Multi-phase flow metering device and metering method for low-gas-content oil well

Abstract

The invention provides a multi-phase flow metering device and metering method for a low-gas-content oil well. The multi-phase flow metering device comprises a first swirler arranged in a to-be-measured pipeline, an inner cone flowmeter arranged on the downstream of the first swirler, a flow dividing pipe penetrating through the center of the inner cone flowmeter, and the inlet end of the flow dividing pipe is located in the center of the to-be-measured pipeline; the metering separator is installed at an inner cone flowmeter of a to-be-measured pipeline, the outlet end of the flow dividing pipe is communicated with the metering separator, the inlet end of the gas metering pipe is communicated with the upper portion of the metering separator, the outlet end of the gas metering pipe is communicated with the downstream of the to-be-measured pipeline, and the gas phase flowmeter is installed between the gas metering pipe and the downstream of the to-be-measured pipeline. The inlet end of the liquid metering pipe is communicated with the lower part of the metering separator, the outlet end is communicated with the downstream of the to-be-measured pipeline, and a liquid phase flowmeter is arranged between the liquid metering pipe and the downstream of the to-be-measured pipeline. According to the multi-phase flow metering device and metering method for the low-gas-content oil well, through two-stage separation of the first cyclone and the second cyclone, the gas-liquid separation efficiency is effectively improved, and thorough separation of a gas phase and a liquid phase is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of flow metering, and particularly to a multiphase flow metering device for low-gas-content oil wells. At the same time, the present invention also relates to a metering method applying the multiphase flow metering device for low-gas-content oil wells. Background Art

[0002] In energy fields such as petroleum, natural gas, chemical industry, and energy, the flow measurement of gas-liquid two-phase flow is of great significance for the optimization of production processes, the rational allocation of resources, and the improvement of economic benefits. With the continuous progress of oil and gas field development technologies, the development of low-gas-content oil wells is increasing day by day, posing higher requirements for the accurate measurement of multiphase flow in low-gas-content oil wells. Traditional flow measurement technologies mostly rely on single flow meters or simple separation devices. When faced with complex gas-liquid two-phase flows, these methods are often difficult to accurately measure and have great limitations under low-gas-content 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 an efficient, accurate, and multiphase flow metering device suitable for low-gas-content oil wells has become an urgent problem 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 the complete separation method, the partial separation method, and the non-separation method. The partial separation method is a commonly used technology in the measurement of gas-liquid two-phase flow. Its core idea is to partially separate the two-phase flow through specific devices or methods without completely separating the gas and liquid phases, so as to realize the separate measurement of the gas-phase and liquid-phase flows. This method is between the complete separation method and the non-separation method, aiming to simplify the device structure, reduce costs and complexity while ensuring a certain measurement accuracy.

[0004] In the prior art, there are certain defects in the multiphase flow measurement of low-gas-content oil wells. The gas phase has formed complex flow patterns such as bubble flow, slug flow, and plug flow in the pipeline. Since the gas phase and the liquid phase cannot be effectively distinguished, existing flow meters are easily affected by factors such as flow pattern changes and flow velocity fluctuations during the measurement process, resulting in large measurement errors and inaccurate measurement results, making it difficult to meet the requirements of low-gas-content oil wells for flow measurement accuracy. Although traditional separators can achieve gas-liquid separation to a certain extent, their separation efficiency is low, and they have strict requirements for the flow velocity and flow direction of the fluid. Under low-gas-content conditions, the separation effect of the gas phase and the liquid phase is not ideal, and accurate fluid phase information cannot be provided for subsequent flow measurement, thus limiting the accuracy and reliability of flow measurement. Summary of the Invention

[0005] In view of this, one of the purposes of the present invention is to provide a multiphase flow metering device for low-gas-content oil wells to solve the technical problems of inaccurate measurement of gas-liquid two-phase flow and low separation efficiency in the prior art.

