Secondary separation flow measurement system based on small GLCC and ERT

Abstract

The invention relates to the technical field of multi-phase flow measurement, in particular to a two-stage separation flow measurement system based on a small GLCC and an ERT, and can solve the problems that when two existing methods are independently used, the flow measurement range is small, the generalization ability is poor and the like, the complex and changeable flow conditions of an oil field cannot be adapted to, and the measurement accuracy is high to a certain extent. And the optimization of a measurement result often needs a complex data processing technology, so that the measurement is difficult and inaccurate. The single-stage separator comprises a separation chamber, the separation chamber is of a cylindrical structure, an inlet of the separation chamber is connected with a system inlet, a liquid outlet of the separation chamber is connected with a system outlet, a gas outlet of the separation chamber is connected with the second-stage separator, the second-stage separator is designed based on a small-sized GLCC, and the sensor is arranged in the separation chamber. A gas outlet and a liquid outlet of the secondary separator are respectively connected with a system outlet; the sensor comprises a flow meter and an ERT.

Description

Technical Field

[0001] The present application relates to the technical field of multiphase flow measurement, and in particular to a two-stage separation flow measurement system based on a small GLCC and an ERT. Background Art

[0002] Multiphase flow is a common phenomenon in the petrochemical industry. "Phase" refers to different physical states or different physical properties or mechanical states of the same physical state. According to the different forms of matter, substances in nature can be divided into three phases: gas, liquid and solid. Usually, a fluid system with two or more substances and a clear interface is regarded as a multiphase flow. For example, gas and water are two different substances that are incompatible. When they are mixed together, a clear interface will appear. Therefore, at room temperature, the gas-water mixture can be regarded as a kind of gas-liquid two-phase flow - gas-water two-phase flow.

[0003] In the field of oil extraction, container separators are mainly used to process the oil, gas and water multiphase flows generated from the wellhead. The gas-liquid cylindrical cyclone separator (GLCC) is a highly efficient gas-liquid separator suitable for gas-liquid two-phase separation and metering in onshore oil and gas fields and offshore oil and gas platforms. Compared with container separators, GLCC has significant advantages such as simple structure, low cost, small size, easy installation and operation, which makes GLCC stand out among many separators and is widely used in major oil fields, especially in offshore oil and gas platforms. Due to limited space, the floor space and weight of the equipment need to be considered. In this regard, GLCC has obvious advantages over traditional separators, so it has shown good application prospects in new offshore gas field projects and capacity expansion and transformation of in-service platforms.

[0004] From oil extraction to transportation, the measurement of multiphase flow is very important. In the petrochemical industry, there are two commonly used multiphase flow measurement methods, namely separation measurement and non-separation measurement.

[0005] Separation measurement is to send the multiphase flow into the gas-liquid separator to separate it into two fluids, gas phase flow and liquid phase flow, and then use a single-phase flow meter to measure the flow rate respectively. In this process, one of the most critical equipment is the separator. The columnar cyclone gas-liquid separator (GLCC) has the advantages of small size, high separation efficiency, easy installation and operation, etc., and is widely used in the oil industry.

[0006] Non-separation measurement is another method of directly measuring multiphase flow without separation. This method does not require a separation device. Turbine flowmeters, ultrasonic flowmeters, electromagnetic flowmeters and other types are commonly used flowmeters. In recent years, electrical tomography (ERT) technology has been widely used due to its advantages such as visualization, non-contact, no interference from the flow field, and little environmental impact. ERT technology is a two-phase flow / multiphase flow measurement technology developed by combining computer application technology with modern detection technology. It can provide relevant information about the flow characteristics of the fluid, such as two-phase flow such as gas / solid, gas / liquid and liquid / liquid. As an online measurement technology with the advantages of visualization, low cost, non-invasiveness and robustness, ERT technology has become a recognized measurement technology in process applications.

[0007] However, in the separation measurement method, the two factors that affect the GLCC efficiency are the liquid carryover (LCO) and the gas carryover (GCU). In the gas-liquid separation process, the phenomenon that the liquid follows the gas flow to leave the gas outlet at the top of the separator is called LCO, and the phenomenon that the gas follows the liquid to the bottom of the separator is called GCU. Affected by the LCO and GCU phenomena, in order to ensure the complete separation of gas and liquid, the separation equipment not only needs to withstand extremely high pressure, but also its effective working flow range will be greatly reduced, resulting in a large measurement error. In addition, when the liquid phase flow rate is small and the gas phase flow rate is large, the liquid phase flow generated by the separator is often mixed with a lot of gas, causing the differential pressure measured by the orifice flowmeter to be larger, resulting in the flow measured by the flowmeter to be larger than the actual flow rate, and there is a certain measurement error.

[0008] For non-separation measurement, turbine flowmeters, ultrasonic flowmeters, electromagnetic flowmeters and other types are commonly used flowmeters, but these devices are easily disturbed by the external flow field and are large in size, with high requirements for installation and measurement space. The image reconstruction effect in ERT technology is greatly affected by the flow type of the fluid. When the fluid flow state is in a laminar flow or wavy flow with stable flow, image reconstruction can relatively accurately reflect the medium distribution in the pipeline. In actual situations, the fluid often has a large flow rate and the flow state is mostly complex slug flow or annular flow, and the image reconstruction results produce large errors.

[0009] Therefore, using the above two methods alone has disadvantages such as small flow measurement range and poor generalization ability, which makes it impossible to adapt to the complex and changeable flow conditions at the oil field site. The optimization of the measurement results often requires complex data processing technology, which makes the measurement difficult and inaccurate. Summary of the invention

[0010] In order to solve the shortcomings of the two existing methods when used alone, such as small flow measurement range and poor generalization ability, which make them unable to adapt to the complex and changeable flow conditions at the oil field site, and the optimization of the measurement results often requires complex data processing technology, which makes the measurement difficult and inaccurate, the present application provides a two-stage separation flow measurement system based on a small GLCC and ERT.

