Electromagnetic borehole flowmeter system

• US 5,297,425 A
• Filed: 03/23/1992
• Issued: 03/29/1994
• Est. Priority Date: 03/23/1992
• Status: Expired due to Fees

• Current Assignee: Tennessee Valley Authority (Government of the United States of America)
• Original Assignee: Tennessee Valley Authority (Government of the United States of America)
• Inventors: Warren, Donald E., Young, Steven C., Hamby, Jimmie W., Waldrop, William R., Pearson, Hubert S.
• Primary Examiner(s): Chilcot, Jr., Richard E.
• Assistant Examiner(s): BIEGEL, RONALD L
• Application Number:
  US07/857,555
• Time in Patent Office: 736 Days
• Field of Search: 73/861.11-861.18
• US Class Current: 73/152.18
• CPC Class Codes: E21B 47/113 using electrical indications; using light radiations
• CPC Class Codes: G01F 1/588 combined constructions of electrodes, coils or magnetic circuits, accessories therefor
• CPC Class Codes: G01F 1/60 Circuits therefor
• CPC Class Codes: G01F 15/063 using electrical means

Abstract

An improved flowmeter system is described, together with circuitry, hardware, and techniques for its utilization for determining the rate of flow of fluids in conduits at a situs substantially remote from the information gathering and analysis situs. Arrangements are provided for utilization of the system in conduits, including deep water wells, having diameters as small as 2 inches, and wherein very low flowrates of liquid therein can be quite accurately measured to depths in the range of hundreds to thousands of feet. The device is configured sans moving parts, which overcomes prior art arrangements heretofore prone to wear and drift from calibration, and utilizes a new unique arrangement of transducer drive signals and sampling signals operatively associated with a plurality of timing networks whereby the precision and accuracy of the resulting system is not only enhanced by sampling well after the switching transients therein have decayed, but is even further substantially improved by compensating for the random drift, albeit relatively small, of the transducer output signals caused thereby through the deselection of the otherwise metered signal just prior to and post a polarity change in the AC-square wave excitation to said transducer, such that the resulting clamped switching transients are effectively prevented from causing noise feedback to the portion of the metering signal received and utilized as determinative of flowrate events at said remotely located situs.

Claims

1. A flowmeter system for determining the flow of fluid through conduit, said system comprising:

(a) probe means for travel within said conduit and for measuring the flow of fluid therethrough, said probe means comprising;

(1) flowmeter transducer means for effecting a magnetic field perpendicular to the axis of said conduit;

(2) electrodes for determining the voltage induced by said magnetic field in the flow of fluid; and

(3) first amplifier means coupled to said electrodes and impedance matched therewith for converting the output from said electrodes to a low impedance signal;

(b) connector means for coupling said probe means and later mentioned external circuit means over distances ranging up to about 5000 feet; and

(c) external circuit means coupled with said probe means through said connector means for applying signals to said flowmeter transducer means and for being responsive to signals from said electrodes, said external circuit means comprising;

(1) timing signal generator means coupled to a first power supply and having first timing means for providing a later mentioned signal sampling delay and second timing means for providing a later mentioned signal blocking pulse;

(2) variable voltage generating means coupled to a second power supply for output of a drive signal to said flowmeter transducer means, said output synchronized with signal sampling from said electrodes and delayed therefrom for about 16×

10^-9 to about 3×

10^-3 seconds, said delay provided by said first timing means, and said second power supply electrically isolated from said first power supply;

(3) input offset circuit means coupled to said electrodes for zeroing the signal under conditions of zero flow of fluid through said probe means;

(4) analog switching means coupled to the output of said input offset circuit means and provided with a blocking pulse for passing to later mentioned sampling means a signal substantially free of switching transients, said blocking pulse provided by said second timing means; and

(5) sampling means coupled to the output of said analog switching means and synchronized with said drive signal to said flowmeter transducer means for coupling the signal from said analog switching means for a full master clock period occurring immediately prior to generation of a timing signal to said first timing means, said sampling means determinative of both the negative and positive peak amplitudes coupled therethrough for converting peak-to-peak AC amplitudes to a DC signal.

2. The flowmeter system of claim 1, wherein said input offset circuit means includes magnitude offset voltage generating means and signal matching means, said offset voltage generating means for coupling with said drive signal to said flowmeter transducer means and said signal matching means for matching said offset voltage with the signal from said electrodes.

3. The flowmeter system of claim 2, wherein said input offset circuit means is operatively associated with second amplifier means for outputting a square wave to said analog switching means and wherein said second amplifier means is AC coupled to said analog switching means for removal of signal DC offset.