[0006] To achieve one of the above purposes, the present invention provides a multiphase flow metering device for low gas-containing oil wells, adopting the following technical solutions:

[0007] A multiphase flow metering device for low gas-containing oil wells includes:

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

[0009] By adopting the above technical solutions, the efficient and accurate measurement of the multiphase flow in low gas-containing oil wells is realized. The first cyclone can effectively induce spiral annular flow and achieve the preliminary separation of gas-liquid two phases, providing a good basis for subsequent flow measurement. The internal cone flowmeter is arranged downstream of the first cyclone and can accurately measure the mainstream liquid phase flow rate after preliminary separation. The shunt pipe passes through the center of the internal 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 respectively communicated with the upper and lower parts of the metering separator, and corresponding gas flowmeter and liquid flowmeter are installed, which can respectively measure the gas phase and liquid phase flow rates, so as to realize the accurate measurement of the multiphase flow in low gas-containing oil wells.

[0010] Further, upstream static pressure tapping pipes and downstream static pressure tapping pipes are arranged on both sides of the internal cone flowmeter in the pipeline to be measured, and a differential pressure transmitter is arranged between the upstream static pressure tapping pipe and the downstream static pressure tapping pipe, and the differential pressure signal generated before and after the internal cone flowmeter is measured through the differential pressure transmitter.

[0011] By adopting the above technical solutions, the differential pressure signal before and after the internal cone flowmeter can be measured more accurately, so as to improve the measurement accuracy of the mainstream liquid phase flow rate.

[0012] Further, a second cyclone is arranged in the pipeline at the outlet end of the shunt pipe, and a separation narrow slit is arranged on the inner wall at the outlet end of the shunt pipe, and the gas phase and a small amount of liquid phase are separated again through the centrifugal force of the second cyclone.

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

[0014] Furthermore, the upper part of the metering separator is a gas phase space, and the lower part is a liquid accumulation cavity. The gas flowmeter measures the gas flow in the gas phase space.

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

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

[0017] By adopting the above technical solution, 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] Furthermore, multiple separation narrow slits are arranged axially at intervals on the inner wall of the outlet end of the shunt pipe. A small amount of liquid phase is thrown towards the separation narrow slits by the centrifugal force of the second cyclone.

[0019] By adopting the above technical solution, 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] Furthermore, the shunt pipe and the inner cone flowmeter are in an embedded structure. After preliminary separation, the main stream liquid phase enters the inner cone flowmeter.

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

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

[0023] A multiphase flow metering device for low-gas-content oil wells according to the present invention can effectively improve the gas-liquid separation efficiency through two-stage separation of the first cyclone and the second cyclone, ensure the complete separation of the gas phase and the liquid phase, and thus improve the accuracy of flow measurement; the combination of the inner cone flowmeter and the differential pressure transmitter can accurately measure the mainstream liquid phase flow, further improving the accuracy of flow measurement; the gas flowmeter and the liquid flowmeter can respectively measure the gas phase and liquid phase flows, realizing the accurate measurement of the multiphase flow in low-gas-content oil wells; the embedded structure of the shunt pipe and the inner cone flowmeter optimizes the spatial layout of the device, improving the compactness and measurement efficiency of the device; the design of 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; by measuring the differential pressure signal before and after the inner cone flowmeter, the mainstream liquid phase flow can be measured more accurately, further improving the accuracy of flow measurement.

[0024] The second object of the present invention is to provide a multiphase flow metering method for low-gas-content oil wells to solve the technical problems of large measurement errors and difficulty in meeting the flow measurement accuracy requirements of low-gas-content oil wells in the prior art.

[0025] To achieve the second object above, the present invention provides a multiphase flow metering method for low-gas-content oil wells, adopting the following technical solutions:

[0026] A multiphase flow metering method for low-gas-content oil wells includes the following steps:

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

[0028] S2. The separated annular liquid column flows through the inner cone flowmeter, and the static pressure difference between its upstream and downstream is measured by the differential pressure transmitter. Combining with the fluid density and the formula to calculate the mainstream liquid phase flow M l .

[0029] S3. The central gas and a small amount of residual liquid droplets are extracted through the shunt pipe and induced to rotate at high speed by the second cyclone, generating centrifugal force. A small amount of the liquid phase is thrown towards the wall of the shunt pipe to form a liquid film and converges at the lower part of the metering separator through the separation narrow slit. The gas phase continues to flow along the central axis, realizing the secondary separation of the gas-liquid phase.

