Multiphase flow metering device and method for low gas content oil wells

Abstract

The application provides a low-gas-content oil well multiphase flow metering device and metering method, which comprises a first cyclone arranged in a pipeline to be measured, an inner cone flow meter arranged downstream of the first cyclone, a shunt pipe passing through the center of the inner cone flow meter, an inlet end of the shunt pipe being located in the center of the pipeline to be measured, a metering separator being installed at the inner cone flow meter of the pipeline to be measured, an outlet end of the shunt pipe being communicated with the metering separator, a gas metering pipe being communicated with the upper part of the metering separator at an inlet end and communicated with the downstream of the pipeline to be measured at an outlet end, a gas phase flow meter being installed between the gas metering pipe and the downstream of the pipeline to be measured, a liquid metering pipe being communicated with the lower part of the metering separator at an inlet end and communicated with the downstream of the pipeline to be measured at an outlet end, and a liquid phase flow meter being installed between the liquid metering pipe and the downstream of the pipeline to be measured. The low-gas-content oil well multiphase flow metering device and metering method can effectively improve the gas-liquid separation efficiency through two-stage separation of the first and second cyclones, and ensure complete separation of the gas phase and the liquid phase.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flow measurement, in particular to a low-gas-oil-well multiphase flow measurement device. Meanwhile, the present application also relates to a measurement method using the low-gas-oil-well multiphase flow measurement device. BACKGROUND

[0002] In the energy field of oil, natural gas, chemical industry, energy and the like, the flow measurement of gas-liquid two-phase flow is of great significance for the optimization of production process, the rational allocation of resources and the improvement of economic benefits. With the continuous progress of oil and gas field development technology, the development of low-gas-oil-well is increasing, and higher requirements are put forward for the accurate measurement of low-gas-oil-well multiphase flow. Traditional flow measurement technology mostly relies on a single flow meter or a simple separation device. When facing complex gas-liquid two-phase flow, these methods are often difficult to accurately measure, and there is great limitation in low-gas working conditions. In recent years, with the development of fluid mechanics theory and the emergence of new measurement technologies, how to combine modern technical means to develop a high-efficiency, accurate and suitable multiphase flow measurement device for low-gas-oil-well has become a problem to be solved in the industry.

[0003] According to whether the two-phase flow is separated during the measurement process, the gas-liquid two-phase flow measurement technology can be divided into complete separation method, partial separation method and non-separation method. The partial separation method is a commonly used technology in gas-liquid two-phase flow measurement. The core idea is to partially separate the two-phase flow through a specific device or method without completely separating the gas-liquid two-phase, so as to realize the separate measurement of gas phase and liquid phase flow. This method is between the complete separation method and the non-separation method, aiming to ensure a certain measurement accuracy while simplifying the device structure and reducing the cost and complexity.

[0004] In the prior art, there are certain defects in the measurement of low-gas-oil-well multiphase flow. The gas phase has formed complex flow patterns such as bubble flow, gas cluster flow and slug flow in the pipeline. Due to the inability to effectively distinguish the gas phase and the liquid phase, the existing flow meter is easily affected by factors such as flow pattern change and flow velocity fluctuation during the measurement process, resulting in large measurement error and inaccurate measurement result, which is difficult to meet the requirements of low-gas-oil-well on flow measurement accuracy. Although the traditional separator can realize gas-liquid separation to a certain extent, its separation efficiency is low, and it is harsh to the flow rate and flow direction of the fluid. In low-gas working conditions, the separation effect of gas phase and liquid phase is not ideal, which cannot provide accurate fluid phase state information for subsequent flow measurement, thereby limiting the accuracy and reliability of flow measurement. SUMMARY

[0005] Therefore, one of the purposes of the present application is to provide a low-gas-oil-well multiphase flow measurement device to solve the technical problems of inaccurate gas-liquid two-phase flow measurement and low separation efficiency in the prior art.

