CN113007606B - Flowing safety early warning method for seabed gas transmission pipeline with falling hydrate deposition structure - Google Patents

Flowing safety early warning method for seabed gas transmission pipeline with falling hydrate deposition structure Download PDF

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CN113007606B
CN113007606B CN202110186299.4A CN202110186299A CN113007606B CN 113007606 B CN113007606 B CN 113007606B CN 202110186299 A CN202110186299 A CN 202110186299A CN 113007606 B CN113007606 B CN 113007606B
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pipeline
representing
hydrate
inhibitor
fluid
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CN113007606A (en
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李孟昕
王大勇
陈天宇
沙婕
宋永臣
范佳瑞
毕晶晶
胡佩
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Dalian University of Technology
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Dalian University of Technology
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17D—PIPE-LINE SYSTEMS; PIPE-LINES
    • F17D5/00—Protection or supervision of installations
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17D—PIPE-LINE SYSTEMS; PIPE-LINES
    • F17D3/00—Arrangements for supervising or controlling working operations
    • F17D3/01—Arrangements for supervising or controlling working operations for controlling, signalling, or supervising the conveyance of a product
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D21/00—Measuring or testing not otherwise provided for
    • G01D21/02—Measuring two or more variables by means not covered by a single other subclass
    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B19/00—Alarms responsive to two or more different undesired or abnormal conditions, e.g. burglary and fire, abnormal temperature and abnormal rate of flow

Abstract

A flow safety early warning method for a seabed gas transmission pipeline with hydrate deposition and falling belongs to the technical field of pipeline flow safety. Collecting basic information of all pipelines in the region, calculating supercooling degree based on the type and concentration of an inhibitor, calculating a change value of a hydraulic diameter along with time according to the generation amount of a hydrate, calculating a flow shearing force of a system, comparing the flow shearing force with a deposition structure stress preset in an early warning system, and judging whether the pipeline falls off or not; and finally, updating the hydraulic diameter, judging the flow safety of the pipeline according to the pressure difference of the inlet and the outlet of the pipeline, and whether early warning is needed. The method realizes dynamic identification of the thickness of the hydrate film along with the size of the hydraulic diameter, reproduces the falling phenomenon of the deposition structure, further improves the accuracy of pipeline prediction, and improves the safety of submarine natural gas transportation.

Description

Flowing safety early warning method for seabed gas transmission pipeline with falling hydrate deposition structure
Technical Field
The invention belongs to the technical field of early warning of a submarine gas pipeline, and particularly relates to a flowing safety early warning method and system of the submarine gas pipeline, wherein a hydrate film falls off along with the physical properties of a fluid under the action of an inhibitor.
Background
The natural gas hydrate is a cage-type compound, and is a solid compound formed by methane gas and water under the conditions of low temperature and high pressure. In the process of oil and gas exploitation and transportation, particularly, the generation of hydrates is more facilitated under the low temperature and high pressure in a deep water environment, however, the situation that the natural gas hydrates block the pipelines cannot be treated on site, the oil and gas exploitation efficiency can be seriously affected, and therefore, the research on the flow safety problem caused by hydrate blockage in the pipelines is a basic guarantee for solving the problems. The simulated inhibitor mainly aims at industrial thermodynamic inhibitor, such as methanol, ethanol, glycol, and the like. The inhibitor system can effectively influence the activity of water so as to reduce the supercooling degree in a pipeline system and finally inhibit the generation of hydrates.
The current flow safety evaluation cannot obtain a real-time image of a hydrate generation blocking process in a submarine pipeline, and no solution for the flow safety problem in the submarine gas pipeline transportation process under the influence of thermodynamic inhibitors with different concentrations exists at present. How to realize the prediction aiming at the blocking risk of the regional submarine pipeline and convert the passive monitoring and processing of the submarine pipeline flow into active prediction and response is a problem to be solved urgently in the field.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a novel regional hydrate deposit structure seabed gas transmission pipeline blockage risk prediction method and system under the influence of an inhibitor, which comprises hydrate generation, transportation, deposition and shedding processes of a seabed pipeline system under the action of the inhibitor. The method realizes the prediction of the blocking risk of the regional submarine gas transmission pipeline, has low cost, wide coverage and high treatment efficiency, and achieves the purpose of improving the overall safety of submarine pipeline flow.
