A method and system for subsea pipeline shutdown replacement decision making

Abstract

The present application relates to the field of oil and gas field development, and discloses a kind of seabed pipeline shutdown replacement decision method and system, it includes: obtaining the fluid in the bypass pipeline communicated with seabed pipeline;Bypass pipeline is communicated with seabed pipeline at the inlet of seabed pipeline;The fluid in bypass pipeline is cooled and handled, and the fluid flow in bypass pipeline is monitored during cooling process;The fluid temperature corresponding to the time when fluid flow is reduced to zero is determined as pipe freezing temperature;According to the comparison result of pipe freezing temperature and seabed pipeline along the line ambient temperature, the shutdown mode of seabed pipeline is decided.The present application can give the best control scheme of seabed pipeline shutdown by accurate evaluation of seabed pipeline shutdown pipe freezing risk.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development technology, and in particular to a decision-making method and system for replacing the shutdown of a subsea pipeline. Background Technology

[0002] Subsea pipelines are vital arteries for transporting offshore energy, serving as crucial channels for oil and gas to reach land from deep and shallow waters. For deep-water oil pipelines, the low-temperature environment and the high pour point of crude oil, leading to the risk of pipe freezing, are among the most significant production challenges. Deep-water subsea pipelines typically need to be shut down during typhoons. To prevent pipe freezing during pipeline shutdowns, a fluid less prone to freezing is used to replace the crude oil within the pipeline. The pour point of crude oil is the primary indicator for determining the likelihood of pipe freezing in deep-water subsea pipelines. Currently, oil samples for pour point testing are mainly collected from the pipeline outlet. However, as crude oil is transported from the pipeline inlet to the outlet, its temperature gradually decreases along the pipeline, causing heavy components such as wax crystals, colloids, and asphaltenes to precipitate and deposit on the pipeline's inner wall. This precipitation means that the pour point measured at the pipeline outlet does not accurately reflect the true pour point of the crude oil, ultimately leading to an inaccurate assessment of the pipe freezing risk. To accurately assess the risk of pipe clogging in deep-sea subsea pipelines, crude oil samples need to be collected from both the pipeline inlet and outlet to test their pour points. However, in deep-water oilfields, oil samples from the pipeline inlet are often not directly collectable, making it impossible to measure the crude oil pour point in situ. Consequently, the risk of pipe clogging is difficult to assess accurately. Summary of the Invention

[0003] To address the aforementioned problems, the purpose of this invention is to provide a method and system for decision-making regarding the shutdown and replacement of subsea pipelines. By accurately assessing the risks of subsea pipeline shutdown and condensation, the optimal control scheme for subsea pipeline shutdown can be provided.

[0004] To achieve the above objectives, in a first aspect, the technical solution adopted by the present invention is as follows: a method for deciding on the shutdown and replacement of a subsea pipeline, comprising: obtaining fluid in a bypass pipe connected to the subsea pipeline; wherein the bypass pipe is connected to the subsea pipeline at the inlet of the subsea pipeline; cooling the fluid in the bypass pipe and monitoring the fluid flow rate in the bypass pipe during the cooling process; determining the fluid temperature corresponding to the fluid flow rate being reduced to zero as the condensation temperature; and deciding on the shutdown method of the subsea pipeline based on a comparison between the condensation temperature and the ambient temperature along the subsea pipeline.

[0005] Furthermore, prior to the cooling process, a pretreatment step is included: heating and isothermal treatment of the fluid in the bypass pipe to dissolve the solid deposits therein; wherein, the heating process involves heating the fluid to a preset temperature; and the isothermal treatment involves maintaining the fluid temperature constant for a preset time period.

[0006] Furthermore, based on the comparison between the condensate temperature and the ambient temperature along the subsea pipeline, the decision on the shutdown method for the subsea pipeline is made, including: if the difference between the lowest ambient temperature along the subsea pipeline and the condensate temperature is greater than a first threshold, the decision is to shut down the pipeline directly; if the difference is less than or equal to the first threshold, the decision is to shut down the pipeline after replacement.

[0007] Furthermore, the first threshold is 3℃.

