Method and apparatus for measuring oil effluent flow rates

• US 6,405,604 B1
• Filed: 03/27/2000
• Issued: 06/18/2002
• Est. Priority Date: 08/26/1997
• Status: Expired due to Term

• Current Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Original Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Inventors: Berard, Michel, Segeral, Gerard
• Primary Examiner(s): NOORI, MAX H
• Application Number:
  US09/486,665
• Time in Patent Office: 813 Days
• Field of Search: 738/610.4, 738/610.8, 738/611.8, 738/615.2, 738/616.1, 738/616.3
• US Class Current: 73/861.63
• CPC Class Codes: G01F 1/74 Devices for measuring flow of a fluid or flow of a fluent solid material in suspension in another fluid
• CPC Class Codes: G01F 1/88 with differential-pressure measurement to determine the volume flow
• CPC Class Codes: G01N 22/00 Investigating or analysing materials by the use of microwaves or radio waves, i.e. electromagnetic waves with a wavelength of one millimetre or more G01N3/00 - G01N17/00, G01N24/00 take precedence
• CPC Class Codes: G01N 23/12 the material being a flowing fluid or a flowing granular solid
• CPC Class Codes: G01N 33/2823 Raw oil, drilling fluid or polyphasic mixtures
• CPC Class Codes: G01N 9/24 by observing the transmission of wave or particle radiation through the material

Abstract

The invention relates to a flow rate measurement method adapted to oil effluents made up of multiphase fluid mixtures comprising water, oil, and gas. The effluent is passed through a Venturi in which the effluent is subjected to a pressure drop (Δp), a mean value (<Δp>) of the pressure drop is determined over a period t₁ corresponding to a frequency f₁ that is low relative to the frequency at which gas and liquid alternate in a slug flow regime, a mean value (<ρ_m>) is determined for the density of the fluid mixture at the constriction of the Venturi over said period t₁, and a total mass flow rate value <Q> is deduced for the period t₁ under consideration from the mean values of pressure drop and of density.

Claims

1. A flow rate measurement method adapted to oil effluents made up of multiphase fluid mixtures comprising water, oil, and gas, comprising the following steps:

the effluent is passed through a Venturi in which the effluent is subjected to a pressure drop (Δ

p);

a mean value (<

Δ

p>

) of the pressure drop is determined over a period t₁ corresponding to a frequency f₁ that is low relative to the frequency at which gas and liquid alternate in a slug flow regime;

a mean value (<

ρ

_m>

) is determined for the density of the fluid mixture at the constriction of the Venturi over said period t₁; and

a total mass flow rate value <

Q>

is deduced for the period t₁ under consideration from the mean values of pressure drop and of density.

2. A method according to claim 1, in which the density of the fluid mixture (ρ

_m) is measured by gamma ray attenuation at a first energy level at a frequency f₂ that is high relative to said frequency of gas/liquid alternation in a slug flow regime, and the mean (<

ρ

_m>

) of the measurements ρ

_m(i) obtained in this way over each period t₁ corresponding to the frequency f₁ is formed to obtain said mean density value.

3. A method according to claim 1, in which the frequency f₁ is not greater than 0.1 Hz.

4. A method according to claim 2, in which the frequency f₂ is not less than 20 Hz.

5. A method according to claim 2, in which the attenuation of gamma rays by the fluid mixture is measured at the frequency f₂ at a second energy level lower than the first energy level, this measurement being performed at the constriction of the Venturi, and a value WLR(i) is deduced therefrom for the mass ratio of water relative to the liquid component of the fluid mixture.

6. A method according to claim 5, in which each of the measurements at said second energy level is associated with a confidence coefficient relating to the corresponding value ρ

_m(i) of the density of the fluid mixture, said coefficient being small when the density is low and higher at densities corresponding to a low proportion of gas.

7. A method according to claim 5, in which approximate values for the mass flow rate Q_o and Q_w and for the volume flow rates q_o and q_w of the oil and of the water are deduced from said total flow rate value <

Q> and

the water ratio WLR.

8. A method according to claim 5, in which the static proportions of liquid α

_l(i) and of gas α

_g(i) at the frequency f₂ are deduced from the measurements of the fluid mixture density ρ

_m(i) and of the water mass ratio WLR(i) at said frequency.

