A system and method for jointly eliminating severe slug flow by a gas-liquid separator and a throttle valve

Abstract

The invention discloses a system and method for jointly eliminating severe slug flow by using a gas-liquid separator and a throttle valve, belonging to the technical field of multiphase flow control in petroleum engineering. A differential pressure sensor and a first pressure sensor are arranged at the top of the riser pipe, the throttle valve is arranged at the outlet end of the riser pipe, a second pressure sensor is arranged at the inlet of the high-pressure gas-liquid separator, an exhaust port control valve is arranged at the exhaust port at the top of the high-pressure gas-liquid separator, and a liquid discharge port control valve is arranged at the liquid discharge port at the bottom of the high-pressure gas-liquid separator; the differential pressure sensor, the first pressure sensor, the throttle valve, the second pressure sensor, the exhaust port control valve and the liquid discharge port control valve are respectively connected to an industrial control computer. The invention can complete the control and elimination of severe slug flow by adjusting the opening of the throttle valve and the pressure of the high-pressure gas-liquid separator, can effectively reduce the system pressure while eliminating the severe slug flow in the gathering-riser system, improve the oil and gas production, and enhance the real-time performance of the control.

Description

Technical Field

[0001] The present invention belongs to the technical field of multiphase flow control in petroleum engineering, and particularly relates to a system and method for jointly eliminating severe slug flow by a gas-liquid separator and a throttle valve. Background Art

[0002] Deep-sea oil and gas resources are extremely rich, and the development of deep-sea oil and gas resources currently faces unprecedented difficulties and huge challenges. The development of deep-sea oil and gas is mainly characterized by long gathering and transportation pipelines, complex pipeline structures, and drastic changes in the temperature of the oil and gas gathering and transportation environment. Due to the special composition structure of the gathering and transportation - riser system, an unstable flow phenomenon in which the pressure difference changes periodically by a large margin and gas and liquid flow out of the riser alternately often occurs in the pipeline when the gas-liquid flow rate is relatively low, which is called severe slug flow. When severe slug flow occurs, there are often long liquid slugs several times the height of the riser in the pipeline, resulting in adverse effects such as separator out-of-flow and overflow, pipeline vibration caused by drastic pressure difference fluctuations, and oilfield production reduction. Therefore, studying the flow characteristics of severe slug flow and its on-line monitoring technology under the conditions of long-distance and complex pipeline structures is an important means to ensure the safe and stable production of the deep-sea oil and gas development system, and provides a strong technical guarantee for the development process of China's deep-sea oil and gas resources.

[0003] Throttling at the top of the riser is a commonly used method to eliminate severe slug flow. This method installs a throttle valve at the top of the riser and appropriately reduces the opening of the throttle valve according to the actual flow situation to control the flow process, so as to achieve the purpose of eliminating severe slug flow. This method is easy to operate and has a low cost, so it is a relatively widely used control method at present. However, the throttling method will cause an increase in back pressure, resulting in adverse effects such as oilfield production reduction.

[0004] The automatic control method refers to using the PID regulator, which is the most widely used in industrial fields. By setting appropriate input parameters and control parameters, when the deviation between the measured actual parameter and the set parameter is detected, specific correction parameters are output to the corresponding control system to control severe slug flow. This method has strong applicability, simple operation, and stable control effect. The technical difficulty lies in that the tuning process of the controller parameters is sometimes complex. Chinese Invention Patent No. 200510042681.9, with the invention title "Dynamic control method of valve throttling for eliminating severe slug flow" (publication date: November 23, 2005), discloses a dynamic throttling control method for eliminating severe slug flow. This method stabilizes the pressure at the bottom of the riser within the desired range by adjusting the opening of the throttle valve at the top of the riser. Chinese Invention Patent No. 201110216748.1, with the invention title "Real-time throttling device and method for eliminating severe slug flow in gathering-riser system" (publication date: April 1, 2012), discloses a real-time throttling device and method for eliminating severe slug flow in gathering-riser system. This method uses the downstream pressure of the wellhead platform and the upstream pressure of the FPSO as the adjustment basis for the throttle valve, and suppresses and eliminates severe slug flow through the PID method.