[0008] Furthermore, the shutdown following the replacement includes: Open the displacement pipeline valve to introduce displacement fluid, and close the subsea pipeline inlet valve; Simultaneously, monitor the fluid information at the outlet of the subsea pipeline, and close all valves when the content of the displacement fluid in the outlet fluid exceeds the second threshold.

[0009] Furthermore, the second threshold is 95%, the displacement fluid is seawater, and the fluid information is water content.

[0010] Secondly, the technical solution adopted by the present invention is: a subsea pipeline shutdown and replacement decision system, used to implement the above-mentioned subsea pipeline shutdown and replacement decision method, comprising: A bypass pipeline connects to the submarine pipeline, and a replacement pipeline is installed between the inlet of the bypass pipeline and the inlet of the submarine pipeline. A temperature control device, installed on the bypass pipe, is used to regulate the temperature of the fluid inside the bypass pipe; The data acquisition system collects data including the open / closed status of the inlet valve of the subsea pipeline, the open / closed status of the inlet valve of the bypass pipeline, the open / closed status of the outlet valve of the bypass pipeline, the open / closed status of the inlet valve of the replacement pipeline, the fluid temperature in the bypass pipeline measured by the temperature sensor, the fluid flow rate in the bypass pipeline, the fluid information detected by the fluid detection device at the outlet of the subsea pipeline, and the operating mode information of the temperature control device; and transmits the data to the condensate risk analysis system, the valve control system, and the temperature control system. The condensate pipe risk analysis system is used to receive data from the data acquisition system to determine the condensate pipe temperature and decide on the shutdown method. The temperature control system is used to receive temperature detection data transmitted from the data acquisition system and temperature control information transmitted from the condensate pipe risk analysis system; and to switch the operating mode of the temperature control device according to the temperature detection data from the data acquisition system and the temperature control information transmitted from the condensate pipe risk analysis system. The valve control system is used to receive valve status data from the data acquisition system and control the opening and closing of the corresponding valves according to the shutdown method determined by the condensate pipeline risk analysis system.

[0011] Furthermore, the condensate risk analysis system is also used to control the temperature control device to sequentially heat, maintain a constant temperature, and cool down the fluid in the bypass pipe.

[0012] Furthermore, the methods for suspending transmission include: When stopping the flow directly, close all valves; When stopping transport after replacement, open the inlet valve of the replacement pipeline and close the inlet valve of the subsea pipeline.

[0013] Furthermore, the condensate pipeline risk analysis system is also used to instruct the valve control system to close all valves when the content of the replacement fluid in the outlet fluid exceeds a preset threshold during the shutdown process after replacement.

[0014] The present invention has the following advantages due to the adoption of the above technical solutions: 1. This invention overcomes the technical challenge of not being able to directly collect oil samples at the inlet of deep-sea subsea pipelines. By setting up a bypass pipeline connected to the subsea pipeline and dynamically cooling the crude oil (e.g., 0.5℃ / min) and monitoring the flow rate within it, the true pour point temperature of the crude oil in the pipeline can be directly and in-situ determined, avoiding the problem of distorted pour point detection of oil samples at the pipeline outlet caused by factors such as wax crystal precipitation.

[0015] 2. This invention eliminates the interference of solid phase deposition on the test results: Before formally measuring the condensate temperature, this invention treats the fluid in the bypass pipe by sequentially heating (e.g., heating to 70°C) and maintaining a constant temperature (70°C for 1 hour), which effectively dissolves any solid phase deposits such as wax that may be present in the bypass pipe. This pretreatment ensures that the condensate temperature measured during the subsequent cooling process is not affected by the deposits, thus improving the accuracy of the assessment.

[0016] 3. This invention scientifically decides whether to "directly stop transport" or "stop transport after replacement" based on the difference between the measured actual condensation temperature and the lowest ambient temperature along the subsea pipeline. This avoids unnecessary replacement operations when the condensation risk is low, while forcibly initiating replacement when the risk is high, thus achieving the best balance between safety and economy.

