Control method for throttling valve of gathering and transportation vertical pipe system of offshore oil and gas platform

Abstract

The invention relates to the technical field of flow safety guarantee of offshore oil and gas fields, and discloses a control method for a throttle valve of a gathering and transportation riser system of an offshore oil and gas platform, which comprises the following steps: acquiring the average gas phase flow and the average liquid phase flow of a riser in the gathering and transportation riser system of the offshore oil and gas platform during a serious slug flow period; target pressure drop values of the two ends of the throttling valve of the stand pipe under the standard working condition are obtained; according to the average gas phase flow and the average liquid phase flow, the valve local resistance coefficient when the pressure drop at the two ends of the throttling valve is controlled to reach the target pressure drop value during the serious slug flow period of the vertical pipe is determined, and the valve flow coefficient corresponding to the valve local resistance coefficient is determined; wherein the valve local resistance coefficient is used for indicating the valve resistance when the throttle valve is controlled, and the valve flow coefficient is used for indicating the flow capacity of the throttle valve; and the target opening degree of the throttling valve is determined through the valve flow coefficient, and the throttling valve is controlled to be adjusted to the target opening degree so as to eliminate the serious slug flow.

Description

Technical Field

[0001] The present invention relates to the technical field of flow safety assurance of offshore oil and gas fields, and in particular to a method for controlling a throttle valve of a gathering and transportation riser system of an offshore oil and gas platform. Background Art

[0002] Harmful flow patterns, represented by severe slugging, and their control are key issues in ensuring flow in offshore oil and gas gathering and transportation pipelines. Severe slugging directly leads to flow interruption or overflow in the gas-liquid separator or slug catcher on the downstream platform, which in turn causes unstable gas sources for the gas turbines and frequent switching to diesel power generation, significantly increasing costs and causing more serious environmental pollution. Therefore, this harmful flow pattern must be eliminated or controlled to ensure the safe operation of the entire gathering and transportation system and downstream equipment on the platform. A common method to eliminate severe slugging in offshore oil and gas field gathering and transportation riser systems is to install a throttle valve at the top of the riser and use the throttle valve to control the flow to eliminate severe slugging.

[0003] Current control methods primarily employ incremental proportional-integral-derivative (PID) control. Control targets are set empirically and fail to incorporate the fundamental theory of gas-liquid two-phase flow in pipes. This results in low control efficiency and prolonged adjustment times. Inappropriate control targets can lead to excessive throttling, impacting production, or even instability of the control system. Summary of the Invention

[0004] The purpose of the present invention is to provide a control method for a throttle valve of a gathering and transportation riser system of an offshore oil and gas platform, which can solve the problems of low control efficiency and poor control effect of the PID control method.

[0005] To solve the above technical problems, an embodiment of the present invention provides a method for controlling a throttle valve of a gathering and transportation riser system of an offshore oil and gas platform, comprising the following steps: Obtain the average gas flow rate and average liquid flow rate of the riser in the offshore oil and gas platform's gathering and transportation riser system during severe slugging. Obtain the target pressure drop value at both ends of the throttle valve of the riser under standard working conditions; Determine, based on the average gas phase flow rate and the average liquid phase flow rate, a valve local resistance coefficient when the pressure drop across the throttle valve reaches a target pressure drop value during severe slugging in the riser, and determine a valve flow coefficient corresponding to the valve local resistance coefficient; wherein the valve local resistance coefficient is used to indicate the valve resistance when the throttle valve is controlled, and the valve flow coefficient is used to indicate the flow capacity of the throttle valve; The target opening of the throttle valve is determined by the valve flow coefficient, and the throttle valve is controlled to adjust to the target opening.

[0006] Furthermore, the target pressure drop value is determined by the following formula: ; ; ; ; ; ; Where, is the target pressure drop value, is the gravity pressure drop of the gas-liquid mixture in the riser, is the average gas holdup in the riser, is the air void fraction at the bottom of the riser, is the air void fraction at the top of the riser, is the converted gas velocity at the bottom of the riser, is the converted gas velocity at the top of the riser, is the liquid phase converted flow rate, is the liquid density, is the gas phase density at the bottom of the riser, is the gas phase density at the top of the riser, is the acceleration due to gravity, is the height of the riser, is the gas phase mass flow rate, is the liquid mass flow rate, is the cross-sectional area of ​​the riser.