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

[0031] S5. The total liquid phase flow M LCalculated by the formula, the separated gas and liquid phases are remixed downstream of the measurement point to complete the return flow.

[0032] By adopting the above technical solution, efficient and accurate measurement of multiphase flow in low-gas-content oil wells is achieved. Through the two-stage separation of the first cyclone and the second cyclone, the gas-liquid separation efficiency can be effectively improved to ensure the complete separation of the gas phase and the liquid phase. The combination of the inner cone flowmeter and the differential pressure transmitter can accurately measure the mainstream liquid phase flow, and the gas flowmeter and the liquid flowmeter can measure the gas phase and the liquid phase flow respectively, so as to achieve accurate measurement of multiphase flow in low-gas-content oil wells.

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

[0034]

[0035] By adopting the above technical solution, the mainstream liquid phase flow rate can be calculated more accurately, and the accuracy of flow measurement can be further improved.

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

[0037] M L =M l +m l

[0038] By adopting the above technical solution, the total liquid phase flow rate can be calculated more accurately, and the accuracy of flow measurement can be further improved.

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

[0040] The multiphase flow measurement method for low-gas-content oil wells described in the present invention has the same beneficial effects as those of the prior art and the first object, and will not be elaborated herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0042] In the drawings:

[0043] Figure 1 is the overall structure diagram of the multiphase flow measurement device for low-gas-content oil wells described in Embodiment 1 of the present invention;

[0044] Figure 2 is the schematic structural diagram of the first cyclone described in Embodiment 1 of the present invention;

[0045] Figure 3Schematic diagram of the shunt pipe embedded in the internal cone flowmeter according to Embodiment 1 of the present invention;

[0046] Figure 4 Schematic diagram of the second cyclone and the separation narrow slit part according to Embodiment 1 of the present invention.

[0047] Explanation of reference numerals:

[0048] 1. Pipeline to be measured; 2. First cyclone; 3. Shunt pipe; 4. Differential pressure transmitter; 5. Internal cone flowmeter; 6. Second cyclone; 7. Gas flowmeter; 8. Liquid flowmeter; 9. Swirl vane; 10. Main rod; 11. Separation narrow slit; 12. Liquid accumulation chamber; 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 implementation manners

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

[0050] In the description of the present invention, it should be noted that if terms indicating orientation or positional relationship such as "upper", "lower", "inner", "back", etc. appear, they are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention. In addition, if terms such as "first" and "second" appear, they are also only for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0051] In addition, in the description of the present invention, unless otherwise clearly defined, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected, or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood in combination with specific situations.

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

[0053] Embodiment 1

[0054] This embodiment relates to a multiphase flow metering device for low gas-containing oil wells. In terms of the overall structure, as Figure 1 shown, it includes a pipeline 1 to be measured, a first cyclone 2, an internal cone flowmeter 5, a shunt pipe 3, a metering separator 17, a gas metering pipe 13, and a liquid metering pipe 14.

[0055] Among them, the first cyclone 2 is arranged in the pipeline 1 to be measured, used to induce spiral annular flow and preliminarily separate the gas-liquid two-phase. The internal cone flowmeter 5 is arranged downstream of the first cyclone 2, used to measure the main liquid phase flow rate after preliminary separation. The shunt pipe 3 passes through the center of the internal cone flowmeter 5. The inlet end of the shunt pipe 3 is located at the center of the pipeline 1 to be measured, used to collect the preliminarily separated gas phase and a small amount of liquid phase. The metering separator 17 is installed at the internal cone flowmeter 5 of the pipeline 1 to be measured. The outlet end of the shunt pipe 3 is communicated with the metering separator 17. The inlet end of the gas metering pipe 13 is communicated with the upper part of the metering separator 17, and the outlet end is communicated with the downstream of the pipeline 1 to be measured. A gas 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 communicated with the lower part of the metering separator 17, and the outlet end is communicated with the downstream of the pipeline 1 to be measured. A liquid 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 the pipeline for the oil well to discharge fluid. The fluid flow in the pipeline 1 to be measured serves as the driving force, which is essentially the differential pressure between the front and the back. The first cyclone 2 is driven, and after the fluid passes through the first cyclone 2, preliminary separation is carried out, thus forming a mixture of the main liquid phase, the gas phase and a small amount of liquid phase. The main liquid phase enters the internal cone flowmeter 5 to measure the main liquid phase flow rate. The gas phase and a 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 the gas flowmeter 7 measures the gas flow rate. The small amount of liquid phase enters the liquid metering pipe 14 to measure the small amount of liquid phase flow rate. The small amount of liquid phase flow rate is added to the main liquid phase flow rate to obtain the total liquid phase flow direction.