[0006] To achieve one of the above purposes, the application provides a multiphase flow metering device for a low-gas-content oil well, which adopts the following technical scheme:

[0007] A multiphase flow metering device for a low-gas-content oil well comprises:

[0008] a to-be-measured pipeline, a first cyclone arranged in the to-be-measured pipeline for inducing spiral annular flow to preliminarily separate gas-liquid two-phase flow, an inner-cone flowmeter arranged downstream of the first cyclone for measuring the flow of the main liquid phase after preliminary separation, a shunt pipe passing through the center of the inner-cone flowmeter, an inlet end of the shunt pipe being located at the center of the to-be-measured pipeline for collecting the preliminarily separated gas phase and a small amount of liquid phase, a metering separator installed at the inner-cone flowmeter of the to-be-measured pipeline, an outlet end of the shunt pipe being in communication with the metering separator, a gas metering pipe, an inlet end of the gas metering pipe being in communication with the upper part of the metering separator, an outlet end of the gas metering pipe being in communication with the downstream of the to-be-measured pipeline, a gas-phase flowmeter being installed between the gas metering pipe and the downstream of the to-be-measured pipeline, and a liquid metering pipe, an inlet end of the liquid metering pipe being in communication with the lower part of the metering separator, an outlet end of the liquid metering pipe being in communication with the downstream of the to-be-measured pipeline, a liquid-phase flowmeter being installed between the liquid metering pipe and the downstream of the to-be-measured pipeline.

[0009] By adopting the above technical scheme, efficient and accurate measurement of the multiphase flow of the low-gas-content oil well is realized. The first cyclone can effectively induce spiral annular flow to preliminarily separate the gas-liquid two-phase flow, thereby providing a good basis for subsequent flow measurement. The inner-cone flowmeter arranged downstream of the first cyclone can accurately measure the flow of the main liquid phase after preliminary separation. The shunt pipe passing through the center of the inner-cone flowmeter collects the preliminarily separated gas phase and a small amount of liquid phase and guides them to the metering separator for further separation. The gas metering pipe and the liquid metering pipe are in communication with the upper part and the lower part of the metering separator, respectively, and are provided with corresponding gas-phase and liquid-phase flowmeters, respectively, so as to measure the flow of the gas phase and the liquid phase, respectively, thereby realizing accurate measurement of the multiphase flow of the low-gas-content oil well.

[0010] Further, upstream and downstream static pressure tapping pipes are arranged on both sides of the to-be-measured pipeline at the inner-cone flowmeter, and a differential pressure transmitter is arranged between the upstream and downstream static pressure tapping pipes to measure the differential pressure signals before and after the inner-cone flowmeter.

[0011] By adopting the above technical scheme, the differential pressure signals before and after the inner-cone flowmeter can be more accurately measured, thereby improving the measurement accuracy of the main liquid phase flow.

[0012] Further, a second cyclone is arranged in the outlet end of the shunt pipe, and a separation narrow gap is arranged on the inner wall of the outlet end of the shunt pipe, so as to realize re-separation of the gas phase and the small amount of liquid phase by the centrifugal force of the second cyclone.

[0013] By adopting the technical scheme, the second cyclone can further improve the gas-liquid separation effect, ensure complete separation of the gas phase and the liquid phase, and thus improve the accuracy of flow measurement.

[0014] Further, the upper part of the metering separator is a gas phase space, and the lower part is a liquid accumulation cavity.

[0015] By adopting the technical scheme, the gas phase flow can be more accurately measured, and the accuracy of flow measurement is further improved.

[0016] Further, the first cyclone is mainly composed of a cyclone blade and a main rod, the inner edge of the cyclone blade is attached to the outer wall of the main rod, the outer edge of the cyclone blade is attached to the inner wall of the pipeline to be measured, and the second cyclone has the same structure as the first cyclone.

[0017] By adopting the technical scheme, the structural design of the first cyclone and the second cyclone can effectively induce spiral annular flow, and improve the gas-liquid separation efficiency.

[0018] Further, the separation narrow slits on the inner wall of the outlet end of the shunt pipe are arranged in multiple rows in an axial direction, and a small amount of liquid phase is thrown to the separation narrow slits by the centrifugal force of the second cyclone.