[0007] Furthermore, the valve local resistance coefficient is determined by the following formula: ; The valve flow coefficient is determined by the following formula: ; Where, is the nominal diameter of the throttle valve.

[0008] Furthermore, the target opening of the throttle valve is determined by the following formula: ; Where, The target opening.

[0009] Furthermore, the gas phase converted flow rate at the bottom of the riser, the gas phase converted flow rate at the top of the riser, and the liquid phase converted flow rate are determined by the following formulas: ; ; ; ; Where, is the gas phase flow rate, is the liquid phase flow rate, is the cross-sectional area of ​​the riser, is the inner diameter of the riser.

[0010] Furthermore, the method of obtaining the average gas flow rate and the average liquid flow rate of the riser in the offshore oil and gas platform gathering and transportation riser system during severe slugging includes: The gas flow rate and liquid flow rate of the riser during severe slugging flow over one slugging cycle are obtained, and the average gas flow rate and liquid flow rate over one slugging cycle are calculated to obtain the average gas flow rate and average liquid flow rate of the riser during severe slugging flow.

[0011] The control method of the throttle valve of the offshore oil and gas platform gathering and transportation riser system provided by the present invention has at least the following beneficial effects: The target quantity of throttle valve control is quantitatively converted into the pressure drop of the valve (i.e., the target pressure drop value). The target pressure drop value can be determined in combination with the state of the riser under standard operating conditions to ensure that the throttle valve is controlled to the optimal state. The average gas phase flow rate and average liquid phase flow rate of the riser during severe slugging flow can be used to determine the valve resistance when controlling the throttle valve when the pressure drop at both ends of the throttle valve reaches the target pressure drop value during severe slugging flow in the riser. The flow capacity of the throttle valve is further determined to obtain the target opening of the throttle valve. At this time, the throttle valve performs flow control at the target opening, which can eliminate severe slugging flow in the offshore oil and gas field gathering and transportation riser system.

[0012] The present invention can directly calculate the control target and its corresponding valve opening. Compared with incremental PID control, it can significantly shorten the time required for regulation and achieve better regulation effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] One or more embodiments are exemplarily described by the figures in the corresponding drawings, and these exemplified descriptions do not constitute limitations on the embodiments.

[0014] Figure 1 This is a flow chart of a method for controlling a throttle valve in a gathering and transportation riser system of an offshore oil and gas platform provided in accordance with one embodiment of the present invention; Figure 2 is a schematic diagram of a main variable provided according to an embodiment of the present invention; Figure 3 is a schematic diagram illustrating a control target provided according to an embodiment of the present invention; Figure 4It is a schematic diagram of comparison between calculated values ​​and measured values ​​provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0015] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, it will be understood by those skilled in the art that in the embodiments of the present invention, many technical details are provided to enable the reader to better understand the present invention. However, even without these technical details and the various changes and modifications based on the following embodiments, the technical solutions claimed in the present invention can be implemented. The division of the following embodiments is for convenience of description and should not constitute any limitation on the specific implementation of the present invention. The various embodiments can be combined with each other and referenced to each other under the premise that there is no contradiction.

[0016] One embodiment of the present invention relates to a method for controlling a throttle valve in a gathering and transportation riser system of an offshore oil and gas platform. The implementation details of the method for controlling a throttle valve in a gathering and transportation riser system of an offshore oil and gas platform of this embodiment are described in detail below. The following content is merely implementation details provided for ease of understanding and is not essential for implementing this solution.

[0017] The specific process of the control method of the throttle valve of the offshore oil and gas platform gathering and transportation riser system of this embodiment can be as follows: Figure 1 As shown, including: Step 101 : obtaining an average gas flow rate and an average liquid flow rate of a riser in a gathering and transportation riser system of an offshore oil and gas platform during a severe slugging period.

[0018] Specifically, the gas and liquid flow rates of the riser during a period of severe slugging are obtained over a period exceeding one slugging cycle. The average gas and liquid flow rates over these periods are then calculated to obtain the average gas and liquid flow rates during the period. If real-time data collection is not available, the daily gas and liquid production from the previous day is calculated.

