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The status quo and development trend of oil well metering technology Abstract: This paper introduces the main oil well production metering methods used in China's oilfields, in which crude oil metering includes glass tube liquid level metering, electrode metering and tipping metering; The measurement of natural gas includes the measurement of gas from orifice latrine, separated gas discharge, gas flow meter and water content. At the same time, this paper introduces the comprehensive measurement methods and related technologies of oil, gas and water production in oil well produced fluid, and expounds the development trend of oil well measurement technology

key words: oil well crude oil measurement gas measurement water cut measurement device development trend

oil well production measurement is an important work in oil field production management. Accurate and timely measurement of oil well production has important guiding significance for mastering reservoir conditions and formulating production plans. At present, the oil well production measurement methods used in domestic oilfields mainly include glass tube oil measuring orifice plate gas measurement, tipping oil measuring orifice plate gas measurement, two-phase separation density method and three-phase separation measurement method. With the progress of technology, oil fields increasingly need oil well metering equipment with strong functions and high degree of automation to improve labor productivity and oil field management level

1. Crude oil measurement

(1) glass tube liquid level measurement oil

install a glass tube liquid level meter with a length of about 80 and forming a connecting pipe with the separator on the oil-gas separator. Certain important oil in the separator will pour the water pressure into the glass tube. According to the relationship between the rising height of water in the glass tube and the amount of oil in the separator, the weight of oil in the separator can be obtained. From this, the time required for the rising height of the liquid level in the glass tube can be measured, and the output of the oil well can be calculated

glass tube oil measurement is a traditional method widely used in domestic oilfields, accounting for more than 90% of the total number of oil wells. This method has the advantages of simple equipment and less investment, but the systematic error of crude oil is 10% ~ 20% due to the intermittent oil measurement. In addition, in the high water cut period, especially in the ultra-high water cut period, it is very difficult for the oil well with low gas-liquid ratio to discharge liquid after metering, which causes great inconvenience

(2) telegram oil measurement

on the basis of measuring oil on the glass tube liquid level, an electrode is installed above and below the specified oil measurement height H. when the water rises to the lower electrode, the chronograph is turned on to start timing. When the water rises to the upper electrode, the ammeter is cut off and stops moving. Record the time t when the water rises to the height H. then the output of the oil well can be calculated according to the method of measuring oil on the glass tube liquid level

(3) tipping oil measuring device is mainly composed of oil measuring device, counter, etc. When one bucket is full, turn it over to drain oil, and the other bucket is filled with oil. This cycle is repeated to accumulate oil. The oil measuring device has simple structure and certain measuring accuracy

2. Measurement of natural gas

(1) gas measurement by orifice plate

gas measurement by orifice plate is a traditional gas measurement method. The gas flow is calculated according to the pressure difference before and after the gas flows through the orifice plate. This measuring method has simple structure and convenient installation, but the measuring range is small, only 1:3, and the measuring accuracy is affected by the accuracy of orifice plate processing and installation

(2) gas measurement by separator discharge

after the oil and gas separator for metering is used to measure the oil, these data are not required, close the natural gas outlet valve of the separator, and calculate the natural gas output according to the discharge time. This method does not need special measuring devices, and the principle is simple, but the operation workload is large and the accuracy is not high

(3) gas measurement by gas flowmeter

with the development of technology, gas flowmeter is more and more used in natural gas measurement, such as gas turbine flowmeter, Precession Vortex flowmeter, vortex street flowmeter, gas Roots flowmeter, etc

gas turbine flowmeter, Precession Vortex Flowmeter and vortex street flowmeter are velocity flow measuring instruments. Gas turbine flowmeter is mainly composed of turbine, guide gas, magnetoelectric converter, etc. it has the advantages of high precision, good repeatability, fast response, wide measurement range, etc. the disadvantage is that it has moving parts and is easy to wear, which affects the measurement accuracy

vortex flowmeter is a flowmeter developed based on "Carmen" vortex principle. A vortex generator is inserted into the pipeline. When there is fluid flowing through the pipeline, vortices will be generated alternately on both sides of the vortex generator. The vortex rows arranged alternately at the downstream are called "vortex streets". The number of vortex streets passing through a certain point in a unit time is proportional to the flow rate of the fluid. The vortex street is detected by the pressure sensor, and the detected weak electrical signal is processed and converted into flow for display or remote transmission

working principle of Precession Vortex flowmeter; The fluid entering the flowmeter generates vortex flow through the vortex generator. The vortex flow rotates in the venturi and reaches the contraction point. Sudden throttling accelerates the vortex flow. When the swirling vortex enters the diffusion section, it is forced to enter the precession secondary rotation due to the effect of reflux. The frequency of vortex flow is proportional to the medium velocity and has a linear relationship. It is detected by the pressure sensor. The weak electrical signal detected can be converted into flow signal after processing

