APPARATUS AND METHOD FOR MEASURING THE FLOW CHARACTERISTICS OF A PETROLEUM STREAM

Abstract: The petroleum stream to be measured flows through a cell of electrically non-conductive material having first, second, third and fourth capacitive sensors (16,35,20,26) mounted thereon. The first and second sensors (16,35) are spaced a predetermined distance apart along the stream and sense a similar capacitance to one another, the third sensor senses a different capacitance, and the fourth sensor senses a further different capacitance. The four sensed capacitances are processed to derive an indication of the presence and/or relative spatial distribution of different fluids such as gas, oil and liquid slugs, within the flowing petroleum stream.

Description: The present invention relates to measurement apparatus and methods in general and, more particularly, to measurement apparatus and methods for measuring flow characteristics of a flowing petroleum stream which may be multi-phase and may include one or more of gas, oil and water. An object of the present invention is to provide improvements in such method and apparatus. US-A-3635082 describes apparatus for measuring a flow characteristic of a mixed phase stream, comprising: a cell of electrically non-conductive material for passage of a mixed phase stream; first and second sensing means mounted on the cell and spaced a predetermined distance apart along the stream, each said sensing means comprising first and second electrodes forming the plates of a capacitor and adapted to provide a signal representative of the capacitance of the stream as it flows between the electrodes, the first and second electrodes of the first sensing means being substantially the same in size and configuration as the first and second electrodes of the second sensing means; signal processing means connected to each said sensing means to derive a measure of the velocity of the stream from said signals. That document particularly describes the use of two substantially identical capacitive sensors spaced a predetermined distance apart along a fluid stream containing finely divided particles, for example coal or iron ore in a stream of compressed air or oxygen. The present invention is characterized in that: said apparatus is adapted for measuring a flow characteristic of a flowing petroleum stream, and includes: third and fourth sensing means mounted on the cell; said first, second, third and fourth sensing means being spaced apart from one another along the stream; said third and fourth sensing means each comprising first and second electrodes forming the plates of a capacitor and adapted to provide a signal representative of the capacitance of the stream as it flows between the electrodes, the electrodes of the third and fourth sensing means being disposed in different spatial configurations from one another and from the configuration of the electrodes of the first and second sensing means; and said signal processing means being connected to all said sensing means to derive a measure of the velocity of the stream from said first and second signals and to derive an indication of the presence and/or relative spatial distribution of at least first and second different fluids within said flowing petroleum stream from said first, third and fourth signals. The present invention is also characterized by measurement method as set out in claim 5. An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 shows a petroleum stream measurement apparatus, constructed in accordance with the present invention, partially in longitudinal section and partially in simplified block diagram form. Figure 2 shows a more detailed longitudinal section of a portion of a sensing means shown in Figure 1. Figures 3A, 3B and 3C show different configurations of capacitor plates for the sensing means shown in Figure 1. Figure 4 is a simplified block diagram of a sensing means shown in Figure 1. With reference to Figure 1, a measurement cell 4 is made of non-conductive material such as a plastics material, designed so that it can be an integral part of a pipeline carrying a petroleum stream which may be multi-phase and include one or more of gas, oil and water. Monitor cell 4 has fittings 8, 10 and 12 affixed to it for connection with a pipeline (not shown). Capacitive sensing means 16, 20, 26 and 35 are located on the monitor cell 4 and provide signals E1, E2, E3 and E4, respectively, representative of the capacitance of the petroleum stream as it flows through monitor cell 4 as hereinafter explained. Signals E1 to E4 are provided to microcomputing means 40. With reference to Figure 2, there is shown in detail the sensor portion of sensing means 16. All of the sensing means are the same except for the