Oil and gas well carbon dioxide on-line monitoring and metering equipment and implementation method thereof

Abstract

The invention discloses oil and gas well carbon dioxide online monitoring and metering equipment and an implementation method thereof, and relates to the technical field of oil field metering. The equipment comprises a gas-liquid separation unit, a liquid production capacity and moisture content analysis and detection unit, a carbon dioxide content detection unit, a gas flow unit, an automatic control unit, a data acquisition and transmission unit and an auxiliary unit, on-line metering and remote data transmission of parameters including liquid production capacity, gas production capacity, water content, carbon dioxide content, pressure and temperature of a wellhead of an oil well can be realized. The gas-liquid separation unit adopts a gravity separation method and is combined with a specific structural design to guarantee the separation effect; each parameter detection unit realizes accurate detection based on an ultrasonic technology, an infrared absorption principle, a thermal measurement principle and the like; data are uploaded to an upper computer through a DTU unvarnished transmission technology, and real-time monitoring and data analysis are supported. The system is adaptive to conventional drive and CCUS drive oil fields, the automation degree is high, the environmental adaptability is high, and data support is provided for accurate management of oil reservoirs.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of CCUS (carbon capture, utilization and storage) flooding, in particular to an oil and gas well carbon dioxide online monitoring and metering device and an implementation method thereof, which is suitable for real-time acquisition, transmission, monitoring and control of parameters such as liquid production rate, gas production rate, water cut, carbon dioxide content, pressure and temperature of gas-liquid multiphase medium at the wellhead of an oil well. BACKGROUND

[0002] With the promotion of intelligent and smart construction of oilfields, single-well digital metering of oil wells has become the core work of digital oilfield construction. The single-well metering of conventional water flooding and polymer flooding oilfields mainly focuses on parameters such as liquid volume, water cut, wellhead pressure and oil temperature, but in CCUS flooding blocks, wellhead gas flow and carbon dioxide content are key parameters that managers focus on, which are directly related to the evaluation of oil displacement efficiency and the monitoring of carbon storage effect.

[0003] It is further pointed out that CCUS flooding technology, as an important means to achieve the "double carbon" goal and increase oil production, its core is to inject captured carbon dioxide into oil reservoirs to improve oil recovery and achieve carbon storage. In the production process of CCUS flooding wells, the wellhead output medium is a multiphase mixture of oil, gas, water and carbon dioxide. Real-time and accurate monitoring of each phase parameter (liquid production rate, gas production rate, water cut, CO2 content, pressure, temperature) is the key to evaluating CO2 flooding effect, optimizing injection and production technology, ensuring production safety and accounting for carbon storage efficiency.

[0004] The existing metering equipment has the following shortcomings: first, the function is single, most of the equipment can only realize conventional parameter metering, which cannot meet the metering demand of gas parameters in CCUS flooding oilfields; second, the gas-liquid separation effect is not good, resulting in large error in multiphase flow metering; third, the environmental adaptability is poor, and equipment failure is easy to occur in winter and other harsh working conditions; fourth, the real-time data transmission is insufficient, which is difficult to support accurate management of oil reservoirs.

[0005] Therefore, it is urgent to develop a CCUS flooding well special metering equipment which integrates multi-parameter metering, has good separation effect, strong environmental adaptability and real-time data transmission. SUMMARY

[0006] The present application aims to provide an oil and gas well carbon dioxide online monitoring and metering device and an implementation method thereof, which integrates accurate detection of carbon dioxide and related parameters while optimizing equipment cost and stability, and meets the needs of various scenarios.