[0011] The embodiment of the present application is implemented as follows:

[0012] The present application provides a two-stage separation flow measurement system based on a small GLCC and an ERT, including a single-stage separator, a two-stage separator and a sensor:

[0013] The single-stage separator comprises a separation chamber, the separation chamber is a cylindrical structure, and the inlet of the separation chamber is connected to the system inlet, the liquid outlet of the separation chamber is connected to the system outlet, and the gas outlet of the separation chamber is connected to the secondary separator, the secondary separator is based on a small GLCC design, and the gas outlet and liquid outlet of the secondary separator are respectively connected to the system outlet;

[0014] The sensors include flow meters and ERTs.

[0015] In a possible implementation, the liquid outlet of the single-stage separator is connected to the system outlet through a primary liquid pipeline, the liquid outlet of the secondary separator is connected to the system outlet through a secondary liquid pipeline, and the gas outlet of the secondary separator is connected to the system outlet through a gas pipeline.

[0016] In a possible implementation, sensors are installed on both the primary liquid pipeline and the secondary liquid pipeline.

[0017] In a possible implementation, the system inlet is arranged at an angle.

[0018] In a possible implementation, the inlet of the separation chamber is inclined and circular with gradually decreasing size.

[0019] In a possible implementation, the ERT corrects the flow meter result by calculating the void fraction of gas and liquid.

[0020] In a possible implementation, the ERT corrects the flow meter result by calculating the void fraction of gas and liquid, further comprising:

[0021] The relationship between the conductivity and the gray value of the reconstructed image is established by an appropriate image reconstruction method to visualize the conductivity distribution within the pipe cross section;

[0022] The measurements were corrected by calculating the void fraction.

[0023] In a possible implementation, establishing a relationship between the conductivity and the grayscale value of the reconstructed image by an appropriate image reconstruction method to visualize the conductivity distribution in the pipe cross section further includes:

[0024] The voltage measurement is normalized, with the measurement when the pipe is full of water as the high calibration. The normalization formula is:

[0025] V n =(V m -V w ) / V w ;

[0026] Where Vn is the normalized voltage measurement value, Vm is the measured voltage data, and Vw is the calibration data;

[0027] The relationship between the normalized voltage measurement and the conductivity distribution can be expressed as:

[0028] V n =-Sσ n ;

[0029] Where S is the normalized sensitivity matrix, σn is the standardized conductivity distribution, the negative sign indicates conductivity, and the direction of change of the measured value is opposite. The equivalent voltage Vx can be assumed to be inversely proportional to the conductivity σx, that is,

[0030] V x ∝1 / σ x ;

[0031] Among them, the equivalent conductivity is σm, which is used as the input of the image reconstruction algorithm to obtain the apparent conductivity distribution;

[0032] The V n =-Sσ n and Vw is measured with full water in the pipe, σw / σm can be described as:

[0033] σ w / σ m =V m / V w ;

[0034] Therefore, combining the formula for calculating liquid volume flow rate based on Bernoulli's equation and V x ∝1 / σ x , can be calculated as:

[0035] σ m =σ w / (V n +1);

[0036] The linear projection method (LBP) is applied to ERT image reconstruction. The LBP algorithm is as follows:

[0037]

[0038] Among them, g is the grayscale of the reconstructed image, which can reflect the field conductivity distribution, and μ is the unit vector, that is, μ=[1,1,···,1]T.

[0039] In a possible implementation, the correcting the measurement result by calculating the void fraction further includes:

[0040] Divide the pipe cross section into different cells and let the number of effective cells in the pipe be denoted as “n”;

[0041] The gray level of the "ith" grid is represented by "x", if the grid is filled with air (GVF = 100%), then "x" is equal to 0; if the grid is filled with water (GVF = 0%), then "x" is equal to 1;

[0042] Assuming a linear relationship between the void content and the gray level of a single grid, when GVF = 60%, the gray level is 0.4. To obtain the air content in the entire duct, simply sum up the gray levels:

[0043]

[0044] The technical solution provided by this application can at least achieve the following beneficial effects:

[0045] The two-stage separation flow measurement system based on a small GLCC and ERT provided in the present application combines the advantages of both separation measurement and non-separation measurement methods, improves measurement accuracy, expands measurement range, and optimizes the design of the GLCC so that it can be reduced in height without reducing separation efficiency.

[0046] In view of the limitations of the traditional GLCC separator in the flow range system, a filter cartridge structure is added to the separator to effectively reduce the LCO phenomenon, and a secondary separator is added at the gas phase outlet to effectively re-separate the liquid entrained in the gas phase after the single-pole separation. The improved GLCC separator effectively improves the separation efficiency of gas and liquid and expands the flow separation range, especially in complex conditions where the liquid phase flow is low and the gas phase flow is large. The flow pattern of the fluid generated by the single-pole separator in the main liquid pipeline is mostly unstable slug flow and annular flow, while the flow pattern of the fluid generated by the secondary separator in the main liquid pipeline is mostly stable laminar flow, which is convenient for the subsequent use of ERT technology for flow measurement correction. In view of the problem that the measurement result is too large due to the entrained gas in the main liquid line, the measurement error of the flow meter is corrected by calculating GVF with the help of ERT integrated into the system.

[0047] In summary, this study combined GLCC and ERT to design a comprehensive and accurate two-phase flow measurement system, which improved the separation efficiency of the system and enhanced the precision and accuracy of flow measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0049] Figure 1 It is a structural schematic diagram of a columnar cyclone gas-liquid separator (GLCC);

[0050] Figure 2 It is a schematic diagram of the structure of the Venturi tube;

[0051] Figure 3 It is the structural schematic diagram of the ERT sensor;

[0052] Figure 4 Schematic diagram of the computational grid for a single-pole separator;

[0053] Figure 5 It is a schematic diagram of velocity value, phase and pressure distribution in GLCC system;

[0054] Figure 6 Schematic diagram of velocity distribution at two inlet cross sections;

[0055] Figure 7 Schematic diagram of radial distribution of axial velocity and tangential velocity in two sections;

[0056] Figure 8 Schematic diagram of the experimental process and equipment;

[0057] Fig. 9 (a) is a schematic diagram of the two-stage separation of gas-water two-phase flow with LCO curve in the system; Fig. 9 (b) is a schematic diagram of the single-stage separation of gas-water two-phase flow with LCO curve in the system;