[0017] 4. When the decision is "stop transmission after replacement", this invention monitors the fluid information (such as water content) at the outlet of the subsea pipeline in real time. When the content of the replacement fluid (seawater) exceeds 95%, all valves are automatically closed to ensure that the crude oil in the pipeline has been fully replaced, effectively preventing pipe condensation accidents, and avoiding waste caused by excessive replacement. Attached Figure Description

[0018] Figure 1 This is a flowchart of the decision-making method for stopping and replacing submarine pipelines in an embodiment of the present invention; Figure 2 This is a schematic diagram of the subsea pipeline shutdown and replacement decision system in an embodiment of the present invention. Detailed Implementation

[0019] To overcome the shortcomings of existing methods for assessing the risk of pipeline shutdown and condensation in deep-sea subsea pipelines, this invention proposes a decision-making method and system for subsea pipeline shutdown and replacement, which can accurately assess the risk of subsea pipeline shutdown and condensation and provide the optimal control scheme for subsea pipeline shutdown.

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0021] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0022] In one embodiment of the present invention, a method for making decisions on the suspension and replacement of subsea pipelines is provided. In this embodiment, as... Figure 1 As shown, the method includes the following steps: 1) Obtain the fluid in the bypass pipe connected to the subsea pipeline; wherein the bypass pipe is connected to the subsea pipeline at the inlet of the subsea pipeline.

[0023] 2) Cool the fluid in the bypass pipe and monitor the fluid flow rate in the bypass pipe during the cooling process.

[0024] 3) The fluid temperature at which the fluid flow rate drops to zero is defined as the condensate temperature.

[0025] 4) Based on the comparison between the condensate temperature and the ambient temperature along the subsea pipeline, decide on the method of stopping the subsea pipeline.

[0026] In the above embodiments, before the cooling process in step 2), a pretreatment step is also included: heating and isothermalizing the fluid in the bypass pipe to dissolve the solid deposits therein.

[0027] Among them, heating treatment involves heating the fluid to a preset temperature; constant temperature treatment involves maintaining the fluid temperature at a constant temperature for a preset time period.

[0028] In step 4) above, the method of stopping the subsea pipeline is determined based on the comparison between the condensate temperature and the ambient temperature along the subsea pipeline. Specifically, if the difference between the lowest ambient temperature along the subsea pipeline and the condensate temperature is greater than the first threshold, the decision is to stop the pipeline directly; if the difference is less than or equal to the first threshold, the decision is to stop the pipeline after replacement.

[0029] In this embodiment, the first threshold is 3°C.

[0030] In this embodiment, the shutdown after replacement includes: Open the displacement pipeline valve to introduce displacement fluid, and close the subsea pipeline inlet valve; Simultaneously, monitor the fluid information at the outlet of the subsea pipeline, and close all valves when the content of the displacement fluid in the outlet fluid exceeds the second threshold.

[0031] The second threshold is 95%, the displacement fluid is seawater, and the fluid information is water content.

[0032] In one embodiment of the present invention, a subsea pipeline shutdown and replacement decision system is provided to implement the subsea pipeline shutdown and replacement decision methods in the above embodiments. In this embodiment, as... Figure 2 As shown, the system includes: A bypass pipeline connects to the submarine pipeline, and a replacement pipeline is installed between the inlet of the bypass pipeline and the inlet of the submarine pipeline. A temperature control device, installed on the bypass pipe, is used to regulate the temperature of the fluid inside the bypass pipe; The data acquisition system collects data including the open / closed status of the inlet valve of the subsea pipeline, the open / closed status of the inlet valve of the bypass pipeline, the open / closed status of the outlet valve of the bypass pipeline, the open / closed status of the inlet valve of the replacement pipeline, the fluid temperature in the bypass pipeline measured by the temperature sensor, the fluid flow rate in the bypass pipeline, the fluid information detected by the fluid detection device at the outlet of the subsea pipeline, and the operating mode information of the temperature control device. It can also transmit the data to the condensate risk analysis system, the valve control system, and the temperature control system. The condensate pipe risk analysis system is used to receive data from the data acquisition system to determine the condensate pipe temperature and decide on the shutdown method. The temperature control system is used to receive temperature detection data from the data acquisition system and temperature control information transmitted from the condensate pipe risk analysis system; and to switch the operating mode of the temperature control device according to the temperature detection data from the data acquisition system and the temperature control information transmitted from the condensate pipe risk analysis system. The valve control system is used to receive valve status data from the data acquisition system and control the opening and closing of the corresponding valves according to the shutdown method determined by the condensate pipeline risk analysis system.

