Electric heating and heat preservation system and method for deep sea gas production seabed wellhead flow channel cold point

Abstract

The invention discloses an electric heating and heat preservation system and method for a deep-sea gas production seabed wellhead flow channel cold point, which are used for solving the problems of natural gas hydrate generation and paraffin precipitation blockage caused by low temperature and throttling of a deep-sea gas production underwater wellhead and an underwater gas production tree flow channel and ensuring efficient and stable operation of deep-sea gas production operation. An electric heating and heat preservation system for a deep sea gas production seabed wellhead flow channel cold point comprises a cold point positioning system, an electric heating device and a control system. The cold spot positioning system performs real-time data acquisition and preprocessing by constructing a temperature sensor network for key cold spots of an underwater christmas tree runner, quantifies the positions and risk levels of the cold spots in combination with a probability statistical model, and provides an accurate targeted heating basis for the distribution positions of electric heating devices. A heating element of the electric heating device is arranged in a cold point area of an underwater christmas tree flow channel; the control system obtains data measured by the temperature sensors in the cold spot areas in real time, and whether the corresponding heating elements are started or not is determined according to the data.

Description

Technical Field

[0001] The present invention belongs to the technical field of deep-sea oil and gas production, and in particular relates to an electric heating and heat preservation system and method for cold spots in a submarine wellhead flow channel of deep-sea gas production. Background Art

[0002] In deepwater gas production, underwater wellheads and subsea Christmas trees are core infrastructure, and their stable operation is directly related to the continuous supply of energy. The unique characteristics of the deepwater environment, such as high water pressure, low temperatures, and complex and changing operating conditions, pose numerous severe challenges to gas production operations. Flow channel blockage is particularly prominent, becoming a key factor restricting the efficiency and safety of deepwater gas production.

[0003] As a key hub in the subsea system, the underwater Christmas tree performs important functions such as suspending the gas pipe string, sealing the annular space of the gas casing, and controlling and regulating gas well production. Since its first application in 1967, more than 1,200 underwater Christmas trees have been used in the development of more than 250 gas production projects worldwide. During deep-sea gas production operations, throttling is very likely to occur within the underwater Christmas tree and in the flow channels connected to the underwater wellhead. According to the principles of fluid mechanics, when gas flows in the flow channel, if it encounters changes in pipe diameter or valve adjustment, the fluid flow rate and pressure will change, resulting in a throttling effect. This throttling effect not only causes pressure loss, but also triggers temperature changes, which in turn creates conditions for the formation of natural gas hydrates and wax deposition.

[0004] Natural gas hydrates are ice-like crystalline substances formed by natural gas and water under low-temperature and high-pressure conditions. Their formation process occupies flow channel space, resulting in a reduction in the effective cross-sectional area of ​​the flow channel, or even complete blockage of the flow channel. At the same time, if the natural gas contains a certain amount of heavy hydrocarbons and other substances, they will gradually precipitate and deposit on the pipe wall in a low-temperature environment, forming a waxing phenomenon. Waxing will also cause the inner diameter of the flow channel to become smaller, increase fluid flow resistance, reduce gas production efficiency, and in severe cases, interrupt gas production operations. In actual deep-sea gas production projects, flow channel blockage problems often lead to a significant drop in gas production and even damage to equipment. Repair costs are high and time-consuming, which has a serious negative impact on the economic benefits and stability of the entire gas production operation.

[0005] Currently, the industry commonly uses the injection of hydrate inhibitors to prevent flow channel blockage. Hydrate inhibitors primarily work by altering the phase equilibrium conditions of natural gas hydrates, inhibiting their formation. However, this method has numerous limitations. First, the precise injection rate of inhibitors is difficult to control. Too little injection will fail to effectively inhibit the formation of natural gas hydrates and wax deposition. Excessive injection not only significantly increases production costs but may also pollute the marine environment. Research has shown that in some deep-sea gas production operations, excessive injection of inhibitors to achieve effective inhibition increases operating costs by 20%-30%. Second, under complex operating conditions, such as those involving complex multiphase flow within the flow channel and large temperature and pressure fluctuations, hydrate inhibitors may not be fully effective. This is because the presence of multiphase flow affects the distribution and diffusion of the inhibitor within the flow channel, making it difficult for the inhibitor to evenly contact the natural gas and water, thereby reducing its inhibitory effectiveness. Furthermore, the actual operating environment of subsea flow channels differs from laboratory simulations, making the inhibitor's effectiveness in practical applications less than expected.

[0006] While attempts have been made to address the throttling issue by employing downhole throttling technology to reduce wellhead temperature and pressure during production, for example, the "105 MPa / 210°C fixed downhole throttle valve for deepwater use" independently developed by the Sichuan Petroleum Drilling and Production Research Institute addresses, to some extent, the challenges of high-temperature, high-pressure sealing and downhole strength in a compact size through innovative multi-slip balancing and stabilization mechanisms, optimized sealing solutions, and rounded throttle nozzle designs. However, this technology primarily focuses on addressing wellhead temperature and pressure issues, and fails to fundamentally address the localized low-temperature areas ("cold spots") within the subsea gas tree and subsea wellhead flow passages caused by throttling. Furthermore, the structures of subsea gas trees and subsea wellhead flow passages are complex and diverse, with various irregularly shaped pipe sections, elbows, and reducers. Downhole throttle valves struggle to fully adapt to these complex flow passages, and thus are unable to effectively and comprehensively control throttling within the flow passages.

[0007] In summary, existing technical means have obvious shortcomings in solving the problems of natural gas hydrate formation and wax blockage caused by low temperature and throttling in deep-sea gas production underwater wellheads and underwater gas tree flow channels. Summary of the Invention

[0008] In view of this, the present invention provides an electric heating and insulation system and method for cold spots in the submarine wellhead flow channel of deep-sea gas production, which solves the shortcomings of traditional inhibitor methods and downhole throttling technology, effectively inhibits the formation of natural gas hydrates and wax blockage, improves the efficiency, safety and environmental friendliness of deep-sea gas production operations, and is suitable for the long-term stable operation of complex deep-sea flow channel structures.