[0005] Currently, most of the control and elimination processes for severe slug flow adopt a single method: throttling at the top of the riser or stabilizing the pressure of the gas-liquid separator. There is less research on the combined control of two or more devices to eliminate severe slug flow, ignoring the possible synergistic effects between control devices. In the current automatic control process, it is necessary to first observe the pressure signal with the naked eye and determine that severe slug flow has occurred before control can be carried out. However, severe slug flow generally has a long cycle, resulting in a significant lag in the start time of control compared to the generation time of severe slug flow, causing untimely control, ultimately affecting production efficiency, and even affecting pipeline safety. Summary of the Invention

[0006] To solve the above problems, the present invention provides a system and method for jointly eliminating severe slug flow by a gas-liquid separator and a throttle valve, which can complete the control and elimination of severe slug flow by adjusting the throttle valve opening and the pressure of the high-pressure gas-liquid separator. While eliminating severe slug flow in the gathering-riser system, it can effectively reduce the system pressure, increase the oil and gas production, and enhance the real-time performance of control.

[0007] The present invention is realized through the following technical solutions:

[0008] The present invention discloses an on-line identification method for two-phase flow patterns in gathering risers, including a differential pressure sensor, an industrial control computer, a first pressure sensor, a throttle valve, a second pressure sensor, an exhaust port control valve, and a drain port control valve;

[0009] The differential pressure sensor and the first pressure sensor are arranged at the top of the riser, the throttle valve is arranged at the outlet end of the riser, the second pressure sensor is arranged at the inlet of the high-pressure gas-liquid separator, the exhaust port control valve is arranged at the exhaust port at the top of the high-pressure gas-liquid separator, and the drain port control valve is arranged at the drain port at the bottom of the high-pressure gas-liquid separator; the differential pressure sensor, the first pressure sensor, the throttle valve, the second pressure sensor, the exhaust port control valve and the drain port control valve are respectively connected to the industrial control computer.

[0010] Preferably, both the throttle valve and the high-pressure gas-liquid separator are connected in series in the pipeline through connecting flanges, and the inner diameter of the throttle valve is equal to the inner diameter of the pipeline where it is located.

[0011] Preferably, the single-action amplitude of the throttle valve is 2% - 10%.

[0012] Preferably, the opening range of the throttle valve is ±15% of the opening set value.

[0013] Preferably, the industrial control computer is built-in with a PID controller, and the PID controller is connected to the throttle valve.

[0014] Preferably, the differential pressure sensor, the first pressure sensor, the throttle valve, the second pressure sensor, the exhaust port control valve and the drain port control valve are communicatively connected to the industrial control computer through a shielded cable.

[0015] The present invention discloses a method for eliminating severe slug flow by using the above system of combining a gas-liquid separator and a throttle valve to eliminate severe slug flow, including:

[0016] The differential pressure sensor collects the local differential pressure signal at the top of the riser, the first pressure sensor collects the pressure signal at the top of the riser, the second pressure sensor collects the pressure signal at the inlet of the high-pressure gas-liquid separator, and the above signals are all transmitted to the industrial control computer. Different signal parameter values corresponding to different flow patterns are preset in the industrial control computer. The flow pattern in the gathering-riser system is identified according to the collected signal parameters. When the flow pattern is severe slug flow, the opening of the throttle valve is controlled to adjust the pressure at the top of the riser; at the same time, the opening of the exhaust port control valve and the drain port control valve is controlled to adjust the pressure of the high-pressure gas-liquid separator, so as to achieve the elimination of severe slug flow.