Both the Precession Vortex Flowmeter and the vortex street flowmeter have the advantages of simple structure, high accuracy, large measurement range, no mechanical movable parts, convenient installation and use, and are not affected by the density and viscosity of the medium

gas Roots flowmeter is a positive displacement flowmeter with high measurement accuracy. It is suitable for precise volume measurement and is widely used in trade and precise storage and transportation measurement management. However, the natural gas separated from the oil well metering contains more droplets, which will affect the lubrication of the rotating mechanism of the flowmeter, and is prone to jamming and blocking accidents. Therefore, this kind of flowmeter is generally not suitable

3. Water content measurement

(1) manual sampling

the operator takes a certain number of oil samples, and uses distillation method, electric stripping method, etc. to determine the water content of oil samples, so as to obtain the water content parameters of oil wells. This is the main detection method used in oil fields in China. It is difficult to obtain accurate oil samples manually. The representativeness is not strong, which increases the error of water content of crude oil

(2) measurement

install instruments on the crude oil pipeline, and use densitometer, capacitance, microwave and other instruments to measure the water content of the liquid

① measure water content with densimeter. Use a liquid densimeter in the form of vibrating tube to measure the density of oil-water mixture, and calculate the water content according to its density

② measure water content by capacitance method. The coaxial barrel capacitance sensor is often used to measure the water content of low water cut crude oil. The principle that the dielectric constant of crude oil emulsion is related to the water content is used to measure the water content of crude oil

③ microwave method. The water content of oil-water mixture is measured according to the different degree of microwave absorption of crude oil and water

④ γ X-ray and X-ray absorption methods. When γ When X-rays and X-rays pass through a substance, the intensity of the rays decays. Because the absorption coefficients of crude oil and water are different, the water content of oil-water mixture can be calculated by measuring the ray intensity

4. New oil well production measurement technology with the development of technology and the needs of oil field management, reducing labor intensity and improving production efficiency, there have been many metering devices that can comprehensively measure the oil, gas and water production of oil wells

(1) three phase separation metering

three phase separation metering is to measure oil, gas and water respectively after separation. After separation, the water content of crude oil is low (generally below 30%), and the measurement error of crude oil is reduced, which is not affected by the water content of oil well. However, in order to separate ultra-high water cut crude oil into low water cut crude oil and measure it, the process technology is very complex, and a large amount of free water often carries part of the crude oil, resulting in a large error, and requires many equipment and instruments, large investment, difficult management and operation, and high maintenance costs

(2) two phase separation metering

two phase separation metering is to separate the produced liquid from the oil well into liquid and gas, and then measure them respectively. The two-phase separation metering equipment is mainly composed of two-phase separator, gas flowmeter, liquid flowmeter, water cut analyzer, etc. the gas flowmeter and liquid flowmeter measure the gas and liquid production of the oil well. The water cut analyzer measures the water cut of the separated liquid, so as to calculate the oil, gas and water production of the oil well

another type of metering equipment consists of two-phase separator, mass flowmeter and gas flowmeter. The mass flowmeter measures the separated liquid volume and calculates the water content, so as to measure the oil, gas and water production of the oil well. This kind of calculation device has less investment and simple operation, and has been widely used in oil fields in China

(3) non Separation Metering

non separation metering is to measure the flow of gas and liquid without separating the produced liquid from the oil well. Venturi, densimeter or different flow sensors are combined to measure the flow of gas and liquid. The liquid part uses double γ X-ray densitometer, capacitance and microwave water content monitor are used to determine the content of oil and water, so as to calculate the respective output of oil, gas and water

the non Separation Metering Technology of oil, gas and water has great advantages in terms of floor area. However, the oil, gas, water and other components in the oil well produced fluid are generally not uniformly mixed. They flow at different speeds, and may interact to form wax and hydroxide, and cause unpredictable complex flow patterns. Therefore, it is very difficult to develop a flowmeter with a wide range of application. Although there have been many schemes to realize non Separation Metering of oil, gas and water at home and abroad, few have been successfully put into use

5. Development trend

(1) towards instrumentation. With the progress of technology and the wide application of various gas and liquid flowmeters, more and more flowmeters with simple operation and convenient reading are used in oil well production measurement. Such as Precession Vortex Flowmeter and vortex street flowmeter for natural gas measurement

(2) develop towards high precision. Most oilfields in our country are in the late stage of development. It is necessary to understand the production status of oil wells accurately and timely in recent years, which is also resistant to high temperature and low temperature, so as to provide authentic and reliable data for production management. The requirements for oil well measurement accuracy are bound to be higher and higher

(3) develop in the direction of rapid development. In order to grasp the production status of oil wells in time, it is necessary to shorten the metering cycle of oil wells and measure oil wells more frequently and timely. Therefore, it is necessary to improve the metering speed of oil wells

(4) develop towards automation. The development of automation technology provides a reliable guarantee for reducing labor intensity and improving labor productivity. At the same time, in order to achieve accurate and rapid measurement of oil wells, automatic measurement methods must also be adopted. The research and application of three-phase separation metering, two-phase separation metering and non Separation Metering will be paid more and more attention. (end)

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