[0009] To solve the above problems, according to one aspect of the present application, an embodiment of the present invention provides an electric heating and insulation system for cold spots in a subsea wellhead flow channel for deep-sea gas production, comprising:

[0010] Cold spot positioning system, electric heating device and control system;

[0011] The cold spot positioning system builds a temperature sensor network at key cold spots in the underwater gas tree flow channel to collect and pre-process real-time data. It then combines a probabilistic statistical model to quantify the location and risk level of cold spots, providing a precise basis for targeted heating of the electric heating device.

[0012] The heating element of the electric heating device is arranged in the cold spot area of ​​the flow channel of the underwater gas tree;

[0013] The control system obtains the data measured by the temperature sensors in each cold spot area in real time, and decides whether to start the corresponding heating element based on the data.

[0014] In some embodiments, the temperature sensing network of the cold spot positioning system includes deploying multiple sets of PT1000 temperature sensors throughout the underwater gas tree flow channel (including valves, elbows, reducers and other throttling sensitive parts), covering all potential low-temperature risk areas. The sensor spacing is adjusted according to the complexity of the flow channel structure, and is encrypted to 0.1-0.5 meter intervals in special-shaped pipe sections, and a standard spacing of 1-2 meters is adopted in straight pipe sections to form a "point" monitoring network, and the data interpolation algorithm is combined to realize "surface" analysis of the flow channel temperature field.

[0015] In some embodiments, during the real-time data collection and preprocessing, the temperature sensor collects temperature data in real time at a frequency of 1 Hz, transmits it to the edge computing unit through a dedicated underwater cable, and then uses a median filtering algorithm to remove outliers (such as sensor transient interference signals), and uses a sliding average method (window width 5-10 minutes) to smooth the temperature fluctuation curve to extract valid data reflecting the actual temperature trend.

[0016] In some embodiments, the cold spot area probability statistical model analyzes the historical data of the same model of underwater gas trees during the analysis process, and defines the area below the wax critical temperature of 2°C as a "cold spot candidate area". When the temperature at a certain location is lower than the threshold for 5 consecutive minutes, it is determined to be a valid cold spot event. The number of cold spot events triggered by each monitoring point in a unit time (such as 30 days) is counted in the time dimension to calculate the frequency of cold spot occurrence. (N iThe spatial weight matrix is ​​established based on the geometric parameters of the flow channel in the spatial dimension, and the cold spot frequencies of adjacent monitoring points are interpolated and fitted to generate a cold spot probability density cloud map for the entire flow channel. The spatial distribution of the probability of cold spot occurrence is intuitively displayed. The darker the color, the higher the probability. The potential cold spot area is divided into three levels according to the probability density: the high-risk area with a probability greater than 60% is prioritized for the deployment of encrypted heating devices; the medium-risk area with a probability of 30%-60% is adopted for conventional heating density + dynamic power adjustment; the low-risk area with a probability less than 30% is maintained for basic insulation.

[0017] In some embodiments, the heating element is a nickel-chromium alloy resistance wire. For circular pipe sections, the wire is spirally wound. For shaped pipe sections (e.g., elbows and spheres), the wire density and spacing are adjusted based on the curvature and diameter. For spherical pipe sections, a combination of spiral and circumferential cross-winding is used. The heating element is wrapped with an insulation layer, the thickness of which is determined based on heat loss calculations to minimize heat loss to the external seawater.

[0018] In some embodiments, the insulation layer is covered with an outer carrier having samarium cobalt permanent magnet adsorption units. The position and spacing of the samarium cobalt permanent magnet adsorption units are adjusted according to the shape and diameter of the pipeline, and the adsorption units are tightly adsorbed on the surface of the pipeline.

[0019] In some embodiments, a power supply device is also included. The power supply device directly branches out a cable from the power supply interface of the underwater gas production tree or the underwater gas production tree umbilical cable, and is connected to an underwater power distribution unit dedicated to the electric heating device. The cable has both power transmission and data communication functions; after the underwater power distribution unit receives the electric energy, it is distributed to the electric heating device and the temperature sensor through the step-down module.

[0020] In some embodiments, in regular areas such as straight pipe sections, multiple electric heating devices are concentrated into modules through bus terminals, and their power lines and signal lines of the temperature sensors in the area are respectively networked through field bus technology and connected to the underwater distribution unit through a single cable; in throttling-sensitive parts such as elbows, reducers and valves, each electric heating device and temperature sensor are directly connected to the distribution unit and control system using independent lines to ensure accurate power supply and independent data transmission in high-risk areas.

[0021] In some embodiments, the control system collects temperature sensor data in real time through cables. When it monitors that the flow channel temperature is lower than the wax deposition critical value, it instructs the underwater power distribution unit to adjust the power of the electric heating device and start the rapid heating mode; after the temperature reaches the standard, it switches to steady-state maintenance and dynamically adjusts the power output through the PID algorithm, thereby achieving a combination of power supply efficiency and control accuracy.

[0022] According to another aspect of the present application, an embodiment of the present invention further provides a method for operating the electric heating and insulation system for the cold point of the deep-sea gas production submarine wellhead flow channel, which comprises the following steps:

[0023] S1: Collect historical production data of the same type of underwater gas trees, and use probabilistic statistical models to classify the risk levels of potential cold spot areas of the same type of underwater gas trees in service, in preparation for the deployment of subsequent heating devices.

[0024] S2: Use a laser rangefinder or 3D scanner to obtain the geometric parameters of the cold spot pipe section. For circular pipe sections, use spiral winding of nickel-chromium alloy resistance wire. For special-shaped pipe sections (such as elbows and spheres), adjust the resistance wire density and spacing according to the curvature and pipe diameter. For spherical pipe sections, use a combination of spiral and circumferential cross winding.

[0025] S3: Deploy multiple sets of PT1000 temperature sensors in candidate cold spot areas and throttling-sensitive locations (including valves, elbows, and reducers) throughout the underwater gas tree flow channel. Spacing between special-shaped pipe sections is increased to 0.1-0.5 meters, while straight pipe sections use a standard spacing of 1-2 meters. This forms a "point" monitoring network, and combines data interpolation algorithms to achieve "surface" analysis of the flow channel temperature field.