[0007] Technical solution: An oil and gas well carbon dioxide online monitoring and metering device, comprising a gas-liquid separation unit, a produced fluid volume water cut analysis and detection unit, a carbon dioxide content detection unit, a gas flow unit, and an automatic control unit, a data acquisition and transmission unit, and an auxiliary unit connected to each detection unit respectively; The metering device comprises a tank body, the bottom of which is provided with a liquid discharge port connected to the produced fluid volume water cut analysis and detection unit, the pressure detection unit, and the temperature detection unit, and the top of which is connected to the gas flow unit and the carbon dioxide content detection unit through a gas pipe; The gas-liquid separation unit is arranged in the tank body, and baffles are arranged on the inner wall to form a flow path of the mixed liquid in the tank body, the baffles are used to impact and diffuse the mixed liquid under the action of gravity, and the gas-liquid separation effect is controlled based on the formed liquid flow path; The produced fluid volume water cut analysis and detection unit comprises an ultrasonic detection device arranged in the tank body, and water cut detection is realized based on ultrasonic Doppler effect, including calculation of water cut; the flow rate of the mixed liquid in the pipeline is measured based on ultrasonic waves, combined with parameters such as oil well stroke cycle and stroke, to calculate single-stroke liquid discharge volume and daily produced fluid volume, and to convert the oil production volume; The carbon dioxide content detection unit is provided with an NDIR type dual-wavelength gas sensor, which compares the transmission amounts of absorbable and non-absorbable wavelengths after infrared radiation of the gas, and calculates the gas concentration combined with the Lambert-Beer law; The gas flow unit is integrated at the gas outlet end of the gas-liquid separation unit, and comprises platinum resistance temperature sensors for detecting heat sources and measuring fluid temperature respectively, which collect the temperature difference between the two sensors and the linear relationship between the flow rate and convert it into a flow signal; The automatic control unit comprises a PLC control module, a field industrial computer, and an actuator, which controls the operation of gas collection, gas distribution, gas exhaust, and each detection unit according to a preset program; The data acquisition and transmission unit uses DTU transparent transmission technology to upload wellhead collected information to the upper computer at regular intervals; The auxiliary unit comprises an electric control box, which is provided with a power supply, a battery, a power supply switching device, a transmission switching device, and an air switch, and the pressure vessel is made of aerogel insulation, an electric heating device is additionally arranged in the tank, and the connecting rubber pipe uses built-in cable heating to realize temperature self-control.

[0008] Further, the gas-liquid separation unit adopts gravity separation method, comprising a tank body, a demister, a floating ball one-way valve, and baffles, the tank body is provided with a mixed liquid inlet, a gas outlet, and a liquid discharge port; The demister is arranged on the path of gas rising after gas-liquid separation in the tank body, and is arranged below the gas outlet or at the inlet end of the top of the tank body, and is used to remove oil and gas mixed bubble foam in the oil and gas mixed liquid; The baffle is arranged in an inclined or arc structure, so that the mixed liquid flows slowly along the surface of the baffle, prolongs the residence path of the liquid flow in the tank, increases the time window of gas-liquid separation, and simultaneously guides the gas to gather in the direction of the top demister and the liquid to sink to the bottom.

[0009] The tank body is provided with a baffle at the mixed liquid inlet, which is used to block the high-speed liquid flow from directly impacting the liquid surface in the tank, avoid the settled liquid being stirred again, and reduce the amount of gas bubbles brought by the liquid flow.

[0010] Further, the carbon dioxide content detection unit includes an automatic detection probe, a rotor flowmeter, an oil-water separator, a pressure reducing valve, a vacuum sampling pump and an explosion-proof electromagnetic valve.

[0011] Further, the oil and gas well carbon dioxide online monitoring and metering equipment includes the following detection and calculation processes: (1) The water content of the mixed liquid in the tank is calculated as follows: Based on the identification of the discrete phase holdup of oil, gas and water three phases through ultrasonic reflection intensity, they are respectively recorded as , and , which satisfy , wherein the oil phase holdup is directly obtained through ultrasonic reflection intensity, and the water phase holdup is calculated by ignoring the influence of the gas phase on the oil-water mixed liquid volume; The water phase flow rate is directly measured through ultrasonic Doppler frequency shift , wherein is the propagation speed of ultrasonic waves in water, is the Doppler frequency shift, is the ultrasonic wave emission frequency, is the included angle between the ultrasonic wave emission direction and the water flow direction; According to the definition of the slip velocity, the oil phase velocity is equal to the sum of the water phase velocity and the oil phase slip velocity relative to the water phase, that is, the oil phase velocity , wherein is an experimental calibration value related to the oil well viscosity; The gas phase velocity , wherein is an experimental calibration value related to the wellhead pressure; The oil phase flow rate ; The water phase flow rate ; The water content .

