Abstract: this paper introduces the production measurement methods of oil Wells mainly used in China's oil fields, including the measurement of crude oil including electromagnetic flow measurement of oil, electrode oil, bucket oil;Natural gas measurement includes orifice lavatory gas, separation gas drainage gas, gas flow meter gas and water content measurement.At the same time, this paper introduces the comprehensive metering method of oil, gas and water output in oil well production fluid and its related technologies, and expounds the development trend of oil well metering technology.
The metering of oil well output is an important work in oilfield production management. Accurate and timely metering of oil well output is of great guiding significance for mastering reservoir conditions and formulating production plans.At present, the oil well production measurement methods adopted by various oilfields in China mainly include glass pipe oil orifice gas measurement, bucket oil orifice gas measurement, two-phase separation density method and three-phase separation measurement method.With the development of technology, oil fields need more and more powerful and automatic oil well metering equipment to improve labor productivity and oil field management.
(1) measure oil by electromagnetic flow
An electromagnetic flowmeter about 80 long and connected with the separator is installed on the oil and gas separator.Some important oil in the separator overcomes water in the glass pipe. According to the relationship between the rising height of water in the glass pipe and the amount of oil in the separator, the weight of oil in the separator is obtained. Therefore, the time required to measure the rising height of liquid level in the glass pipe can be converted into the output of the oil well.
Measuring oil with glass tube is a traditional method widely used in various oil fields in China, which accounts for more than 90% of the total number of oil Wells.The method is simple in equipment and low in investment, but the systematic error of crude oil is 10% ~ 20% due to the intermittent oil measurement method.In addition, in the period of high water cut, especially in the period of extremely high water cut, it is very difficult to measure the drainage of oil Wells with low gas-liquid ratio, which causes great inconvenience to the metering operation.
(2) measure oil by telegraph
On the basis of electromagnetic flow measurement of oil, under the regulations on oil height H, the installation of an electrode, when the water rose to the electrode, timing meter through to start timing, when the water rose to the top electrode, electric meter cut stop walking, record water in H high time t, can be in accordance with the oil glass tube liquid level measurement method to calculate the production of oil well.
(3) turn the bucket to measure oil
The oil measuring device is mainly composed of oil measuring device and counter.When one bucket is full, turn over to drain oil, and the other bucket to fill oil, so that the repeated cycle to accumulate oil.The oil measuring device is simple in structure and has certain measuring accuracy.
(1) orifice plate gas measurement
Orifice gas measurement is a traditional gas measurement method. The orifice plate and bellows differential pressure meter are used to measure the gas flow.This metering method has simple structure and convenient installation, but the range is small, only 1:3, and the metering accuracy is affected by the precision of orifice plate machining and installation.
(2) the separator discharges liquid and measures gas
After the oil is measured by the metering oil and gas separator, close the gas outlet valve of the separator and calculate the natural gas output according to the discharge time.This method does not need special measuring device, the principle is simple, but the operation workload is large, and the accuracy is not high.
(3) the gas flow meter measures the gas
With the development of technology, gas flowmeter has been applied more and more in the measurement of natural gas, commonly used gas turbine flowmeter, precingvortex flowmeter, vortex flowmeter, gas roots flowmeter and so on.
Gas turbine flowmeter, precession vortex flowmeter and vortex flowmeter are velocity flowmeter.Gas turbine flowmeter is mainly composed of turbine, flow guide gas, magnetoelectric converter and so on. It has the advantages of high accuracy, good repeatability, fast response, wide measurement range and so on. The disadvantage is that it has moving parts, easy to wear, which affects the measurement accuracy.
Vortex flowmeter is a kind of flowmeter based on kamen vortex principle.When a vortex generating body is inserted into the pipe, when a fluid flows through the pipe, vortexes will be generated alternately on both sides of the vortex generating body. The vortex columns arranged alternately in the downstream are called "vortex ", and the number of vortex passing through a certain point in unit time is proportional to the flow rate of the fluid.Vortex is detected by pressure sensor, and the detected weak electrical signal is processed and converted into flow rate for display or remote transmission.
Principle of precession vortex flowmeter;The fluid entering the flowmeter generates vortex flow through the vortex generator. The vortex flow precession in the venturi tube, reaches the contraction and shortens the sudden throttling to accelerate the vortex flow.When the vortex flow 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 directly proportional to and linearly related to the medium velocity. The weak electrical signal detected by the pressure sensor can be converted into a flow signal after processing.
Precession vortex flowmeter and vortex flowmeter have the advantages of simple structure, high accuracy, large measurement range, no mechanical movable parts, easy installation and use, and are not affected by the density and viscosity of the medium.