In order to achieve the purpose, the invention adopts the following technical scheme: a flow safety early warning method for a seabed gas transmission pipeline with a hydrate deposition structure falling off comprises the following steps:
s1, collecting basic information of all pipelines in the area, wherein the basic information comprises the inner diameter of the pipeline, the outer diameter of the pipeline, the length of the pipeline, the material of the pipeline, the ambient temperature, the type of an inhibitor, the concentration of the inhibitor, the temperature of fluid and the pressure of a fluid inlet; obtaining a hydrate equilibrium triple point through input parameters, fluid pressure and fluid temperature at an inlet of a seabed gas transmission pipeline;
s2, calling a corresponding model from a preset system according to the type and concentration of the inhibitor to obtain the activity of the water of the submarine pipeline system, and calculating to obtain the supercooling degree;
ΔTsub＝(teq-ΔtI)-t；
ΔTsubrepresented by the degree of supercooling, t, of the control systemeqRepresented by the equilibrium temperature of the control system, t is represented by the temperature of the control system, Δ tIRepresents a shift in equilibrium temperature due to the presence of inhibitor;
ΔtI＝-72ln[αW·(1-xI)]；
when the inhibitor is a glycol, the inhibitor is,
Figure GDA0003377054750000021
when the inhibitor is methanol,
Figure GDA0003377054750000022
when the inhibitor is ethanol,
Figure GDA0003377054750000023
when the inhibitor is sodium chloride, the inhibitor is,
Figure GDA0003377054750000024
when the inhibitor is potassium chloride,
Figure GDA0003377054750000025
αWrepresenting the activity of water in a subsea pipeline system, xIRepresents the molarity of the thermodynamic inhibitor;
the supercooling degree of the pipeline system of the corresponding thermodynamic inhibitor under different concentrations is calculated through a formula arranged in the supercooling degree module; when different pipeline system inhibitors are different, calling different equations from the early warning system to predict the pipeline flow safety;
s3, calculating the hydrate generation amount through a first order kinetic formula of hydrate generation based on the supercooling degree of the pipeline system, and obtaining the variation trend of the hydraulic diameter of the pipeline along with the temperature and the pressure:
Figure GDA0003377054750000031
wherein
Figure GDA0003377054750000032
Denotes the amount of hydrate formed per unit time, FkRepresenting the formation coefficient of hydrates, whose value is related to the flow pattern of the fluid in the submarine pipeline, C1、C2Is a constant number, MgRepresents the average molar mass of the system fluid,
Figure GDA0003377054750000033
representing the average density of the system fluid, A representing the gas-water interface area in the control system;
A＝Adrop+Afilm；
wherein A isdropRepresenting the gas-water interface area of the droplets dispersed in the gas phase in the system, AfilmRepresenting the gas-water interface area of a liquid film on the pipe wall of the submarine pipeline in the system;
Figure GDA0003377054750000034
Figure GDA0003377054750000035
represents a temperature change per unit length, i.e., a temperature gradient; beta is aJTRepresents the scorched soup coefficient, U represents the comprehensive heat transfer coefficient of the fluid and the environment in the control system, and T represents the temperature of the fluid in the control systemDegree, TextRepresents the ambient temperature,. DELTA.H represents the exotherm during hydrate formation, QmRepresenting the flow rate of fluid in the pipe per unit time, pmRepresenting the average density of the mixed fluid in the control system, CpmRepresenting the heat capacity of the mixed fluid in the control system;
Qm＝Qg+Ql；
Qgrepresenting the flow rate of gas per unit time in the control system, QlRepresenting the flow rate of liquid per unit time in the control system;
s4, gradually thickening the hydrate film, namely when the water conservancy diameter is reduced, the flowing speed of the fluid in the pipeline is continuously increased, and meanwhile, the flowing shearing force is continuously increased; due to the porous property of the structure of the hydrate film, namely the deposition structure, the deposition structure falls off, so that the water conservancy diameter is increased, and the blocking condition of a local pipeline is temporarily relieved;
Figure GDA0003377054750000036
σwrepresenting flow shear of the pipe system, DhRepresenting the hydraulic diameter of the piping system,
Figure GDA0003377054750000041
representing a pressure gradient of the pipeline system;
σw(x,t)＝σhDh(x,ts)＝Df(x,ts)；
σhrepresenting the critical shear force of the hydrate deposit structure, DfRepresents a stable hydrate film structure, tsRepresenting the corresponding time of the falling moment of the hydrate deposition structure;
Dh(x,ts)＝Df(x,ts)，xs＜x＜x(ts)；
Dh(x,ts)＝Df(x,t)，x≥x(ts)；
xsrepresenting the structure of a hydrateA place corresponding to the moment of falling;
s5, judging whether the hydrate film falls off or not, updating the hydraulic diameter of the pipeline system when the porous deposition structure falls off, obtaining the pressure difference of the inlet and the outlet of the pipeline according to a pressure drop formula, determining that the submarine pipeline is blocked when the pressure difference of the two ends of the inlet and the outlet of the pipeline reaches a preset value, judging the state of the early warning system, and prompting early warning information for platform equipment;
Figure GDA0003377054750000042
Figure GDA0003377054750000043
representing pressure changes per unit length in the pipe, f representing the coefficient of friction, pnsRepresenting the density of the fluid in the control system without sliding friction, DhHydraulic diameter, v, of the pipe systemmRepresenting the flow rate of the mixed fluid within the control system.