[0012] (2) The produced liquid volume calculation includes the following processes: Based on the ultrasonic Doppler effect, the original flow rate is calculated first, and then the accurate flow rate is obtained after temperature correction: In the formula, is the propagation speed of the ultrasonic wave in water after temperature correction, is the Doppler shift, is the ultrasonic wave transmission frequency, is the angle between the ultrasonic wave transmission direction and the water flow direction; The single stroke liquid discharge volume is the accurate flow rate multiplied by the pipe cross-sectional area and the single stroke effective liquid discharge time, and the single stroke effective liquid discharge time is identified by the pressure sensor, including identifying the following three stages: Pressure rising section: the oil pumping unit goes up, the single flow valve opens, the liquid enters the pipeline, and the pressure rises from the baseline; Pressure stable section: the liquid continues to flow, and the pressure maintains a stable value; Pressure falling section: the oil pumping unit goes down, the single flow valve closes, and the pressure falls to the baseline; The effective liquid discharge time is the time interval from the starting point of the pressure rising section to the starting point of the pressure falling section, which is collected and automatically identified by the equipment pressure sensor in real time; (3) The daily liquid production volume is the total of the liquid volumes of all effective strokes in a day, and after calculating the total number of strokes, abnormal strokes are excluded, and the abnormal strokes refer to empty strokes without pressure change; Abnormal stroke exclusion uses criterion, is the standard deviation in the normal distribution to which the stroke belongs.

[0013] (4) The calculation formula of the NDIR type dual-wavelength gas sensor for carbon dioxide concentration satisfies: In the formula, is the transmittance, is the transmitted light intensity, is the incident light intensity, is the absorbance, is the carbon dioxide gas concentration, is the optical path length of infrared light through the gas medium.

[0014] Further, the gas flow unit includes auxiliary components added in the gas outlet pipeline in the tank body, which cooperates with the double platinum resistance sensor, specifically including: The rotor flowmeter is arranged upstream of the heating probe and is used for visual monitoring of the gas flow rate. The built-in valve is used to fine-tune the flow rate to ensure that the gas flow rate entering the sensor detection area is stable in the effective measurement interval; A filter screen is installed upstream of the rotor flow meter to filter the oil mist and dust remaining in the gas; A temperature compensation module is integrated in the sensor housing and linked to the temperature measuring probe. When the gas temperature fluctuates beyond , the heating current of the heating probe is automatically adjusted to maintain a constant temperature difference in the gas inside the heating probe, offsetting the interference of the ambient temperature on the measurement The gas flow unit performs the following online metering calculation process: The resistance values of the heating probe and the temperature measuring probe are read and converted into corresponding temperatures through the platinum resistance temperature calculation formula, and the difference between the two is calculated , The temperature of the heating probe, The temperature of the temperature measuring probe; The real-time temperature of the gas flowing through the sensor And the real-time pressure of the gas are obtained, preprocessed, and smoothed through the moving average method; The real-time density of the gas is corrected according to the real-time temperature and pressure, and the correction formula is based on the ideal gas state equation: In the formula, The real-time density of the gas, The density of the gas under standard conditions, The standard atmospheric pressure, The standard temperature; According to the thermal constant temperature difference principle, the gas flow rate and the heating power Temperature difference are fixed functions, combined with the corrected gas density The calculation formula of the real-time flow rate of the gas is as follows: In the formula, The balance coefficient; The instantaneous flow calculation formula is: In the formula, The cross-sectional area of the gas outlet pipeline; The calculation formula of the accumulated flow is: In the formula, The number of acquisitions.

[0015] ​For the detection calculation process, the application provides a calibration method for the online monitoring and metering equipment for carbon dioxide in the oil and gas well, which is characterized by including liquid production calibration, water cut calibration and carbon dioxide content detection unit calibration; the liquid production calibration takes water and transformer oil as medium, controls flow rate through a frequency converter, and calculates liquid production in combination with oil well working condition parameters; the water cut calibration adopts mixed liquid with different water cut ratios to fit the corresponding relationship between frequency and water cut; and the carbon dioxide content detection unit calibration is calibrated with standard CO2 gas under the environment of-40 DEG C-80 DEG C according to standard requirements.

[0016] Advantages: Compared with the prior art, the substantial features and significant effects of the application include: 1. High gas-liquid separation efficiency and strong adaptability: through the three-stage separation structure of three types of modular tank bodies, baffle plates, floating ball one-way valves and demisters, different liquid production oil wells are accurately adapted, the purity of gas and liquid after separation is high, the problems of gas carrying liquid and liquid carrying gas are effectively avoided, the foundation is laid for subsequent parameter collection, and the separation effect is improved by more than 40% compared with traditional devices.

[0017] 2. Accurate and comprehensive multi-parameter collection: each detection module is designed in a targeted manner, combined with data preprocessing technology and standardized calibration method, high-precision online collection of core parameters such as liquid production, water cut and CO2 content is realized, the error is significantly lower than that of existing equipment, and the accuracy requirement of CCUS oil displacement monitoring is met.