[0026] S4: Wrap the electric heating module with polyurethane foam as an insulation layer. Determine the thickness of the insulation layer based on heat loss calculations to reduce heat loss to the external seawater. Install the outer carrier and auxiliary fixing components of the samarium cobalt permanent magnet magnetic adsorption unit to ensure a tight fit and a good seal between the device and the pipeline.

[0027] S5: Integrate the electric heating device, temperature sensor, insulation layer and magnetic structure into the flow channel of the gas tree to simulate the cold spot temperature to trigger heating. Verify that the device response time is less than 10 seconds and the sensor data error is ≤±0.5℃. Test the adsorption force of the magnetic structure under a pressure of 40MPa.

[0028] S6: Connect the cables of the electric heating device and the sensor to the branch interface at the bottom end of the umbilical cable. Use a composite cable (inner ±10kV power line, outer shielded communication line), pre-install an underwater power distribution unit, and build in a step-down module and surge protector to complete the power distribution circuit debugging.

[0029] S7: The pre-assembled underwater gas tree is transported to the target sea area by an engineering vessel, lowered to the predetermined position on the seabed, and mechanically connected and sealed to the wellhead.

[0030] S8: Use the ROV manipulator to connect the umbilical cable branch interface to the power supply system. After activating the loop, test the composite cable power loss and communication rate. Simulate the cold spot temperature to verify the electric heating device starts the rapid heating mode and PID dynamic adjustment function.

[0031] S9: After the underwater tree begins producing gas, the electric heating system automatically starts and stops according to preset thresholds. When the monitored temperature drops below the activation threshold, the electric heating device is activated and the power is initially adjusted according to the dynamic power regulation model. Once the temperature reaches the target, the system switches to a steady-state maintenance mode. The cold spot probability model is automatically updated weekly. If the prediction deviation exceeds 15%, the spatial weight coefficient is automatically adjusted to optimize the heating power density in high-risk areas.

[0032] S10: During the heating process, the heating power is continuously adjusted using the PID algorithm to ensure that the temperature fluctuation is ≤±1°C. The umbilical cable interface sealing and electrical heating uniformity are inspected monthly using an ROV, and any faulty sensors or adsorption units are remotely replaced or repaired.

[0033] Compared with the prior art, the electric heating and heat preservation system for cold spots of deep-sea gas production submarine wellhead flow passages of the present invention has at least the following beneficial effects:

[0034] (1) Accurate cold spot positioning

[0035] By deploying multiple sets of temperature sensing networks and dynamic probability statistical models across the entire area, real-time monitoring and risk grading of low-temperature cold spots in the flow channel are achieved. The spatial distribution probability of cold spots can be intuitively presented, and low-temperature risks in throttling-sensitive areas such as valves, elbows, and reducer sections can be accurately identified. This solves the problem of ambiguous positioning of local cold spots using traditional methods, providing precise targeting for heating devices.

[0036] (2) Heating scheme: The efficient electric heating device is optimized for different pipe section structures (circular, special-shaped, spherical). Through differentiated resistance wire winding density (such as denser in areas with large curvature), heat loss control of the insulation layer, and samarium cobalt permanent magnet adsorption installation structure, efficient and uniform heating of cold spot areas is achieved, significantly improving heat utilization, effectively inhibiting the formation of natural gas hydrates and wax blockage, and ensuring smooth flow.

[0037] (3) Intelligent control system

[0038] The closed-loop control system combines real-time temperature feedback with PID dynamic adjustment algorithm, which can automatically respond to temperature changes, quickly switch between "heating-maintenance" mode, and accurately control the flow channel temperature; the use of a hierarchical power supply mode (centralized networking in regular areas and independent power supply in high-risk areas) and an abnormal fault-tolerant mechanism enhances the stability and reliability of the system in complex deep-sea environments, while avoiding the environmental pollution and cost waste of traditional inhibitor methods.

[0039] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0041] Figure 1 A cold spot location diagram according to an embodiment of the present invention;

[0042] Figure 2 This is an application diagram of the electric heating device;

[0043] Figure 3 Schematic diagram of power supply and control connections for the gas tree;

[0044] Figure 4 This is the flow chart of the closed-loop control system. DETAILED DESCRIPTION

[0045] To further illustrate the technical means and effects employed by the present invention to achieve its intended objectives, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention is provided in conjunction with the accompanying drawings and preferred embodiments. In the following description, different references to "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics of one or more embodiments may be combined in any suitable manner.

[0046] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; and direct or indirect connections through an intermediary. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0047] The present invention proposes an electric heating and insulation system for cold spots in the flow channel of a submarine wellhead for deep-sea gas production, comprising a cold spot positioning system, an electric heating device and a control system; the cold spot positioning system performs real-time data acquisition and preprocessing by constructing a temperature sensor network at key cold spots in the flow channel of an underwater gas tree, and quantifies the location and risk level of the cold spots in combination with a probability statistical model, thereby providing an accurate targeted heating basis for the distribution position of the electric heating device; the heating elements of the electric heating device are arranged at the cold spot positions of the flow channel of the underwater gas tree; the control system obtains data measured by the temperature sensors at each cold spot position in real time, and decides whether to start the corresponding heating element based on the data.

[0048] Specifically, the cold spot positioning system acquires flow channel temperature data by building a temperature sensing network at key cold points in the underwater gas tree flow channel, and combines a probabilistic statistical model to quantify the location and risk level of the cold spots, providing an accurate targeted heating basis for the electric heating device.

[0049] In terms of temperature sensing network construction, multiple PT1000 temperature sensors are deployed throughout the underwater gas tree flow channel (including valves, elbows, reducers, and other throttling-sensitive areas), covering all potential low-temperature risk areas. The sensor spacing is adjusted according to the complexity of the flow channel structure, with an interval of 0.1-0.5 meters in special-shaped pipe sections and a standard spacing of 1-2 meters in straight pipe sections. This forms a "point" monitoring network, and a data interpolation algorithm is combined to achieve "surface" analysis of the flow channel temperature field. During real-time data acquisition and preprocessing, the temperature sensor collects temperature data in real time at a frequency of 1Hz and transmits it to the edge computing unit via a dedicated underwater cable. The median filter algorithm is then used to remove outliers (such as transient sensor interference signals). The temperature fluctuation curve is smoothed using the sliding average method (window width 5-10 minutes) to extract valid data reflecting the actual temperature trend.