The invention carries out simulation by a backward iteration method, can know that the pressure and temperature change in a control body under the influence of an inhibitor and the water conservancy diameter real-time update caused by the instability of a hydrate deposition structure through the formula lead the pressure difference at the inlet and the outlet of the pipeline to continuously change and finally reach the preset value of an early warning module, carries out simulation prediction on the flow safety of the pipeline by the parameters, and judges whether the submarine gas pipeline is blocked.
According to the invention, by introducing the falling of the hydrate deposition structure, the early warning system can track the dynamic change of the water conservancy diameter of the pipeline system more easily, so that the prediction system is closer to the actual production condition, and then the generation amount of the hydrate in the pipeline is calculated by using the first-order hydrate generation formula under the action of the inhibitor, so that the prediction of the time and the place of the hydrate blockage in the pipeline is more accurate, and the flow safety of the whole system is judged more accurately.
The invention also provides a dynamic regional submarine gas pipeline flow safety prediction system, which is used for realizing the regional submarine gas pipeline flow safety prediction method, and comprises the following steps:
the acquisition module is used for collecting basic information of all pipelines in the region, wherein the basic information comprises the inner diameter of the pipeline, the outer diameter of the pipeline, the length of the pipeline, the material of the pipeline, the ambient temperature, the temperature of fluid, the flow of the fluid, the pressure of a fluid inlet, the type, concentration and volume ratio of an inhibitor and the water content ratio;
the supercooling degree module and the thermodynamic inhibitor have been practically applied in the oil and gas field for more than 60 years, have remarkable effects and are adopted by most oil exploitation platforms at present. The module calculates the activity of water according to the concentration of the thermodynamic inhibitor, so as to obtain the supercooling degree of the gas transmission pipeline system;
and the hydrate generation module is used for obtaining the total hydrate generation amount of the system by utilizing a first-order kinetic equation of hydrate generation based on the supercooling degree and the gas-water interface area of the submarine pipeline system. Based on physical conditions, the generation amount of the hydrate cannot be a negative value, so that the condition that no hydrate is generated if the obtained supercooling degree in the supercooling degree module is a negative value or equal to 0 is limited, the condition that the phase change occurs in a pipeline if the supercooling degree is more than 0 is considered, and the heat transfer and the pressure distribution are violently changed due to the phase change.
The hydraulic diameter module, at a low inhibitor concentration, although the hydrate formation is inhibited, still has a certain amount of hydrate formation, most of which will follow the flow of the fluid to the discharge pipeline. A small part of the water flow is settled and attached to the pipe wall due to gravity and flow factors, so that the flow diameter of the fluid is reduced, the quantity describing the flow diameter is called water conservancy diameter, and the water conservancy diameter is the limit of the flow velocity of the fluid in the system under the condition of constant flow of the submarine pipeline;
the invention provides a solution for the phenomenon that a deposition structure of hydrate in a pipeline system is divided into a compact non-porous stable structure and a porous unstable structure based on field result speculation and laboratory observation, wherein the unstable porous structure can fall off.