Gas roots flowmeter is a kind of volumetric flowmeter with high measuring precision, which is suitable for precise volume measurement and widely used in trade and precise storage and transportation measurement management.However, the natural gas separated from the oil well metering contains more liquid droplets, which will affect the lubrication of the rotating mechanism of the flowmeter, and it is easy to get stuck or blocked. Therefore, it is generally inappropriate to use this kind of flowmeter.
(1) manual sampling
Operators take a certain number of oil samples and measure the water content of oil samples by distillation and electric dewatering, so as to obtain the water content parameters of oil Wells.This is currently the main detection method used in China's oil fields.Manual oil sampling is not easy to be accurate.Low representativeness increases the error of water content of crude oil.
(2) online measurement
Install online instrument in crude oil pipeline, use densitometer, capacitance, microwave and other instruments to measure the moisture content of liquid online.
Density meter to measure moisture content.Liquid densitometer in the form of vibrating pipe is used to measure the density of oil-water mixture and calculate the water content according to its density.
(3) capacitance method to measure water content.Coaxial barrel capacitance sensor is often used to measure the water content of low water-cut crude oil, and 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.
Microwave method.The moisture content of oil-water mixture was determined according to the degree of microwave absorption of crude oil and water.
Gamma rays and X-ray absorption method.Gamma rays and x-rays decay when they pass through material.Since the absorption coefficients of oil and water are different, the moisture content of oil-water mixture can be calculated by measuring the intensity of the radiation.
With the development of technology and the need of oilfield management, reducing labor intensity of workers and improving production efficiency, many metering devices that can comprehensively measure oil, gas and water output of oil Wells have appeared one after another.
(1) three-phase separation and measurement
Three-phase separation measurement is to measure oil, gas and water separately after separation. After separation, the water content of crude oil is lower (generally less than 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 super-high water-cut crude oil into low-water-cut crude oil for measurement, the technology is very complex, and a large amount of free water often carries part of the crude oil, causing a great error, and the required equipment and instruments, large investment, difficult management and operation, maintenance costs are high.
(2) two-phase separation measurement
Two-phase separation metering is to separate the produced fluid of oil well into liquid and gas, and then measure them separately.Two-phase separation and measurement equipment is mainly composed of two-phase separator, gas flow meter, liquid flow meter, water-cut analyzer, etc., gas flow meter and liquid flow meter measure the gas production and liquid production of oil Wells, water-cut analyzer measures the water cut of the separated liquid, and thus calculates the oil, gas and water output of oil Wells.
The other type of metering equipment consists of a two-phase separator, a mass flowmeter and a gas flowmeter.The mass flow meter measures the amount of separated liquid and calculates the moisture content, so as to measure the oil, gas and water output of oil Wells.This kind of computing device has less investment and simple operation, and has been widely used in oil fields in China.
(3) do not separate measurement
Non-separation metering is not separated oil well produced fluid, venturi pipe, densitometer or different flow sensor together to measure the flow of gas and liquid, liquid part with double gamma ray densitometer, capacitance, microwave water content monitor to determine the content of oil and water, so as to calculate the oil, gas, water output.
The non-separation metering technology of oil, gas and water has great advantages in area occupied and so on.However, the oil, gas, water and other components in the production fluid of oil Wells are generally not uniformly mixed. They flow at different speeds and may interact to form waxes and hydroxides, causing unpredictable and complex flow patterns.Therefore, it is very difficult to develop flow meters with a wide range of applications. Although there are many schemes to realize the non-separation measurement of oil, gas and water at home and abroad, few of them have been successfully put into use.
(1) develop toward instrumentation.With the development of technology and the wide application of various gas and liquid flowmeters, more and more flowmeters with simple operation and convenient reading must be used in oil well production measurement.For example, for the measurement of natural gas precession vortex flowmeter, vortex flowmeter, etc.
(2) develop towards high precision.Many oil fields in China have entered the later stage of development, so it is necessary to accurately and timely understand the production status of oil Wells and provide authentic and reliable data for production management. Therefore, the requirements for measuring accuracy of oil Wells are bound to be higher and higher.
(3) to speed up the direction of development.In order to grasp the production status of oil well in time, it is necessary to shorten the measuring period of oil well and make more frequent and timely measurement of oil well, so the measuring speed of oil well must be improved.
(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 realize accurate and rapid measurement of oil well, automatic measurement method must also be adopted.More and more attention will be paid to the research and application of three-phase separation metering two-phase separation metering and non-separation metering.