4. The flowmeter system of claim 3, wherein the output of said second amplifier means and the output of a second timing means are determinative and adapted for calibration of the period of said blocking pulse.

5. The flowmeter system of claim 4, wherein the output of said analog switching means is coupled to third amplifier means, said third amplifier means for selecting a flowmeter range and adjusting the overall system gain, said third amplifier means coupled to said synchronous sampling means, and being in concert with said first and second amplifier means and with fourth amplifier means for effecting an integrator to provide noise filtering or signal averaging, which said fourth amplifier means is coupled to the output of said sampling means to thereby effect a total system gain of signal from said electrodes for detection and determination by a digital voltmeter.

6. The flowmeter system of claim 5, wherein said timing signal generator means is coupled to said first power supply through a rectifier and a wave clipper for providing generation of a square wave having positive and negative amplitudes of about 5 volts.

7. The flowmeter system of claim 6, wherein said timing signal generator means includes oscillator means for generation of said master clock wave.

8. The flowmeter system of claim 7, wherein said timing signal generator means includes a counter with the clock input thereto coupled to the output of said oscillator means and said counter having a carryout and 2X outputs wherein X ranges from about 2 to 10.

9. The flowmeter system of claim 8, in combination with inverted gate means coupled to two of said outputs of said counter, said outputs synchronized with said carryout, wherein the polarity of the carryout waveform switches each time the waveform from either output switches from activated mode to inactivated mode.

10. The flowmeter system of claim 9, wherein the output of said inverted gate means is coupled to said first timing means for generation of said delay of said drive signal to said flowmeter transducer means, and wherein said output from said inverted gate means is coupled to said second timing means for generation of the period of said blocking pulse adapted for control of said analog switching means for clamping switching transients from the signal passed therethrough.

11. The flowmeter system of claim 10, wherein said first timing means includes a first multivibrator with a output thereof and the output of said carryout coupled to flip-flop means for generation of synchronization signals for said flowmeter transducer means.

12. The flowmeter system of claim 11, wherein said second timing means includes a second multivibrator with a output thereof adapted for generation of synchronization signals for said analog switching means.

13. The flowmeter system of claim 12, in combination with integrator means coupled to said synchronous sampling means for averaging the signal therefrom and for providing a DC voltage proportional to the average rate of fluid flowing through said probe means.

14. The flowmeter system of claim 13, wherein said integrator means is provided with at least two time constants wherein the shortest time constants thereof provides for minimum output signal settling time and the longest time constants thereof provides for maximum output signal stability.

15. The flowmeter system of claim 14, in combination with display means and scaling means, said scaling means calibrated and coupled with said integrator means for output to said display means of a signal, indicative of fluid velocity in said conduit through the range of about 0.001 to about 1 foot per second a the range of about 0.1 to about 5 feet per second.

16. The flowmeter system of claim 15, wherein said timing signal generating means is synchronized to the line frequency of said first power supply means.

17. The flowmeter system of claim 15, in combination with gated oscillator timing means for effecting operation of said timing signal generator means independent of line frequency.

18. The flowmeter system of claim 15, in combination with probe packer means for directing the fluid flowing in said conduit, in the direction of and juxtaposed said probe means, through a hollow core thereof to thereby prevent substantial by-passing of said probe means, said probe packer means comprising:

(a) first tube means comprising a rigid material for enclosing at least a substantial portion of the peripheral surface of said probe means and provided, at least at one end thereof, with end stop means for limiting the relative axial movement between said tube means and said probe means; and

(b) second tube means comprising a resilient material for enclosing at least a substantial portion of the peripheral surface of said first tube means and provided at both ends thereof with sealing means for preventing leakage of fluids introduced under positive pressure axially between such sealing means and radially between the outer surface of said first tube means and the inner surface of said second tube means, whereby introduction of fluid under positive pressure between said first and second tube means effects deformation of said second tube means in a direction radially away from said first tube means and into intimate contact with the inner wall of said conduit to thereby form a stop for effecting prevention of by-passing of said hollow core of said probe means by fluid flowing in said conduit.

19. The flowmeter system of claim 18, in combination with second tube expansion means for connecting an end portion of said probe means and an aperture in the peripheral wall thereof, and an aperture in the peripheral wall of said first tube means for introduction of fluid under positive pressure from outside said probe means to the interface between said first tube means and said second tube means.

20. The flowmeter system of claim 19, in combination with packing means for preventing by-passing axially along the interface between said probe means and said first tube means of fluids introduced under positive pressure into said second tube expansion means.