9. A method according to claim 8, in which the dynamic proportions of liquid γ

_l(i) and of gas γ

_g(i) at the frequency f₂ are deduced from the corresponding static proportions using a determined relationship.

10. A method according to claim 9, in which, from said dynamic proportions, mean values <

γ

_l> and

<

γ

_g>

are determined over each interval t₁ corresponding to said frequency f₁.

11. A method according to claim 10, in which the total volume flow rate is deduced from the total mass flow rate <

Q>

, from said mean values <

γ

_l> and

<

γ

_g>

, and from the liquid and gas densities, and the volume flow rates of oil and of water are deduced therefrom.

12. A method according to claim 9, in which total mass flow rate values Q(i) are determined at the frequency f₂ as a function of the corresponding density values ρ

_m(i), gas flow rate values q_g(i) are deduced from said values Q(i), from the dynamic proportions of liquid γ

_l(i) and of gas γ

_g(i), and from the liquid and gas densities, and the mean of the values q_g(i) is calculated to obtain a value for the gas flow rate over each interval t₁.

13. A flow rate measurement method comprising the following steps:

determining a mean value (<

Δ

p>

) of the pressure drop of a fluid mixture over a period t₁ corresponding to a frequency f₁ that is low relative to the frequency at which gas and liquid alternate in a slug flow regime;

determining a mean value (<

ρ

_m>

) of the density of the fluid mixture over said period t₁; and

determining a total mass flow rate value <

Q>

for the period t₁ under consideration from the mean values of pressure drop and of density.

14. The method according to claim 13, in which a density of the fluid mixture (ρ

_m(i)) is measured by gamma ray attenuation at a frequency f₂ that is high relative to said frequency f1.

15. The method according to claim 14, in which the mean value (<

ρ

_m>

) is determined from ρ

_m(i) over the period t₁ corresponding to the frequency f₁.

16. The method according to claim 13, in which the frequency f₁ is not greater than 0.1 Hz.

17. The method according to claim 14, in which the frequency f₂ is not less than 20 Hz.

18. The method according to claim 14, wherein said density of the fluid mixture ρ

_m(i) is measured by gamma ray attenuation at a first energy level.

19. The method according to claim 18, wherein said density of the fluid mixture is measured by gamma ray attenuation at a second energy level lower than the first energy level.

20. The method according to claim 19, wherein a value WLR(i) is deduced for the mass ratio of water relative to the liquid component of the fluid mixture.

21. The method according to claim 19, wherein each value WLR(i) is associated a confidence coefficient relating to the corresponding value ρ

_m(i) of the density of the fluid mixture.

22. The method according to claim 21, wherein a mean value <

WLR>

is determined from the values WLR(i).

23. The method of claim 22, wherein said mean value <

WLR>

is determined over a period t₁ corresponding to a frequency f₁ that is low relative to the frequency at which gas and liquid alternate in a slug flow regime.

24. The method according to claim 23, wherein approximate values for the mass flow rate Q_o and Q_w and for the volume flow rates q_o and q_w of the oil and of the water are deduced from said total flow rate value <

Q> and

the mean value <

WLR>

.

25. The method according to claim 20, wherein static proportions of liquid α

_l(i) and of gas α

_g(i) at the frequency f₂ are deduced from the measurements of the fluid mixture density ρ

_m(i) and of WLR(i) at said frequency.

26. The method according to claim 25, in which dynamic proportions of liquid γ

_l(i) and of gas γ

_g(i) at the frequency f₂ are deduced from the corresponding static proportions.

27. The method according to claim 26, wherein mean values <

γ

_l> and

<

γ

_g>

are determined from said dynamic proportions over each interval t₁ corresponding to said frequency f₁.

28. The method according to claim 27, wherein the total volume flow rate is deduced from the total mass flow rate <

Q>

, from said mean values <

γ

_l> and

<

γ

_g>

, and from the liquid and gas densities, and the volume flow rates of oil and of water are deduced therefrom.

29. The method according to claim 14, wherein total mass flow rate values Q(i) are determined at the frequency f₂ as a function of the corresponding density values ρ

_m(i).

30. The method of claim 29, wherein gas flow rate values q_g(i) are deduced from said values Q(i), from the dynamic proportions of liquid γ

_l(i) and of gas γ

_g(i), and from the liquid and gas densities.