[0019] By adopting the technical scheme, the multiple separation narrow slits can further improve the separation effect of the liquid phase, ensure that the liquid phase can be effectively collected, and thus improve the accuracy of flow measurement.

[0020] Further, the shunt pipe and the inner cone flowmeter have an embedded structure, and after preliminary separation, the main flow liquid phase enters the inner cone flowmeter.

[0021] By adopting the technical scheme, the embedded structure can optimize the spatial layout of the device, improve the compactness of the device, and improve the measurement efficiency.

[0022] Compared with the prior art, one of the purposes of the present application has the following beneficial effects:

[0023] The low-gas-content oil well multiphase flow metering device can effectively improve the gas-liquid separation efficiency, ensure the complete separation of the gas phase and the liquid phase, and improve the accuracy of flow measurement; the combination of the inner cone flow meter and the differential pressure transmitter can accurately measure the main stream liquid phase flow, further improving the accuracy of flow measurement; the gas phase flow meter and the liquid phase flow meter can measure the flow of the gas phase and the liquid phase, respectively, realizing the accurate measurement of the low-gas-content oil well multiphase flow; the embedded structure of the shunt pipe and the inner cone flow meter optimizes the spatial layout of the device, improving the compactness and measurement efficiency of the device; the design of the multiple separation narrow slots can further improve the separation effect of the liquid phase, ensuring that the liquid phase can be effectively collected, thereby improving the accuracy of flow measurement; by measuring the differential pressure signals before and after the inner cone flow meter, the main stream liquid phase flow can be more accurately measured, further improving the accuracy of flow measurement.

[0024] The second purpose of the present application is to provide a low-gas-content oil well multiphase flow metering method to solve the technical problem of large measurement error in the prior art, which is difficult to meet the accuracy requirements of low-gas-content oil well flow measurement.

[0025] To achieve the second purpose, the present application provides a low-gas-content oil well multiphase flow metering method, which adopts the following technical solution:

[0026] A low-gas-content oil well multiphase flow metering method, comprising the following steps:

[0027] S1. After the low-gas-content fluid enters the pipeline to be measured, it is induced to rotate at high speed by the first cyclone, generating a centrifugal force, and the liquid phase with a higher density is thrown to the pipe wall to form an annular liquid column, and the gas phase with a lower density is gathered in the center of the pipeline to form a central gas;

[0028] S2. The separated annular liquid column flows through the inner cone flow meter, and the differential pressure between the upstream and downstream is measured by the differential pressure transmitter, and the main stream liquid phase flow M l is calculated by combining the fluid density and the formula;

[0029] S3. The central gas and a small amount of residual liquid droplets are extracted through the shunt pipe, induced to rotate at high speed by the second cyclone, generating a centrifugal force, a small amount of liquid phase is thrown to the shunt pipe wall to form a liquid film and gathered in the lower part of the metering separator through the separation narrow slot, and the gas phase continues to flow along the main rod of the second cyclone, realizing the separation of the gas and liquid phases again;

[0030] S4. The pure gas phase flow m g after the second separation by the second cyclone is measured directly by the gas phase flow meter; a small amount of liquid phase after the second separation by the second cyclone is collected by the metering separator, and the small amount of liquid phase flow m l is measured by the liquid phase flow meter;

[0031] S5. The total liquid phase flow ML The separated gas-liquid two-phase is mixed again from the gas flow meter and the liquid flow meter to the pipeline to be measured to complete the flow returning.

[0032] By adopting the technical scheme, the low-gas-content oil well multiphase flow can be measured efficiently and accurately. The two-stage separation of the first cyclone and the second cyclone can effectively improve the gas-liquid separation efficiency and ensure the complete separation of the gas phase and the liquid phase. The combination of the inner cone flow meter and the differential pressure transmitter can accurately measure the main flow liquid phase flow, and the gas flow meter and the liquid flow meter can measure the gas phase flow and the liquid phase flow respectively, so that the low-gas-content oil well multiphase flow can be measured accurately.

[0033] Further, the main flow liquid phase flow in S2 is calculated by the following formula:

[0034]

[0035] By adopting the technical scheme, the main flow liquid phase flow can be calculated more accurately, and the flow measurement accuracy is further improved.

