus according 39, further comprising a computer, and wherein said means for means for normalizing said selected portion of said measured component intensities and said means for determining said concentration of said constituent comprises software program into said computer.

45. A method of determining the concentration of at least one predetermined constituent in a fluid flowing through a downhole portion a well, comprising the steps of:

a) generating a beam of light;

b) directing said beam of light into said fluid flowing through said downhole portion of said well so as to cause light to emerge from said fluid, said light directed into said fluid having at least one component having a wavelength that causes said constituent to emit fluorescent radiation so that at least a portion of said light emerging from said fluid comprises fluorescent radiation emitted by said fluid, said emerging light having been scattered by said fluid and comprised of a plurality of components each of which has a different wavelength;

c) transmitting at least a portion of said emerging light to a location proximate to the surface of the earth;

d) measuring the intensity of each of at least a portion of said components of said transmitted light, each of said light components in said portion of light components having a wavelength falling within a predetermined range of wavelengths, said light component intensity measurements being conducted at said location proximate said surface;

e) normalizing at least those of said measured light component intensities having selected wavelengths by dividing said intensities by a characteristic derived from said measured component intensities, so as to reduce the effect of said scattering of said light components;

f) raising each of said normalized light component intensities at said selected wavelengths by a respective exponent, said exponents being any non-zero numbers;

g) multiplying each of said exponentially raised normalized light component intensities at said selected wavelengths by a predetermined weighting factor based upon its respective wavelength so as to obtain a weighted and normalized light component intensity at each of said selected wavelengths; and

h) combining said weighted and normalized light component intensities at said selected wavelengths so as to calculate said concentration of said constituent.

46. The method according to claim 45, wherein said beam of light directed into said fluid is essentially monochromatic, and wherein the step of normalizing said measured component intensities comprises dividing each of said measured component intensities by the intensity of said measured light component having a wavelength equal to that of said essentially monochromatic beam of light.

47. The method according to claim 45, wherein said beam of light directed to said fluid is essentially monochromatic.

48. The method according to claim 47, wherein said monochromatic beam of light directed to said fluid has a wavelength of approximately 852 nm.

49. The method according to claim 45, wherein at least a portion of said respective exponents by which said normalized light component intensities are raised in step (f) have a value that is not equal to one.

50. The method according to claim 45, wherein each of said respective exponents by which said normalized light component intensities are raised in step (f) has a value equal to one.

51. The method according to claim 45, wherein said selected wavelengths for which said component intensities are normalized in step (e) comprise less than every wavelength at which said component intensity is measured.

52. A method of determining the concentration of at least one predetermined constituent in a fluid flowing through a downhole portion of a well, comprising the steps of:

a) generating a beam of light;

b) directing said beam of light into said fluid flowing through said downhole portion of said well so as to cause light to emerge from said fluid, said emerging light having been scattered by said fluid and comprised of a plurality of components each of which has a different wavelength;

c) transmitting at least a portion of said emerging light to a location proximate to the surface of the earth;

d) measuring the intensity of each of at least a portion of said components of said transmitted light, each of said light components in said portion of light components having a wavelength falling within a predetermined range of wavelengths, said light component intensity measurements being conducted at said location proximate said surface;

e) normalizing only those of said measured light component intensities that have wavelengths corresponding to a selected predetermined set of wavelengths, so as to produce normalized light component intensities at only said predetermined wavelengths, said predetermined set of wavelengths selected by;

(A) directing a calibration beam of light into a plurality of fluid calibration mixtures so as to cause light to emerge from each of said calibration mixtures, each of said calibration mixtures containing predetermined varying concentrations of said constituent, said light emerging from said calibration mixtures comprised of components each of which has a different wavelength;

(B) measuring the intensity of at least a portion of said components of said light emerging from said calibration mixtures;

(C) normalizing said measured intensities of said light components emerging from said calibration mixtures;

(D) performing a regression analysis on said normalized intensities of said calibration mixtures;

f) multiplying by predetermined weighting factors only said normalized light component intensities at said predetermined set of wavelengths, so as to obtain a set of weighted and normalized light component intensity at each of said wavelengths in said predetermined set of wavelengths; and

h) combining said weighted and normalized light component intensities at said predetermined set of wavelengths so as to calculate said concentration of said constituent.

53. The apparatus according to claim 52, further comprising means for raising each of said normalized light component intensities by a respective exponent, at least a portion of said exponents not being equal to one.