[0017] Preferably, specifically:

[0018] The industrial control computer includes a signal acquisition module, a flow pattern identification module, and a slug control module. After the acquired signals are preprocessed by the signal acquisition module, the flow pattern is identified by the flow pattern identification module. When the identification result is severe slug flow, the slug control model is called to calculate the set value of the top pressure of the riser required to eliminate the severe slug flow, and the change range of the throttle valve opening is deduced by using the set value of the top pressure of the riser, and the set value of the pressure of the high-pressure gas-liquid separator is given within the allowable pressure range. The PID controller is used to control the pressure of the high-pressure gas-liquid separator. The drain port control valve is used to control the stability of the liquid level of the high-pressure gas-liquid separator, and the exhaust port control valve is used to control the stability of the pressure of the high-pressure gas-liquid separator. The set value of the top pressure of the riser is compared with the measured value of the top pressure of the riser obtained by actual measurement, and the obtained difference is subjected to PID logic operation through the PID controller to obtain the valve opening of the corresponding throttle valve. After the valve opening changes, it will affect the flow state. When the difference approaches 0, the flow reaches a stable state and the severe slug flow phenomenon is eliminated.

[0019] Further preferably, the valve opening of the throttle valve is calculated by the following valve pressure drop formula:

[0020]

[0021] Where DP is the pressure drop across the throttle valve; C is the throttle valve coefficient, which is related to the valve characteristics;

[0022] U MIX is the gas-liquid mixed flow velocity, which is calculated by the following formula:

[0023]

[0024] Where a G is the gas holdup at the throttle valve, ρ G and ρ L are the gas and liquid phase densities respectively, U G and U L are the gas and liquid phase flow velocities respectively;

[0025] The PID control process is calculated according to the following formula:

[0026]

[0027] Where z(t) is the valve opening adjustment value; e(t) is the output signal deviation value, and e(t) = measured value of the top pressure of the riser - set value of the top pressure of the riser; K P is the proportional gain coefficient of the controller; T I is the integral time constant of the controller; T D is the differential time constant of the PID controller.

[0028] Further preferably, when the output signal deviation value > 20% of the measured value of the riser top pressure, set the proportional gain coefficient K of the first controller P1 and the integral time constant T of the first controller I1 ; when the output signal deviation value < 20% of the measured value of the riser top pressure, set the proportional gain coefficient K of the second controller P2 and the integral time constant T of the second controller I2 ; where, K P1 = 10K P2 and T I1 = 0.2T I2 .

[0029] Compared with the prior art, the present invention has the following beneficial technical effects:

[0030] The system for jointly eliminating severe slug flow by the gas-liquid separator and the throttle valve disclosed by the present invention collects the local pressure difference signal at the top of the riser through a differential pressure sensor, the pressure signal at the top of the riser through a first pressure sensor, and the pressure signal at the inlet of the high-pressure gas-liquid separator through a second pressure sensor. After being processed by an industrial control computer, the opening of the throttle valve is controlled to adjust the pressure at the top of the riser; at the same time, the opening of the exhaust port control valve and the drain port control valve is controlled to adjust the pressure of the high-pressure gas-liquid separator, and severe slug flow in the system is eliminated in time when it occurs. Among them, the separator is responsible for stabilizing the system pressure, and the throttle valve is responsible for controlling severe slug flow. Compared with the control methods of separately using throttling or separator pressure, it can effectively reduce the system pressure, increase the oil and gas production, and enhance the real-time performance of control while eliminating severe slug flow in the gathering-riser system.

[0031] Furthermore, the throttle valve is connected in series in the pipeline through a connecting flange, and the inner diameter of the throttle valve is equal to the inner diameter of the pipeline where it is located, ensuring that the multi-phase fluid flow state is not affected when the valve is fully open.

[0032] Furthermore, the single action amplitude of the throttle valve is 2% - 10%, and the opening range is ±15% of the opening set value, avoiding too frequent valve action and too large action amplitude.

[0033] Furthermore, the industrial control computer is built-in with a PID controller, and the PID controller is connected to the throttle valve, with a high degree of automation.