[0058] Fig.10 This is a schematic diagram of the flow pattern of the fluid in the pipeline after passing through the separator observed in the experiment;

[0059] Fig.11 A schematic diagram of the image reconstruction results of the main liquid pipeline in time series;

[0060] Fig.12 is a schematic diagram of the volume flow of gas entering the main liquid pipeline;

[0061] Fig.13 It is a schematic diagram of the measurement results of the gas-liquid two-phase flow orifice flowmeter and the flow correction results based on the ERT technology;

[0062] Fig.14 It is a structural schematic diagram of a two-stage GLCC separator system shown in an exemplary embodiment of the present application. DETAILED DESCRIPTION

[0063] In order to make the purpose, implementation mode and advantages of the present application clearer, the exemplary implementation mode of the present application will be clearly and completely described below in conjunction with the drawings in the exemplary embodiments of the present application. Obviously, the described exemplary embodiments are only part of the embodiments of the present application, not all of the embodiments. It should be understood that the specific embodiments described here are only used to explain the present application and are not used to limit the present application.

[0064] It should be noted that the brief description of the terms in this application is only for the convenience of understanding the implementation methods described below, and is not intended to limit the implementation methods of this application. Unless otherwise specified, these terms should be understood according to their ordinary and usual meanings.

[0065] The terms "first", "second", "third", etc. in the specification and claims of this application and the above-mentioned drawings are used to distinguish similar or similar objects or entities, and are not necessarily meant to limit a specific order or sequence. Unless otherwise noted, it should be understood that the terms used in this way can be interchangeable under appropriate circumstances.

[0066] The terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover but not exclude inclusion, for example, a product or device comprising a list of components is not necessarily limited to all the components expressly listed but may include other components not expressly listed or inherent to such product or device.

[0067] To facilitate the technical solution of the application, some concepts involved in the application are first explained below.

[0068] Multiphase flow is a common phenomenon in the petrochemical industry. "Phase" refers to different physical states or different physical properties or mechanical states of the same physical state. According to the different forms of matter, substances in nature can be divided into three phases: gas, liquid and solid. Usually, a fluid system with two or more substances and a clear interface is regarded as a multiphase flow. For example, gas and water are two different substances that are incompatible. When they are mixed together, a clear interface will appear. Therefore, at room temperature, the gas-water mixture can be regarded as a kind of gas-liquid two-phase flow - gas-water two-phase flow.

[0069] In the field of oil extraction, container separators are mainly used to process the oil, gas and water multiphase flows generated from the wellhead. The gas-liquid cylindrical cyclone separator (GLCC) is a highly efficient gas-liquid separator suitable for gas-liquid two-phase separation and metering in onshore oil and gas fields and offshore oil and gas platforms. Compared with container separators, GLCC has significant advantages such as simple structure, low cost, small size, easy installation and operation, which makes GLCC stand out among many separators and is widely used in major oil fields, especially in offshore oil and gas platforms. Due to limited space, the floor space and weight of the equipment need to be considered. In this regard, GLCC has obvious advantages over traditional separators, so it has shown good application prospects in new offshore gas field projects and capacity expansion and transformation of in-service platforms.

[0070] Figure 1 It is a schematic diagram of the structure of a columnar cyclone gas-liquid separator (GLCC).

[0071] The structure of GLCC is as follows Figure 1 As shown, its main body is a vertical pipe with a tangentially inclined gas-liquid multiphase flow inlet. When the multiphase flow enters the GLCC main body from the inlet under a certain pressure, a vortex will be generated, causing the fluid to rotate at a high speed in the separator, thereby generating a centrifugal force and buoyancy on the fluid that is an order of magnitude higher than gravity. Under the combined action of gravity, centrifugal force and buoyancy, the liquid phase with high density is forced to flow radially toward the pipe wall and flow along the pipe wall to the bottom of the separator for collection; the gas phase with low density forms a central gas column along the center of the vortex and rises to the top of the separator, ultimately achieving the discharge of the gas phase from the top and the outflow of the liquid phase from the bottom.

[0072] In order to better control the liquid level and pressure in the GLCC, the separator is equipped with a liquid control valve on the liquid pipe section and a gas control valve on the gas pipe section. The liquid level control valve ensures correct operation under different flow conditions, eliminates or reduces the liquid that enters the gas line and the gas that enters the liquid pipeline. When the GLCC is used for metering applications, the liquid and gas parts are combined in the composite part to form a multi-phase metering loop.

[0073] The orifice flowmeter is a device for measuring fluid pressure difference. The principle of measuring fluid flow is based on Bernoulli's law and the continuity equation. When gas or liquid flows in the flowmeter, the dynamic pressure reaches the maximum value and the static pressure reaches the minimum value at the narrowest part of the pipe (the throat), so a pressure difference is generated before and after the throat of the pipe. The ratio of this pressure difference value to the product of the average flow velocity of the fluid flowing through this point is the flow coefficient of this point. Therefore, the flow rate and velocity of the fluid can be calculated by measuring the pressure difference and the geometric parameters of the flowmeter.

[0074] Figure 2Schematic diagram of the Venturi tube structure.

[0075] like Figure 2 As shown, the flow meter is a pipeline that contracts first and then gradually expands, where T in the figure represents the fluid temperature in the pipeline, P represents the dynamic pressure, P represents the differential pressure before the Venturi tube, that is, the pressure difference of the contracting pipe section, P represents the differential pressure after the Venturi tube, that is, the pressure difference of the expanding pipe section, D represents the pipeline diameter, and d represents the pipeline throat diameter.

[0076] Assuming that the fluid is an incompressible ideal fluid and the density of the fluid is constant, the orifice flowmeter can be effectively used for transient measurement. Ignoring the slip between the gas and liquid phases, the formula for calculating the liquid volume flow rate based on the Bernoulli equation is as follows:

[0077]

[0078] In the formula, ε s is the expansion coefficient of the fluid, D is the outflow coefficient of the orifice flowmeter, β is the ratio of the throat diameter to the pipe diameter, r is the throat radius, and ρ s Represents the unidirectional flow density.