[0033] In the above embodiments, the condensate risk analysis system is also used to control the temperature control device to sequentially heat, maintain a constant temperature, and cool down the fluid in the bypass pipe.

[0034] Specifically, the condensate pipeline risk analysis system receives data from the data acquisition system including: the open / closed status of valve 1 at the subsea pipeline inlet, the open / closed status of valve 2 at the bypass pipeline inlet, the open / closed status of valve 3 at the bypass pipeline outlet, the open / closed status of valve 4 at the replacement pipeline inlet, the fluid temperature inside the bypass pipeline measured by a temperature sensor, the external ambient temperature of the bypass pipeline measured by a temperature sensor, the fluid flow rate inside the bypass pipeline, the fluid information detected by the fluid detection device at the subsea pipeline outlet, and the shutdown decision activation command. Through calculation and analysis, the condensate pipeline risk analysis system can feed back control information to both the temperature control system and the valve control system.

[0035] In this embodiment, the condensate pipe risk analysis system is also used to instruct the valve control system to close all valves when the content of the replacement fluid in the outlet fluid exceeds a preset threshold during the shutdown process after replacement.

[0036] In the above embodiments, the valve control system switches the open / closed states of valve 1 at the submarine pipeline inlet, valve 2 at the bypass pipeline inlet, valve 3 at the bypass pipeline outlet, and valve 4 at the replacement pipeline inlet based on the valve status data received from the data acquisition system and the valve control information transmitted from the condensate pipeline risk analysis system.

[0037] In the above embodiments, the methods for stopping transmission include: When directly stopping the pipeline, close all valves; these valves include the submarine pipeline inlet valve 1, the bypass pipeline inlet valve 2, the bypass pipeline outlet valve 3, and the replacement pipeline inlet valve 4.

[0038] When stopping transport after replacement, open the inlet valve 4 of the replacement pipeline and close the inlet valve 1 of the subsea pipeline.

[0039] In the above embodiments, the data acquisition system includes a fluid temperature detection sensor in the bypass pipeline, a fluid flow detection sensor in the bypass pipeline, and a fluid detection device installed at the outlet of the subsea pipeline.

[0040] In the above embodiments, the temperature control system switches the operating mode of the temperature control device based on the temperature detection data from the data acquisition system and the temperature control information transmitted by the condensate pipe risk analysis system. The operating modes of the temperature control device include: heating mode, cooling mode, constant temperature mode, and shutdown mode.

[0041] In summary, the use of this invention specifically includes the following steps: (1) When the subsea pipeline is operating normally, valve 1 at the subsea pipeline inlet is open, while valve 2 at the bypass pipeline inlet, valve 3 at the bypass pipeline outlet, and valve 4 at the replacement pipeline inlet are all closed, and the temperature control device is in shutdown mode. At this time, crude oil flows in from the subsea pipeline inlet and flows out from the subsea pipeline outlet.

[0042] (2) When a subsea pipeline needs to be shut down, its operational status must be adjusted and controlled through a subsea pipeline shutdown replacement decision system to prevent pipeline condensation accidents after shutdown. Specifically, this includes the following steps: (21) After receiving the shutdown decision activation command, the condensate pipe risk analysis system receives data sent from the data acquisition system in real time. The condensate pipe risk analysis system sends "switch to heating mode" control information to the temperature control system and "open bypass pipeline" control information to the valve control system.

[0043] After receiving the "switch to heating mode" control information sent by the condensate pipe risk analysis system, the temperature control system switches the operating mode of the temperature control device from the shutdown mode to the heating mode. The heating mode of the temperature control device heats the crude oil in the bypass pipe, causing any solid deposits such as wax that may exist in the bypass pipe to dissolve, thereby eliminating the influence of solid deposits on the condensate pipe temperature detection.

