Circuit Design Of The Electromagnetic Wave Water Holdup Meter

High frequency electromagnetic wave water holdup meter is one kind the instrument for measuring water content of crude oil, it finish the measure through detecting the electromagnetic waves phase shift induced by oil-water mixture. According to the coaxial transmission theory, medium between the external and internal conductors of coaxial line will affects the propagation characteristic of electromagnetic wave, the change of dielectric constant will cause signal amplitude and phase change at the coaxial line sensor receiving terminal. Therefore, when the oil-water mixed medium of different water holdup flows through the coaxial line, the dielectric constant and conductivity between the external and internal conductors will have bigger change, these features provide favorable conditions for us to determine the water holdup by detecting the signal phase shift which is induced by oil-water mixture when the signal passes through the coaxial line.First of all, the text introduces the background and significance of the topic. With the oil field fluid volume is accumulated ceaselessly, underground oil layer appeared pressure deficit phenomenon, in order to make up for the deficit caused by continuous oil production, maintain the pressure, realize high and stable oil yield, usually adopt the water injection method for increase profits. However, in late development stage of oilfield produced, water holdup will grow with each passing day. At present, most of eastern China onshore oil field has entered the late development stage, comprehensive water holdup has reached more than80%, and some of the oilfield has reached more than90%. For this reason, as the produced liquid increasing, the energy consumption also will grow considerably. But our country has nearly80%oil well only has litter oil be stored in it, after development peak, oil content in the produced fluid is more and more small. In this case, still need high power machinery to maintain the normal operation of the pumping well, this "air-pump" state waste a lot of energy, and leading to the sharp increase in costs of the production. Therefore, to achieve each well oil-water mixture water holdup change’s real-time monitoring is necessary, when the value of the produced crude oil is worth less than its energy needed for exploitation, the mining should be temporarily stopped, adopt suitable exploitation scheme, improve efficiency. In order to realize the real time monitoring of oil well water holdup, it requires a high performance water holdup meter to meet the requirement. At present, after comprehensive analysis the water holdup meter characteristics and other aspect between domestic and foreign we found foreign instruments is more superior than the domestic equipment when it be used to measure low water holdup well in terms of resolution, and it is expensive the production of instrument use rights restrictions, those are no conducive to the apparatus rational utilization, and its application range is small, only suitable for low water holdup well, obviously it doesn’t suitable for domestic onshore oil field. Compared with it, the price of domestic equipment is low, but it can’t meet the requirement of real time dynamic monitoring for the influence by mineralization. In this case, it is great significant that designing a high accuracy and real time monitoring water holdup instrument. One side, it can meet the domestic demand, and break the foreign oil equipment block, the other, the capacity of independent research and development of oil equipment can be improved.Second, the text researches the whole design scheme through theory and methods. It has analyzed the propagation characteristic of electromagnetic wave, come to a conclusion:the relationship between equivalent dielectric constant of oil water mixed fluid and water holdup is monotonic; combined with the electromagnetic wave actual state when it pass though the coaxial line, come to a conclusion: the relationship between the phase shift introduced oil-water mixture medium and the water holdup is monotonic increasing, and the relationship between amplitude characteristic and water holdup is not monotonic. Therefore, the scheme for measure water holdup by detecting the signal’s phase shift which is caused by hybrid medium between external and internal conductors when the signal pass though the coaxial line. Consider to the special working environment and technical requirement, in order to prevent salinity effect on measurements, this paper chooses80MHz high frequency excitation signal and80.02MHz local oscillator signal, in order to accurately measure the signal phase shift, the design of the circuit adopts the mixing scheme, removal the high-frequency signal phase shift to low frequency signal and without distortion. Finally, in the circuit part, it accomplished the water holdup measurement based on the phase shift.In third, the design of hardware circuit. The hardware circuit is divided into four parts:signal source module, mixing circuit, phase discriminator, the pulse width detecting and processing unit. Signal source module is achieved by the use of direct digital synthesis (DDS) technology and AD9954chip, it is supplied to the circuit input80MHz signals and80.02MHz local oscillating signal; mixer circuit is to realize the analog multiplication function of two signals, and the circuit is completed by using the analog multiplier chip MC1596, complete the analog multiplication between the local oscillating signal and the excitation signal, then pass the band pass filter, the phase shift information has been moved to20KHz low frequency signal; after high-frequency signal phase shift information successfully moved to low frequency signal,it is sent to the phase detector circuit, firstly the circuit will shape the sine signal, and then transform two square wave into a pulse signal, the phase discriminator circuit mainly adopts the comparator chip LM139and D trigger to complete; pulse width detection unit is used to measure the pulse width, the text finished pulse width measurement based on the use of counter CD54HC4040, finally through the external interrupt mode to trigger the SCM to read the pulse width information, and realized the data primary processing in the MCU internalFourth, experiments and scale. Firstly, do a large number of repeated sample experiment and debugging at different temperatures (25℃-170℃), respectively fill the coaxial line with21groups of oil-water mixture which are pre-configured and in different proportions, at the terminal of the phase discriminator we can get21groups of pulse signals with different pulse width. And then the external counter measure corresponding pulse width, the more pulse width wider and the more greater number counter get. At the same time of the counter finish measuring, the SCM reads the number of the counter. Final sent it to PC through the serial port, and record the experiment data. Then we change the temperature, and repeat the above experiment. Finally, we can draw a searchable3D form(temperate、counter data、water holding rate), complete instrument scale.At last, the text summaries the fruits of this text and gives the prospect of future work. Pose the existing problem, analyzing the circuit deficiencies, and puts forward improving plan.