[0079] ERT provides a non-invasive method to visualize the conductivity distribution of a conductive medium by measuring the voltage change between the measuring electrode pairs. The principle is that when the distribution of the conductive medium in the pipeline changes, the distribution of conductivity will change, which will lead to a change in the potential distribution in the pipeline.

[0080] Figure 3 Schematic diagram of the structure of the ERT sensor.

[0081] like Figure 3 As shown in the figure, a traditional 8-electrode ERT structure is adopted. The electrodes and shielding layer are evenly attached to the outer wall of the pipe. Each electrode can be configured as an excitation or detection electrode. When a pair of adjacent electrodes (as excitation electrodes) is selected for current injection, the voltage between all other combinations of adjacent electrodes (as detection electrodes) is measured, and then the next pair of electrodes is selected (for example, after first selecting 1 and 2 electrode pairs, then 2 and 3 electrode pairs are selected), and then all other electrodes are selected. The total number of measurements of the N-electrode ERT sensor is N(N-3) / 2. The 8-electrode system used in the experiment can produce 20 independent measurement results.

[0082] For ERT, the boundary condition is that when the selected electrode pair is excited by current, the other electrode pairs are in a grounded state. In the sensitive field area of ​​ERT, the relationship between the conductivity distribution and the potential distribution can be expressed by the following Laplace equation:

[0083]

[0084] In the formula, σ(x, y) and φ(x, y) are the spatial conductivity distribution and potential distribution of the sensitive field area, respectively. Combining the boundary conditions and formula (2), it can be deduced that the voltage between adjacent electrodes is uniquely determined. Therefore, for a certain excitation current, the voltage change on the measuring electrode pair can be used to reflect the conductivity distribution of the measured area.

[0085] The gas void fraction (GVF) in gas-liquid multiphase flow is an important parameter for measuring fluid flow. It indicates the ratio of gas volume to total volume in gas-liquid two-phase flow. The ERT system can visualize the flow conditions between the phases of multiphase flow in the pipeline and monitor the distribution of various phase media. Its application in fluid void fraction measurement is one of the current research hotspots.

[0086] In the process from oil extraction to transportation, the measurement of multiphase flow is very important. In the petrochemical industry, there are two commonly used multiphase flow measurement methods, namely separation measurement and non-separation measurement.

[0087] Separation measurement is to send the multiphase flow into the gas-liquid separator to separate it into two fluids, gas phase flow and liquid phase flow, and then use a single-phase flow meter to measure the flow rate respectively. In this process, one of the most critical equipment is the separator. The columnar cyclone gas-liquid separator (GLCC) has the advantages of small size, high separation efficiency, easy installation and operation, etc., and is widely used in the petroleum industry.

[0088] Non-separation measurement is another method of directly measuring multiphase flow without separation. This method does not require a separation device. Turbine flowmeters, ultrasonic flowmeters, electromagnetic flowmeters and other types are commonly used flowmeters. In recent years, electrical tomography (ERT) technology has been widely used due to its advantages of visualization, non-contact, no interference from the flow field, and little environmental impact. ERT technology is a two-phase flow / multiphase flow measurement technology developed by combining computer application technology with modern detection technology. It can provide information about the flow characteristics of the fluid, such as two-phase flow such as gas / solid, gas / liquid and liquid / liquid. As an online measurement technology with the advantages of visualization, low cost, non-invasiveness and robustness, ERT technology has become a recognized measurement technology in process applications.

[0089] In the separation measurement method, the two factors that affect the GLCC efficiency are the liquid carryover (LCO) and the gas carryover (GCU). In the gas-liquid separation process, the phenomenon that the liquid follows the gas flow to leave the gas outlet at the top of the separator is called LCO, and the phenomenon that the gas follows the liquid to the bottom of the separator is called GCU. Affected by the LCO and GCU phenomena, in order to ensure the complete separation of gas and liquid, the separation equipment not only needs to withstand extremely high pressure, but also its effective working flow range will be greatly reduced, resulting in a large measurement error. In addition, when the liquid phase flow rate is small and the gas phase flow rate is large, the liquid phase flow generated by the separator is often mixed with a lot of gas, causing the differential pressure measured by the orifice flowmeter to be larger, resulting in the flow measured by the flowmeter to be larger than the actual flow rate, and there is a certain measurement error.

[0090] For non-separation measurement, turbine flowmeters, ultrasonic flowmeters, electromagnetic flowmeters and other types are commonly used flowmeters, but these devices are easily disturbed by the external flow field and are large in size, with high requirements for installation and measurement space. The image reconstruction effect in ERT technology is greatly affected by the flow type of the fluid. When the fluid flow state is in a laminar flow or wavy flow with stable flow, image reconstruction can relatively accurately reflect the medium distribution in the pipeline. In actual situations, the fluid often has a large flow rate and the flow state is mostly complex slug flow or annular flow, and the image reconstruction results produce large errors.

[0091] Therefore, using the above two methods alone has disadvantages such as small flow measurement range and poor generalization ability, which makes it impossible to adapt to the complex and changeable flow conditions at the oil field site. The optimization of the measurement results often requires complex data processing technology, which makes the measurement difficult and inaccurate.

[0092] Based on this, the present application provides a two-stage separation flow measurement system based on a small GLCC and ERT. The system combines the advantages of both separation measurement and non-separation measurement methods, improves measurement accuracy, and expands the measurement range.

[0093] Next, the technical solution of the present application and how the technical solution of the present application solves the above-mentioned technical problems will be described in detail through embodiments and in combination with the accompanying drawings. The embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments.

[0094] Fig.14 It is a structural schematic diagram of a two-stage GLCC separator system shown in an exemplary embodiment of the present application.

[0095] In an exemplary embodiment, Fig.14As shown, a two-stage separation flow measurement system based on a small GLCC and an ERT is provided. In this embodiment, the system includes a single-stage separator, a two-stage separator and a sensor:

[0096] The single-stage separator comprises a separation chamber, the separation chamber is a cylindrical structure, and the inlet of the separation chamber is connected to the system inlet, the liquid outlet of the separation chamber is connected to the system outlet, and the gas outlet of the separation chamber is connected to the secondary separator, the secondary separator is based on a small GLCC design, and the gas outlet and liquid outlet of the secondary separator are respectively connected to the system outlet;

[0097] The sensors include flow meters and ERTs.