[0018] 3. Stable data transmission and strong compatibility: a combination of multi-link communication mode and self-defined MODBUS protocol is adopted to adapt to the complex signal environment of oil fields and existing RTU equipment, and CRC16 check is used to ensure that there is no packet loss and miscommunication during data transmission, and the transmission stability is greatly improved.

[0019] 4. High environmental adaptability and intelligence: explosion-proof, protection and temperature control design make the system adapt to harsh outdoor working conditions, the automatic control unit realizes programmed control of the equipment, reduces manual intervention, and the software of the upper computer and the lower computer cooperates to realize intelligent processing of data in the whole process, and the operation and maintenance efficiency is improved by more than 60%.

[0020] 5. Strong practicality and expansibility: modular design can be flexibly combined according to the working conditions of oil wells, external system integration interfaces are reserved, existing CCUS oil displacement monitoring requirements can be met, and subsequent process upgrades can be adapted, reliable data support is provided for process optimization, capacity improvement and carbon sequestration accounting, and the application prospect is broad. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a structural schematic view of a tank body in the online monitoring and metering equipment for carbon dioxide in the oil and gas well; Figure 2 is a whole structural schematic view of the online monitoring and metering equipment for carbon dioxide in the oil and gas well. Figure 3 is an integrated component of the liquid production rate water cut analysis detection unit; Figure 4 is the overall assembly effect diagram of the present application; Figure 5 is the detection principle diagram of the gas flow detection unit; Figure 6 is the detection principle diagram of the carbon dioxide detection unit; Figure 7 is the technical principle diagram of the liquid online metering; Figure 8 is the measurement principle diagram of the ultrasonic wave generating device; Figure 9 is the communication system architecture diagram of the device. DETAILED DESCRIPTION

[0022] To illustrate the technical solutions disclosed by the present application in detail, the following further introduces in combination with the accompanying drawings and the implementation process of functions.

[0023] In combination with Figures 1-4 the drawings, the tank structure of the oil and gas well carbon dioxide online monitoring and metering device provided by the present application includes a tank 1, a mixed liquid inlet 2 (DN50) is arranged in the middle of the tank 1, a flow path of the mixed liquid is arranged in the tank 1 through a baffle 3, and the drawing shows that a baffle is arranged at the inlet position to prevent the mixed liquid from impacting the inside of the tank 1, and the baffle 3 is gradually arranged in the lower layer to achieve step-by-step impact and mixed liquid diffusion, which helps to improve the gas-liquid separation effect. A liquid discharge port 4 (DN50) is arranged at the bottom of the tank 1, a demister 5 is arranged at the top of the tank 1, and a float ball one-way valve 6 is arranged inside a gas outlet 7 (DN20). The whole adopts a cylindrical vertical design, the outside of the tank is wrapped with a 50mm thick aerogel thermal insulation layer, the thermal insulation layer is covered with a galvanized iron protective layer, the influence of the environmental temperature on the temperature of the medium in the tank is reduced, three supporting feet (height 100mm) are welded at the bottom of the tank, which are used for fixing the tank and ensuring that the liquid discharge port at the bottom of the tank is at a horizontal low position to avoid liquid accumulation; a manhole (diameter 200mm) is further arranged in the middle of the side wall of the tank, which is convenient for periodic cleaning of impurities in the tank and maintenance of internal components.

[0024] The overall height of the tank 1 is 1.2m, and according to the difference of the liquid production rate of the oil well, it is divided into three modular types, and the diameters and total volumes of different types correspond as follows: 1 type tank body: diameter 0.18m, total volume 0.1225m³, adapt to the liquid production of low liquid production oil well ≤5m³ / d; 2 type tank body: diameter 0.25m, total volume 0.2363m³, adapt to the liquid production of medium liquid production oil well 5-15m³ / d; 3 type tank body: diameter 0.35m, total volume 0.4633m³, adapt to the liquid production of high liquid production oil well ≥15m³ / d; The gas-liquid space ratio of the three types of tank bodies is uniformly controlled to 0.75-0.83 (gas accounts for liquid), to ensure that there is enough settling space for liquid and stable gathering channel for gas during gas-liquid separation.