[0050] During the analysis of the cold spot location probability statistical model, the area below the wax deposition critical temperature of 2°C in the historical data of the same model underwater gas tree is defined as a "cold spot candidate area". When the temperature at a certain location is below the threshold for 5 consecutive minutes, it is determined to be a valid cold spot event. In the time dimension, the number of cold spot events triggered by each monitoring point in a unit time (such as 30 days) is counted to calculate the frequency of cold spot occurrence. (N i is the number of cold spot events at point i, T is the length of the statistical period), a spatial weight matrix is ​​established based on the geometric parameters of the flow channel in the spatial dimension, the cold spot frequencies of adjacent monitoring points are interpolated and fitted, and a probability density cloud map of cold spots in the entire flow channel is generated to intuitively display the spatial distribution of the probability of cold spot occurrence. The darker the color, the higher the probability. The cold spot candidate areas are divided into three levels according to the probability density: the high-risk area with a probability greater than 60% is given priority for deploying encrypted heating devices; the medium-risk area with a probability of 30%-60% is adopted for conventional heating density + dynamic power adjustment; the low-risk area with a probability less than 30% is only maintained for basic insulation.

[0051] During dynamic updating and verification, the cold spot probability model is automatically updated every week to incorporate the latest monitoring data to adapt to changes in operating conditions, and the accuracy of the probability model is verified through historical cold spot event data. If the prediction deviation is greater than 15%, the model parameter optimization process is automatically triggered, such as adjusting the spatial weight coefficient and correcting the temperature threshold.

[0052] See also Figure 1This diagram, based on a simplified schematic of the subsea tree flow path, illustrates low-temperature areas (cold spots) identified by the cold spot location system. Circles are used to indicate cold spots, visually demonstrating their association with these areas and helping technicians quickly identify locations requiring attention and heating measures.

[0053] Specifically, the electric heating device is designed to closely address the unique operating conditions of cold spots in the flow channel of underwater gas trees, aiming to achieve efficient, precise, and reliable heating. In terms of heating element selection, for circular pipe sections, nickel-chromium alloy resistance wire is used, tightly spirally wound around the pipe section surface. Using the formula:

[0054]

[0055] (k: thermal conductivity of insulation layer (W / m·K), L: length of heating pipe section (m), T pipe : Target pipe wall temperature (℃), T sea :Deep sea ambient temperature (℃), r pipe :Pipeline outer diameter (m), r ins : Outer diameter of insulation layer (m)) is used to determine steady-state maintenance power, and then the spacing and density are determined in combination with the power of the resistance wire.

[0056] When designing electric heating for irregularly shaped pipe sections, first use a laser rangefinder or 3D scanner to accurately measure geometric parameters such as length, curvature radius, and pipe diameter change, and calculate the external surface area. Adjust the resistance wire density based on the structural characteristics: At locations where pipe diameters change suddenly, the spacing between the wires at the large-diameter end, due to its larger heat dissipation area, should be reduced to 60% to 80% of that of a straight pipe section. The spacing at the small-diameter end can be maintained or slightly increased. For areas with large curvature, the spacing is adjusted based on the ratio of the curvature radius to the pipe diameter. The smaller the curvature radius, the smaller the spacing. For example, when the curvature radius to pipe diameter ratio is less than 1.5, the spacing is reduced to 50% to 70% of that of a straight pipe section.

[0057] See also Figure 2 , the figure shows in detail the installation structure of the electric heating device on the circular pipe section and the special-shaped pipe section. For the circular pipe section, you can see that the nickel-chromium alloy resistance wire is evenly spirally wound on the surface of the pipe section, and the winding spacing is clearly shown. At the same time, the polyurethane foam insulation material wrapped around the outside of the resistance wire is shown. In the special-shaped pipe section, the figure shows the situation of adjusting the density and spacing of the resistance wire according to the change in pipe diameter and curvature. The spherical pipe adopts a combination of spiral winding and circumferential cross winding. It is first spirally wound along the latitude direction (circumferential direction) near the center of the sphere (large curvature), and the spacing near the connecting pipe section is increased. Then it is cross-wound along the warp direction (longitudinal direction) to form a mesh structure to ensure uniform heating across the entire area.

[0058] When calculating steady-state power, first project the elbow-shaped pipe section into a straight pipe section of the same length, using the formula:

[0059]

[0060] Calculate the steady-state power of the equivalent straight pipe section, then introduce the heat loss empirical coefficient K (such as 90° elbow K is 1.5~2.0, the smaller the curvature radius, the larger the K value), and obtain the actual steady-state power of the special-shaped pipe section.

[0061] P 异形管实际 =P 等效直管 ×K

[0062] Finally, taking the elbow as an example, the resistance wires are evenly arranged along the circumference of its outer surface. The required total length of the resistance wires is calculated based on the total power and the power per meter of the resistance wires, and then the spacing between the resistance wires is evenly divided according to the circumference.

[0063] For special shaped structures like spherical pipes, we use laser scanning to obtain the spherical geometry parameters, combined with heat transfer calculations, to employ a combination of spiral winding and circumferential cross-winding. First, we evenly spirally wind the resistance wire along the spherical pipe's latitude (circumferential) direction. Near the center of the sphere, where the curvature is greater, the spacing is controlled at 0.1-0.3 meters, and near the connecting pipe section, where the curvature is less, the spacing is increased to 0.3-0.5 meters. The resistance wire is then cross-wound along the longitudinal (longitudinal) direction, forming a mesh structure with the latitude direction to ensure uniform heating across the entire pipe.

[0064] When calculating steady-state power, it is necessary to base it on the surface area of ​​the sphere and the heat conduction characteristics. The formula is:

[0065]

[0066] (where r pipe is the outer radius of the spherical pipe, r ins is the outer radius of the insulation layer, and the other parameters are consistent with the definition of the circular pipe segment).