[0036] Further, the total liquid phase flow in S5 is calculated by the following formula:

[0037] M L = M l + m l

[0038] By adopting the technical scheme, the total liquid phase flow can be calculated more accurately, and the flow measurement accuracy is further improved.

[0039] Compared with the prior art, the second purpose of the present application has the following beneficial effects:

[0040] The low-gas-content oil well multiphase flow metering method has the same beneficial effects as the first purpose, and will not be repeated here. BRIEF DESCRIPTION OF DRAWINGS

[0041] The accompanying drawings, which form a part of the present application, are included to provide a further understanding of the application, and are incorporated herein for explanation by reference. The present application and its specification are explained with the aid of the illustrative embodiments and will not be limited by the description.

[0042] In the drawings:

[0043] Figure 1 The low-gas-content oil well multiphase flow metering device is shown in the overall structure diagram of the first embodiment of the present application.

[0044] Figure 2 The first cyclone structure is shown in the structural schematic diagram of the first embodiment of the present application.

[0045] Figure 3The schematic diagram of the inner cone flowmeter embedded in the shunt pipe for the first embodiment of the present application;

[0046] Figure 4 The schematic diagram of the second cyclone and separation narrow slit part for the first embodiment of the present application.

[0047] Explanation of reference signs:

[0048] 1, pipe to be measured; 2, first cyclone; 3, shunt pipe; 4, differential pressure transmitter; 5, inner cone flowmeter; 6, second cyclone; 7, gas phase flowmeter; 8, liquid phase flowmeter; 9, cyclone blade; 10, main rod; 11, separation narrow slit; 12, liquid accumulation cavity; 13, gas metering pipe; 14, liquid metering pipe; 15, upstream static pressure tapping pipe; 16, downstream static pressure tapping pipe; 17, metering separator; 18, gas phase space. DETAILED DESCRIPTION

[0049] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0050] In the description of the present application, it should be noted that if terms indicating orientation or positional relationship such as "upper", "lower", "inner", "back" appear, they are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as limiting the devices or elements indicated to have a specific orientation, to be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present application. In addition, if the terms "first", "second", etc. appear, they are also only for the purpose of description and cannot be understood as indicating or implying relative importance.

[0051] In addition, in the description of the present application, unless otherwise explicitly limited, the terms "mounting", "connection", and "connection" should be understood broadly. For example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood in combination with the specific circumstances.

[0052] The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0053] Embodiment one

[0054] This embodiment relates to a multiphase flowmetering device for a low-gas-content oil well, and the overall structure is as shown in Figure 1 It comprises a pipe to be measured 1, a first cyclone 2, an inner cone flowmeter 5, a shunt pipe 3, a metering separator 17, a gas metering pipe 13, and a liquid metering pipe 14.

[0055] The first cyclone 2 is arranged in the pipeline 1 to be measured to induce a spiral annular flow to preliminarily separate gas and liquid phases, the inner cone flowmeter 5 is arranged downstream of the first cyclone 2 to measure the flow of the main liquid phase after the preliminary separation, the shunt pipe 3 passes through the center of the inner cone flowmeter 5, the inlet end of the shunt pipe 3 is located at the center of the pipeline 1 to be measured to collect the preliminarily separated gas phase and a small amount of liquid phase, the metering separator 17 is installed at the inner cone flowmeter 5 of the pipeline 1 to be measured, the outlet end of the shunt pipe 3 is connected with the metering separator 17, the inlet end of the gas metering pipe 13 is connected with the upper part of the metering separator 17, and the outlet end is connected with the downstream of the pipeline 1 to be measured, the gas phase flowmeter 7 is installed between the gas metering pipe 13 and the downstream of the pipeline 1 to be measured, the inlet end of the liquid metering pipe 14 is connected with the lower part of the metering separator 17, and the outlet end is connected with the downstream of the pipeline 1 to be measured, and the liquid phase flowmeter 8 is installed between the liquid metering pipe 14 and the downstream of the pipeline 1 to be measured.