[0025] Mixed liquid inlet 2: located in the middle and lower part of the side wall of the tank, 0.9m from the tank bottom, with DN50 interface specification, used for connecting the oil, gas, water and carbon dioxide multi-phase mixed liquid produced by the wellhead; The inside of the inlet is welded with an arc baffle to avoid the high-speed mixed liquid directly impacting the liquid surface in the tank, causing the already settled liquid to be stirred again; Gas outlet 7: opened in the center of the top of the tank, with DN20 interface specification, connected with the gas pipe of the gas flow unit and the carbon dioxide content detection unit, used for discharging the separated gas; A stainless steel mesh demister (mesh aperture 0.5mm) is installed below the outlet, which can intercept the small oil mist and liquid droplets entrained in the gas, improving the gas purity; Liquid discharge port 4: arranged at the lowest point of the bottom of the tank, with DN50 interface specification, connected with the liquid production rate and water cut analysis and detection unit, pressure detection unit and temperature detection unit; A float ball one-way valve is connected inside the liquid discharge port, which automatically controls the opening and closing of the valve through the buoyancy of the float ball, avoiding liquid backflow, and can also assist in identifying single stroke liquid discharge time.

[0026] Baffle 3: 3 groups of inclined baffles (inclination angle 30°) are welded along the inner wall of the tank; The mixed liquid enters along the baffle surface and flows slowly downward, prolonging the residence path of the liquid flow in the tank (total path length is about 2.5 times the height of the tank), increasing the gas-liquid separation time window; At the same time, it guides the gas to gather at the top and the liquid to settle at the bottom, realizing the preliminary separation of gas and liquid; Demister 5: In addition to the wire mesh demister below the top gas outlet, a set of baffling demister is additionally arranged in the middle of the tank (0.4m from the top), which separates the liquid droplets remaining in the gas through the multiple turning of the gas between the baffles, and the two-stage demisting design reduces the liquid-carrying rate of the gas to below 0.5%; Temperature and pressure monitoring interface: two sensor mounting holes are reserved in the middle of the inner wall of the tank body (0.6 m from the tank bottom) for embedding platinum resistance temperature sensors (measurement range -40℃~+85℃, accuracy ±1℃) and pressure sensors (measurement range 0-5 MPa, accuracy ±1% F・S), respectively, to monitor the temperature and pressure data of the mixed liquid in the tank in real time, providing a basis for subsequent parameter correction.

[0027] Example 1: Taking type 3 separation tank body as an example to introduce the implementation process of the gas-liquid separation unit For the liquid in the oil-gas mixed bubble foam state, theoretically, the produced liquid can be separated into gas and liquid after 25 minutes of sedimentation. According to the maximum liquid production of 15 m³ / d, if the average flushing frequency of the oil well is 4 times per minute, the theoretical tank liquid volume of each flushing is 0.0026 m³, and the tank liquid volume per minute is 0.0104 m³. The produced liquid enters the tank from the upper part and is discharged from the lower part. The liquid volume entering the tank with each flushing can be sedimented for at least 38 minutes in the tank, which is greater than the theoretical sedimentation time of 25 minutes.

[0028] Figure 2 The system structure shown includes a gas-liquid separation unit 100, a liquid production rate and water cut analysis and detection unit 400, a carbon dioxide content detection unit 300, and a gas flow unit 200. The liquid separation unit 100 is located in the tank body 1 and uses the gravity separation method. The mixed liquid entering the tank utilizes the different densities, inertias, and gravitational sedimentations of gas and liquid, and the liquid flow path is guided and designed by the baffle 3, to realize gas-liquid separation by utilizing the differences in physical properties of gas and liquid. The separated liquid is mainly composed of oil and water. After detection by the automatic oil sampler, the separated liquid re-enters the oil pipeline 9 after the gas-liquid phase is combined at the outlet. The gas flow unit 200 obtains a part of the separated gas through the gas pipe 8 and delivers it to the carbon dioxide content detection unit 300 for detection. The detection is as follows: The gas flow unit 200 adopts the thermal gas flow measurement principle, as shown in Figure 5 The constant temperature difference method is used to accurately measure the gas mass flow. The sensor part is composed of two reference level platinum resistance temperature sensors, one of which is used as a heat source and the other is used to measure the fluid temperature. When the fluid flows, the temperature difference between the two is linearly related to the size of the flow. Through microelectronic control technology, this relationship is converted into a linear output of the flow signal.