The heat transfer module, in this early warning system, the heat transfer module contains 3 bold, is the heat that joule-thomson effect, the interaction and the phase transition of environment produced respectively. Joule-thomson effect refers to the temperature change of the fluid in the pipe flow due to a drastic change in pressure; the environment interaction means that the temperature of fluid transported by a submarine pipeline is usually higher than the environment temperature, so that the temperature of the fluid in the pipeline is continuously reduced to a hydrate stable region in the process of submarine long-distance transportation; the temperature change caused by phase change is easy to generate the hydrate under the conditions of high pressure and low temperature, and the environment of the submarine pipeline is just the hydrate generation interval, and the reaction is an exothermic reaction that gas molecules react with liquid water molecules to become solid.
In the field measurement of the pressure module, due to the particularity of a submarine pipeline system, data capable of being directly detected is limited, most relevant numerical values are obtained in an approximate range through an empirical formula by monitoring pressure changes, and therefore the pressure changes of a fluid inlet and a fluid outlet have great significance for evaluating the flow safety in the whole pipeline system. The pressure drop is increased due to hydrate generation, hydraulic diameter reduction and the like, the viscosity of the fluid is increased due to the hydrate generation, and the system needs larger energy to drive the fluid to advance; the water conservancy diameter of the pipeline is reduced due to adsorption and sedimentation of the hydrate, so that the pressure drop is greatly influenced, and in addition, the pressure difference between an inlet and an outlet is also increased due to the loss of gas and liquid caused by the generation of the hydrate;
and the early warning module is used for giving an early warning to the operating platform or carrying out related pipeline safety operation when the pressure drop before and after the system judges reaches a preset value, such as heating a pipeline or cleaning the pipeline.
The design of the invention simulates physical and chemical changes in the actual flow process of the conveying pipeline, reveals the formation, sedimentation mode and flow blockage condition of the hydrate in the submarine pipeline under the influence of inhibitors with different concentrations, so as to provide reference for the safety scheme design of the submarine pipeline, better provide technical support for the exploitation of the hydrate in the sea area, and have practical and scientific significance. Compared with the prior art, the invention has the following advantages:
the method has the advantages that the dynamic change of the water conservancy diameter of the pipeline caused by the instability of the sedimentary structure is realized, the problem of the existing prediction of the flow safety of the pipeline is solved, and the vacancy of the prediction and evaluation of the flow safety risk of the existing regional submarine gas transmission pipeline is made up;
according to field data and experimental observation, the layered structure of hydrate deposition is considered, the dynamic change of the hydraulic diameter of the pipeline, namely the dynamic change of the pressure drop of the inlet and the outlet of the pipeline, can be realized, the flow condition of the submarine gas pipeline can be accurately predicted by a prediction system, and the overall safety of the submarine pipeline flow is obviously predicted;
the method can evaluate the regional submarine gas pipeline more accurately, can predict the overall level of the regional submarine pipeline, can process each section of submarine pipeline with different risks more accurately, reduces the transport risk of the submarine pipeline, and changes passive monitoring and processing on the flow safety of the submarine gas pipeline into active prediction and coping.
The method fills the blank of predicting the seabed gas transmission pipeline, and takes the falling of the hydrate deposition structure into consideration of the flowing safety of the pipeline, so that the early warning system is closer to the practical application and can more accurately predict the pipeline blocking time and place.
Drawings
Fig. 1 is a structural diagram of a flow safety warning method for a seabed gas pipeline with a hydrate deposition structure falling off.
Fig. 2 is a flow chart of a flow safety warning method for a seabed gas pipeline with a hydrate deposition structure falling off.
Detailed Description
S1, collecting basic information of all pipelines in the area, wherein the basic information comprises inner diameters of the pipelines, outer diameters of the pipelines, lengths of the pipelines, materials of the pipelines, ambient temperature, types of inhibitors, concentrations of the inhibitors, fluid temperatures, fluid inlet pressures and the like. Obtaining a hydrate equilibrium triple point through input parameters, fluid pressure and fluid temperature at an inlet of a seabed gas transmission pipeline;
s2, calling a corresponding model from a preset system according to the type and concentration of the inhibitor to obtain the activity of the water of the submarine pipeline system, and calculating the supercooling degree of the submarine gas pipeline system;
s3, calculating the generation amount of the hydrate through a first-order kinetic formula of the generation of the hydrate based on the supercooling degree of the pipeline system, and obtaining the dynamic change of the hydraulic diameter of the pipeline and the change trend of the temperature and the pressure in the pipeline;
s4, when the hydrate film gradually thickens, namely the water conservancy diameter is reduced, the flowing speed of fluid in the pipeline is continuously increased, and meanwhile, the flowing shearing force is continuously increased, and due to the fact that the structure of the hydrate film, namely the porous property of the deposition structure, the deposition structure falls off, the water conservancy diameter is increased, and the blocking condition of a local pipeline is temporarily relieved;
and S5, after judging whether the hydrate film falls off or not, updating the hydraulic diameter of the pipeline system, obtaining the pressure difference of the inlet and the outlet of the pipeline according to a pressure drop formula, determining that the submarine pipeline is blocked when the pressure difference of the two ends of the inlet and the outlet of the pipeline reaches a preset value, judging the state of the early warning system, and prompting early warning information for the platform equipment.