[0044] After receiving the "Open Bypass Pipeline" control message from the condensate pipeline risk analysis system, the valve control system switches the bypass pipeline inlet valve 2 and bypass pipeline outlet valve 3 from closed to open. Once the bypass pipeline inlet valve 2 and bypass pipeline outlet valve 3 are open, fluid will flow into the bypass pipeline.

[0045] (22) The condensate risk analysis system receives the fluid temperature in the bypass pipeline from the data acquisition system in real time. When the fluid temperature in the bypass pipeline is higher than 70°C, the condensate risk analysis system will send a "switch to constant temperature mode" control message to the temperature control system.

[0046] After receiving the "switch to constant temperature mode" control message from the condensate pipe risk analysis system, the temperature control system will switch the operating mode of the temperature control device to constant temperature mode. In constant temperature mode, the fluid temperature in the bypass pipe will be maintained at 70℃.

[0047] After the temperature control device switches to constant temperature mode, it continues to run in constant temperature mode for 1 hour, that is, it keeps the fluid in the bypass pipe at 70°C for 1 hour, so that any deposits that may exist in the bypass pipe can be completely dissolved.

[0048] (23) One hour after the temperature control device switches to constant temperature mode, the condensate pipe risk analysis system sends a “switch to cooling mode” control message to the temperature control system.

[0049] After receiving the "switch to cooling mode" control information sent by the condensate risk analysis system, the temperature control device will cool the fluid temperature in the bypass pipe at a rate of 0.5℃ / min in the cooling mode.

[0050] During the fluid cooling process in the bypass pipeline, the condensate risk analysis system will analyze the changes in fluid flow rate in the bypass pipeline in real time.

[0051] (24) When the fluid flow rate in the bypass pipe drops to 0, the condensation risk analysis system sends a “switch to shutdown mode” control message to the temperature control system and records the fluid temperature in the bypass pipe, which is the condensation temperature of the submarine pipeline.

[0052] After receiving the "switch to shutdown mode" control message from the condensate pipe risk analysis system, the temperature control system shuts down.

[0053] The condensate risk analysis system sends a "close bypass pipeline" control message to the valve control system.

[0054] After receiving the "close bypass pipeline" control information, the bypass pipeline inlet valve 2 and bypass pipeline outlet valve 3 are changed from open to closed.

[0055] (25) The condensate risk analysis system makes a shutdown operation decision based on the recorded condensate temperature and the lowest ambient temperature along the submarine pipeline. If the lowest ambient temperature along the submarine pipeline minus the condensate temperature is greater than 3°C, the condensate risk analysis system sends a "direct shutdown" control message to the valve control system; if the lowest ambient temperature along the submarine pipeline minus the condensate temperature is less than or equal to 3°C, the condensate risk analysis system sends a "shutdown after replacement" control message to the valve control system.

[0056] If the valve control system receives a "direct stop" control message, valve 1 at the submarine pipeline inlet, valve 2 at the bypass pipeline inlet, valve 3 at the bypass pipeline outlet, and valve 4 at the replacement pipeline inlet will all be adjusted to the closed state; if the valve control system receives a "stop after replacement" control message, it will open valve 4 at the replacement pipeline inlet and close valve 1 at the submarine pipeline inlet.

[0057] After the inlet valve 4 of the replacement pipeline is opened, seawater will flow into the replacement pipeline and into the subsea pipeline.

[0058] (26) The condensate risk analysis system analyzes the fluid information detected by the subsea pipeline outlet fluid detection device sent by the data acquisition system in real time. When the water content of the fluid at the subsea pipeline outlet is detected to be greater than 95%, the condensate risk analysis system sends a "direct stop" control message to the valve control system.

[0059] After the valve control system receives the "direct stop" control information, valve 1 at the submarine pipeline inlet, valve 2 at the bypass pipeline inlet, valve 3 at the bypass pipeline outlet, and valve 4 at the replacement pipeline inlet will all be adjusted to the closed state.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A decision-making method for the suspension and replacement of subsea pipelines, characterized in that, include: Obtain fluid from a bypass pipe connected to the subsea pipeline; wherein the bypass pipe is connected to the subsea pipeline at the inlet of the subsea pipeline. The fluid in the bypass pipe is cooled, and the fluid flow rate in the bypass pipe is monitored during the cooling process. The fluid temperature at which the fluid flow rate drops to zero is defined as the condensate temperature. The method of shutting down the subsea pipeline is determined based on a comparison of the condensate temperature with the ambient temperature along the pipeline route.