[0098] In one possible implementation, Fig.14 As shown, the system mainly consists of a single-stage separator, a secondary separator and a sensor. The single-stage separation component includes a separation chamber connected to an inlet, the separation chamber is provided with a cylindrical structure, one end of the separation chamber is connected to the gas outlet of the cylindrical structure, and the other end is connected to the single-stage separation liquid outlet. The inlet is an angled, reduced-size circular design. The second separator is connected to the gas outlet of the first separator and is designed based on a small GLCC. The sensor includes a flow meter and an ERT. The ERT corrects the flow meter result by calculating the void fraction of the gas and liquid.

[0099] In one possible implementation, the gas-water two-phase is a complex system due to the existence of various flow patterns. The ERT system can establish the relationship between the conductivity and the grayscale value of the reconstructed image through an appropriate image reconstruction method to visualize the conductivity distribution within the pipe cross section, which helps to understand the mixing of the gas-water mixture and correct the measurement results by calculating the void fraction.

[0100] In image reconstruction, in order to reduce the systematic errors caused by finite element mesh generation, measurement circuit, experimental environment and other methods, the voltage measurement should be normalized. Generally, the measurement when the pipe is full of water is used as the high calibration. The normalization formula is:

[0101] V n =(V m -V w ) / V w (3)

[0102] Where Vn is the normalized voltage measurement, Vm is the measured voltage data, and Vw is the calibration data. The relationship between the normalized voltage measurement and the conductivity distribution

[10] can be expressed as:

[0103] V n =-Sσ n (4)

[0104] Where S is the normalized sensitivity matrix, σn is the standardized conductivity distribution, the negative sign indicates conductivity, and the direction of change of the measured value is opposite. In theory, the equivalent voltage Vx can be assumed to be inversely proportional to the conductivity σx, that is,

[0105] V x ∝1 / σ x (5)

[0106] In this work, the equivalent conductivity σm is used as the input of the image reconstruction algorithm to obtain the apparent conductivity distribution. Starting from Eq. (4) and Vw which is measured with full water in the pipe, σw / σm can be described as:

[0107] σ w / σ m =V m / V w (6)

[0108] Therefore, combining equation (1) and equation (5), we can calculate: m

[0109] σ m =σ w / (V n +1) (7)

[0110] The linear projection method (LBP) has the characteristics of simple algorithm and accuracy that meets the requirements of image reconstruction. Therefore, it is applied to ERT image reconstruction. The LBP algorithm is as follows:

[0111]

[0112] Where g is the grayscale of the reconstructed image, which can reflect the field conductivity distribution, and μ is a unit vector, that is, μ = [1,1,···,1]T.

[0113] In order to calculate the air content rate of each section based on the gray level of the pixels captured by the ERT system, the pipe section is divided into different units. Let the number of valid grids in the pipe be denoted as "n" and the gray level of the "ith" grid be denoted as "x". From the normalization in formula (5), if the grid is full of air (GVF = 100%), then "x" is equal to 0; if the grid is full of water (GVF = 0%), then "x" is equal to 1. Assuming that there is a linear relationship between the void content and the gray level of a single grid, for example, when GVF = 60%, the gray level is 0.4. To obtain the air content in the entire pipe, just sum up the gray levels:

[0114]

[0115] Working process:

[0116] The gas-liquid mixture first enters the system through an inclined inlet pipe, where a gas-liquid stratified flow is formed. The inclined inlet pipe is connected to the vertical cylinder of the separation chamber. The separation chamber has a tangential conical nozzle at the connection point. The conical nozzle accelerates the mixed liquid. The accelerated gas-liquid mixture forms two vortexes in the vertical cylinder of the separation chamber, namely the gas phase and the liquid phase. Under the combined action of centrifugal force and gravity, the liquid droplets in the gas phase are pushed to the side wall and eventually flow out of the liquid outlet. At the same time, the gas phase rotates and converges to the central axis to form a gas core. The gas core is then discharged from the gas outlet through the barrel structure, and the carried liquid passes through the second separator for another separation.

[0117] Figure 4 Schematic diagram of the computational grid for a single-pole separator. Figure 5 Schematic diagram of velocity value, phase and pressure distribution in GLCC system. Figure 6 Schematic diagram of velocity distribution at two inlet cross sections. Figure 7 is a schematic diagram of the radial distribution of the axial velocity and tangential velocity in the two sections. Figure 8 The schematic diagram of the experimental process and equipment is shown in Figure 2. Fig. 9 (a) is a schematic diagram of the two-stage separation of gas-water two-phase flow with LCO curve in the system; Fig. 9 (b) is a schematic diagram of the single-stage separation of the LCO curve gas-water two-phase flow in the system. Fig.10 This is a schematic diagram of the flow pattern of the fluid in the pipeline after passing through the separator observed in the experiment. Fig.11 Schematic diagram of the image reconstruction results of the main liquid pipeline in time series Fig.12 is a schematic diagram of the gas volume flow entering the main liquid pipeline. Fig.13 Schematic diagram of the measurement results of the gas-liquid two-phase flow orifice flowmeter and the flow correction results based on ERT technology.

[0118] In order to verify this application, the Euler multiphase model was used to simulate the gas-liquid two-phase flow field. The first phase represented gas, the second phase represented liquid, and the discrete liquid diameter was set to 0.1 mm. The multiphase flow model adopted a multiphase VOF solution algorithm to facilitate the geometric reconstruction of the two-phase interface. The simulation assumed that the gas was incompressible and isothermal.

[0119] The Euler model establishes separate conservation equations for each phase, so the continuous phase equation for the qth phase is as follows:

[0120]

[0121] where ρ is the phase density and is The velocity vector is the volume fraction, is the mass transfer from phase p to phase q, is the mass transfer from phase q to phase p, is the source term, S q

[0122] According to Newton's second law, the momentum change formula of the qth phase in the control volume is as follows:

[0123]

[0124] The first three terms on the right side of the equation are pressure, shear, and gravity, and the fourth term is the momentum change caused by interphase mass transfer. It is an interaction force between phases, which depends on friction, pressure, etc. is the velocity between phases. When mass is transferred from one phase to another, the velocity of the transferred phase is taken. The fifth term is the applied interphase force. is the external volume force, is the lifting force, is the wall lubrication force, is the virtual mass force, is the turbulent dissipation force, and the sum is 1.