[0034] The method for eliminating severe slug flow by using the system of combining a gas-liquid separator and a throttle valve disclosed in the present invention, which adopts the method of organically combining automatic control and flow pattern recognition technology, can realize rapid flow pattern recognition and control process at the initial stage of the generation of severe slug flow, solves the problem of control lag caused by using full-cycle signal recognition, and greatly improves the real-time performance of control. By using the self-established slug control model without manually setting parameter values, it can effectively improve the degree of automation of control, reduce the system pressure at the same time, and increase the oil and gas production. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic diagram of the overall structure of the system of the present invention;

[0036] Figure 2 It is a schematic diagram of the control principle of the system of the present invention;

[0037] Figure 3 It is the effect diagram of controlling and eliminating severe slug flow of the present invention;

[0038] Figure 4 It is a schematic diagram of the increase in the opening degree of the throttle valve of the present invention;

[0039] Figure 5 It is a schematic diagram of the reduction amplitude of the bottom pressure of the riser pipe of the present invention;

[0040] Figure 6 It is a schematic diagram of the reduction amplitude of the stable pressure difference of the riser pipe of the present invention.

[0041] In the figure, 1 is a differential pressure sensor, 2 is an industrial control computer, 3 is a first pressure sensor, 4 is a throttle valve, 5 is a second pressure sensor, 6 is a high-pressure gas-liquid separator, 7 is an exhaust port control valve, and 8 is a drain port control valve. DETAILED DESCRIPTION OF THE INVENTION

[0042] The following further describes the present invention in detail with reference to the drawings, and the content is an explanation rather than a limitation of the present invention:

[0043] As Figure 1 , the system of combining a gas-liquid separator and a throttle valve for eliminating severe slug flow of the present invention includes a differential pressure sensor 1, an industrial control computer 2, a first pressure sensor 3, a throttle valve 4, a second pressure sensor 5, an exhaust port control valve 7, and a drain port control valve 8.

[0044] The differential pressure sensor 1 and the first pressure sensor 3 are arranged at the top of the riser. The throttle valve 4 is arranged at the outlet end of the riser. The second pressure sensor 5 is arranged at the inlet of the high-pressure gas-liquid separator 6. The exhaust port control valve 7 is arranged at the exhaust port at the top of the high-pressure gas-liquid separator 6. The drain port control valve 8 is arranged at the drain port at the bottom of the high-pressure gas-liquid separator 6. The differential pressure sensor 1, the first pressure sensor 3, the throttle valve 4, the second pressure sensor 5, the exhaust port control valve 7 and the drain port control valve 8 are respectively connected to the industrial control computer 2.

[0045] In a preferred embodiment of the present invention, the throttle valve 4 is connected in series in the pipeline through a connecting flange, and the inner diameter of the throttle valve 4 is equal to the inner diameter of the pipeline where it is located.

[0046] In a preferred embodiment of the present invention, the single-action amplitude of the throttle valve 4 is 2% - 10%. At the same time, the opening range of the throttle valve 4 is ±15% of the opening set value.

[0047] In a preferred embodiment of the present invention, the industrial control computer 2 is internally provided with a PID controller, and the PID controller is connected to the throttle valve 4.

[0048] In a preferred embodiment of the present invention, the differential pressure sensor 1, the first pressure sensor 3, the throttle valve 4, the second pressure sensor 5, the exhaust port control valve 7 and the drain port control valve 8 are communicatively connected to the industrial control computer 2 through a shielded cable.

[0049] A method for eliminating severe slug flow by using the above system of combining a gas-liquid separator and a throttle valve includes:

[0050] The differential pressure sensor 1 collects the local differential pressure signal at the top of the riser, the first pressure sensor 3 collects the pressure signal at the top of the riser, and the second pressure sensor 5 collects the pressure signal at the inlet of the high-pressure gas-liquid separator 6. The above signals are all transmitted to the industrial control computer 2. Different signal parameter values corresponding to different flow patterns are preset in the industrial control computer 2. The flow pattern in the gathering-riser system is identified according to the collected signal parameters. When the flow pattern is severe slug flow, the opening of the throttle valve 4 is controlled to adjust the pressure at the top of the riser. At the same time, by controlling the opening of the exhaust port control valve 7 and the drain port control valve 8, the pressure of the high-pressure gas-liquid separator 6 is adjusted to achieve the elimination of severe slug flow.