[0029] In combination with Figure 6As shown, in the carbon dioxide content detection unit 300, the sensor is composed of an infrared radiation light source, a photosensitive element, an optical filter, a detection cartridge body containing them, and a signal processing circuit. In a single light source dual-wavelength type sensor, optical filters with different transmission wavelength range thresholds are respectively arranged in front of the two photosensitive elements, and by comparing the transmission amounts of the absorbable detection object gas wavelength range and the non-absorbable wavelength range, the corresponding gas concentration can be converted. Therefore, the dual-wavelength method can realize long-term and stable detection. After the gas is irradiated with mid-band infrared rays, because the vibration number of the gas molecules and the energy level of the infrared rays are in the same spectral range, after the infrared rays and the inherent vibration number of the molecules resonate, they are absorbed by the gas molecules when the molecules vibrate. The relationship between gas concentration and infrared transmittance can be explained by the following Lambert-Beer law. For NDIR type gas sensors, the absorbance of the object gas is constant with the optical path d, and in the spectral range consistent with the absorption energy (wavelength) of the gas to be detected, the concentration c of the object gas can be obtained by measuring the transmittance T of the infrared rays. The incident light intensity from the radiation source is set after calibration using a zero-point gas that does not absorb infrared rays. The absorbance is initially set after calibration using a known concentration of the object gas.

[0030] The produced fluid volume and water cut analysis detection unit 400 adopts an integrated device, as shown in Figure 7 The mixed liquid (mainly oil and water) in the tank 1 after gas-liquid separation enters the produced fluid volume and water cut analysis detection unit 400 through the mixed liquid transmission pipeline 101 at the bottom of the tank, and the produced fluid volume and water cut analysis detection unit 400 realizes liquid volume measurement, water cut measurement, pressure measurement, and temperature measurement through the calculation module 103. The specific implementation is as follows: Ultrasonic Doppler measurement of fluid flow is based on the reflection characteristics of ultrasonic waves and the Doppler effect. Figure 8 The measurement technology principle is shown. We take the separated mixed liquid from the tank and set an ultrasonic wave generating device on the pipeline through which the mixed liquid passes to monitor the fluid flow. When ultrasonic waves of a fixed frequency encounter moving objects with a relative velocity in the direction of the ultrasonic waves, the reflection wave frequency of the sound waves on the surface of the objects will be shifted, and the shift amount is related to the movement speed of the objects.

[0031] Using the principle of ultrasonic wave measurement of flow rate, the flow rate of the mixed liquid in the pipeline is measured in real time, and the liquid volume time of each cycle of the oil well is calculated based on the parameters of the pressure change of the single-flow valve, and then the daily liquid production of the oil well is calculated. Based on the water cut and the produced fluid volume, the oil production can also be converted.

[0032] The liquid production amount calculation mainly considers removing outliers, and in the selection of daily report data, the liquid amount is calculated by cumulatively calculating the liquid production of each stage in the day. In the arithmetic mean, outliers need to be removed, and the data preprocessing method mainly includes removing extreme values, standardization, and neutralization.

[0033] Figure 9 The system communication framework of the monitoring metering device is displayed, the DTU transparent transmission technology is adopted to directly upload the wellhead collection information to the upper computer in time, the information can also be linked to the existing wellhead RTU and uploaded to the upper computer, and each parameter is analyzed in time, the intuitive understanding of the change of the single well wellhead parameter of the technical and management personnel is improved, and the accurate management and efficient analysis of the oil reservoir are assisted. The application also supports RS232 / RS485, 4G / 3G / 2G, ZIGBEE multiple transmission modes, the communication parameter is baud rate 9600, data bit 8 bits, no check bit, a self-defined MODBUS communication protocol is adopted, real-time data uploading, historical data query and system parameter configuration are supported.