arrangement of the capacitor plates (electrodes) which will be described more fully hereinafter. Measurement cell 4 has three circumferentially extending grooves 30 for each sensing means. Electrodes 45 and 46 are laid in the center groove and are connected to electronics described in detail hereinafter, but not shown in Figure 2. Further, electrodes 45 and 46 are separated from each other and there is no electrical connection between them. Guards 50, 52, 70, 72 are located in the two other grooves. A protective non-conductive covering of fiberglass tape may be provided to hold the electrodes 45, 46 and guards 50, 52, 70, 72 in place and to protect them from a harsh environment. Electrode 45, and guards 50 and 52 are maintained at a signal ground potential. That is, the amplitudes of signals E1 to E4, are with reference to signal ground. Guards 70 and 72 are held at the same potential as electrode 46. Also mounted on monitoring cell 4 are mounting blocks 57 and 60. The mounting block 57 is used at the end of a series of sensing means, while mounting block 60 is used internally in the series of sensing means 16 to 26. It should be noted that sensing means 35 utilizes only mounting blocks 57. The purpose of mounting blocks 57 and 60 is to support shielding around the capacitor electrodes 45 and 46. In this regard shield 64 is maintained at the signal ground potential and provides shielding and shield 66 is maintained at the potential of electrode 46. Further, another shield 68 is maintained at an environmental ground such as the pipeline ground to reduce noise on the pipeline from affecting the measurements. With reference to Figures 3A, 3B and 3C, there are shown the three different arrangements of the capacitor plates respectively of the sensing means 16, 20 and 26. With regard to Figure 3A and Figure 3B, the capacitor plates are substantially the same except Figure 3B differs by 90° in relationship to Figure 3A. Figure 3C represents the configuration of the capacitor plates of sensing means 26. In this example sensing means 35 uses the same capacitor plate configuration as sensing means 16 but is spaced a known distance from sensing means 16. This results in signal E4 differing from signal E1 by a time factor related to the velocity of the petroleum stream. With reference to Figure 4, sensing means 16 includes an RC oscillator means 75. The capacitor for RC oscillator means 75 is formed by the electrodes 45 and 46, mounted on monitor cell 4 with the petroleum stream flowing between electrodes 45 and 46. The resistor (not shown) has a known resistance value and therefore the signal provided by RC oscillator means 75 is related to the capacitance of the dielectric medium between electrodes 45 and 46. Variations in the dielectric constant of the petroleum stream flowing through monitor cell 4 result in corresponding changes in frequency of the oscillator means 75 signal. As the petroleum stream flows between the various capacitor plates, slugs of gas, bubbles of gas, more water, less water and so forth will alter the capacitance between the capacitor plates causing signal E1 to vary accordingly. A phase lock loop means 80 is connected to the oscillator 75 to provide pulse signals whose pulse repetition rate is representative of the sensed capacitance. It should be noted in an example just given, that sensing means 16 and sensing means 35 have their plates arranged in the same spatial manner but a predetermined distance apart so that the velocity of the stream can now be determined in accordance with the time difference between signals E1 and E4. Microcomputing means 40 is of a conventional type utilizing a microprocessor with associated memories. Stored in the memories are look-up tables for the various values of capacitance associated with different fluid distributions within measurement cell 4. This percent volume of water, gas and oil may be determined using the look-up table memory. Measurement apparatus and method according to the present invention can provide qualitative information such as capacitance vs. time traces on a graph. The apparatus can measure velocity and length of liquid slugs. The apparatus, for each point of time, can measure approximate cross-sectional fluid distribution by a comparison of signals E1, E2 and E3, and this in turn leads to a determination of volume fractions and hold-ups. (A hold-up in this art is defined as the cross-sectional area of the liquid flow divided by the cross-sectional area of the pipe). Further, the apparatus and method can determine the flow regime of a petroleum stream from the measured cross-sectional distributions and their time evolution. The apparatus can also measure the flow rates of the individual fluids for some flow regimes.