[0056] It is worth mentioning that the pipeline 1 to be measured is a pipeline for discharging fluid outward from an oil well, the fluid flow in the pipeline 1 to be measured is essentially a differential pressure before and after as a driving force, the first cyclone 2 is driven, and the fluid after passing through the first cyclone 2 is preliminarily separated, so that the main liquid phase and the gas phase mixed with a small amount of liquid phase are formed, the main liquid phase enters the inner cone flowmeter 5 to measure the flow of the main liquid phase, the gas phase and the small amount of liquid phase enter the shunt pipe 3 and are discharged from the shunt pipe 3 to the metering separator 17, at this time, the gas phase rises and the small amount of liquid phase descends, the gas phase enters the gas metering pipe 13 and passes through the gas phase flowmeter 7 to measure the flow of the gas phase, the small amount of liquid phase enters the liquid metering pipe 14 to measure the flow of the small amount of liquid phase, and the flow of the small amount of liquid phase is added to the flow of the main liquid phase to obtain the total liquid phase flow.

[0057] Based on the above overall introduction, an exemplary structure of the low-gas-content oil well multiphase flow metering device of the embodiment is shown in Figure 1 The upstream static pressure tapping pipe 15 and the downstream static pressure tapping pipe 16 are arranged on both sides of the inner cone flowmeter 5, a differential pressure transmitter 4 is arranged between the upstream static pressure tapping pipe 15 and the downstream static pressure tapping pipe 16, and the differential pressure transmitter 4 is used to measure the differential pressure generated before and after the inner cone flowmeter 5.

[0058] It should be noted that the upstream static pressure tapping pipe 15 and the downstream static pressure tapping pipe 16 are respectively installed on the pipeline 1 to be measured, and the specific positions are that the upstream static pressure tapping pipe 15 is located at the liquid inlet of the inner cone flowmeter 5, and the downstream static pressure tapping pipe 16 is located at the liquid outlet of the inner cone flowmeter 5, the differential pressure transmitter 4 connects the upstream static pressure tapping pipe 15 and the downstream static pressure tapping pipe 16, and such arrangement can measure the throttling differential pressure and facilitate calculation of the flow of the main liquid phase.

[0059] As a preferred, as shown in Figure 4As shown, in this embodiment, the outlet end of the shunt pipe 3 is provided with a second cyclone 6, and the driving force of the second cyclone 6 is the same as that of the first cyclone 2, which is the kinetic energy of the fluid itself. It is a common knowledge of fluid mechanics that the inner wall of the outlet end of the shunt pipe 3 is provided with a separation narrow gap 11. Through the centrifugal force of the second cyclone 6, the gas phase and a small amount of liquid phase are separated again.

[0060] Specifically, the second cyclone 6 has the same structure as the first cyclone, and the second cyclone 6 separates the gas phase and a small amount of liquid phase again. The small amount of liquid phase enters the separation narrow gap 11 through centrifugal force and then falls from the separation narrow gap 11 to the lower part of the metering separator 17, while the gas phase is located in the upper part of the metering separator 17. Such an arrangement ensures that the separation can be performed again, thereby improving the measurement accuracy.

[0061] As a preferred embodiment, in this embodiment, the upper part of the metering separator 17 is a gas phase space 18, and the lower part is a liquid accumulation chamber 12. The gas phase flowmeter 7 measures the flow of the gas phase in the gas phase space 18. It should be noted that the gas metering pipe 13 is installed in the upper part of the metering separator 17, that is, in the gas phase space 18. The gas phase inside enters the gas metering pipe 13 and is directly measured by the gas phase flowmeter 7 when passing through the gas phase flowmeter 7. The liquid metering pipe 14 is installed in the lower part of the metering separator 17, that is, in the liquid storage chamber. The liquid phase inside enters the liquid metering pipe 14 and is directly measured by the liquid phase flowmeter 8 when passing through the liquid phase flowmeter 8.