[0057] Based on the above overall introduction, an exemplary structure of the multiphase flow metering device for low gas-content oil wells in this embodiment is as follows Figure 1 As shown, upstream static pressure tapping pipes 15 and downstream static pressure tapping pipes 16 are arranged on both sides of the internal cone flowmeter 5 in the pipeline 1 to be measured. 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 generated before and after the internal cone flowmeter 5 through the differential pressure transmitter.

[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. Specifically, the upstream static pressure tapping pipe 15 is located at the liquid inlet of the internal cone flowmeter 5, and the downstream static pressure tapping pipe 16 is located at the liquid outlet of the internal cone flowmeter 5. The differential pressure transmitter 4 connects the upstream static pressure tapping pipe 15 and the downstream static pressure tapping pipe 16. Such a setting can measure the throttling differential pressure and is convenient for calculating the main liquid phase flow rate.

[0059] Preferably, as Figure 4As shown in the figure, in this embodiment, a second cyclone 6 is provided in the outlet pipe of the shunt pipe 3. The driving forces of the second cyclone 6 and the first cyclone 2 are the same, both being the kinetic energy of the fluid itself, which is common knowledge in fluid mechanics. A separation narrow slit 11 is provided on the inner wall of the outlet end of the shunt pipe 3. 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. 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 slit 11 under the action of centrifugal force and then drops from the separation narrow slit 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 a setting ensures that separation can be carried out again and the measurement accuracy is improved.

[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 flowmeter 7 measures the gas flow rate 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, at the gas phase space 18. The gas inside enters the gas metering pipe 13, and the gas flow rate is directly measured when passing through the gas flowmeter 7. The liquid metering pipe 14 is installed in the lower part of the metering separator 17, that is, at the liquid storage chamber. The liquid phase inside enters the liquid metering pipe 14, and the liquid flow rate at this place is directly measured when passing through the liquid flowmeter 8.

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

[0063] Specifically, when the fluid passes through the swirl blade 9, through the high-speed rotation of the swirl blade 9, a spiral annular flow is induced. At this time, the gas phase is located at the center of the pipeline to be measured 1, forming a central gas, and the liquid phase is located at the periphery of the pipeline to be measured 1, forming an annular liquid column. Such a setting completes the preliminary separation. The inner edge and outer edge of the swirl blade 9 are attached to the outer wall of the main rod 10 and the inner wall of the pipeline to be measured 1, respectively, and the purpose is to ensure the quality of the preliminary separation. The swirl blade 9 of the second cyclone 6 is attached to the inner wall of the shunt pipe 3, and its purpose is the same as that of the first cyclone 2.

[0064] As a preferred embodiment, as Figure 3 and Figure 4 shown, in this embodiment, multiple separation narrow slits 11 are arranged axially at intervals on the inner wall of the outlet end of the shunt pipe 3. Under the centrifugal force of the second cyclone 6, a small amount of liquid phase is thrown towards the separation narrow slits 11; the shunt pipe 3 and the inner cone flowmeter 5 are in an embedded structure. After preliminary separation, the main stream liquid phase enters the inner cone flowmeter 5.

[0065] It should be noted that the purpose of adopting multiple separated narrow slits 11 arranged at intervals is to ensure that a small amount of liquid phase thrown out can gather and fall into the liquid accumulation cavity 12, thereby improving the separation effect and preventing a small amount of liquid phase from being dispersed into the gas phase. The embedded structure is that the shunt pipe 3 passes through the center of the inner cone flowmeter 5. They are independent in structure but cooperate in function. The inner cone flowmeter 5 is a hollow structure, which not only serves as the support of the shunt pipe 3 but also guides the separation of the gas phase and the liquid phase. The inner cone flowmeter 5 is a conical structure similar to the inner cone flowmeter in the prior art, except that the shunt pipe 3 penetrates from the inlet end and passes through the pipe wall behind the conical body.

