CN108872321B - Moisture content measuring device based on plug-in conductivity sensor - Google Patents
Moisture content measuring device based on plug-in conductivity sensor Download PDFInfo
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- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/048—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance for determining moisture content of the material
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Abstract
The invention relates to a water content measuring device based on an inserted conductivity sensor, which comprises a conductivity sensor, a signal processing unit, an effective value measuring unit and a calculating unit. The conductivity sensor comprises an excitation measuring electrode and two protective electrodes, wherein the excitation measuring electrode is used as an excitation electrode and a measuring electrode simultaneously, and the two protective electrodes are fixed above and below the excitation measuring electrode; the signal processing unit comprises a front-end amplifier, a coaxial cable, an alternating current signal generator and a differential amplifier, wherein the negative input end of the front-end amplifier is connected with an excitation measuring electrode in the conductivity sensor through a coaxial cable signal wire, and the positive input end of the front-end amplifier is connected with the alternating current signal generator and is simultaneously connected with two protective electrodes in the conductivity sensor, a shielding layer of the coaxial cable and the negative input end of the differential amplifier; a standard resistor is connected with the negative input end and the output end of the front-end amplifier; the output of the front-end amplifier is connected to the positive input of the differential amplifier.
Description
Technical Field
The invention relates to the field of oilfield exploitation, in particular to a water content measuring device based on an insertion type conductivity sensor.
Background
The demand of the development of the current society for energy is continuously increased, and petroleum has a very important position in national economy and national strategy as the first energy. However, petroleum is a non-renewable energy source, so it is of great significance to minimize the mining loss and fully utilize resources in the mining process. In oil engineering, in order to improve the extraction efficiency of crude oil, a technique of injecting water and polymer at high pressure is often used in secondary extraction of an oil well. However, the process causes the produced crude oil to contain water, so that oil-water two-phase flow generally exists in the process of oil well production and conveying after production, and the water content is even up to more than 70%. The processes of crude oil extraction, dehydration, gathering, transportation, metering, smelting and the like are directly influenced by the water content of the crude oil. In the transmission pipeline, the accurate measurement of the water content of the crude oil plays an important role in the aspects of determining a water outlet or oil outlet layer position, estimating the yield, predicting the development life of an oil well, controlling the yield and quality of the oil field, detecting the state of the oil well, improving the quality of secondary oil recovery and the like. Therefore, the moisture content is an important detection parameter, and the real-time online detection of the moisture content has an important significance.
In the current measurement of the water content, the measurement of the water content is very difficult because the flowing condition of the oil-water two-phase flow is very complex and the ion concentration in water is high. In addition, the water content measuring technology and the measuring instrument have poor application effects due to a plurality of influence factors such as crude oil medium, working conditions, measuring instruments and the like. Therefore, the measurement of the water content of the oil-water two-phase flow is still a difficult problem of accurate online measurement of an oil field.
Among the existing measurement techniques, the measurement principle based on the conductance characteristics is most commonly used. A conventional conductivity sensor is comprised of a pair of plate electrodes, one of which serves as an excitation electrode and the other of which serves as a measurement electrode. Although the excitation field of the electrode is uniformly distributed, the problems of power line edge effect, electrode dead-front area, electrode spacing difficult determination and the like exist, and the electrode is suitable for square pipelines; the problem of parallel plate electrodes is solved by the opposite wall arc electrodes, but the distance distribution among the electrodes is uneven, namely the distance between the middle of the electrodes is far and the distance between the edges of the electrodes is close, so that the excitation field distribution is uneven, and the measurement information is influenced; the mesh electrode structure can better reflect the information on the section of the whole pipeline at the same time, and in addition, a section multi-electrode (such as an ERT imaging technology) can also accurately measure the distribution condition of two-phase flow in the pipeline, but the two have the problems of complex structure, inconvenient installation and high cost. Therefore, it is desirable to provide a sensor and a measuring device with uniform excitation field, simple structure and easy installation.