[0125] As a centrifugal separator, GLCC exhibits a complex three-dimensional turbulent field involving gas and liquid phases. Usually, two turbulence models are used to simulate the swirl flow field: the RNGk-ε model and the RSM model. The RSM model is more suitable for robust swirl flow fields, while the RNGk-ε model is more suitable for milder swirl flow fields. wg When characterizing the swirl intensity of GLCC, the geometric swirl intensity number () is used to describe the swirl flow field at the inlet convergence position, which can be expressed as the equation:

[0126]

[0127] Where D is the cylinder diameter GLCC (mm), β is the inclination angle of the inlet (°), and r is the minimum radius of the reduced nozzle (mm). In this study, since the swirl intensity of the geometric model is 4.17, the RNG k-ε model is more suitable.

[0128] A. CFD simulation geometry

[0129] This paper numerically simulates a single-pole separator with a cylindrical structure. In order to ensure the feasibility and accuracy of the simulation, it is necessary to appropriately simplify the geometric shape. The height of the separator cylinder is 0.5m and the diameter is 0.11m. Figure 4 The computational mesh for a single-pole separator is shown.

[0130] B. Simulation conditions and parameter settings

[0131] The simulation selected a transient model with an accuracy of 10-3, a time step of 0.0001, and a maximum of 100 iterations. The entire two-phase flow field adopted a fast flow scheme, and an unstructured grid division method with polyhedrons was used for geometric modeling. After grid independence verification, a grid consisting of 951125 units was selected as the final grid scheme. The inlet used a velocity boundary, the outlet used a pressure boundary, the liquid outlet surface pressure was greater than the gas outlet, and the remaining devices were all walled.

[0132] C. Simulation Verification

[0133] To evaluate the simulation accuracy, we compared the pressure drop obtained from the simulation data with the experimental pressure drop under the conditions described in the table. 2. The pressure drop is defined as the pressure difference between the inlet and the gas outlet. The experimental results show that the simulation results are in good agreement with the experimental results. It is worth noting that there are differences in the viscosity and density of the oil used for the numerical simulation compared to the experimental setup. The numerical simulation uses engine oil, while the experiment uses white oil. Therefore, due to the change in the properties of the oil, the difference in pressure drop is more obvious than that of water, while the pressure drops of the simulation and experiment show the same trend. Therefore, the above simulation method seems to be able to be used to simulate the gas-liquid two-phase flow in GLCC.

[0134] Table 1 Pressure drop (Pa)

[0135]

[0136] Displayed in the format of "gas flow-liquid flow", unit is m3 / h

[0137] D. Results and Discussion

[0138] 4.1 Flow field characteristics

[0139] In order to improve the understanding of the GLCC separation process, a flow field analysis based on CFD simulation was first performed.

[0140] Figure 5 The distribution of three key parameters in the GLCC system is described, where (a) represents the velocity distribution, (b) represents the phase inclusion rate distribution, and (c) represents the pressure distribution. When the two-phase mixed fluid enters through the inlet and passes through the inclined decreasing inlet, the reduction in the inclination of the flow channel causes a significant increase in velocity, which leads to a downward swirling flow along the wall, as shown in Figure 5 (a). Figure 5 (b) shows the swirling flow formed along the wall, showing obvious stratification. The upper blue area represents the gas phase, while the lower red area corresponds to the liquid phase inside the inlet. In addition, Figure 5 (c) shows the relative pressure distribution in the GLCC, indicating that the inlet pressure reaches a maximum and gradually decreases along the wall vortex, where pressure is converted into power.

[0141] Figure 6 Radial distribution of velocity amplitude on two sections 1) x = 37 mm; (P2) x = 165 mm. (x = 0 at the rightmost end of the inlet, air flow rate is 75-2 m3 / h)

[0142] Figure 6 The velocity distribution for two inlet cross sections is shown: P1, a non-contracting cross section, and P2, an inclined inlet cross section. Figure 6 (a) shows the cross-sectional velocity distribution, indicating that the acceleration of the inclined inlet increases gradually from top to bottom. Figure 6 (b) shows the lateral distribution of two cross sections, initially showing a uniform inlet. Under the influence of the gas, the liquid velocity increases, resulting in the gas and liquid velocities being close under the same cross section, but the liquid velocity is smaller than the gas velocity. The lateral display of the inclined inlet is not completely symmetrical, with higher velocities at the non-tangential end.

[0143] In GLCC, the interaction of resistance, centrifugal effect on membrane or droplets, and gravity jointly determine the gas-liquid flow and separation process. When the centrifugal force exceeds the radial resistance, it will push the liquid phase to move toward the wall. On the other hand, if the axial resistance exceeds the gravity, the liquid phase will eventually exit through the upper gas outlet. Therefore, the tangential velocity and axial velocity of the gas are the key factors affecting the separation of gas and liquid phases in GLCC.

[0144] (P3) z = 175 mm; (P4) z = 400 mm, the bottom of the cylinder is z = 0, and the air-water flow rate is 75-2 m3 / h)

[0145] Figure 7 The tangential velocity and axial velocity of the gas-water two-phase separation at a flow rate of 75-2m3 / h are shown. The axial velocity of the gas exceeds the tangential velocity at the same cross section. At P3, the flow field presents a clockwise downward eccentric swirl. At P4, the axial symmetry is improved. Both the axial velocity and the tangential velocity decrease along the axial direction. The increase in axial velocity causes the gradual rise or removal of droplets or liquid films, while the increase in tangential velocity promotes the rotation of the liquid film. P3 is located below the inlet, while P4 is located above the inlet. At P3, both the axial velocity and the tangential velocity are high. Driven by the high axial velocity, the rapid rise of the film and the rotation caused by the increase in tangential velocity lead to thinning of the film. On the contrary, at P4, the lower axial velocity causes the film to rise more slowly. The decrease in tangential velocity indicates that P4 is more likely to form a thicker liquid film than P3.