[0066] The multiphase flow metering device for low gas-containing oil wells in this embodiment solves the technical problems of low separation efficiency, large metering error, and complex structure in the traditional technology through the first cyclone 2 and the differential pressure transmitter 4, greatly reducing the pressure loss of the traditional separation device and enabling accurate metering of low gas-containing gas-liquid two-phase flow under pipeline conditions; through the setting of the first cyclone 2 and the second cyclone 6, a two-stage cyclone separation structure is ensured to achieve efficient stratification and accurate metering of the gas-liquid two-phase, completely eliminating liquid phase residues, and finally the single-phase measurement is completed by the independent gas phase and liquid phase flowmeters 8; through the integrated design of the hollow design of the shunt pipe 3 and the swirl vane 9, the structure is made compact. At the same time, through the re-separation of the separation narrow slit 11, the capture efficiency of micro liquid droplets of a small amount of liquid phase is enhanced, improving the re-separation effect.

[0067] Embodiment Two

[0068] This embodiment relates to a multiphase flow metering method for low gas-containing oil wells, which includes the following steps:

[0069] S1. After the low gas-containing fluid enters the pipeline to be measured 1, it is induced to rotate at high speed by the first cyclone 2 to generate centrifugal force. The liquid phase with a larger density is thrown towards the pipe wall to form an annular liquid column, and the gas phase with a smaller density gathers at the center of the pipeline to form a central gas.

[0070] S2. The separated annular liquid column flows through the inner cone flowmeter, and the differential pressure transmitter 4 measures the static pressure difference between its upstream and downstream, and combines with the fluid density and the formula to calculate the mainstream liquid phase flow rate M l 。

[0071] S3. The central gas and a small amount of residual liquid droplets are extracted through the shunt pipe 3 and are induced to rotate at high speed by the second cyclone 6 to generate centrifugal force. The small amount of liquid phase is thrown towards the pipe wall of the shunt pipe 3 to form a liquid film and converges to the lower part of the metering separator 17 through the separation narrow slit 11, while the gas phase continues to flow along the central axis, realizing the re-separation of the gas-liquid phase.

[0072] S4. The pure gas phase flow rate m after re-separation gDirectly measured by the gas flowmeter 7; after a small amount of liquid phase is collected by the metering separator 17, the liquid phase flowmeter 8 measures the liquid phase flow rate m after re-separation. l .

[0073] S5. Total liquid phase flow rate M L Calculated by the formula, the separated gas-liquid two-phase is remixed downstream of the measurement point to complete the return flow.

[0074] Preferably, in this embodiment, the formula in S2 is:

[0075]

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

[0077] Preferably, in this 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 rate; M l is the mainstream liquid phase flow rate; m l is the small amount of liquid phase flow rate. Specifically, the small amount of liquid phase flow rate is directly measured by the liquid phase flowmeter, and then added to the above-calculated mainstream liquid phase flow rate to obtain the total liquid phase flow rate.

[0080] In this embodiment, the multiphase flow measurement method for low gas-content oil wells directly measures by the differential pressure method through the formula in S2. Through primary separation and secondary separation, the liquid phase residue is completely eliminated, and finally, the single-phase measurement is completed by independent gas and liquid flowmeters. The total liquid phase flow rate is measured by "measuring the main liquid flow + secondary capture of residual liquid", constructing an orderly "separation-measurement-return flow" closed-loop system.