[0019] Step 102: Obtain target pressure drop values ​​at both ends of the throttle valve of the riser under standard working conditions.

[0020] Specifically, the flow rate or production is converted to the equivalent flow rate under standard conditions, and the target pressure drop value is calculated using the gas-liquid two-phase flow model. , gas content at the bottom of the riser Calculated using the no-slip model, the specific calculation formula is as follows:

[0021] First, calculate the gas phase converted flow rate at the bottom of the riser, the gas phase converted flow rate at the top of the riser, and the liquid phase converted flow rate: ; ; ; ; The target pressure drop value is determined by the following formula: ; ; ; ; ; ; Where, is the gravity pressure drop of the gas-liquid mixture in the riser, which is equal to the pressure at the bottom of the riser Subtract the pressure at the top of the riser , is the target pressure drop value, is the average gas holdup in the riser, is the air void fraction at the bottom of the riser, is the air void fraction at the top of the riser, is the converted gas velocity at the bottom of the riser, is the converted gas velocity at the top of the riser, is the liquid phase converted flow rate, is the liquid density, is the gas phase density at the bottom of the riser, is the gas phase density at the top of the riser, is the acceleration due to gravity, is the height of the riser, is the gas phase mass flow rate, is the liquid mass flow rate, is the cross-sectional area of ​​the riser, is the inner diameter of the riser.

[0022] Step 103: Determine the valve local resistance coefficient when the pressure drop across the throttle valve reaches a target pressure drop value during severe slugging in the riser based on the average gas flow rate and the average liquid flow rate, and determine the valve flow coefficient corresponding to the valve local resistance coefficient; wherein the valve local resistance coefficient is used to indicate the valve resistance when controlling the throttle valve, and the valve flow coefficient is used to indicate the flow capacity of the throttle valve.

[0023] Specifically, calculate the The corresponding valve local resistance coefficient under the target value and flow rate , and calculate the Corresponding valve flow coefficient K v or C v .

[0024] The valve local resistance coefficient is determined by the following formula: ; The valve flow coefficient is determined by the following formula: ; Where, is the nominal diameter of the throttle valve, the metric flow coefficient K v and Imperial flow coefficient C v The conversion relationship is K v =0.865C v .

[0025] Step 104 : determining the target opening of the throttle valve by using the valve flow coefficient, and controlling the throttle valve to adjust to the target opening.

[0026] Specifically, the valve opening Z is determined based on the valve flow characteristics. The valve flow characteristics are obtained through pure water experiment calibration. The target opening of the throttle valve is determined by the following formula: ; Where, The target opening.

[0027] The parameters involved in the control method of the throttle valve of the offshore oil and gas platform gathering and transportation riser system of this embodiment can be found in Figure 2 , Figure 3 The time period marked in the middle is the optimal state of regulation (double-frequency fluctuation occurs).

[0028] The flow characteristics of the valve can be obtained from the valve's factory documents or calculated according to ideal conditions. Figure 3 The measured opening under optimal control conditions for an experimental system is compared with the opening calculated using the above method. Because all valves have deadbands, some with an accuracy of up to ±2%, an average deviation of the calculated opening within ±2% meets the accuracy requirements.

[0029] In a specific embodiment, taking an offshore oil field as an example, the offshore oil field cannot directly measure the flow rate in the pipeline, so the daily production data is used to calculate the converted flow rate.

[0030] The parameters are as follows: H=138.9m; d=250.9mm; d v =250mm; separator pressure p at the gas-liquid separator position s =560kPa; Q L =1985m 3 / d;Q G =102705m 3 / d (standard conditions); ρ L =850.7kg / m3 ρ G =1.179kg / m 3 (Standard conditions); C v,max =1000, C v,min =20; the throttle valve flow characteristic type is "equal percentage", and the ideal formula is as follows: ; According to the above conditions, we can calculate f=1810, K v =63.69, Z=33.06%.

[0031] The actual on-site opening degree of this working condition is 34%, and the deviation between the two does not exceed ±2%.