21. The flowmeter system of claim 20, wherein the diameter of said second tube means can be varied over a range of about 1 d to about 3 d, wherein d represents the diameter of said second tube means prior to introduction of fluid under positive pressure thereinto.

22. A flowmeter system for measuring a rate of fluid flowing through a conduit, said system comprising:

(a) probe means for insertion in and travel within said conduit, and provided with flow channel means for flow of fluid axially therethrough, said probe means comprising;

(1) electromagnetic flowmeter transducer means having magnetic field generating means for establishing alternately building and collapsing flux linkage perpendicular to the axis of said conduit and electrode means for determining the voltage induced by the change in said flux linkage, said electrode means having two electrodes in a line mutually perpendicular to both the direction of said flux linkage and the axial direction of said conduit, said electrodes separated one from the other by at least the smallest diameter of said flow channel means; and

(2) first amplifier means operatively associated with said electrode means and having low input bias current and high input impedance characteristics, said low input bias current characteristics being sufficient to prevent loading of a voltage induced signal from said electrodes and said high input impedance being sufficient to substantially match the impedance of said electrodes across said flow channel means, said first amplifier means arranged in AC coupling with said electrodes for elimination of DC offset voltage therefrom, and provided with low frequency and high frequency bypass means and second amplifier means coupled with said first amplifier means and provided with buffering for converting the output therefrom to a low impedance signal, the output of said second amplifier means coupled to later mentioned cable connector means;

(b) multicable connector means for providing coupling between said probe means and later mentioned external circuit means, said multicable connector means adapted for insertion into at least a substantial length of said conduit with one end thereof releasably connected to said probe means therein and the other end thereof adapted for operable association with later mentioned external circuit means and the length of said multicable connector means which is adapted for insertion into said conduit ranging up to about 5000 feet; and

(c) external circuit means coupled with said probe means through said multicable connector means for applying signals to said probe means and for processing signals received therefrom, said external circuit means comprising;

(1) drive means for said magnetic field generating means, said drive means coupled with first power supply means for effecting constant current of a predetermined level to said magnetic field generating means;

(2) comparator means coupled with second power supply means for amplifying and converting a rectified AC signal to a square wave having substantially equal positive and negative amplitudes and at least the ground path of said second power supply means electrically insulated from the return ground path of said first power supply means;

(3) oscillator means coupled with said comparator means for outputting a square wave;

(4) counter means for effecting a plurality of outputs, said counter means coupled to said oscillator means with the output of said counter means synchronized with the output of said oscillator means, said counter means having 2X outputs, wherein X ranges from 2 to 10, wherein each output of said counter means is high for one clock period and low for (2X-1) clock periods and wherein one full clock period of said counter means is equal to T₁ ;

(5) gate means coupled with two outputs of said counter means, said two outputs separated, one from the other by a period of XT₁, said gate means for triggering both later mentioned first monostable multivibrator means and later mentioned second monostable multivibrator means when either of said two outputs changes to activated mode;

(6) first monostable multivibrator means coupled to said gate means for output of a pulse of period T₂, wherein T₂ is sufficient to trigger later mentioned flip-flop means and ranges between about 16×

10^-9 to about 3×

10^-3 seconds, and within each period of (2XT₁) the initiation of T₂ coinciding with the end of periods T₁ and XT₁ ;

(7) second monostable multivibrator means coupled to said gate means for output of a pulse of a period T₃, wherein T₃ is both greater than T₂ and sufficient to provide for substantial decay of switching transients generated during square wave AC excitation of said magnetic field generating means and less than about 1/3(XT₁) and within each period of (2XT₁) the initiation of T₃ coinciding with the end of periods T₁ and XT₁ ;

(8) flip-flop means coupled to said first monostable multivibrator means, to the carryout of said counter means, and to second power supply means for switching, within each period of (2XT₁), the polarity of the control signal to said magnetic field generating means at the end of period (T₁ +T₂) and at the end of period (T₁ +T₂ +XT₁);

(9) analog pi switching means coupled to said second amplifier means and to said second monostable multivibrator means for outputting to later mentioned synchronous sampling means that portion of the signal from said second amplifier means which is free of switching transients and represented by (XT₁ -T₃); and

(10) synchronous sampling means operatively associated with said analog pi switching means and said two outputs of said counter means for sampling within each period of (2XT₁) for a period of T₁ just prior to switching of said polarity of the control signal to said magnetic field generating means, and wherein the inception of each period of T₁ within each such period of (2XT₁) occurs at time zero and after a period of (XT₁), and said synchronous sampling means provided with separate storage means for both the positive and the negative peak amplitude determined during each sampling period of T₁ with the outputs therefrom operatively associated with third amplifier means of high impedance for alternately determining the positive peak value and the negative peak value of the AC signal input thereto and for converting the resulting determined peak-to-peak AC amplitudes to a DC signal directly proportional to the rate of fluid flowing through said flow channel means.