[0067] In the design of the insulation material, polyurethane foam was selected, which has excellent thermal insulation properties and a thermal conductivity as low as 0.02-0.03W / (m·K). The polyurethane foam was wrapped around the exterior of the electric heating device at a certain thickness. For circular pipe sections, the wrapping thickness was uniform. For special-shaped pipe sections, the insulation material was adjusted according to the actual situation to ensure that the insulation material effectively covered the electric heating device, reducing heat loss to the external seawater and improving the efficiency of the electric heating. Using the heat transfer formula:

[0068]

[0069] (Q is the heat loss, k is the thermal conductivity of the polyurethane foam, A is the heat dissipation area of ​​the special-shaped pipe section, ΔT is the temperature difference between the pipe section and the seawater, and δ is the thickness of the insulation material.) To calculate the heat loss, first measure or determine the surface area A of each part of the special-shaped pipe section through modeling. Given the seawater temperature and the target temperature inside the pipe, the temperature difference ΔT is calculated. Then, the insulation material thickness is inferred based on the maximum allowable heat loss.

[0070] In terms of the device installation structure, in order to solve the problem of entanglement between the electric heating wire and the insulation layer on the irregular pipeline of the underwater gas tree, the surface of the irregular pipeline of the underwater gas tree is first cleaned and polished to remove dirt, rust and oxide layer; then the electric heating wire is evenly wound and wrapped with the insulation layer according to the design requirements to ensure that the electric heating wire has no cross-over and the insulation layer is well sealed; then the outer carrier with the magnetic adsorption unit is covered on the electric heating wire and the insulation layer. The magnetic adsorption installation structure uses samarium cobalt permanent magnet as the core adsorption unit. Its magnetic energy product can reach 35-50MGOe, and it can provide an adsorption force of not less than 500N under a deep-sea pressure environment of 60MPa, ensuring that the device fits tightly to the pipeline surface. The layout of the adsorption units is dynamically adjusted according to the shape of the pipe section: in the circular straight pipe section, the magnetic modules are evenly distributed at intervals of 300-500mm, and at least three adsorption points are installed on a single section of pipe to balance the force; for special-shaped pipe sections with a curvature radius of less than 500mm (such as elbows and spherical pipe sections), the spacing between the adsorption units is increased to 100-150mm, and the curvature of the pipe surface is matched through three-dimensional laser scanning data to ensure that the gap between the magnetic module and the pipe wall is less than 0.5mm to avoid displacement caused by seawater erosion. Finally, auxiliary fixing components such as rubber pads and sealing rings are installed to ensure the sealing and stability of the structure. At the same time, in response to the differences in heat demand at different cold spots, the density of the device layout is intelligently optimized. In cold spot areas with severe throttling such as valves and reducers, the heating film is laid in an overlapping manner to increase the heating power per unit area; in ordinary cold spot areas, a conventional single-layer layout is adopted to achieve precise heating.

[0071] In response to the connection requirements of different areas, a hybrid connection method is adopted: in regular areas such as straight pipe sections, multiple electric heating devices are concentrated into modules through bus terminals. Their power lines and the signal lines of the temperature sensors in the area are networked through fieldbus technology and connected to the underwater power distribution unit via a single cable. In throttling-sensitive areas such as elbows, reducers and valves, each electric heating device and temperature sensor is directly connected to the power distribution unit and control system using independent lines to ensure accurate power supply and independent data transmission in high-risk areas. The bus networking cable adopts multi-core cross-linked polyethylene (XLPE) insulated cable with a voltage rating of ≥30MPa, which is adapted to the low-voltage power supply requirements of regular areas. Its signal transmission adopts the Modbus RTU bus protocol, which can support up to 32 modules cascaded and a transmission rate of ≥9600bps, realizing centralized power supply and data communication for electric heating devices in regular areas. The independent power supply cable utilizes an armored copper-core composite cable. Its inner power line extends directly from the bottom of the underwater gas tree umbilical cable, transmitting ±10kV DC power. The outer steel-wire armor layer withstands a voltage of ≥40MPa, and the signal control line is a twisted-pair shielded cable that complies with the RS485 protocol. This cable connects to the underwater power distribution unit and, through the unit's high-voltage step-down module and DC-DC converter module, provides independent and precise power supply to electric heating devices in high-risk, irregularly shaped areas and transmits weak current signals to temperature sensors. Its twisted-pair shielding structure offers strong anti-interference capabilities, meeting the requirements of deep-sea electromagnetic environments and ensuring power supply reliability and data transmission stability in high-risk areas.

[0072] In terms of power control, a dynamic power regulation model is constructed based on the principles of fluid thermodynamics and heat transfer. This model collects real-time flow channel temperature, fluid flow rate, pressure, and other parameters monitored by temperature sensors. Combined with preset thresholds for natural gas hydrate formation and wax deposition, the model automatically adjusts the input voltage to the resistor wire or heating film through a fuzzy control algorithm, achieving stepless power regulation. When the monitored temperature approaches the threshold, the system automatically activates rapid heating mode, heating at maximum power. When the temperature reaches the set shutdown temperature, it enters maintenance power mode, dynamically adjusting the heating power based on the ambient heat dissipation to ensure that the flow channel temperature remains stable within a safe range.

[0073] When the system is in normal operation, only the steady-state maintenance power needs to be calculated. This power is used to compensate for the continuous heat loss from the pipeline to the deep-sea environment, ensuring that the pipe wall temperature is always maintained within a safe range. The calculation of steady-state power is based on the principles of heat transfer, taking into account factors such as insulation layer performance, pipe size, and temperature difference. The calculation formula is:

[0074]

[0075] When the system detects that the local temperature drops to the hydrate formation critical point, the transient heating power needs to be calculated, which is used to quickly raise the pipe wall temperature from the dangerous value to the safe range in a short time. The calculation of transient power needs to consider the heat capacity characteristics and the heating rate requirements of the pipe section, and the formula is:

[0076]

[0077] m: pipe section mass (kg), considering metal pipe + insulation layer during calculation

[0078] c p : specific heat capacity (J / (kg·pK))

[0079] ΔT: temperature rise requirement (℃)

[0080] t: heating time (s)

[0081] Referring to Figure 3 , it is a schematic diagram of power supply and control connection of the Christmas tree, which shows the power supply and control architecture of the deep-sea gas production system. The electric heating device adopts the "umbilical cable-underwater power distribution unit" architecture, which realizes the integration of power transmission and data communication of the electric heating device through the umbilical cable of the underwater Christmas tree. The underwater Christmas tree has been configured with a special umbilical cable for its communication and power supply. The power supply line and signal line are branched from the branch interface module at the bottom of the umbilical cable. The power supply line transmits ±10kV DC high voltage, and the signal line is a twisted shielded communication line, which is directly connected to the underwater power distribution unit and control system near the underwater Christmas tree. The outer layer is wrapped with a high-strength polyethylene insulation layer with a pressure rating of ≥40MPa, which can simultaneously transmit power and temperature data, power adjustment instructions, etc. of the closed-loop control system. The underwater power distribution unit is built-in with a voltage reduction module, a surge protector and an intelligent electric meter, which distributes power to the electric heating device and temperature sensor, and monitors energy consumption in real time.

