Study On On-line Detection Method Of Crude Oil Content In Water

With the continuous consumption of petroleum resources,some oilfields represented by Daqing Oilfield in China have entered the late stage of mining.The pressure of underground oil layers has decreased and the fluidity has deteriorated,which makes the mining difficulty increase.At present,high-pressure water injection is the main method of oil recovery in oilfields.Good fluidity reduces the difficulty of extraction,so the water in the produced oil-water mixture accounts for the majority.Due to the complexity of the oil-water two-phase flow system,the accurate measurement of crude oil content in water is extremely difficult,and some common measurement methods have many limitations.At this stage,the production line still relies on manual timing sampling,and the distillation method is used as the main method in the laboratory.In this paper,based on the current situation,an on-line detection method based on the principle of ultrasonic reflection is designed,which converts the detection of crude oil content into the detection of layered oil and water thickness.This method is different from the conventional low-frequency ultrasonic detection method.Because the crude oil is extremely viscous,the ordinary low-frequency ultrasonic waves cannot penetrate the oil layer at all.Therefore,it is necessary to make use of the characteristics of ultra-high frequency ultrasound,such as strong penetration and good directivity,in order to penetrate the viscous crude oil reservoir,detect effective signals and achieve high detection resolution.In this paper,a 20 MHz ultrasonic probe is selected and the corresponding driving and receiving circuits are designed independently.A relatively complete measuring system is built to achieve high-precision online measurement of crude oil content.The overall work of this paper is as follows:(1)Introduce common measurement techniques at home and abroad.According to the advantages of UHF ultrasonic waves,the crude oil content is measured by the principle of reflection after it penetrates the measured oil layer and water layer.(2)Introduce the knowledge of ultrasonic,and derive the propagation characteristics of ultrasonic waves at different medium interfaces by calculation.It is only related to the acoustic impedance of the medium,which provides a theoretical basis for the feasibility of the system.(3)Designing the matching circuit and software corresponding to the UHF ultrasonic wave,including the demonstration and implementation of the high-voltage narrow pulse generating circuit;limiting the high-voltage pulse;effectively detecting the high-frequency small signal,wherein,the high The frequency weak echo signal realizes 0-80 dB program-controlled amplification;the 9-step band-pass filtering of the echo signal;the high-speed A/D acquisition,storage and upload of the echo signal;the preparation of the measurement algorithm.(4)Test and verify the system device.The standard oil with different oil content is configured,and the corresponding oil content is calculated by the time relationship between the ultrasonic echo signals.The results show that the relative error of the system for measuring the crude oil content can be up to 3%,and the measurement error of the oil layer thickness can reach within 0.03 mm.Repeated experiments on the same oil content sample showed that the repeatability was good;the oil-water ratio was changed in real time,and the waveform change was observed,indicating that the system can realize online real-time measurement.(5)Analyze the experimental error and propose compensation and solutions.Plan and design the actual application device on site.This design has certain impetus to the difficult measurement problem caused by the current status of oilfield exploitation.By taking advantage of high-frequency ultrasound,through careful design of hardware and software,the measurement error is reduced,the sensitivity of the system is improved,and the online real-time accuracy is achieved.The measurement effect has a broader development prospect than some conventional measurement methods.However,this design has certain shortcomings and shortcomings in data processing algorithms and calibration experiments at different temperatures,and needs further analysis and improvement.