23. The flowmeter system of claim 22, in combination with input offset circuit means for zeroing the signal from said first amplifier means under conditions of zero fluid flow rate in said flow channel, said input offset circuit means including means for generating a magnitude offset voltage generating means and said input offset circuit means including signal matching means, said signal matching means for matching said offset voltage with the signal from said first amplifier means.

24. The flowmeter system of claim 23, wherein said input offset circuit means is operatively associated with fourth amplifier means for signal amplification to said analog switching means and wherein said fourth amplifier means is AC coupled to said analog switching means for removal of signal DC offset.

25. The flowmeter system of claim 24, wherein the output of said fourth amplifier means and the output of said second monostable vibrator means are for calibration of T₃.

26. The flowmeter system of claim 25, wherein the output of said first multivibrator means and the carryout of said counter means are determinative of T₂.

27. The flowmeter system of claim 26, wherein the output of said analog pi switching means is coupled to the fifth amplifier means, said fifth amplifier means for selecting the flowmeter range and adjusting the overall system gain, and said fifth amplifier means being in concert with said first, second, third, and fourth amplifier means, to thereby effect a total system gain of signal from said electrode means suitable for detection and determination by a digital voltmeter.

28. The flowmeter system of claim 27, wherein the comparator means is coupled to the second power supply means through a wave clipper and a rectifier.

29. The flowmeter system of claim 28, wherein the oscillator means comprises a gated oscillator.

30. The flowmeter system of claim 29, in combination with integrator means coupled to said synchronous sampling means for averaging the signal therefrom and for providing a DC voltage proportional to the average rate of fluid flowing through said flow channel means.

31. The flowmeter system of claim 30, wherein said integrator means is provided with at least two time constants wherein the shortest thereof provides for minimum output signal setting time and the longest thereof provides for maximum output signal stability.

32. The flowmeter system of claim 31, in combination with display means, and scaling means, said scaling means for coupling with said integrator means for scaling the signal for outputting to said display means, and said display means for direct indication of fluid velocity in said conduit through a range of about 0.001 to about 1 foot per second or the range of about 0.1 to about 5 feet per second.

33. The flowmeter system of claim 32, wherein said gate means coupled to said two counter outputs is a NOR gate and triggers both said multivibrator means when either of said two counter outputs goes low.

34. The flowmeter system of claim 32, wherein said oscillator means is synchronized to the line frequency of said first power supply means.

35. The flowmeter system of claim 32, in combination with oscillator timing means for effecting operation of said oscillator timing means independent of line frequency.

36. The flowmeter system of claim 22, in combination with probe packer means for directing the fluid flowing in said conduit means in the direction of and juxtaposed said probe means, through said channel means to thereby prevent substantial by-passing of said probe means, said probe packer means comprising:

(a) first tube means comprising a rigid material for enclosing at least a substantial portion of the peripheral surface of said probe means and provided, at least at one end thereof, with end stop means for limiting relative axial movement between said tube means and said probe means; and

(b) second tube means comprising a resilient material for enclosing at least a substantial portion of the peripheral surface of said first tube means and provided at both ends thereof with sealing means for preventing leakage of fluids introduced under positive pressure axially between such sealing means and radially between an outer surface of said first tube means and an inner surface of said second tube means, whereby introduction of fluid under positive pressure between said first and second tube means effects deformation of said second tube means in a direction radially away from said first tube means and into intimate contact with the inner wall of said conduit to thereby form a stop for effecting prevention of by-passing of said flow channel means by fluid flowing in said conduit.

37. The flowmeter system of claim 36, in combination with second tube expansion means for connecting an end portion of said probe means, an aperture in the peripheral wall thereof, and an aperture in the peripheral wall of said first tube means for introduction of fluid under positive pressure from outside said probe means into an interface between said first tube means and said second tube means.

38. The flowmeter system of claim 37, in combination with packing means for preventing by-passing axially along the interface between said probe means and said first tube means of fluids introduced under positive pressure into said second tube expansion means.

39. The flowmeter system of claim 38, wherein the diameter of said second tube means can be varied over a range of about 1 d to about 3 d, wherein d represents the diameter of said second tube means prior to introduction of fluid under positive pressure thereinto.