[0082] In the sub-module heating design, the regular area electric heating device is concentrated into a modular unit through the bus networking power supply, which is suitable for conventional cold spot areas; high-risk special-shaped areas (such as elbows, valves) use independent electric heating devices and temperature control modules, which realize differentiated heating in cold spot areas by dynamically adjusting the resistance wire spacing, heating film laying density and power supply priority. The bus networking cable in the regular area is represented by a virtual line bundle, which is concentrated along the straight pipe section after being led out from the underwater power distribution unit, and is connected to each heating module through the bus terminal box; the independent power supply cable in the high-risk area is represented by a solid line single cable, which is directly led out from the power distribution unit independent port and connected to the electric heating device at the elbow, valve and other positions. Each cable is marked with "high voltage" and "independent control" identification.

[0083] The power demand of the power supply system is calculated based on the steady-state and transient power of the electric heating device: the steady-state power is calculated according to a patented formula for the total power of all pipe sections, with a 20% redundancy reserved; the transient power is 1.5 times the steady-state power, achieved through dynamic adjustment of the distribution unit's energy storage capacitors or the platform's power supply. Regarding safety, the cable connectors are constructed with a titanium alloy shell and epoxy resin potting, and the electric heating device's resistance wire is wrapped in a polytetrafluoroethylene insulation layer; the distribution unit has built-in overcurrent protection and leakage detection, and the surface platform is equipped with a remote power disconnect switch. This power supply system is compatible with the patented "dedicated underwater cable data transmission" design, transmitting monitoring data via cable to achieve real-time "monitoring-control-power supply" linkage. The magnetic adsorption structure adapts to the installation of the electric heating device to avoid cable stress concentration.

[0084] Specifically, see Figure 4 ,The figure shows the working logic of the closed-loop control system in a clear process framework.

[0085] For closed-loop control systems, temperature monitoring is the foundation of closed-loop temperature control systems. The system achieves comprehensive perception of flow channel temperature through rationally arranged temperature sensors. Multiple PT1000 temperature sensors are deployed in cold spots of the underwater gas tree flow channel to accurately capture subtle local temperature changes and precisely measure single-point temperature. PT1000 temperature sensors are used as temperature sensors, which have the characteristics of high precision and good stability. They are deployed at key nodes of the underwater gas tree flow channel, such as valves, reducers, and other areas with obvious throttling effects. The temperature sensors can accurately capture subtle local temperature changes and accurately measure single-point temperature. The sensor network adopts a hybrid wiring strategy: sensors in regular pipe sections transmit data centrally through the bus protocol, while sensors in special-shaped pipe sections and key nodes are directly connected to the control system with independent shielded cables to avoid multi-node signal interference and ensure the real-time and accuracy of monitoring data in low-temperature areas.

[0086] The control system has pre-set temperature control thresholds. To prevent wax deposition, the lower limit can be set at around 2°C. This ensures the temperature inside the pipe is above the critical temperature for wax deposition, minimizing wax precipitation and deposition. When the temperature sensor detects that the temperature has dropped to the set activation threshold of 2°C, the monitoring data is transmitted to the control system in real time via a dedicated underwater transmission line. Upon receiving this data, the control system quickly activates the electric heating device and initially adjusts the heating power based on a pre-set dynamic power regulation model and temperature deviations.

[0087] During the heating process, the temperature sensor continuously collects real-time temperature data and feeds back to the control system. The control system compares the collected real-time temperature with the set target temperature of 8℃, and calculates the temperature deviation. Then, the control system uses the PID (Proportion-Integral-Derivative) control algorithm to dynamically adjust the power output of the electric heating device according to the temperature deviation, the rate of change of the deviation, and the integral of the deviation. When the temperature approaches the target temperature, the PID algorithm will automatically reduce the power output to avoid temperature overshoot. If the temperature rises slowly, the PID algorithm will increase the power to ensure that the temperature can reach the target value smoothly and quickly. When the temperature sensor detects that the temperature rises to the closing threshold of 8℃, the control system immediately issues an instruction to turn off the electric heating device and stop heating, thereby realizing continuous and stable control of the temperature of the flow passage of the underwater gas production tree.

[0088] A working method of an electric heating and heat preservation system for cold spots in the flow passage of a deep-sea gas production subsea wellhead, comprising the following steps:

[0089] S1: Collect historical production data of the same type of underwater gas production tree, and use a probability statistical model to classify the potential cold spot positions of the same type of in-service underwater gas production tree according to risk levels, to prepare for the deployment of the subsequent heating device.

[0090] S2: Use a laser range finder or a three-dimensional scanner to obtain the geometric parameters of the cold spot pipe section. For circular pipe sections, use nickel-chromium alloy resistance wire to spiral wrap. For special-shaped pipe sections (such as elbows and spheres), adjust the resistance wire density and spacing according to the curvature and pipe diameter. For spherical pipe sections, use a combination of spiral and hoop cross wrapping.

[0091] S3: Deploy multiple sets of PT1000 temperature sensors at the throttle sensitive parts (including valves, elbows, and variable diameter pipe sections) in the entire flow passage of the underwater gas production tree. The spacing of special-shaped pipe sections is encrypted to 0.1-0.5 meters, and the spacing of straight pipe sections is 1-2 meters, forming a "point" monitoring network. The sensors of regular pipe sections transmit data through the RS485 bus protocol, and the sensors of special-shaped pipe sections and key nodes are directly connected to the control system through independent shielded cables, forming a "point-line" monitoring network. The "point-line" monitoring network realizes "surface" analysis of the flow passage temperature field in combination with data interpolation algorithms.