31. The method of claim 30, wherein a mean a value for the gas flow rate qg is determined over each interval t₁ from the values q_g(i).

32. The method of claim 13, wherein said fluid mixture is passed through a Venturi.

33. An apparatus for flow rate measurement comprising:

a Venturi to receive a fluid mixture;

a pressure sensor, coupled to said Venturi, to determine a mean value (<

Δ

p>

) of a pressure drop of said fluid mixture over a period t₁ corresponding to a frequency f₁ that is low relative to the frequency at which gas and liquid alternate in a slug flow regime; and

a data processing unit, coupled to said pressure sensor and to said Venturi, to determine a mean value (<

ρ

_m>

) of the density of the fluid mixture over said period t₁ and to determine a total mass flow rate value <

Q>

for the period t₁ under consideration from the mean values of pressure drop and of density.

34. The apparatus of claim 33, further including a source of gamma rays and a detector of said gamma rays.

35. The apparatus of claim 34, wherein said source of gamma rays configured to produce gamma rays through said Venturi and said detector configured to produce a signal sensitive to a density ρ

_m of the fluid mixture in response to the gamma rays produced through said Venturi.

36. The apparatus of claim 35, wherein said detector coupled to said data processing unit to provide said signal.

37. The apparatus of claim 36, in which a density (ρ

_m(i)) of the fluid mixture is measured by gamma ray attenuation at a frequency f₂ that is high relative to said frequency f1.

38. The apparatus of claim 37, in which the mean value (<

ρ

_m>

) is determined from ρ

_m(i) over the period t₁ corresponding to the frequency f₁.

39. The apparatus of claim 33, in which the frequency f₁ is not greater than 0.1 Hz.

40. The apparatus of claim 37, in which the frequency f₂ is not less than 20 Hz.

41. The apparatus of claim 37, wherein said density of the fluid mixture ρ

_m(i) is measured by gamma ray attenuation at a first energy level.

42. The apparatus of claim 41, wherein said density of the fluid mixture is measured by gamma ray attenuation at a second energy level lower than the first energy level.

43. The apparatus of claim 42, wherein a value WLR(i) is deduced for the mass ratio of water relative to the liquid component of the fluid mixture.

44. The method according to claim 37, wherein each value WLR(i) is associated a confidence coefficient relating to the corresponding value ρ

_m(i) of the density of the fluid mixture.

45. The apparatus of claim 44, wherein a mean value <

WLR>

is determined from the values WLR(i).

46. The apparatus of claim 45, wherein said mean value <

WLR>

is determined over a period t₁ corresponding to a frequency f₁ that is low relative to the frequency at which gas and liquid alternate in a slug flow regime.

47. The apparatus of claim 46, wherein approximate values for the mass flow rate Q_o and Q_w and for the volume flow rates q_o and q_w of the oil and of the water are deduced from said total flow rate value <

Q> and

the mean value <

WLR>

.

48. The apparatus of claim 47, wherein static proportions of liquid α

_l(i) and of gas α

_g(i) at the frequency f₂ are deduced from the measurements of the fluid mixture density ρ

_m(i) and of WLR(i) at said frequency.

49. The apparatus of claim 48, in which dynamic proportions of liquid γ

_l(i) and of gas γ

_g(i) at the frequency f₂ are deduced from the corresponding static proportions.

50. The apparatus of claim 49, wherein mean values <

γ

_l> and

<

γ

_g>

are determined from said dynamic proportions over each interval t₁ corresponding to said frequency f₁.

51. The apparatus of claim 50, wherein the total volume flow rate is deduced from the total mass flow rate <

Q>

, from said mean values <

γ

_l> and

<

γ

_g>

, and from the liquid and gas densities, and the volume flow rates of oil and of water are deduced therefrom.

52. The apparatus of claim 37, wherein total mass flow rate values Q(i) are determined at the frequency f₂ as a function of the corresponding density values ρ

_m(i).

53. The apparatus of claim 52, wherein gas flow rate values q_g(i) are deduced from said values Q(i), from the dynamic proportions of liquid γ

_l(i) and of gas γ

_g(i), and from the liquid and gas densities.

54. The apparatus of claim 53, wherein a mean a value for the gas flow rate qg is determined over each interval t₁ from the values q_g(i).