Further, the step S2 includes:
ΔTsub＝(teq-ΔtI)-t；
ΔTsubrepresented by the degree of supercooling, t, of the control systemeqRepresented by the equilibrium temperature of the control system, t is represented by the temperature of the control system, Δ tIRepresenting a shift in equilibrium temperature due to the presence of inhibitor.
ΔtI＝-72ln[αW·(1-xI)]&When the inhibitor is ethylene glycol
Figure GDA0003377054750000081
Figure GDA0003377054750000082
xIRepresents the molar concentration of molecules of the thermodynamic inhibitor. The supercooling degrees of the pipeline systems of the corresponding thermodynamic inhibitors at different concentrations can be calculated through the formulas arranged in the three supercooling degree modules. Alpha is alphaWRepresenting the activity of water in a subsea pipeline system, xIRepresents the molar concentration of molecules of the thermodynamic inhibitor. Therefore, when different pipeline system inhibitors are different, different equations are called from the early warning system to predict the pipeline flow safety.
Further, the step S3 includes:
Figure GDA0003377054750000091
wherein
Figure GDA0003377054750000092
Denotes the amount of hydrate formed per unit time, FkRepresenting the formation coefficient of hydrates, whose value is related to the flow pattern of the fluid in the submarine pipeline, C1、C2Is a constant number, MgRepresents the average molar mass of the system fluid,
Figure GDA0003377054750000093
represents the average density of the system fluid and A represents the gas-water interface area in the control system.
A＝Adrop+Afilm；
Wherein A isdropRepresenting the gas-water interface area of the droplets dispersed in the gas phase in the system, AfilmRepresenting the gas-water interface area of a liquid film on the pipe wall of the submarine pipeline in the system.
Figure GDA0003377054750000094
Figure GDA0003377054750000095
Representative unitTemperature variation over length, i.e. temperature gradient, betaJTRepresents the char water coefficient, U represents the integrated heat transfer coefficient between the fluid and the environment in the control system, T represents the temperature of the fluid in the control system, and T represents the temperature of the fluid in the control systemextRepresents the ambient temperature,. DELTA.H represents the exotherm during hydrate formation, QmRepresenting the flow rate of fluid in the pipe per unit time, pmRepresenting the average density of the mixed fluid in the control system, CpmRepresenting the heat capacity of the mixed fluid within the control system.
Qm＝Qg+Ql；
QgRepresenting the flow rate of gas per unit time in the control system, QlRepresenting the flow rate of liquid per unit time in the control system.
Further, the step S4 includes:
Figure GDA0003377054750000096
representing flow shear of the pipe system, DhRepresenting the hydraulic diameter of the piping system,
Figure GDA0003377054750000097
representing the pressure gradient of the pipe system.
σw(x,t)＝σhDh(x,ts)＝Df(x,ts)；
σhRepresenting the critical shear force of the hydrate deposit structure, DfRepresents a stable hydrate film structure, tsRepresenting the corresponding time at the moment when the hydrate deposit structure falls off.
Dh(x,ts)＝Df(x,ts) When x iss＜x＜x(ts)；
Dh(x,ts)＝Df(x, t) when x ≧ x (t)s)；
xsRepresenting the corresponding place of the shedding moment of the hydrate structure, therefore, the simulation early warning system can be seen to update the hydraulic diameter of the pipeline system when the porous sedimentary structure is shed, and the iteration is carried out laterAnd (4) calculating and using the updated water conservancy diameter for simulation prediction.
Further, the step S5 includes:
Figure GDA0003377054750000101
Figure GDA0003377054750000102
representing pressure changes per unit length in the pipe, f representing the coefficient of friction, pnsRepresenting the density of the fluid in the control system without sliding friction, DhRepresenting hydraulic diameter in a subsea pipeline, vmRepresenting the flow rate of the mixed fluid within the control system.