[0062] As a preferred embodiment, as shown in Figure 2 As shown, the first cyclone 2 of this embodiment is mainly composed of a cyclone blade 9 and a main rod 10. The inner edge of the cyclone blade 9 is attached to the outer wall of the main rod 10, and the outer edge of the cyclone blade 9 is attached to the inner wall of the pipeline 1 to be measured. The second cyclone 6 has the same structure as the first cyclone 2.

[0063] Specifically, when the fluid passes through the cyclone blade 9, it is subjected to high-speed rotation of the cyclone blade 9, inducing a spiral annular flow. At this time, the gas phase is located in the center of the pipeline 1 to be measured, forming a central gas. The liquid phase is located in the closed pipeline 1 to be measured, forming an annular liquid column. Such an arrangement completes the preliminary separation. The inner and outer edges of the cyclone blade 9 are attached to the outer wall of the main rod 10 and the inner wall of the pipeline 1 to be measured, which is to ensure the quality of the preliminary separation. The cyclone blade 9 of the second cyclone 6 is attached to the inner wall of the shunt pipe 3, which has the same effect as the first cyclone 2.

[0064] As a preferred embodiment, as shown in Figure 3 and Figure 4 As shown in this embodiment, the separation narrow gap 11 on the inner wall of the outlet end of the shunt pipe 3 is arranged in multiple axially spaced rows. Through the centrifugal force of the second cyclone 6, a small amount of liquid phase is thrown to the separation narrow gap 11. The shunt pipe 3 and the inner cone flowmeter 5 have an embedded structure. After preliminary separation, the main stream of liquid phase enters the inner cone flowmeter 5.

[0065] It should be noted that the purpose of the multiple separation narrow slots 11 arranged at intervals is to ensure that the small amount of liquid phase that is thrown off can gather and fall into the liquid accumulation chamber 12, thereby improving the separation effect and avoiding the dispersion of the small amount of liquid phase into the gas phase. The embedded structure is that the flow divider 3 passes through the center of the inner cone flowmeter 5, and the two are independent in structure but work cooperatively in function. The inner cone flowmeter 5 is a hollow structure, which not only supports the flow divider 3, but also guides the separation of the gas phase and the liquid phase. The inner cone flowmeter 5 is a simulated conical structure, which is the same as the inner cone flowmeter in the prior art, except that the flow divider 3 is inserted from the inlet end and exits from the pipe wall after the simulated conical body.

[0066] The low-gas-content oil well multiphase flow metering device in the embodiment solves the technical problems of low separation efficiency, large measurement error and complex structure in the conventional technology through the first cyclone 2 and the differential pressure transmitter 4, greatly reduces the pressure loss of the conventional separation device, and can complete the accurate measurement of the low-gas-content gas-liquid two-phase flow under the pipeline working condition; through the arrangement of the first cyclone 2 and the second cyclone 6, the two-stage cyclone separation architecture is ensured, the efficient separation and accurate measurement of the gas-liquid two-phase are realized, the liquid phase residue is completely eliminated, and finally the single-phase measurement is completed by the independent gas phase and liquid phase flowmeter 8; through the hollow design of the flow divider 3 and the integrated design of the cyclone blade 9, the compact structure is realized, and through the re-separation of the separation narrow slots 11, the micro-liquid droplet capture efficiency of the small amount of liquid phase is strengthened, and the re-separation effect is improved.

[0067] Embodiment two

[0068] The embodiment relates to a low-gas-content oil well multiphase flow metering method, which comprises the following steps:

[0069] S1. After the low-gas-content fluid enters the pipeline 1 to be measured, the fluid is induced to rotate at a high speed by the first cyclone 2, a centrifugal force is generated, the liquid phase with a large density is thrown to the pipe wall to form a ring-shaped liquid column, and the gas phase with a small density is gathered in the center of the pipeline to form a central gas.

[0070] S2. The ring-shaped liquid column after separation flows through the inner cone flowmeter, and the differential pressure between the upstream and downstream of the ring-shaped liquid column is measured by the differential pressure transmitter 4. The main flow liquid phase flow M is calculated by combining the fluid density and the formula. l .