Disclosure of Invention
The invention provides a water content measuring device based on an inserted conductivity sensor, aiming at solving the problem of measuring the water content of oil-water two-phase flow with high water content in an oil well, and aiming at designing a sensor form with simple structure and uniform excitation field for measuring the water content of the oil-water two-phase flow with high water content and providing a new measuring device. The invention equates the mixed medium in the pipeline to a conductance, when the phase content of the mixed medium changes, the conductance changes, and finally the water content can be obtained by the functional relation between the two. The technical scheme of the invention is as follows:
a water content measuring device based on an insertion type conductivity sensor is used for measuring the water content in an oil-water two-phase flow pipeline with water as a continuous phase and comprises the conductivity sensor, a signal processing unit, an effective value measuring unit and a calculating unit. It is characterized in that the preparation method is characterized in that,
the conductance sensor is fixed at the elbow joints of the vertical pipeline and the transverse pipeline and is inserted from top to bottom along the direction of the vertical pipeline, and comprises an excitation measuring electrode which is used as an excitation electrode and a measuring electrode at the same time and two protective electrodes which are fixed above and below the excitation measuring electrode;
the signal processing unit comprises a front-end amplifier, a coaxial cable, an alternating current signal generator and a differential amplifier, wherein the negative input end of the front-end amplifier is connected with an excitation measuring electrode in the conductivity sensor through a coaxial cable signal wire, and the positive input end of the front-end amplifier is connected with the alternating current signal generator and is simultaneously connected with two protective electrodes in the conductivity sensor, a shielding layer of the coaxial cable and the negative input end of the differential amplifier; a standard resistor is connected with the negative input end and the output end of the front-end amplifier; the output of the front-end amplifier is connected to the positive input of the differential amplifier.
And the effective value measuring unit is used for converting the alternating current output sinusoidal voltage signal of the differential amplifier into a voltage effective value to obtain an output voltage in direct proportion to the conductance value of the oil-water two-phase flow in the measured pipeline.
And the calculation unit is used for calculating the water content by adopting a functional relation model of the oil-water two-phase flow conductance value and the water content according to the obtained output voltage in direct proportion to the oil-water two-phase flow conductance value in the pipeline to be measured.
In the plug-in structure, the excitation measuring electrode of the invention shares the same electrode of the sensor, and the metal pipeline is used as a reference ground, so that the excitation measuring electrode is more convenient to install than a pipe section structure; the invention adopts a coaxial cable signal wire to transmit a measuring signal, and a shielding layer of the coaxial cable is connected with an alternating current signal generator to eliminate the influence of distributed capacitance in a measuring circuit on the measuring signal; in the invention, the signal processing unit and the plug-in sensor are mutually matched, 1) the influence of cable distribution parameters is reduced; 2) the uniformity of the electric field at the excitation measuring electrode is ensured; 3) an output voltage proportional to the measured conductivity value is obtained.
Drawings
FIG. 1 is a measurement schematic;
FIG. 2 is a measurement equivalent circuit;
FIG. 3 is a sensor block diagram;
the labels in the above figures are:
1. excitation measuring electrode, 2, protective electrode, 3, coaxial cable, 4, shielding layer, 5, alternating current signal generator, 6, front end amplifier, 7, differential amplifier, 8, metal pipeline, 9, display instrument shell, 10 and flange
Detailed Description
The invention is described in detail below with reference to the figures and examples.
The invention mainly comprises the design of a sensor, a signal processing unit, an effective value measuring unit and a calculating unit, and the specific design is as follows:
1. sensor design
As shown in fig. 1, the plug-in conductivity sensor consists of an excitation measuring electrode in the middle and two guard electrodes above and below. Wherein the same electrode of the common sensor is excited and measured, and the metal pipeline connected with the ground is used as a reference ground. During installation, the sensor is inserted from top to bottom along the direction of the vertical pipeline, so that the electrode is positioned at the axis of the vertical pipeline. The excitation measuring electrode and the protection electrode of the sensor are respectively led to the signal processing unit, and the leads are led out from the center of the sensor by adopting a shielding cable. The specific design of the plug-in conductivity sensor provided by the present embodiment is shown in fig. 3.