2. The subsea pipeline shutdown and replacement decision-making method as described in claim 1, characterized in that, Before the cooling process, a pretreatment step is also included: The fluid in the bypass pipe is heated and kept at a constant temperature to dissolve the solid deposits therein; Among them, heating treatment involves heating the fluid to a preset temperature; constant temperature treatment involves maintaining the fluid temperature at a constant temperature for a preset time period.

3. The subsea pipeline shutdown and replacement decision-making method as described in claim 1, characterized in that, Based on a comparison of the condensate temperature and the ambient temperature along the subsea pipeline route, a decision is made regarding the method of stopping the subsea pipeline, including: If the difference between the lowest ambient temperature along the subsea pipeline and the condensate temperature is greater than the first threshold, the decision is to directly stop the pipeline; if the difference is less than or equal to the first threshold, the decision is to stop the pipeline after replacement.

4. The subsea pipeline shutdown and replacement decision-making method as described in claim 3, characterized in that, The first threshold is 3℃.

5. The subsea pipeline shutdown and replacement decision-making method as described in claim 3, characterized in that, The shutdown after replacement includes: Open the displacement pipeline valve to introduce displacement fluid, and close the subsea pipeline inlet valve; Simultaneously, monitor the fluid information at the outlet of the subsea pipeline, and close all valves when the content of the displacement fluid in the outlet fluid exceeds the second threshold.

6. The subsea pipeline shutdown and replacement decision-making method as described in claim 5, characterized in that, The second threshold is 95%, the replacement fluid is seawater, and the fluid information is water content.

7. A subsea pipeline shutdown and replacement decision-making system, used to implement the subsea pipeline shutdown and replacement decision-making method as described in any one of claims 1 to 6, characterized in that, include: A bypass pipeline connects to the submarine pipeline, and a replacement pipeline is installed between the inlet of the bypass pipeline and the inlet of the submarine pipeline. A temperature control device, installed on the bypass pipe, is used to regulate the temperature of the fluid inside the bypass pipe; The data acquisition system collects data including the open / closed status of the inlet valve of the subsea pipeline, the open / closed status of the inlet valve of the bypass pipeline, the open / closed status of the outlet valve of the bypass pipeline, the open / closed status of the inlet valve of the replacement pipeline, the fluid temperature in the bypass pipeline measured by the temperature sensor, the fluid flow rate in the bypass pipeline, the fluid information detected by the fluid detection device at the outlet of the subsea pipeline, and the operating mode information of the temperature control device; and transmits the data to the condensate risk analysis system, the valve control system, and the temperature control system. The condensate pipe risk analysis system is used to receive data from the data acquisition system to determine the condensate pipe temperature and decide on the shutdown method. The temperature control system is used to receive temperature detection data transmitted from the data acquisition system and temperature control information transmitted from the condensate pipe risk analysis system. Based on the temperature detection data from the data acquisition system and the temperature control information transmitted from the condensate pipe risk analysis system, the operating mode of the temperature control device is switched. The valve control system is used to receive valve status data from the data acquisition system and control the opening and closing of the corresponding valves according to the shutdown method determined by the condensate pipeline risk analysis system.

8. The submarine pipeline shutdown and replacement decision system as described in claim 7, characterized in that, The condensate risk analysis system is also used to control the temperature control device to sequentially heat, maintain a constant temperature, and cool down the fluid in the bypass pipeline.

9. The subsea pipeline shutdown and replacement decision system as described in claim 7, characterized in that, The methods for suspending transmission include: When stopping the flow directly, close all valves; When stopping transport after replacement, open the inlet valve of the replacement pipeline and close the inlet valve of the subsea pipeline.

10. The subsea pipeline shutdown and replacement decision system as described in claim 7, characterized in that, The condensate risk analysis system is also used to instruct the valve control system to close all valves when the content of the replacement fluid in the outlet fluid exceeds a preset threshold during the shutdown process after replacement.

Images