AU649020B2

AU649020B2 - Dual frequency microwave water cut monitoring means and method

Info

Publication number: AU649020B2
Application number: AU72647/91A
Authority: AU
Inventors: Michael Gregory Durrett; Gregory John Hatton; David Albert Helms
Original assignee: Texaco Development Corp
Current assignee: Texaco Development Corp
Priority date: 1991-03-05
Filing date: 1991-03-05
Publication date: 1994-05-12
Anticipated expiration: 2011-03-05
Also published as: AU7264791A

Description

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649020 COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 Form SUBSTITUTE COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE Short Title: Int Cl: Application Number: Lodged: Complete Specification-Lodged: Accepted: Lapsed: Published: Priority: Related Art: TO BE COMPLETED BY APPLICANT Name of Applicant: TEXACO DEVELOPMENT CORPORATION Address of Applicant: 2000 Westchester Avenue, White Plains, NEW YORK 10650, U.S.A.

Actual Inventor: David Albert Helms; Michael Gregory Durrett and Gregory John Hatton Address for Service: GRIFFITH HACK CO 71 YORK STREET SYDNEY NSW 2000 Complete Specification for the invention entitled: DUAL FREQUENCY MICROWAVE WATER CUT MONITORING MEANS AND

METHOD

The following statement is a full description of this invention, including the best method of performing it known to us:- GH&CO REF: 10447-RF:PJW:RK S O 2758A:rk DUAL FREQUENCY MICROWAVE WATER CUT MONITORING MEANS AND METHOD The present invention relates to apparatus and methods for determining the water cut, i.e. the percentage water content by volume, in a petroleum stream.

According to the invention there is provided an apparatus for determining the percentage water content, by volume in a petroleum stream, comprising: a sou~rce for supplying microwave energy selectively at first. and second frequencies; antenna means for transmitting microwave energy at the selected frequency into the petroleum stream and for receiving test microwave energy that has either been reflected back from the stream or has transmitted through the stream; a detector responsive to the test microwave energy to provide an intensity signal representative of the intensity of the test microwave energy; phase difference means responsive to the microwave energy as supplied at the selected frequency and to -the *test microwave energy, said phase difference means comprising a voltage controlled phase shif ter for shifting the phase of the selected supplied microwave energy in accordance with a phase shift signal to provide reference microwave energy, and difference means responsive to the test microwave energy and -the reference microwave energy to provide said phase shif t signal as the phase dif ference between .said test and ref erence energies until there is substantially a 906 said phase difference, whereupon said phase shifter provides an enabling signal; a temperature sensor -to provide, a temperaiture signal representative of the temperature of the petroleum stream; and indicator means connected -to the detector, the phase shifter, the phase difference means and the temperature p~LL~sensor to provide an indication of the percentage water /Jcontent in accordance with said intensity signal, said Senabling signal, said phase shift signal, and said 1B temperature signal, said indication means including a stored table of phase shifts at each of said first and second frequencies whereby to permit resolution of ambiguity where the phase difference signal may represent a correct phase shift plus an integral multiple of 3600.

The antenna means may include an antenna adapted to transmit the selected supplied microwave energy into the stream and to receive test microwave energy that has been reflected back from the stream, and a circulator connected to said source and to said antenna to direct energy from the source to the antenna and to direct energy from the antenna to the detector.

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2 In another embodiment the antenna means includes an antenna adapted to receive test microwave energy that has propagated through the stream and to pass the test microwave energy to the detector.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing which is a simplified block diagram of a microwave water cut monitor according to the invention.

The water cut monitor shown in the drawing includes a microwave source 3 for supplying microwave energy at two microwave frequencies. Preferred frequencies of 10.119 GHz and 10.369 GHz are used, although the true criteria is that there be a substantial difference between the two frequencies.

Source 3 is low powered and may use a microwave gun source.

Source 3 provides the microwave energies to switch means 4 via microwave conductors 5 and 6. switch means 4 is controlled by a signal El 'o pass the microwave energy from either conductor 5 or 6 and p- vide it to a directional coupler 7. Directional coupler 7 provides the selected microwave energy to a circ'alator 8 and to a conventional voltage controlled phase shifter 9. All conductance or carrying of microwave energy is accomplished by using conventional waveguides.

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o eS go -3- Circulator 8 provides microwave energy to an antenna 12. Antenna 12 provides the microwave energy through a window 14, which may be made of a conductive ceramic or Teflon, to a petroleum stream comprising at least oil and water, passing through a pipe 17. Pipe 17 may be a portion of a pipeline having windows 14 or it may be made of the "window" material. The microwave energy provided by antenna 12 passes through the petroleum stream and another window 14 and is received by an antenna 20. Antenna 20 provides the received microwave energy to a switch means 24 which in turn provides the received microwave as test microwave energy to a directional coupler 28, as hereinafter explained. Directional coupler 28 provides the o* test microwave energy to a detector 32 and to a mixer 34.

Detector 32 provides a signal E2 corresponding to the intensity of the microwave energy received by antenna *5 0* The petroleum stream also reflects some of the microwave energy back to antenna 12 which passes back through antenna 12 to circulator 8. Circulator 8 blocks the reflected microwave energy from feeding back to source 3 and provides the reflected microwave energy to switch means 24. Reflected microwave energy becomes more important as the distance between

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antennas 12 and 20 increases. This is especially true where a large pipeline carrying the petroleum stream is being monitored.

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A positive direct current voltage +V is provided to a switch 36 which is connected to switch means 24. With switch 36 open, switch means 24 provides microwave energy from antenna 20 as test microwave energy. When switch 36 is closed, the reflected microwave energy from circulator 8 is provided by switch means 24 as the test microwave energy.