When the technical scheme is adopted for working, firstly, the equilibrium temperature of the pipeline of the ith section is calculated according to the collected pipeline related data of the ith section and the environment data, then the supercooling degree of the pipeline system of the ith section is calculated, the generation amount of hydrate in the pipeline of the ith section is obtained, then the change value of the hydraulic diameter of the pipeline of the ith section along with time can be obtained, the change of the hydraulic diameter along with time influences the initial state of the temperature and the pressure of the (i + 1) th section, and further, the iteration is carried out continuously, so that all values from the fluid inlet to the fluid outlet are obtained. The specific process is as follows:
(1) and setting initial conditions of the system according to the information collected by the collection module, and calling different formulas according to the types of the inhibitors added in the pipeline system.
The data collected includes: the i-th section of the pipeline D has the environmental temperature t of 277KiInner diameter of 0.02m, i-th section of pipeline DoThe outer diameter is 0.025m, the pipeline length Deltax is 0.2m, the inlet pressure of the ith section is kept consistent with the outlet pressure of the ith-1 section, the inlet temperature of the ith section is kept consistent with the outlet temperature of the ith-1 section, and the gas flow Q of the ith section of pipelineg170L/min, the liquid flow of the ith section of pipeline is 2.0L/min, the inhibitor is glycol, namely MEG, the formula of the inhibitor being glycol is called to calculate the activity of the water, further according to the amount of the inhibitor added in the system,if the quantity concentration of the ethylene glycol is 10%, the supercooling degree of the i-th section of the pipeline system is about 2.2 ℃.
(2) And when the supercooling degree of the ith section is obtained, judging whether the hydrate is generated according to the supercooling degree.
And (3) because the supercooling degree of the ith section is a value larger than 0, determining that the hydrate is generated in the ith section, calling a hydrate first-order kinetic generation formula, and calculating the generation amount of the hydrate in the ith section to be 0.4L/min. Obtaining the deposition thickness of the hydrate to be 0.002m, and calculating the water conservancy diameter D of the ith section of pipelinehIs 0.018 m. The pressure drop of the i-th section is calculated to be 4.7KPa through a pressure gradient and temperature gradient formula, and the temperature gradient is 0.0118 ℃.
(3) After the pressure drop of the ith section of pipeline system is obtained, the flow shearing force sigma of the ith section of fluid is calculatedwIf σ iswThe value of (a) is greater than sigma preset by the early warning systemhDetermining that the porous loose structure of the hydrate deposit in the i-th section of pipeline falls off, and determining the hydraulic diameter DhAnd (6) updating.
The ith segment sigma is obtained by calculationwThe value is 130Pa, and the stress sigma of the deposition structure set by the pipeline of the early warning systemhAt 125Pa, the porous structure of the hydrate film was considered to be exfoliated. And the data is saved and substituted into the initial condition of the next iteration, namely the (i + 1) th section.
(4) And when the flow safety condition of the pipeline at a certain time t is calculated, subtracting the pressure at the pipeline inlet from the pressure at the pipeline outlet to obtain a pressure difference, and if the pressure difference is greater than a preset value of the early warning system.
The pressure difference value of each 100m pipeline which is monitored by the system in a default mode is 1.2MPa, if the pressure difference value calculated by the simulation system is larger than the pressure difference value, the pipeline is determined to be blocked, and the early warning module is started. If the differential pressure value calculated by the embodiment is 1.0MPa, the pipeline is determined not to be blocked, and the early warning module is not started.