[0146] Therefore, the interior of the GLCC can be roughly divided into three regions: the inlet acceleration region, the swirl region (below the barrel inlet), and the escape region (above the barrel inlet).

[0147] (1) Inlet acceleration area: The gas-liquid mixed fluid is accelerated in this area to form a high-speed fluid.

[0148] (2) Cyclone region: Located below the barrel inlet, it has high axial and radial velocities, and the liquid film rotates and rises under the combined action of gas lift and gravity.

[0149] (3) Escape zone: This area is located above the cylinder inlet. The axial and tangential velocities are low, and liquid film accumulation is prone to occur. Under a sufficiently large gas flow rate, the liquid film can be carried into the cylinder by the gas, forming a short-circuit flow.

[0150] Experimental device and overall process

[0151] Table 2 Experimental working conditions

[0152]

[0153]

[0154] Figure 8 The experimental setup of the multiphase flow testing laboratory is shown: In a test loop with a diameter of 50 mm, air and tap water are used as the gas phase and water phase, respectively, to simulate the pipeline of a single oil well. In the separation tank, if the liquid phase flow rate is kept below 20 m / s, the flow rate of the liquid phase is 100 m / s. 3 / h, the gas phase velocity is maintained at 150m 3 / h or less, the experimental working conditions are shown in Table 2, and the process of multiphase flow experiment is as follows:

[0155] 1) First, start the air compressor to establish a certain static pressure in the entire experimental system;

[0156] 2) Next, the air stored in the tank is delivered to the pipeline of the experimental device through the circulation compressor pump, and the water is delivered to the pipeline through the centrifugal pump;

[0157] 3) The valves and standard flowmeters installed on the pipelines respectively control and record the reference volume flow rates of the two single-phase fluids;

[0158] 4) After the air and water are mixed in the pipeline, the generated gas-liquid two-phase flow is separated into a single-phase flow after passing through the GLCC separator. The separated fluids flow through three horizontal test pipelines equipped with glass windows and multiple sensors respectively;

[0159] 5) Finally, the outflowing fluid from the horizontal test pipeline is mixed and recycled into the gas-water separation tank, in which the mixed flow is statically separated into a single-phase flow for recycling.

[0160] Experimental results analysis

[0161] A. Comparison of Experimental Results

[0162] Fig. 9 The LCO phenomenon observed in the experiment is shown in Fig. 9 In (a), the LCO curve below the two-stage separation of gas-water two-phase flow shows more operating points, indicating superior separation performance. Fig. 9 (b) is the LCO curve for single-stage separation of gas phase and water phase, comparing the one-stage separation system with the two-stage separation system. Fig. 9 (b) It can be seen that the LCO curve of the two-stage separation system has a large upward shift, which confirms that the addition of the two-stage separator significantly improves the LCO phenomenon of the entire measurement system.

[0163] Generally speaking, the flow rate measurement system currently used for gas-liquid two-phase separation is very suitable for liquid flow rates between 0.5 and 1 m 3 For small oil fields between / h, higher liquid flow rates can be adjusted at lower gas flow rates.

[0164] Fig.10 The flow pattern under the two-stage separation system is shown. The LCO separation curve is distinguished by the image taken by the high-speed camera. After the gas phase passes through the first-stage separator, the gas phase pipeline mainly presents an annular flow. Then, as shown in Fig.10 As shown in (a) and (b), after passing through the second-stage separator, the gas phase pipeline tends to be laminar flow. After the liquid phase passes through the first-stage separator, the main liquid pipeline mainly presents stratified flow or is full of liquid. Usually, only when the liquid flow rate is 0.5m 3 / h. After passing through the two-stage separation system, the flow state in the pipeline has greater stability, which is convenient for measuring flow rate.

[0165] B. Analysis of image reconstruction results based on ERT technology

[0166] In the case of high water content, the image reconstruction results using ERT technology can well reflect the distribution of gas-water two-phase flow in the pipeline, and have a qualitative understanding of the gas-water mixing conditions at different flow rates and different flow ratios. Fig.11 The image reconstruction results of the gas-water two-phase flow in the main liquid pipeline under different flow conditions are shown. In the figure, blue represents water and red represents gas. Fig.12 The volume flow rate of gas entering the liquid pipeline under different flow conditions is shown.

[0167] When the water flow rate is low (Qw≤1.0m3h-1), as the gas flow rate increases, the GLCC separator cannot completely separate the gas-water two-phase flow, resulting in part of the gas entering the main liquid pipeline. Due to gravity, water is concentrated at the bottom of the pipeline and air is located at the top of the pipeline. As the gas flow rate increases, the gas volume flow rate entering the liquid pipeline also increases. For the unipolar separation system, when the liquid flow rate is 0.5m3h-1, the gas volume flow rate entering the main liquid channel can reach up to 15.58m3h-1, and when the liquid flow rate is 1.0m3h-1, the gas volume flow rate can reach up to 7.68m3h-1; for the secondary separation system, when the liquid flow rate is 0.5m3h-1, the gas volume flow rate entering the main liquid channel can reach 9.65m3h-1, and when the liquid flow rate is 1.0m3h-1, the gas volume flow rate can reach 3.42m3h-1.

[0168] Fig.11 (a) shows the image reconstruction result of the two-stage separation system. Fig.11 (b) shows the image reconstruction results of the single-stage separation system. By comparing the image reconstruction results of the single-stage separator and the two-stage separator, it can be found that at a lower liquid flow rate, as the gas flow rate increases, the gas entering the main liquid channel of the former is significantly more than that of the latter. The maximum GVF of the former reaches 44.1%, while that of the latter is 29.3%, which indicates that the separation performance of the two-stage separation system is better than that of the single-stage separation system. In addition, the gas and water layers in the pipeline are clearly separated and do not mix with each other, so the accuracy of calculating GVF using the image reconstruction method is higher.