The microwave energy from voltage controlled phase 35 shifter 9, hereinafter called the reference microwave energy, and the test microwave energy from directional coupler 28, are provided to mixer 34 which mixes them to provide two electrical signals E3, E4, representative of the phases of the reference microwave energy and the test microwave energy, respectively.

A differential amplifier 40 provides an output signal E0 in accordance with the difference between signals E3 and E4.

Signal EQ is a function of the phase difference between the reference microwave energy and the test microwave energy and is provided to a feedback network 44. Feedback network 44 provides a signal C to voltage control phase shifter 5, controlling the phase of the reference microwave energy, and to a mini-computer means 50. Signal EO, and hence the signal C, decreases in amplitude until there is substantially 90 phase difference between the reference microwave energy and the test microwave energy. Voltage control phase shifter 5 indicates .000 the amount of phase shift required to eliminate the phase e difference.

Signal E2 from detector 32 is also provided to couputer means 50 which contains within it memory means having data related to temperature and phase and amplitude for various percentages of water cuts that could be encountered in the production stream. It has been discovered that the phase 0 difference for measurements in a fluid stream may exceed 360 degrees under certain circumstances. These circumstances include cases where the dielectric of the stream is large, for example when he percentage of water in the petroleum is large, and when the emulsion is water continuous and in cases where the distance between antennas is large as in the case of using larger pipe 17 of F!gure 1.

In those cases the true phase shift may be the measured phase shift plus some integer multiple of 360 degrees.

The present invention resolves this ambiguity by monitoring the petroleum at two substantially different frequencies, the main frequency fl, and a secondary frequency, f 2 and using the difference in measured phase shift, (phase 1 phase 2) at the two frequencies to determine the correct integer multiplier to use when computing the true phase shift. The correct integer is chosen from a table created from knowledge of the frequencies involved. The maximum possible size of the integer that may be resolved is limited by the separation of frequencies fl and f2-. In the present case integer size of up to 40 can be resolved. Reduction of frequency separation would increase the maximum integer size further limited only by resolution of the phase shift 'measurement.

A temperature sensor 52 sensing the temperature of the petroleum stream in pipe 17 and provides a signal T to computer. means 50 representative of the sensed temperature.

Phase Shifter 9 also provides an enable signal to computer means 50 allowing computer means 50 to utilize signals T, C and E2. Computer means 50 also provides signal El to switch means 4 so that computer means 50 can correlate signal o E2 to a particular frequency. Internally computer means uses the phase shift signal C, signal T and the two amplitude levels of signal E2 to address computer means 50 memory means to select the proper water cut values. Computer means S provides signals, corresponding to the selected water cut value, to readout means 54 which may be either digital display means or record means or a combination of the two.

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Claims

1. Apparatus for determining the percentage water content by volume in a petroleum stream, comprising: a source for supplying microwave energy selectively at first. and second frequencies; antenna means for transmitting microwave energy at the selected frequency into the petroleum stream and for receiving test microwave energy that has either been reflected back from the stream or has transmitted through the stream; a detector responsive to the test microwave energy to provide an intensity signal representative of the intensity of the test microwave energy; phase difference means responsive to the microwave energy as supplied at the selected frequency and to the test microwave energy, said phase difference means comprising a voltage controlled phase shifter for shifting the phase of the selected supplied microwave energy in accordance with a phase shift signal to provide reference microwave energy, and difference means responsive to the test microwave energy and the reference microwave energy to provide said phase shift signal as the phase difference between said test and reference energies until there is substantially a 90 said phase difference, whereupon said phase shifter provides an enabling signal; a temperature sensor to provide, a temperature signal representative of the temperature of the petroleum stream; and indicator means connected to the detector, the phase shifter, the phase difference means and the temperature sensor to provide an indication of the percentage water content in accordance with said intensity signal, said enabling signal, said phase shift signal, and said 7 temperature signal, said indication means including a stored table of phase shifts at each of said first and second frequencies whereby to permit resolution of ambiguity where the phase difference signal may represent a correct phase shift plus an integral multiple of 360*.

2. Apparatus according to Claim 1 wherein said difference means comprises a mixer responsive to the test and reference energies to provide electrical signals representative of the phases of the test and reference energies respectively, a differential amplifier connected to the mixer to provide an output signal representative of the difference between said two electrical signals, and a feedback network connected to the differential amplifier to provide said phase difference signal in accordance with said output signal.

3. Apparatus according to Claim 1 or Claim 2 wherein said antenna means includes an antenna adapted to transmit o: the selected supplied microwave energy into the stream and to receive test microwave energy that has been reflected back from the stream, and a circulator connected to said source and to said antenna to direct energy from the source to the antenna and to direct energy from the antenna to the detector.

4. Apparatus according to any oTe of Claims 1 to 3 wherein said antenna means includes an antenna adapted to receive test microwave energy that has propagated through the stream and to pass the test microwave energy to the detector.

C/ ,Apparatus accoraing to Claim 4 including switch means operable to select test microwave energy from said circulator or from said last-mentioned antenna for passing to said detector.

6. Apparatus according to any one of Claims 1 to -9 including a switch operable to select a supply of microwA"'., energy at said first or said second frequency for supply to said antenna means.

7. ,Apparatus for determining the percentage water content by volume in a petroleum stream, substantially as described herein witht reference to the accompanying drawing. Dated this 1st day of March 1994 TEXACO DEVELOPMENT CORPORATION By their Patent Attorney GRIFFITH RACK CO.