2. The signal processing unit consists of a front-end amplifier, a coaxial cable, an alternating current signal generator and a differential amplifier. The input of the signal processing unit is a signal collected by the sensor, and the signal is converted into a voltage signal v through a front-end amplifiero1(t) obtaining a sinusoidal voltage v through a differential amplifiero2(t) as output of the signal processing unit. The specific situation is as follows:
(1) firstly, the sensor and the signal processing unit are connected through a coaxial cable, namely, one end of a coaxial cable signal wire is connected with an excitation measuring electrode of the sensor, and the other end of the coaxial cable signal wire is connected with a negative input end of a front-end amplifier, so that a measuring signal is transmitted to the front-end amplifier through the coaxial cable signal wire;
(2) using an ac signal generator to provide an excitation voltage v to the sensori(t)＝Vimsin (ω t). In order to reduce the influence of the electrode edge effect at the excitation measuring electrode, the output of an alternating current signal generator is applied to a protective electrode of a sensor and a positive input end of a front-end amplifier, the potentials of the excitation measuring electrode connected with a negative input end of the front-end amplifier and the protective electrode are the same according to the 'virtual short' principle, and the influence of the electrode edge effect on the measurement conductivity of the excitation measuring electrode is avoided because the distortion of an electrode edge electric field is generated near the protective electrode;
(3) in the connection mode in (2), the output of the alternating current signal generator is applied to the shielding layer of the coaxial cable connected with the excitation measuring electrode and the positive input end of the front-end amplifier, and the signal line and the shielding line of the coaxial cable are in equal potential according to the virtual short principle, so that the influence of the distributed capacitance of the cable on the measurement is reduced;
(4) the invention makes the mixed medium in the pipeline equivalent to a conductance, and the equivalent measuring circuit is shown in figure 2. A standard resistor RfA current flowing through the excitation measuring electrode and the metal pipeline and a conductance value G of the oil-water two-phase flow, which are connected with the negative input end and the output end of the front-end amplifierxProportional relationThe output voltage of the front-end amplifier circuit is vo1(t)＝vi(t)+vi(t)GxRf；
(5) At a voltage signal vo1In (t), in order to obtain a voltage signal proportional to the measured electrical conductor, the invention introduces a differential amplifier, and the output end of the front-end amplifier and the output end of the alternating current signal generator are respectively connected with the positive input end and the negative input end of the differential amplifier. The above voltage vo1(t) the signal is converted into a sinusoidal voltage signal v by a differential amplifiero2(t)＝vo1(t)-vi(t)＝vi(t)GxRf；
3. The AC output voltage v of the differential amplifier is measured by an effective value measuring unito2(t) into an effective value VoThe effective value is in direct proportion to the conductance value of the oil-water two-phase flow in the pipeline to be measured;
4. computing unit
After obtaining the output voltage proportional to the measured electric conduction value, the formula Vo＝ViGxRfCan obtain the conductance value G of the oil-water two-phase flowx. And finally, calculating the water content by adopting a function relation model of the conductivity value of the oil-water two-phase flow and the water content. Wherein, the common function relation model mainly comprises a Maxwell model, a Bruggeman model and a Begovich model&Watson model, etc. In addition, specific conductance values and water contents can be obtained through experimental calibration, and a specific relation between the conductance values and the water contents is established, so that a functional relation model is obtained.
The design of the plug-in conductivity sensor provided by the embodiment is shown in fig. 3, and the sensor is applied to a pipeline with an inner diameter of 50mm and a bent pipe part. The plug-in conductivity sensor is installed from top to bottom along the vertical pipeline direction, so that the electrode is positioned at the axis of the vertical pipeline. The same electrode of the common sensor is excited and measured, with the grounded metal pipe as a reference ground. The sensor consists of a middle excitation measuring electrode and an upper protective electrode and a lower protective electrode. The excitation measuring electrode and the protection electrode are respectively led to the signal processing unit, and the leads are led out from the center of the sensor by adopting a shielding cable. The sensor is connected to the pipeline by a flange mounted above the electrode.