The present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims (1)

1. A flow safety early warning method for a seabed gas transmission pipeline with a hydrate deposition structure falling off is characterized by comprising the following steps:
s1, collecting basic information of all pipelines in the area, wherein the basic information comprises the inner diameter of the pipeline, the outer diameter of the pipeline, the length of the pipeline, the material of the pipeline, the ambient temperature, the type of an inhibitor, the concentration of the inhibitor, the temperature of fluid and the pressure of a fluid inlet;
s2, calculating the supercooling degree according to the type of the inhibitor and the concentration of the inhibitor;
ΔTsub＝(teq-ΔtI)-t；
ΔTsubrepresented by the degree of supercooling, t, of the control systemeqRepresented by the equilibrium temperature of the control system, t is represented by the temperature of the control system, Δ tIRepresents a shift in equilibrium temperature due to the presence of inhibitor;
ΔtI＝-72ln[αW·(1-xI)]；
when the inhibitor is a glycol, the inhibitor is,
Figure FDA0003377054740000011
when the inhibitor is methanol,
Figure FDA0003377054740000012
when the inhibitor is ethanol,
Figure FDA0003377054740000013
when the inhibitor is sodium chloride, the inhibitor is,
Figure FDA0003377054740000014
when the inhibitor is potassium chloride,
Figure FDA0003377054740000015
αWrepresenting the activity of water in a subsea pipeline system, xIRepresents the molarity of the thermodynamic inhibitor;
the supercooling degree of the pipeline system of the corresponding thermodynamic inhibitor under different concentrations is calculated through a formula arranged in the supercooling degree module; when different pipeline system inhibitors are different, calling different equations from the early warning system to predict the pipeline flow safety;
s3, calculating the hydrate generation amount through a first order kinetic formula of hydrate generation based on the supercooling degree of the pipeline system, and obtaining the variation trend of the hydraulic diameter of the pipeline along with the temperature and the pressure:
Figure FDA0003377054740000016
wherein
Figure FDA0003377054740000017
Denotes the amount of hydrate formed per unit time, FkRepresenting the formation coefficient of hydrates, whose value is related to the flow pattern of the fluid in the submarine pipeline, C1、C2Is a constant number, MgRepresents the average molar mass of the system fluid,
Figure FDA0003377054740000021
representing the average density of the system fluid, A representing the gas-water interface area in the control system;
A＝Adrop+Afilm；
wherein A isdropRepresenting the gas-water interface area of the droplets dispersed in the gas phase in the system, AfilmRepresenting the gas-water interface area of a liquid film on the pipe wall of the submarine pipeline in the system;
Figure FDA0003377054740000022
Figure FDA0003377054740000023
represents a temperature change per unit length, i.e., a temperature gradient; beta is aJTRepresents the char water coefficient, U represents the integrated heat transfer coefficient between the fluid and the environment in the control system, T represents the temperature of the fluid in the control system, and T represents the temperature of the fluid in the control systemextRepresents the ambient temperature,. DELTA.H represents the exotherm during hydrate formation, QmRepresenting the flow rate of fluid in the pipe per unit time, pmRepresenting the average density of the mixed fluid in the control system, CpmRepresenting the heat capacity of the mixed fluid in the control system;
Qm＝Qg+Ql；
Qgrepresenting the flow rate of gas per unit time in the control system, QlRepresenting the flow rate of liquid per unit time in the control system;
s4, gradually thickening the hydrate film, namely when the water conservancy diameter is reduced, the flowing speed of the fluid in the pipeline is continuously increased, and meanwhile, the flowing shearing force is continuously increased; due to the porous property of the structure of the hydrate film, namely the deposition structure, the deposition structure falls off, so that the water conservancy diameter is increased, and the blocking condition of a local pipeline is temporarily relieved;
Figure FDA0003377054740000024
σwrepresenting flow shear of the pipe system, DhRepresenting the hydraulic diameter of the piping system,
Figure FDA0003377054740000025
representing a pressure gradient of the pipeline system;
σw(x，t)＝σhDh(x，ts)＝Df(x，ts)；
σhrepresenting the critical shear force of the hydrate deposit structure, DfRepresents a stable hydrate film structure, tsRepresenting the corresponding time of the falling moment of the hydrate deposition structure;
Dh(x，ts)＝Df(x，ts)，xs＜x＜x(ts)；
Dh(x，ts)＝Df(x，t)，x≥x(ts)；
xsrepresenting the corresponding place at the moment of the falling off of the hydrate structure;
s5, judging whether the hydrate film falls off or not, updating the hydraulic diameter of the pipeline system when the porous deposition structure falls off, obtaining the pressure difference of the inlet and the outlet of the pipeline according to a pressure drop formula, determining that the submarine pipeline is blocked when the pressure difference of the two ends of the inlet and the outlet of the pipeline reaches a preset value, judging the state of the early warning system, and prompting early warning information for platform equipment;
Figure FDA0003377054740000031
Figure FDA0003377054740000032
representing pressure changes per unit length in the pipe, f representing the coefficient of friction, pnsRepresenting the density of the fluid in the control system without sliding friction, DhHydraulic diameter, v, of the pipe systemmRepresenting the flow rate of the mixed fluid within the control system.
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