Claims

1. An online monitoring and metering device for carbon dioxide in oil and gas wells, characterized in that, It includes a gas-liquid separation unit, a liquid yield and moisture content analysis and detection unit, a carbon dioxide content detection unit, a gas flow unit, and an automated control unit, a data acquisition and transmission unit, and an auxiliary unit connected to each detection unit respectively; The metering device includes a tank, with a drain port at the bottom of the tank. The drain port is connected to a liquid production and moisture content analysis and detection unit, a pressure detection unit, and a temperature detection unit. The top of the tank is connected to a gas flow unit and a carbon dioxide content detection unit via a gas pipe. A gas-liquid separation unit is installed inside a tank. Baffles are installed on its inner wall to form a flow path for the mixture inside the tank. The baffles are used to impact and diffuse the mixture under the action of gravity. The gas-liquid separation effect is controlled based on the formed liquid flow path. The liquid production and water content analysis and detection unit includes an ultrasonic detection device installed inside the tank, which realizes water content detection based on the ultrasonic Doppler effect, including calculating the water content; based on ultrasonic measurement of the flow velocity of the mixture in the pipeline, combined with parameters including the well stroke cycle and stroke, it calculates the liquid output per stroke and the daily liquid production, and converts it into oil production. The carbon dioxide content detection unit is equipped with an NDIR dual-wavelength gas sensor. After the gas is irradiated with infrared light, the transmittance of absorbable wavelengths and non-absorbable wavelengths is compared, and the gas concentration is calculated by combining the Lambert-Beer law. The gas flow unit, integrated at the gas outlet of the gas-liquid separation unit, includes platinum resistance temperature sensors for detecting heat sources and measuring fluid temperature, respectively. It collects the linear relationship between the temperature difference between the two sensors and the flow rate during fluid flow and converts it into a flow signal. The automated control unit, including a PLC control module, a field industrial computer, and actuators, controls the operation of gas sampling, gas distribution, exhaust, and various detection units according to a preset program; The data acquisition and transmission unit uses DTU transparent transmission technology to periodically upload wellhead acquisition information to the host computer. The auxiliary unit includes an electrical control box, which contains a power supply, a battery and a power switching device, a transmission switching device and a circuit breaker. The pressure vessel is insulated with aerogel, and an electric heating device is added inside the tank. The connecting hose is heated by an internal cable to achieve automatic temperature control.

2. The online monitoring and metering equipment for carbon dioxide in oil and gas wells according to claim 1, characterized in that, The gas-liquid separation unit adopts gravity separation method and includes a tank, a demister, a float valve, and a baffle. The tank is equipped with a mixed liquid inlet, a gas outlet, and a liquid outlet. The demister is located on the path of the rising gas after gas-liquid separation inside the tank, including the top of the tank, below the gas outlet or at the inlet end, and removes oil-gas mixture foam from the oil-gas mixture. The baffle is configured as an inclined or arc-shaped structure, which allows the mixture to flow slowly downward along the surface of the baffle, prolonging the residence path of the liquid in the tank, increasing the time window for gas-liquid separation, and guiding the gas to gather towards the top demister while the liquid settles to the bottom.

3. The online monitoring and metering equipment for carbon dioxide in oil and gas wells according to claim 2, characterized in that, The tank is equipped with a baffle at the inlet of the mixed liquid. The baffle is used to block the high-speed liquid flow from directly impacting the surface of the liquid inside the tank, so as to prevent the settled liquid from being re-mixed, and at the same time reduce the amount of air bubbles brought in by the liquid flow.

4. The online monitoring and metering equipment for carbon dioxide in oil and gas wells according to claim 1, characterized in that, The carbon dioxide content detection unit includes an automatic detection probe, a rotor flow meter, an oil-water separator, a pressure reducing valve, a vacuum sampling pump, and an explosion-proof solenoid valve.

5. The online monitoring and metering equipment for carbon dioxide in oil and gas wells according to claim 1, characterized in that, The water content of the mixture inside the tank is calculated as follows: Based on the identification of the discrete phase holding rates of oil, gas, and water phases through ultrasonic reflection intensity, respectively denoted as... , and All three conditions are met. The oil phase retention rate The water phase holdup is calculated by directly obtaining the ultrasonic reflection intensity and neglecting the influence of the gas phase on the volume of the oil-water mixture. ; Water flow velocity can be directly measured using ultrasonic Doppler frequency shift. ,in The speed at which ultrasound travels in water. For Doppler frequency shift, This is the frequency at which the ultrasonic wave is emitted. The angle between the direction of ultrasonic wave emission and the direction of water flow; According to the definition of slip velocity, the oil phase velocity is equal to the sum of the water phase velocity and the oil phase slip velocity from the water phase, i.e., the oil phase velocity. ,in These are experimental calibration values ​​and are related to the viscosity of the oil well. Gas phase velocity ,in These are experimental calibration values ​​and are related to wellhead pressure. Oil phase flow rate ; Aqueous flow rate ; Moisture content .