[0051] Specifically, the industrial control computer 2 includes a signal acquisition module, a flow pattern recognition module, and a slug control module. After the acquired signals are preprocessed by the signal acquisition module, the flow pattern recognition module is used to identify the flow pattern. When the recognition result is severe slug flow, the slug control model is called to calculate the set value of the top pressure of the riser required to eliminate the severe slug flow, and the opening range of the throttle valve 4 is deduced by using the set value of the top pressure of the riser, and the set value of the pressure of the high-pressure gas-liquid separator is given within the allowable pressure range. The PID controller is used to control the pressure of the high-pressure gas-liquid separator. The drain port control valve 8 is used to control the liquid level stability, and the exhaust port control valve 7 is used to control the pressure stability of the high-pressure gas-liquid separator. The set value of the top pressure of the riser is compared with the measured value of the top pressure of the riser obtained by actual measurement, and the obtained difference is subjected to PID logic operation through the PID controller to obtain the valve opening of the corresponding throttle valve 4. After the valve opening changes, it will affect the flow state. When the difference approaches 0, the flow reaches a stable state, and the severe slug flow phenomenon is eliminated.

[0052] The valve opening of the throttle valve 4 is calculated by the following valve pressure drop formula:

[0053]

[0054] where DP is the pressure drop across the throttle valve; C is the throttle valve coefficient, which is related to the valve characteristics;

[0055] U MIX is the gas-liquid mixed flow velocity and is calculated by the following formula:

[0056]

[0057] where a G is the gas holdup at the throttle valve 4, ρ G and ρ L are the gas and liquid phase densities respectively, U G and U L are the gas and liquid phase flow velocities respectively;

[0058] The PID control process is calculated according to the following formula:

[0059]

[0060] where z(t) is the valve opening adjustment value; e(t) is the output signal deviation value, and e(t) = measured value of the top pressure of the riser - set value of the top pressure of the riser; K P is the proportional gain coefficient of the controller; T I is the integral time constant of the controller; T D is the derivative time constant of the PID controller.

[0061] When the actual value of the riser top pressure > 20% of the measured value of the riser top pressure, set the proportional gain coefficient K of the first controller P1 and the integral time constant T of the first controller I1 ; when the actual value of the riser top pressure < 20% of the measured value of the riser top pressure, set the proportional gain coefficient K of the second controller P1 and the integral time constant T of the second controller I1 ; where, K P1 = 10K P2 , T I1 = 0.2T I2 .

[0062] The following uses a specific embodiment to further explain and illustrate the present invention:

[0063] The system of this embodiment, its hardware part mainly includes a differential pressure sensor 1 at the top of the riser, an industrial computer 2, a first pressure sensor 3, a throttle valve 4, a second pressure sensor 5 and a high-pressure gas-liquid separator 6; among them, the differential pressure sensor 1 is located at the top of the riser, the industrial computer 2 is located in the console of the experimental system, and realizes the signal transmission process with the above devices through a shielded cable. The pressure sensors include a first pressure sensor 3 at the top of the riser and a second pressure sensor 5 at the inlet of the high-pressure gas-liquid separator. The throttle valve 4 and the high-pressure gas-liquid separator 6 are both connected in series to the gathering-riser system through flanges. The throttle valve 4 is generally installed at the outlet end of the riser in the gathering-riser system, and its inner diameter is the same as that of the gathering-riser system. When the valve is fully open, it does not affect the flow state of the multiphase fluid. The high-pressure gas-liquid separator 6 is generally located at the end of the gathering-riser system, including a gas-liquid inlet end and two outlet ends. Among them, the exhaust port control valve 7 is located at the top of the high-pressure gas-liquid separator 6 to control the outflow process of the gas phase and stabilize the system pressure. The drain port control valve 8 is located at the bottom of the high-pressure gas-liquid separator 6 to control the discharge process of the liquid phase and adjust the liquid level height.