[0092] S4: Wrap the electric heating module with polyurethane foam material as a heat insulation layer, and determine the thickness of the heat insulation layer according to heat loss calculation to reduce heat loss to the external seawater. Install the outer carrier and auxiliary fixing parts of the samarium-cobalt permanent magnet magnetic adsorption unit to ensure that the device is tightly attached to the pipe and sealed well.

[0093] S5: Integrate the electric heating device, temperature sensor, heat insulation layer, and magnetic structure in the flow passage of the gas production tree, simulate the cold spot temperature to trigger heating, verify that the response time of the device is less than 10 seconds, the sensor data error is less than or equal to ±0.5℃, and test the adsorption force of the magnetic structure under a pressure of 40MPa.

[0094] S6: Connect the cables of the electric heating device and the sensor to the branch interface at the bottom end of the umbilical cable. Use a composite cable (inner ±10kV power line, outer shielded communication line), pre-install an underwater power distribution unit, and build in a step-down module and surge protector to complete the power distribution circuit debugging.

[0095] S7: The pre-assembled underwater gas tree is transported to the target sea area by an engineering vessel, lowered to the predetermined position on the seabed, and mechanically connected and sealed to the wellhead.

[0096] S8: Electric heating devices in regular areas are concentrated into modules through bus terminals and powered by bus technology. High-risk special-shaped areas (such as elbows and valves) are directly connected to the power distribution unit and control system through independent lines to achieve precise power supply and independent data transmission.

[0097] S9: Based on the principles of fluid thermodynamics and heat transfer, a dynamic power regulation model is constructed to automatically adjust the heating power according to real-time temperature, flow, pressure and other parameters to achieve "rapid heating-steady-state maintenance" mode switching.

[0098] S10: Preset temperature control thresholds (start threshold and shut-down threshold). When the monitored temperature is lower than the start threshold, the electric heating device is started and the power is preliminarily adjusted; when the temperature reaches the shut-down threshold, heating is stopped.

[0099] S11: During the heating process, temperature data is continuously collected and compared with the target temperature. The PID control algorithm is used to dynamically adjust the power output to ensure that the temperature reaches the target value smoothly and avoids overshoot or slow heating.

[0100] S12: Establish an abnormal situation handling mechanism, such as activating a backup monitoring plan when a sensor fails, taking emergency measures when data transmission is interrupted, using ROV to inspect the sealing of the umbilical cable interface and the uniformity of electric heating, and remotely replacing or repairing faulty sensors or adsorption units to ensure system stability and reliability.

[0101] ROV is a remote-controlled underwater robot equipped with a high-definition camera, ultrasonic thickness gauge, infrared thermal imager and robotic arm. It communicates with the surface control platform in real time via an umbilical cable, transmitting video, sensor data and control commands to perform inspections, remote replacement and repairs.

[0102] In summary, the present invention discloses an electric heating and insulation device for cold spots in the flow channel of a submarine wellhead for deep-sea gas production. The device constructs a key cold spot temperature sensing network through a cold spot positioning system, and combines a probability statistical model to identify low-temperature risk areas in the flow channel in real time and classify them into levels; the electric heating device optimizes the winding method and insulation design of the resistance wire for different pipe section structures, and adopts a magnetic adsorption structure and a "submarine cable-underwater distribution unit" architecture to achieve precise heating of the cold spot area; the closed-loop control system collects data in real time through a temperature sensor, and dynamically adjusts the heating power in combination with a PID algorithm to ensure that the flow channel temperature is stable in a safe range. The present invention solves the shortcomings of traditional inhibitor methods and downhole throttling technologies, effectively inhibits the formation of natural gas hydrates and wax blockage, improves the efficiency, safety and environmental friendliness of deep-sea gas production operations, and is suitable for the long-term stable operation of complex deep-sea flow channel structures.

[0103] The above are merely preferred embodiments of the present invention and do not constitute any form of limitation to the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. An electric heating and heat preservation system for cold spots in a deep-sea gas wellhead flow channel, characterized by: Including cold spot positioning system, electric heating device and control system; The cold spot positioning system collects and pre-processes real-time data by building a temperature sensor network at key cold spots in the underwater gas tree flow channel. Combining historical data with a probabilistic statistical model, the system determines the location of cold spots and classifies risk levels, providing precise targeted heating information for the distribution of electric heating devices. The heating element of the electric heating device is arranged in the cold spot area of ​​the flow channel of the underwater gas tree; The control system obtains data measured by temperature sensors at each cold spot in real time and decides whether to start the corresponding heating element based on the data.

2. The electric heating and heat preservation system for cold spots of deep-sea gas production submarine wellhead flow passages according to claim 1 is characterized in that: The temperature sensing network of the cold spot positioning system includes multiple temperature sensors deployed throughout the underwater gas tree flow channel, covering all potential low-temperature risk areas. The sensor spacing is adjusted according to the complexity of the flow channel structure, and is encrypted to 0.1-0.5 meter intervals in special-shaped pipe sections and a standard spacing of 1-2 meters is used in straight pipe sections to form a point monitoring network. Combined with a data interpolation algorithm, the flow channel temperature field analysis is realized.

3. The electric heating and heat preservation system for cold spots of deep-sea gas production submarine wellhead flow passages according to claim 2, characterized in that: During real-time data collection and preprocessing, the cold spot positioning system uses a temperature sensor to collect temperature data at a frequency of 1 Hz in real time, transmits the data to the edge computing unit via a dedicated underwater cable, and then uses a median filter algorithm to remove outliers. The temperature fluctuation curve is smoothed using a sliding average method to extract valid data reflecting the actual temperature trend.

4. The electric heating and heat preservation system for cold spots of deep-sea gas production submarine wellhead flow passages according to claim 3 is characterized by: During the analysis process, the probabilistic statistical model analyzes historical data of the same model of underwater gas trees, defines the area below the wax critical temperature of 2°C as the cold spot candidate area, and determines that a valid cold spot event occurs when the temperature at a certain location is below the threshold for 5 consecutive minutes. The number of cold spot events triggered by each monitoring point in a unit time is counted in the time dimension (such as 30 days) to calculate the frequency of cold spot occurrence. In the spatial dimension, a spatial weight matrix is ​​established based on the geometric parameters of the flow channel, and the cold spot frequencies of adjacent monitoring points are interpolated and fitted to generate a probability density cloud map of cold spots in the entire flow channel, which intuitively displays the spatial distribution of the probability of cold spot occurrence. The darker the color, the higher the probability. The potential cold spot areas are divided into three levels according to the probability density: the areas with a probability greater than 60% are high-risk areas, and encrypted heating devices are deployed first; the areas with a probability of 30%-60% are medium-risk areas, and conventional heating density + dynamic power adjustment is adopted; the areas with a probability less than 30% are low-risk areas, and only basic insulation is maintained in this part.