[0071] S3. The central gas and a small amount of residual liquid droplets are extracted through the flow divider 3, induced to rotate at a high speed by the second cyclone 6, a centrifugal force is generated, the small amount of liquid phase is thrown to the pipe wall of the flow divider 3 to form a liquid film, and the liquid film is gathered into the lower part of the metering separator 17 through the separation narrow slots 11. The gas phase continues to flow along the main rod of the second cyclone 6, and the gas-liquid phase is re-separated.

[0072] S4. The pure gas phase flow m after re-separation by the second cyclone 6 is measured by the independent gas phase and liquid phase flowmeter 8. gThe small amount of liquid phase is measured by the liquid flow meter 8 after being collected by the metering separator 17 after being separated again by the second cyclone l .

[0073] S5. Total liquid phase flow M L The separated gas-liquid phases are mixed again after flowing from the gas flow meter and the liquid flow meter to the pipeline to be measured, and the flow is completed.

[0074] As preferred, in the embodiment, the formula in S2 is:

[0075]

[0076] In the formula, M l is the main liquid phase flow, with a unit of kg / s; C is the outflow coefficient; ε is the expandable coefficient; β is the throttling ratio; D is the pipeline inner diameter, with a unit of m; Δp is the throttling pressure difference before and after the inner cone flow meter 5, with a unit of Pa; ρ L is the density. Specifically, the outflow coefficient, the expandable coefficient, the throttling ratio, the pipeline inner diameter, and the density are known, the throttling pressure difference can be obtained by checking the differential pressure transmitter, and thus the main liquid phase flow can be calculated according to the formula.

[0077] As preferred, in the embodiment, the formula in S5 is:

[0078] M L = M l + m l

[0079] In the formula, M L is the total liquid phase flow; M l is the main liquid phase flow; and m l is the small amount of liquid phase flow. Specifically, the small amount of liquid phase flow is directly measured by the liquid flow meter, and the total liquid phase flow can be measured by adding the main liquid phase flow calculated above.

[0080] The multiphase flow metering method for the low-gas-content oil well in the embodiment directly measures by the formula in S2, completely eliminates the liquid phase residues by the primary separation and the secondary separation, and finally completes the single-phase measurement by the independent gas flow meter and the liquid flow meter. The total liquid phase flow is completed by the metering through the “main liquid flow measurement + residual liquid secondary capture”, and an ordered “separation-metering-flow returning” closed loop system is constructed.

[0081] The above merely describes the preferred embodiments of the present application and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A multiphase flow metering device for a low gas oil well, characterized in that, It includes: A pipeline (1) to be measured; A first cyclone (2) arranged in the pipeline (1) to be measured to induce spiral annular flow and preliminarily separate gas and liquid phases; An inner cone flowmeter (5) arranged downstream of the first cyclone (2) to measure the flow of the main liquid phase after preliminary separation; A shunt pipe (3) passing through the center of the inner cone flowmeter (5), with an inlet end located in the center of the pipeline (1) to be measured to collect the preliminarily separated gas phase and a small amount of liquid phase; A metering separator (17) installed at the inner cone flowmeter (5) of the pipeline (1) to be measured, with an outlet end of the shunt pipe (3) communicating with the metering separator (17); A gas metering pipe (13) with an inlet end communicating with the upper part of the metering separator (17) and an outlet end communicating with the downstream of the pipeline (1) to be measured, and a gas phase flowmeter (7) installed between the gas metering pipe (13) and the downstream of the pipeline (1) to be measured; A liquid metering pipe (14) with an inlet end communicating with the lower part of the metering separator (17) and an outlet end communicating with the downstream of the pipeline (1) to be measured, and a liquid phase flowmeter (8) installed between the liquid metering pipe (14) and the downstream of the pipeline (1) to be measured.

2. The multiphase flow metering device for low gas content oil wells according to claim 1, characterized in that: The pipeline (1) to be measured is arranged with an upstream static pressure tapping pipe (15) and a downstream static pressure tapping pipe (16) on both sides of the inner cone flowmeter (5), and a differential pressure transmitter (4) is arranged between the upstream static pressure tapping pipe (15) and the downstream static pressure tapping pipe (16) to measure the differential pressure signals before and after the inner cone flowmeter (5).