[0064] The industrial computer 2 is preset with a signal acquisition module, a flow pattern identification module and a slug control module. Among them, the signal acquisition module is written using the LabVIEW program, which is used to receive the real-time signals sent by the sensors in the gathering-riser system and perform preprocessing processes such as digital-to-analog conversion and noise reduction filtering; the flow pattern identification module constructs an identification model using the binary tree algorithm, and through 6-layer wavelet multi-scale decomposition, extracts feature quantities to complete the rapid flow pattern identification process; the slug control module is established according to the experimental database, which is used to calculate control parameters, send control commands to the throttle valve and maintain it at a preset opening.

[0065] See Figure 2The schematic diagram of the control principle shown obtains the local pressure difference at the top of the riser through the differential pressure sensor 1 installed at the top of the riser, and obtains the pressures at the top of the riser and the inlet of the high-pressure gas-liquid separator through the first pressure sensor 3 and the second pressure sensor 5. First, based on signals such as the local pressure difference at the top of the riser, the fast identification process of severe slug flow is carried out using the flow pattern fast identification technology, and other pressure signals can also be used to complete the flow pattern identification process. When the identification result is severe slug flow, the slug control model will be called, and the set value SP of the pressure at the top of the riser required to eliminate the severe slug flow will be calculated according to the identification result and other pressure parameters. TOP , and using this set value SP TOP to inversely deduce the change range of the valve opening, and give the set value SP of the pressure of the gas-liquid separator within the allowable pressure range. S . The PID controller is used to control the pressure of the gas-liquid separator. Among them, the bottom liquid discharge valve is used to control the stability of the liquid level in the separator, and the top exhaust valve is responsible for controlling the stability of the pressure in the separator. Compare the set value SP TOP of the pressure at the top of the riser with the actually measured pressure value P TOP at the top of the riser to obtain the difference ΔP TOP . Perform PID logic operation through the PID controller on ΔP to calculate the corresponding valve opening of the throttle valve 4. After the valve opening changes, it will affect the flow state. When ΔP TOP approaches 0, the flow reaches a stable state, and the severe slug flow phenomenon disappears.

[0066] In this embodiment, the flow pattern identification model is constructed using the binary tree algorithm. Through 6-layer wavelet multi-scale decomposition, characteristic quantities are extracted to complete the fast flow pattern identification process; the establishment of the slug control model is based on the data accumulation of a large number of multiphase flow experiment databases. Using the obtained experimental data, corresponding statistical analysis is completed, and a mathematical relationship of one-to-one correspondence between pressure and flow pattern is established. The set value of the pressure at the top of the riser required for control can be automatically calculated according to the flow pattern identification result, and this pressure is set as the set value of the PID control process, and the set value of the valve opening and its change range are given according to the valve pressure drop formula.

[0067] The PID controller for controlling the throttle valve 4 at the top of the riser adopts two sets of control parameters, and its parameters are determined according to the conventional PID parameter tuning rules. When the deviation between the actual value and the set value of the pressure at the top of the riser is large, that is, e(t)>0.2SP TOP , a larger proportional gain coefficient K P1 and a smaller integral time constant T I1 are used to make the control variable quickly approach the target value; when the deviation between the actual value and the set value of the pressure at the top of the riser is small, that is, e(t)<0.2SP TOP , a smaller proportional gain coefficient K P2 and a larger integral time constant T I2 are used. In this example, KP1 = 10K P2 , T I1 = 0.2T I2 , preventing large fluctuations of the control parameters near the target value and maintaining the system stability. The cyclic sampling period is set to 0.5 s, and the average value of the data within the period is taken as the input value to reduce the signal noise.

[0068] Based on the above system and method, an experiment on eliminating severe slug flow in the gathering and transportation - riser system was carried out. As Figure 3 shown, the diagram of the riser pressure difference fluctuation is given when the reduced gas superficial velocity at the inlet U SG0 = 0.4 m·s -1 , and the reduced liquid superficial velocity U SL = 0.25 m·s -1 . When no control process is applied, the flow in the pipeline is the first type of severe slug flow, the amplitude of the riser pressure difference fluctuation is about 155 KPa, and the slug period is about 150 s. When the control is started using the system and method of the present invention, it can be seen that after about 240 s (1.6 severe slug flow periods), the amplitude of the riser pressure difference fluctuation decreases to about 40 KPa. At this time, the severe slug flow phenomenon in the system has disappeared, and the flow has changed to a stable flow pattern.