[0169] C. Measurement Error Analysis

[0170] The flow rate measured by the orifice flowmeter, the flow rate corrected based on the ERT technology, and the reference flow rate input to the GLCC separator were compared. Fig.13 The left side shows the comparison between the flow rate measured experimentally using the orifice flow meter and the reference flow rate. The dashed line in the figure represents the error limit. Compared with the reference data, the data obtained by the orifice flow meter has good consistency. Fig.13 The right side shows the relationship between the relative error and the reference flow rate. Before correction, the positive error is larger when the liquid flow rate is lower and the gas flow rate is higher, and the negative error is larger when the liquid flow rate is higher and the gas flow rate is lower. After correction, the overall error of the data remains in the range of 5% to 10%, the distribution is more uniform, and the negative error is larger, which indirectly reflects the LCO phenomenon.

[0171] Based on the analysis of the flow pattern observed through the glass window in 3.2.5.B, under low flow conditions affected by gas (water flow rate less than 1.0m3 / h), the pipeline presents a stratified flow pattern. Due to the entrainment of gas in the liquid phase, this causes the flow meter reading to be overestimated. Conversely, under high flow conditions (water flow rate greater than 2.5m3 / h), some liquid enters the gas pipeline, causing the measured liquid value to be significantly lower than the actual value.

[0172] It can be seen that the present application reduces the measurement error by combining GLCC and ERT, expands the applicable working conditions of flow measurement, and uses the image reconstruction function of ERT to detect the percentage of liquid volume in the pipeline to correct the flow measurement error while developing a new type of secondary separation equipment to improve the separation efficiency. The following are the main effects of this technology:

[0173] (1) Compared with the single-stage separator, the two-stage separator has a larger adjustable operating range. In addition, compared with the obvious slug flow in the main liquid path generated by the single-stage separator, the multiphase flow generated by the two-stage separator is a laminar flow or full liquid with a more stable flow pattern, making flow measurement easier.

[0174] (2) With the help of ERT's image reconstruction function, the cross-sectional phase content of the liquid pipeline is calculated, so that the error correction of the flow measurement results of the pipeline when the liquid phase flow is small but the gas phase flow is large is performed. The error after correction is controlled within ±10%, which meets the needs of industrial field measurement.

[0175] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0176] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A two-stage separation flow measurement system based on a small GLCC and ERT, characterized in that: Including single-stage separator, two-stage separator and sensor: The single-stage separator comprises a separation chamber, the separation chamber is a cylindrical structure, and the inlet of the separation chamber is connected to the system inlet, the liquid outlet of the separation chamber is connected to the system outlet, and the gas outlet of the separation chamber is connected to the secondary separator, the secondary separator is based on a small GLCC design, and the gas outlet and liquid outlet of the secondary separator are respectively connected to the system outlet; The sensors include flow meters and ERTs.

2. The two-stage separation flow measurement system based on small GLCC and ERT as claimed in claim 1, characterized in that: The liquid outlet of the single-stage separator is connected to the system outlet through a primary liquid pipeline, the liquid outlet of the secondary separator is connected to the system outlet through a secondary liquid pipeline, and the gas outlet of the secondary separator is connected to the system outlet through a gas pipeline.

3. The two-stage separation flow measurement system based on small GLCC and ERT as claimed in claim 2, characterized in that: Sensors are installed on both the primary liquid pipeline and the secondary liquid pipeline.

4. The two-stage separation flow measurement system based on small GLCC and ERT as claimed in claim 1, characterized in that: The system inlet is arranged inclined.

5. The two-stage separation flow measurement system based on small GLCC and ERT as claimed in claim 1, characterized in that: The inlet of the separation chamber is inclined and circular with gradually decreasing size.

6. The two-stage separation flow measurement system based on small GLCC and ERT as claimed in claim 5, characterized in that: The ERT corrects the flow meter results by calculating the gas-liquid void fraction.

7. The two-stage separation flow measurement system based on small GLCC and ERT as claimed in claim 6, characterized in that: The ERT corrects the flow meter result by calculating the void fraction of gas and liquid, and further comprises: The relationship between the conductivity and the gray value of the reconstructed image is established by an appropriate image reconstruction method to visualize the conductivity distribution within the pipe cross section; The measurements were corrected by calculating the void fraction.

8. The two-stage separation flow measurement system based on small GLCC and ERT as claimed in claim 1, characterized in that: The method of establishing a relationship between the conductivity and the grayscale value of the reconstructed image by an appropriate image reconstruction method to visualize the conductivity distribution in the pipe cross section further includes: The voltage measurement is normalized, and the measurement when the pipe is full of water is used as the high calibration. The normalization formula is: V n =(V m -V w ) / V w ; Where Vn is the normalized voltage measurement value, Vm is the measured voltage data, and Vw is the calibration data; The relationship between the normalized voltage measurement and the conductivity distribution can be expressed as: In n =-Sσ n ; Where S is the normalized sensitivity matrix, σn is the standardized conductivity distribution, the negative sign indicates conductivity, and the direction of change of the measured value is opposite. The equivalent voltage Vx can be assumed to be inversely proportional to the conductivity σx, that is, V x ∞1 / s x ; Among them, the equivalent conductivity is σm, which is used as the input of the image reconstruction algorithm to obtain the apparent conductivity distribution; The V n =-Sσ n and Vw is measured with full water in the pipe, σw / σm can be described as: s w / s m =V m / V w ; Therefore, combining the formula for calculating liquid volume flow rate based on Bernoulli's equation and V x ∞1 / σ x , can be calculated as: s m =s w / (V n +1); The linear projection method (LBP) is applied to ERT image reconstruction. The LBP algorithm is as follows: Among them, g is the grayscale of the reconstructed image, which can reflect the field conductivity distribution, and μ is the unit vector, that is, μ=[1,1,···,1]T.

9. The two-stage separation flow measurement system based on small GLCC and ERT as described in claim 1, characterized in that. The correcting the measurement result by calculating the void fraction further comprises: Divide the pipe cross section into different cells, and let the number of effective cells in the pipe be denoted as "n"; The gray level of the "ith" grid is represented by "x", if the grid is filled with air (GVF = 100%), then "x" is equal to 0; if the grid is filled with water (GVF = 0%), then "x" is equal to 1; Assuming a linear relationship between the void content and the gray level of a single grid, when GVF = 60%, the gray level is 0.

4. To obtain the air content in the entire duct, simply sum up the gray levels:

Images