5. The electric heating and heat preservation system for cold spots of deep-sea gas production submarine wellhead flow passages according to claim 4 is characterized in that: The heating element is a nickel-chromium alloy resistance wire. For circular pipe sections, the nickel-chromium alloy resistance wire is spirally wound. For special-shaped pipe sections, the resistance wire density and spacing are adjusted according to the curvature and pipe diameter. For spherical pipe sections, a combination of spiral and circumferential cross-winding is used. The outside of the heating element is wrapped with an insulation layer, and the thickness of the insulation layer is determined based on heat loss calculations to reduce heat loss to the external seawater.

6. The electric heating and heat preservation system for cold spots of deep-sea gas production submarine wellhead flow passages according to claim 5, characterized in that: The thermal insulation layer is covered with an outer carrier with samarium cobalt permanent magnet adsorption units. The positions and spacings of the samarium cobalt permanent magnet adsorption units are adjusted according to the shape and diameter of the pipeline, and the adsorption units are tightly adsorbed on the pipeline surface.

7. The electric heating and heat preservation system for cold spots of deep-sea gas production submarine wellhead flow passages according to claim 6, characterized in that: It also includes a power supply device, which directly branches out a cable from the power supply interface of the underwater gas tree or the underwater gas tree umbilical cable, and is connected to an underwater power distribution unit dedicated to the electric heating device. The cable has both power transmission and data communication functions; after the underwater power distribution unit receives the electric energy, it distributes it to the electric heating device and the temperature sensor through the step-down module.

8. The electric heating and heat preservation system for cold spots of deep-sea gas production submarine wellhead flow passages according to claim 7, characterized in that: In regular cold spot pipeline areas, multiple electric heating devices are concentrated into modules through bus terminals. Their power lines and the signal lines of the temperature sensors in the area are networked through fieldbus technology and connected to the underwater distribution unit via a single cable. In irregular cold spot pipeline areas, each electric heating device and temperature sensor is directly connected to the distribution unit and control system using independent lines to ensure accurate power supply and independent data transmission in high-risk areas.

9. The electric heating and heat preservation system for cold spots of deep-sea gas production submarine wellhead flow passages according to claim 8, characterized in that: The control system collects temperature sensor data in real time through cables. When it detects that the flow channel temperature is lower than the wax deposition critical value, it instructs the underwater power distribution unit to adjust the power of the electric heating device and start the rapid heating mode. After the temperature reaches the standard, it switches to steady-state maintenance and dynamically adjusts the power output through the PID algorithm, achieving a combination of power supply efficiency and control accuracy.

10. The operating method of the electric heating and heat preservation system for cold spots of deep-sea gas production submarine wellhead flow passages according to claim 9 is characterized in that: The following steps are involved: S1: Collect historical production data of the same type of underwater gas trees and use probabilistic statistical models to classify the risk level of potential cold spots in the same type of underwater gas trees in service, in preparation for the subsequent deployment of heating devices; S2: Use a laser rangefinder or 3D scanner to obtain the geometric parameters of the cold spot pipe segment. For circular pipe segments, spiral winding of nickel-chromium alloy resistance wire is used. For special-shaped pipe segments, the resistance wire density and spacing are adjusted according to the curvature and pipe diameter. For spherical pipe segments, a combination of spiral and circumferential cross winding is used. S3: Multiple PT1000 temperature sensors are deployed at throttling-sensitive locations throughout the underwater tree flow channel. The spacing between shaped pipe sections is increased to 0.1-0.5 meters, while the standard spacing for straight pipe sections is 1-2 meters. This forms a "point" monitoring network, and a data interpolation algorithm is used to analyze the flow channel temperature pattern. S4: Wrap the electric heating module with polyurethane foam as an insulation layer. Determine the thickness of the insulation layer based on heat loss calculations to reduce heat loss to the external seawater. Install the outer carrier and auxiliary fixing components of the samarium cobalt permanent magnet magnetic adsorption unit to ensure a tight fit and good seal between the device and the pipeline. S5: Integrate the electric heating device, temperature sensor, insulation layer, and magnetic structure into the flow channel of the gas tree to simulate the cold spot temperature to trigger heating. Verify that the device response time is less than 10 seconds and the sensor data error is ≤±0.5°C. Test the adsorption force of the magnetic structure under a pressure of 40MPa. S6: Connect the cables of the electric heating device and the sensor to the branch interface at the bottom end of the umbilical cable. Use a composite cable and pre-install an underwater power distribution unit with a built-in step-down module and surge protector to complete the power distribution circuit debugging. S7: The pre-assembled underwater Christmas tree is transported to the target sea area by an engineering vessel, lowered to the predetermined position on the seabed, and mechanically connected and sealed to the wellhead. S8: Use the ROV manipulator to connect the umbilical cable branch interface to the power supply system. After activating the loop, test the composite cable power loss and communication rate. Simulate the cold spot temperature to verify the electric heating device starts the rapid heating mode and PID dynamic adjustment function. S9: After the underwater tree officially produces gas, the electric heating system automatically starts and stops according to the preset threshold. When the monitored temperature is lower than the start threshold, the electric heating device is started and the power is initially adjusted according to the dynamic power regulation model. After the temperature reaches the standard, it switches to steady-state maintenance. The cold spot probability model is automatically updated weekly. If the prediction deviation is greater than 15%, the spatial weight coefficient is automatically adjusted to optimize the heating power density in high-risk areas. S10: During the heating process, the heating power is continuously adjusted using the PID algorithm to ensure that the temperature fluctuation is ≤±1°C. The umbilical cable interface sealing and electrical heating uniformity are inspected monthly using an ROV, and any faulty sensors or adsorption units are remotely replaced or repaired.

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