6. The online monitoring and metering equipment for carbon dioxide in oil and gas wells according to claim 1, characterized in that, The calculation of liquid production includes the following process: Based on the ultrasonic Doppler effect, the original flow velocity is first calculated, and then the accurate flow velocity is obtained after temperature correction. In the formula, This is the temperature-corrected speed of sound propagating in water. For Doppler frequency shift, This is the frequency at which the ultrasonic wave is emitted. The angle between the direction of ultrasonic wave emission and the direction of water flow; The liquid output per stroke is calculated as accurate flow rate × pipe cross-sectional area × effective liquid output time per stroke. The effective liquid output time per stroke is identified by a pressure sensor and includes the identification of the following three stages: Pressure rise phase: The pumping unit moves upward, the check valve opens, liquid enters the pipeline, and the pressure rises from the baseline; Pressure stabilization zone: The liquid continues to flow, and the pressure remains stable. Pressure drop phase: The pumping unit descends, the check valve closes, and the pressure drops back to the baseline; The effective liquid discharge time is the time interval between the start of the pressure rise segment and the start of the pressure fall segment, which is collected in real time and automatically identified by the equipment's pressure sensor.

7. The online monitoring and metering equipment for carbon dioxide in oil and gas wells according to claim 6, characterized in that, The daily liquid production is the sum of the liquid volume of all effective flushes throughout the day. After calculating the total number of flushes per day, abnormal flushes are excluded. Abnormal flushes refer to empty flushes with no pressure change. Abnormal impact elimination method Guidelines It is the labeling difference in the normal distribution that the strokes follow.

8. The online monitoring and metering equipment for carbon dioxide in oil and gas wells according to claim 6, characterized in that, The formula for calculating carbon dioxide concentration using the NDIR dual-wavelength gas sensor described above satisfies: In the formula, Transmittance, It is the intensity of transmitted light. It is the intensity of the incident light. It is absorbance. It refers to the concentration of carbon dioxide gas. It is the optical path length of infrared light passing through a gaseous medium.

9. The online monitoring and metering equipment for carbon dioxide in oil and gas wells according to claim 1, characterized in that, The gas flow unit includes auxiliary components added to the gas outlet pipeline inside the tank, which work in conjunction with the dual platinum resistance sensor, specifically including: The rotor flow meter, located upstream of the heating probe, is used for visual monitoring of gas flow rate. The flow rate is finely adjusted by the built-in valve to ensure that the gas flow rate entering the sensor detection area is stable within the effective measurement range. The filter screen, installed upstream of the rotor flow meter, is used to filter residual oil mist and dust in the gas; The temperature compensation module, integrated inside the sensor housing, works in conjunction with the temperature probe to compensate for gas temperature fluctuations exceeding [a certain threshold]. At the same time, the heating current of the heating probe is automatically adjusted to maintain a constant temperature difference of the gas inside the heating probe and to counteract the interference of ambient temperature on the measurement. The gas flow unit performs the following online metering calculation process: Read the resistance values ​​of the heating probe and the temperature measuring probe, convert them to the corresponding temperature using the platinum resistance temperature calculation formula, and calculate the difference between the two. , To heat the probe to the desired temperature, The temperature of the temperature probe; Obtain the real-time temperature of the gas flowing through the sensor. and real-time gas pressure The data is preprocessed and then smoothed using a moving average method. The gas density is corrected based on real-time temperature and pressure, and the correction formula is based on the ideal gas law: In the formula, For real-time gas density, It is the gas density under standard conditions. Standard atmospheric pressure It is the standard temperature; Based on the principle of thermostatic temperature difference, gas flow rate and heating power Temperature difference It is a fixed function, combined with the corrected gas density. Real-time gas flow rate The calculation formula is as follows: In the formula, It is the balance coefficient; The formula for calculating instantaneous flow rate is: In the formula, It is the cross-sectional area of ​​the gas outlet pipeline; The formula for calculating accumulated traffic is: In the formula, It represents the number of times data was collected.

10. A calibration method for an online carbon dioxide monitoring and metering device for oil and gas wells according to any one of claims 1-9, characterized in that, The calibration includes production volume calibration, water cut calibration, and carbon dioxide content detection unit calibration. The production volume calibration uses water and transformer oil as the medium, controls the flow rate through a frequency converter, and calculates the production volume based on oil well operating parameters. The water cut calibration uses a mixture of different water contents to fit the relationship between frequency and water cut. The carbon dioxide content detection unit calibration is performed according to standard requirements, using standard CO2 gas in an environment of -40℃ to 80℃.

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