Claims: Apparatus for measuring a flow characteristic of a mixed phase stream, comprising: a cell (4) of electrically non-conductive material for passage of a mixed phase stream; first and second sensing means (16,35) mounted on the cell and spaced a predetermined distance apart along the stream, each said sensing means comprising first and second electrodes (45,46) forming the plates of a capacitor and adapted to provide a signal (E1,E4) representative of the capacitance of the stream as it flows between the electrodes, the first and second electrodes of the first sensing means (16) being substantially the same in size and configuration as the first and second electrodes of the second sensing means (35); signal processing means (40) connected to each said sensing means (16,35) to derive a measure of the velocity of the stream from said signals (E1,E4); characterised in that: said apparatus is adapted for measuring a flow characteristic of a flowing petroleum stream, and includes: third and fourth sensing means (20,26) mounted on the cell; said first, second, third and fourth sensing means (16,35,20,26) being spaced apart from one another along the stream; said third and fourth sensing means each comprising first and second electrodes (45,46) forming the plates of a capacitor and adapted to provide a signal (E2,E3) representative of the capacitance of the stream as it flows between the electrodes, the electrodes of the third and fourth sensing means (20,26) being disposed in different spatial configurations from one another and from the configuration of the electrodes of the first and second sensing means (16,35); and said signal processing means (40) being connected to all said sensing means to derive a measure of the velocity of the stream from said first and second signals (E1,E4) and to derive an indication of the presence and/or relative spatial distribution of at least first and second different fluids within said flowing petroleum stream from said first, third and fourth signals (E1,E2,E3). Apparatus according to Claim 1 characterised in that each said sensing means (16,35,20,26) comprises: shielding means (64,66) associated with said electrodes (45,46); an oscillator (75) connected to said electrodes to provide a signal whose frequency at a point in time is representative of the capacitance of the portion of the petroleum stream passing at that time between said first and second electrodes (45,46); and phase lock loop means (80) connected to said oscillator (75) to provide pulse signals whose pulse repetition rate is representative of said sensed capacitance. Apparatus according to Claim 1 or Claim 2 characterized in that the first and second electrodes (45,46) of the third sensing means (20) are substantially the same in size as the respective first and second electrodes of the first and second sensing means (16,35) but have a configuration displaced by substantially 90° from the configuration of the first and second sensing means about the longitudinal axis of the flowing stream. Apparatus according to any one of Claim 1 to 3 characterised in that the first electrode (45) of the fourth sensing means (26) is larger than its second electrode (46). A method of measuring a flow characteristic of a mixed phase stream, comprising: causing the stream to flow through a cell of electrically non-conductive material; sensing the capacitance of the stream as it flows between the first and second electrodes of each of first and second sensing means mounted on the cell and spaced at predetermined distance apart along the stream, the first and second electrodes of the first sensing means being substantially the same in size and configuration as the first and second electrodes of the second sensing means, and providing first and second signals (E1,E4) representative of the respective sensed capacitances; and processing the first and second signals to derive a measure of the velocity of the stream; characterised in that: said method is adapted for measuring a flow characteristic of a flowing petroleum stream, and includes: sensing the capacitance of the stream as it flows between the first and second electrodes of each of third and fourth sensing means mounted on the cell, said first, second, third and fourth sensing means being spaced apart from one another along the stream, the electrodes of the third and fourth sensing means being disposed in different spatial configurations from one another and from the configuration of the electrodes in the first and second sensing means, and providing third and fourth signals (E2,E3) representative of the respective sensed capacitances; and said processing step including processing said first and second signals (E1,E4) to derive a measure of the velocity of the stream, and processing said first, third and fourth signals (E1,E2,E3) to derive an indication of the presence and/or relative spatial distribution of at least first and second different fluids within said flowing petroleum stream. A method according to Claim 5 characterised in that each said sensing step comprises: shielding the electrodes; providing an oscillatory signal whose frequency at a point in time is representative of the capacitance of the portion of the petroleum stream passing at that time between the first and second electrodes; and providing pulse signals whose pulse repetition rate is representative of the sensed capacitance. A method according to Claim 5 or Claim 6 characterised in that the sensing step carried out by the third sensing means is carried out utilizing using first and second electrodes of substantially the same size as the respective first and second electrodes of the first and second sensing means but having a configuration displaced by substantially 90° from the configuration of the first and second sensing means about the longitudinal axis of the flowing stream. A method according to any one of Claims 5 to 7 characterised in that the sensing step carried out by the fourth sensing means is carried out utilizing a first electrode larger than the second electrode.

Inventors: BOE, ARILD, EKRANN, STEINAR, JACOBSEN, ENDRE, SCHMIDT, FRANK, TIME, RUNE W., VATNE, HARALD
Applicants: TEXACO DEVELOPMENT CORPORATION
Application year: 1987
Main classification: G01F1
IPC codes: G01N33, G01N27