3. The multiphase flow metering device for low gas content oil wells according to claim 2, characterized in that: A second cyclone (6) is arranged in the outlet end of the shunt pipe (3), and a separation narrow gap (11) is arranged on the inner wall of the outlet end of the shunt pipe (3), and the gas phase and a small amount of liquid phase are separated again by the centrifugal force of the second cyclone (6).

4. The multiphase flow metering device for low gas content oil wells according to claim 3, characterized in that: The upper part of the metering separator (17) is a gas phase space (18), and the lower part is a liquid accumulation chamber (12), and the gas phase flowmeter (7) measures the flow of the gas phase in the gas phase space (18).

5. The multiphase flow metering device for low gas content oil wells according to claim 3, characterized in that: The first cyclone (2) is mainly composed of a cyclone blade (9) and a main rod (10), the inner edge of the cyclone blade (9) is attached to the outer wall of the main rod (10), the outer edge of the cyclone blade (9) is attached to the inner wall of the pipeline (1) to be measured, and the second cyclone (6) has the same structure as the first cyclone (2).

6. The multiphase flow metering device for low gas content oil wells according to claim 3, characterized in that: The separation narrow gaps (11) on the inner wall of the outlet end of the shunt pipe (3) are arranged in multiple axially spaced rows, and a small amount of liquid phase is thrown to the separation narrow gaps (11) by the centrifugal force of the second cyclone (6).

7. The low gas cut oil well multiphase flow metering device according to claim 1, characterized in that: the shunt pipe (3) is in an embedded structure with the inner cone flow meter (5), and after preliminary separation, the main flow liquid phase enters the inner cone flow meter (5).

8. A method of multiphase flow metering of a low gas oil well, characterized by, The metering method is based on the low gas cut oil well multiphase flow metering device according to any one of claims 3-7, and the metering method comprises the following steps: S1. After the low gas cut fluid enters the pipeline (1) to be measured, it is induced to rotate at high speed by the first cyclone (2), a centrifugal force is generated, the liquid phase with a larger density is thrown to the pipe wall to form a ring-shaped liquid column, and the gas phase with a smaller density is gathered in the center of the pipeline to form a central gas; S2. The separated annular liquid column flows through the inner cone flowmeter (5), and the differential pressure transmitter (4) measures the differential pressure between the upstream and downstream static pressures, and the main liquid phase flow M is calculated by combining the fluid density and the formula l ; S3. The central gas and a small amount of residual liquid droplets are extracted through the shunt pipe (3), induced to rotate at high speed by the second cyclone (6), a centrifugal force is generated, a small amount of liquid phase is thrown to the pipe wall of the shunt pipe (3) to form a liquid film and is gathered in the lower part of the metering separator (17) through the separation narrow gap (11), and the gas phase continues to flow along the main rod of the second cyclone (6) to realize the separation of the gas and liquid phases again; S4. Pure gas phase flow rate m after separation by the second cyclone (6) g measured directly by a gas phase flow meter (7); the small amount of liquid phase after separation by the second cyclone (6) is collected by a metering separator (17) and the small amount of liquid phase flow rate m is measured by a liquid phase flow meter (8) l ; S5. Total liquid flow rate M L The separated gas and liquid phases are mixed again from the gas flow meter (7) and the liquid flow meter (8) to the pipeline (1) to be measured, and the flow is completed.

9. The method of multiphase flow metering of a low gas oil well of claim 8, characterized in that: The main flow liquid phase flow in S2 is calculated by the following formula: wherein: M l is the main stream liquid flow rate, in kg / s; C is the discharge coefficient; ε is the expandable coefficient; β is the throttle ratio; D is the pipe inner diameter, in m; Δp is the pressure difference before and after the internal cone flowmeter (5), in Pa; ρ L is the density.

10. The method of claim 8, wherein: The total liquid phase flow in S5 is calculated by the following formula: M L = M l + m l wherein: M L is the total liquid flow rate; M l is the main liquid flow rate; m l For small liquid phase flow rates.

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