[0069] Figure 4 The method of jointly controlling severe slug flow by platform separation and throttling is given, compared with the increase in the throttle valve opening when only using the throttling method to control severe slug flow. The entire experimental range is as follows: the reduced gas superficial velocity at the inlet U SG0 = 0.25 - 16 m·s -1 , and the reduced liquid superficial velocity at the inlet U SL = 0.065 - 0.7 m·s -1 . It can be seen from Figure 4 that in most regions, especially within all operating conditions where severe slug flow occurs, the throttle valve opening has increased to a certain extent. In the case of a relatively large reduced gas superficial velocity and a very small liquid superficial velocity, that is, in the region where the reduced gas superficial velocity is about U SG0 = 1.5 - 3 m·s -1 , the throttle valve opening has decreased to a certain extent. The former is generally a near - stable flow condition, and the latter belongs to an irregular flow region, which is rarely encountered in engineering practice and does not need to be controlled. The increase in the throttle valve opening means a smaller throttle valve pressure drop, a larger fluid flow area, which can effectively reduce the flow resistance, extend the service life of the throttle valve, and increase the oil and gas production to a certain extent.

[0070] Figure 5 and Figure 6When using this system and method for control, it shows the reduction amplitude of the bottom pressure of the riser and the stable pressure difference of the riser compared with manual control of the throttle valve. The experimental range is as follows: the reduced gas-phase velocity at the inlet U SG0 = 0.25 - 7 m·s -1 , and the reduced liquid-phase velocity at the inlet U SL = 0.065 - 0.7 m·s -1 . It can be seen from Figure 5 and Figure 6 that when using this method for control compared with the manual throttling method, it can effectively reduce the bottom pressure of the riser. In the occurrence area of severe slug flow, the average pressure reduction is about 20%, and the maximum is close to 60%. At the same time, the stable pressure difference of the riser also has a significant reduction, with an average reduction of about 10 - 20%. Similar effects can also be achieved for unstable oscillating flow patterns and irregular flow patterns. Therefore, it can be shown that better effects can be obtained when using the system and method of the present invention to control severe slug flow.

[0071] As mentioned above, it is only a part of the embodiments of the present invention. Although some terms are used in the present invention, it does not exclude the possibility of using other terms. These terms are only used for convenient description and explanation of the essence of the present invention, and it is contrary to the spirit of the present invention to interpret them as any additional restrictions. The above is only described by examples to further illustrate the content of the present invention for easier understanding, but it does not mean that the embodiments of the present invention are limited to this. Any technical extension or re-creation based on the present invention is protected by the present invention.