[0081] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A multiphase flow metering device for low-gas wells, characterized in that, Comprising: A pipeline to be measured (1); A first cyclone (2) arranged inside the pipeline to be measured (1) for inducing a spiral annular flow to preliminarily separate the gas-liquid two-phase; An internal cone flowmeter (5) arranged downstream of the first cyclone (2) for measuring the mainstream liquid phase flow rate after preliminary separation; A shunt pipe (3) passing through the center of the internal cone flowmeter (5), the inlet end of the shunt pipe (3) being located at the center of the pipeline to be measured (1) for collecting the preliminarily separated gas phase and a small amount of liquid phase; A metering separator (17) installed at the internal cone flowmeter (5) of the pipeline to be measured (1), the outlet end of the shunt pipe (3) being communicated with the metering separator (17); A gas metering pipe (13) with its inlet end communicated with the upper part of the metering separator (17) and its outlet end communicated with the downstream of the pipeline to be measured (1), a gas flowmeter (7) being installed between the gas metering pipe (13) and the downstream of the pipeline to be measured (1); A liquid metering pipe (14) with its inlet end communicated with the lower part of the metering separator (17) and its outlet end communicated with the downstream of the pipeline to be measured (1), a liquid flowmeter (8) being installed between the liquid metering pipe (14) and the downstream of the pipeline to be measured (1).

2. The multiphase flow metering device for low gas-containing oil wells according to claim 1, wherein: Upstream static pressure tapping pipes (15) and downstream static pressure tapping pipes (16) are arranged on both sides of the internal cone flowmeter (5) of the pipeline to be measured (1), 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 signal generated before and after the internal cone flowmeter (5) through the differential pressure transmitter.

3. The multiphase flow metering device for low gas-containing oil wells according to claim 1, wherein: A second cyclone (6) is arranged inside the pipeline at the outlet end of the shunt pipe (3), and a separation narrow slit (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 through the centrifugal force of the second cyclone (6).

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

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

6. The multiphase flow metering device for low gas-containing oil wells according to claim 3, wherein: Multiple separation narrow slits (11) are arranged axially at intervals on the inner wall of the outlet end of the shunt pipe (3), and a small amount of liquid phase is thrown towards the separation narrow slit (11) through the centrifugal force of the second cyclone (6).

7. The multiphase flow metering device for low gas-content oil wells according to claim 1, wherein: The shunt pipe (3) and the internal cone flowmeter (5) are in an embedded structure. After preliminary separation, the main liquid phase enters the internal cone flowmeter (5).

8. A multiphase flow metering method for low gas - containing oil wells, characterized in that, including the following steps: S1. After the fluid with low gas content enters the pipeline to be measured (1), it is induced to rotate at high speed by the first cyclone (2) to generate centrifugal force. The liquid phase with a larger density is thrown towards the pipe wall to form an annular liquid column, and the gas phase with a smaller density gathers at 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 static pressure difference between its upstream and downstream. Combining the fluid density and the formula, the mainstream liquid phase flow rate M is calculated. l . S3. The central gas and a small amount of residual liquid droplets are extracted through the shunt pipe (3) and are induced to rotate at high speed by the second cyclone (6) to generate centrifugal force. A small amount of the liquid phase is thrown towards the wall of the shunt pipe (3) to form a liquid film and converges at the lower part of the metering separator (17) through the separation narrow slit (11), while the gas phase continues to flow along the main rod, realizing the secondary separation of the gas-liquid phase. S4. The pure gas flow rate m after re-separation g is directly measured by the gas flowmeter (7); a small amount of liquid phase is collected by the metering separator (17) and the re-separated liquid phase flow rate m is measured by the liquid phase flowmeter (8). l . S5. Total liquid flow rate M L It is calculated by the formula. The separated gas-liquid two-phase is remixed downstream of the measurement to complete the return flow.

9. The multiphase flow metering method for low-gas-content oil wells according to claim 8, wherein: The calculation formula for the main liquid phase flow rate in S2 is as follows: Where: M l is the mainstream liquid phase flow rate, unit kg / s; C is the discharge coefficient; ε is the expansibility coefficient; β is the throttling ratio; D is the inner diameter of the pipeline, unit m; Δp is the throttling pressure difference before and after the inner cone flowmeter (5), unit Pa; ρ L is the density.

10. The multiphase flow metering method for low-gas-content oil wells according to claim 8, characterized in that: The calculation formula for the total liquid phase flow rate in S5 is as follows: M L = M l + m l Where: M L is the total liquid flow rate; M l is the main liquid flow rate; m l is a small liquid-phase flow rate.

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