In this embodiment, the diameter of the insertion portion of the sensor is 10-15mm, the length of the excitation measuring electrode is 100mm, and the lengths of the upper and lower guard electrodes are 50mm and 10mm, respectively. In order to ensure that the relative position between the excitation electrode and the guard electrode is fixed, the insulation interval of 1-2mm between the excitation electrode and the guard electrode is ensured during processing. In order to make the electric field distribution in the vicinity of the measuring electrode more uniform, it is required in this embodiment that the tube section where the measuring electrode is excited is free of bent portions, i.e. it is completely ensured that the tube section is vertical. In this embodiment, since the tube wall is made of a conductive material and the grounding operation is performed, it is necessary to prevent a short circuit between the guard electrode and the tube wall, and therefore, the upper edge of the upper guard electrode is required to be 10 to 15mm lower than the intersection point of the insertion portion and the elbow.
After the excitation is started, the signal measured by the sensor is transmitted to the signal processing unit through the coaxial cable signal wire. Obtaining a voltage signal v after the processing of a front-end amplifier and a differential amplifiero2(t)＝vi(t)GxRf. Inputting the signal into an effective value measuring circuit, and finally obtaining an output voltage V which is in direct proportion to the conductance value of the oil-water two-phase flow in the measured pipeline after the circuit processingo＝RfViGx。
Obtaining the conductance value G of the oil-water two-phase flowxAnd then, deducing a specific corresponding function relation between the conductivity value and the water content by adopting a Maxwell formula, and finally obtaining a corresponding water content value. The derivation process is as follows:
(1) as can be seen from the foregoing, the excitation voltage is vi(t) mixed phase conductance GxThe effective value of the measured voltage after being processed by the circuit is Vo＝RfViGx；
(2) Adopting Maxwell formula
The derivation shows:
wherein G isWIs the electrical conductance of the aqueous phase, alphaWThe water content of the oil-water two-phase flow;
(3) by measuring the proportional relationship between voltage and conductance, one can deduce:
(4) the water content alpha of the oil-water two-phase flow can be calculated by the formulaW。
Claims (1)
1. A water content measuring device based on an inserted conductivity sensor is used for measuring the water content in an oil-water two-phase flow pipeline taking water as a continuous phase, and comprises the conductivity sensor, a signal processing unit, an effective value measuring unit and a calculating unit,
the conductance sensor is fixed at the elbow joints of the vertical pipeline and the transverse pipeline and is inserted from top to bottom along the direction of the vertical pipeline, and comprises an excitation measuring electrode which is used as an excitation electrode and a measuring electrode at the same time and two protective electrodes which are fixed above and below the excitation measuring electrode;
the signal processing unit comprises a front-end amplifier, a coaxial cable, an alternating current signal generator and a differential amplifier, wherein the negative input end of the front-end amplifier is connected with an excitation measuring electrode in the conductivity sensor through a coaxial cable signal wire, and the alternating current signal generator is connected with the positive input end of the front-end amplifier and is simultaneously connected with two protective electrodes in the conductivity sensor, a shielding layer of the coaxial cable and the negative input end of the differential amplifier; a standard resistor is connected with the negative input end and the output end of the front-end amplifier; the output end of the front-end amplifier is connected to the positive input end of the differential amplifier;
the effective value measuring unit is used for converting an alternating current output sinusoidal voltage signal of the differential amplifier into a voltage effective value to obtain an output voltage in direct proportion to the conductance value of the oil-water two-phase flow in the measured pipeline;
and the calculation unit is used for calculating the water content by adopting a functional relation model of the oil-water two-phase flow conductance value and the water content according to the obtained output voltage in direct proportion to the oil-water two-phase flow conductance value in the pipeline to be measured.
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| CN111189881A (en) * | 2020-01-09 | 2020-05-22 | 天津大学 | Two-phase flow grid sensor visualization method based on differential measurement mode |
| CN113219240A (en) * | 2021-05-28 | 2021-08-06 | 北京中科飞龙传感技术有限责任公司 | Non-invasive cable voltage measurement sensor |
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