Claims

1. A method for eliminating severe slug flow by using a system combining a gas-liquid separator and a throttle valve to eliminate severe slug flow, characterized in that, The system for jointly eliminating severe slug flow by a gas-liquid separator and a throttle valve includes a differential pressure sensor (1), an industrial control computer (2), a first pressure sensor (3), a throttle valve (4), a second pressure sensor (5), an exhaust port control valve (7) and a drain port control valve (8); The differential pressure sensor (1) and the first pressure sensor (3) are arranged at the top of the riser pipe, the throttle valve (4) is arranged at the outlet end of the riser pipe, the second pressure sensor (5) is arranged at the inlet of the high-pressure gas-liquid separator (6), the exhaust port control valve (7) is arranged at the exhaust port at the top of the high-pressure gas-liquid separator (6), the drain port control valve (8) is arranged at the drain port at the bottom of the high-pressure gas-liquid separator (6). The throttle valve (4) and the high-pressure gas-liquid separator (6) are both connected in series in the pipeline through connecting flanges, and the inner diameter of the throttle valve (4) is equal to the inner diameter of the pipeline where it is located. The single-action amplitude of the throttle valve (4) is 2% - 10%, and the opening range of the throttle valve (4) is ±15% of the opening set value; the differential pressure sensor (1), the first pressure sensor (3), the throttle valve (4), the second pressure sensor (5), the exhaust port control valve (7) and the drain port control valve (8) are all connected to the industrial control computer (2) respectively; The method includes: The differential pressure sensor (1) collects the local differential pressure signal at the top of the riser pipe, the first pressure sensor (3) collects the pressure signal at the top of the riser pipe, and the second pressure sensor (5) collects the pressure signal at the inlet of the high-pressure gas-liquid separator (6). The above signals are all transmitted to the industrial control computer (2). Different signal parameter values corresponding to different flow patterns are preset in the industrial control computer (2). The flow pattern in the gathering-riser pipe system is identified according to the collected signal parameters. When the flow pattern is severe slug flow, the opening of the throttle valve (4) is controlled to adjust the pressure at the top of the riser pipe; at the same time, by controlling the opening of the exhaust port control valve (7) and the drain port control valve (8), the pressure of the high-pressure gas-liquid separator (6) is adjusted to eliminate the severe slug flow; The industrial control computer (2) includes a signal acquisition module, a flow pattern identification module and a slug control module. The collected signals are preprocessed by the signal acquisition module and then the flow pattern is identified by the flow pattern identification module; when the identification result is severe slug flow, the slug control model is called to calculate the set value of the pressure at the top of the riser pipe required to eliminate the severe slug flow, and the change range of the opening of the throttle valve (4) is deduced by using the set value of the pressure at the top of the riser pipe, and the set value of the pressure of the high-pressure gas-liquid separator is given within the allowable pressure range; the PID controller is used to control the pressure of the high-pressure gas-liquid separator. The drain port control valve (8) is used to control the stability of the liquid level of the high-pressure gas-liquid separator, and the exhaust port control valve (7) is used to control the stability of the pressure of the high-pressure gas-liquid separator; the set value of the pressure at the top of the riser pipe is compared with the measured value of the pressure at the top of the riser pipe actually measured, and the obtained difference is subjected to PID logic operation by the PID controller to obtain the corresponding valve opening of the throttle valve (4); after the valve opening changes, it will affect the flow state. When the difference approaches 0, the flow reaches a stable state and the severe slug flow phenomenon is eliminated; The PID control process is calculated according to the following formula: wherein, z(t) is the valve opening adjustment value; e(t) is the output signal deviation value, and there is e(t)= measured value of the top pressure of the riser - set value of the top pressure of the riser; K P is the proportional gain coefficient of the controller; T I is the integral time constant of the controller; T D is the derivative time constant of the PID controller; When the output signal deviation value > 20% of the measured value of the riser top pressure, set the proportional gain coefficient of the first controller K P1 and the integral time constant of the first controller T I1 ; When the output signal deviation value < 20% of the measured value of the riser top pressure, set the proportional gain coefficient of the second controller K P2 and the integral time constant of the second controller T I2 ; Among them, K P1 = 10 K P2 , T I1 = 0.2 T I2 .

2. A method for eliminating severe slug flow by using a system that combines a gas-liquid separator and a throttle valve according to claim 1, characterized in that The valve opening of the throttle valve (4) is calculated by the following valve pressure drop formula: Among them, DP is the pressure drop across the throttle valve; C is the throttle valve coefficient, which is related to the valve characteristics; U MIX is the gas-liquid mixed flow rate, which is calculated by the following formula: wherein a G is the gas holdup at the throttle valve (4) valve, ρ G and ρ L are the gas and liquid phase densities respectively, U G and U L are the gas and liquid phase flow velocities respectively.

3. The method for eliminating severe slug flow by using the system of combining a gas-liquid separator and a throttle valve according to claim 1, characterized in that, An industrial control computer (2) is internally provided with a PID controller, and the PID controller is connected to the throttle valve (4).

4. A method for eliminating severe slug flow by using the system of combining a gas-liquid separator and a throttle valve according to claim 1, characterized in that, The differential pressure sensor (1), the first pressure sensor (3), the throttle valve (4), the second pressure sensor (5), the exhaust port control valve (7) and the drain port control valve (8) are communicatively connected to the industrial control computer (2) through a shielded cable.

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