[0032] Therefore, the present invention can directly determine the control target and its corresponding valve opening, significantly reducing the time required for control compared to incremental PID control. Furthermore, the valve opening calculated by the present invention is not much different from the actual critical opening. After adjusting to this opening, the target parameter values ​​required for PID control are measured and set, and then the switch to PID control is made. This ensures the stability of the control system and eliminates the need for empirical experience in parameter setting.

[0033] The steps of the above methods are divided only for clarity of description. When implemented, they can be combined into one step or some steps can be split and decomposed into multiple steps. As long as they include the same logical relationship, they are all within the scope of protection of the present invention.

[0034] Those skilled in the art will appreciate that the above-described embodiments are specific embodiments for implementing the present invention, and that in actual applications, various changes in form and detail may be made thereto without departing from the spirit and scope of the embodiments of the present invention. Any person skilled in the art may make various changes and modifications without departing from the spirit and scope of the embodiments of the present invention. Therefore, the scope of protection of the embodiments of the present invention shall be subject to the scope defined in the claims.

Claims

1. A method for controlling a throttle valve in a gathering and transportation riser system of an offshore oil and gas platform, characterized in that: include: Obtain the average gas flow rate and average liquid flow rate of the riser in the offshore oil and gas platform's gathering and transportation riser system during severe slugging. Obtain the target pressure drop value at both ends of the throttle valve of the riser under standard working conditions; Determine, based on the average gas phase flow rate and the average liquid phase flow rate, a valve local resistance coefficient when the pressure drop across the throttle valve reaches a target pressure drop value during severe slugging in the riser, and determine a valve flow coefficient corresponding to the valve local resistance coefficient; wherein the valve local resistance coefficient is used to indicate the valve resistance when the throttle valve is controlled, and the valve flow coefficient is used to indicate the flow capacity of the throttle valve; The target opening of the throttle valve is determined by the valve flow coefficient, and the throttle valve is controlled to adjust to the target opening.

2. The control method for a throttle valve of a gathering and transportation riser system of an offshore oil and gas platform according to claim 1, characterized in that: The target pressure drop value is determined by the following formula: ； ； ； ； ； ； Where, is the target pressure drop value, is the gravity pressure drop of the gas-liquid mixture in the riser, is the average gas holdup in the riser, is the air void fraction at the bottom of the riser, is the air void fraction at the top of the riser, is the converted gas velocity at the bottom of the riser, is the converted gas velocity at the top of the riser, is the liquid phase converted flow rate, is the liquid density, is the gas phase density at the bottom of the riser, is the gas phase density at the top of the riser, is the acceleration due to gravity, is the height of the riser, is the gas phase mass flow rate, is the liquid mass flow rate, is the cross-sectional area of ​​the riser.

3. The control method of the throttle valve of the offshore oil and gas platform gathering and transportation riser system according to claim 2 is characterized in that: The valve local resistance coefficient is determined by the following formula: ； The valve flow coefficient is determined by the following formula: ； Where, is the nominal diameter of the throttle valve.

4. The method for controlling a throttle valve of a gathering and transportation riser system of an offshore oil and gas platform according to claim 3, characterized in that: The target opening of the throttle valve is determined by the following formula: ； Where, The target opening.

5. The method for controlling a throttle valve of a gathering and transportation riser system of an offshore oil and gas platform according to claim 2, characterized in that: The gas phase converted flow rate at the bottom of the riser, the gas phase converted flow rate at the top of the riser, and the liquid phase converted flow rate are determined by the following formulas: ； ； ； ； Where, is the gas phase flow rate, is the liquid phase flow rate, is the cross-sectional area of ​​the riser, is the inner diameter of the riser.

6. The method for controlling a throttle valve of a gathering and transportation riser system of an offshore oil and gas platform according to claim 1, characterized in that: The method of obtaining the average gas flow rate and the average liquid flow rate of the riser in the offshore oil and gas platform gathering and transportation riser system during severe slugging includes: The gas flow rate and liquid flow rate of the riser during severe slugging flow over one slugging cycle are obtained, and the average gas flow rate and liquid flow rate over one slugging cycle are calculated to obtain the average gas flow rate and average liquid flow rate of the riser during severe slugging flow.

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