Multi-parameter optical fiber sensing submarine cable for safety monitoring of deep sea riser and monitoring system

Abstract

The invention provides a multi-parameter optical fiber sensing submarine cable for safety monitoring of a deep sea riser and a monitoring system, and relates to the technical field of ocean optical cables, the multi-parameter optical fiber sensing submarine cable comprises a central reinforcing core, and an inner cladding, an inner sheath, an outer cladding and an outer sheath which sequentially cover the periphery of the central reinforcing core from inside to outside, the inner cladding comprises a plurality of inner layer sensing units, and the outer cladding comprises a plurality of outer layer sensing units; the plurality of inner-layer sensing units are distributed in an annular array, each inner-layer sensing unit comprises any one of a single-mode optical fiber, a weak grating array and a multimode optical fiber, the peripheries of the single-mode optical fiber, the weak grating array and the multimode optical fiber are all coated with a first fiber paste layer, and the periphery of the first fiber paste layer is coated with a first stainless steel pipe; the inner wrapping layer comprises outer layer sensing units and armored steel wires, the outer layer sensing units and the armored steel wires are distributed in an annular array, a plurality of armored steel wires are arranged between any two adjacent outer layer sensing units, and each outer layer sensing unit comprises a first fiber grating array and a second fiber grating array. According to the invention, the monitoring precision of the submarine cable on the marine oil and gas riser can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of marine optical cables, and in particular to a multi-parameter optical fiber sensing submarine cable and a monitoring system for deep-sea riser safety monitoring. Background Art

[0002] During offshore oil and gas production, seabed resources are usually transported to surface platforms for processing and storage through risers. As the only key structure connecting the underwater production system and the floating platform, the marine riser is the core of deep-sea engineering technology. Due to the time-varying complex marine service environment and the complexity of the interaction between the riser, the floating platform, and the seabed soil, the marine riser is susceptible to the influence of natural factors such as submarine geological disasters and hydrodynamics, as well as human factors. During service, it is inevitable that excessive deformation, corrosion, fatigue and other types of damage will occur, which directly affects the service life of the marine riser and may even cause pipeline accidents, resulting in personal injury, economic losses, environmental pollution and social problems. The safe management of marine risers during operation is one of the key issues in marine oil and gas engineering.

[0003] Chinese patent publication number CN118112713A discloses a thin-diameter, bend-resistant sensing optical fiber for ocean monitoring, comprising a core and, from the inside out, an inner cladding, a porous nanoring, and an outer cladding surrounding the core, respectively, as well as a fiber Bragg grating (FBG) inscribed within the bend-resistant sensing optical fiber. However, while maintaining a relatively small diameter while ensuring stable optical performance in the fiber core and sensing region, this solution is prone to degradation in sensing fiber performance under size constraints, leading to reduced submarine cable monitoring accuracy. Therefore, it is highly desirable to provide a multi-parameter fiber optic sensing submarine cable for deep-sea riser safety monitoring that would help improve the cable's monitoring accuracy of offshore oil and gas risers. Summary of the Invention

[0004] In light of this, the present invention proposes a multi-parameter fiber-optic sensing submarine cable and monitoring system for deep-sea riser safety monitoring. By installing two distinct sets of sensor units, one inside the cable, the multi-parameter fiber-optic sensing cable can simultaneously monitor multiple parameters, enabling comprehensive safety monitoring of the entire deep-sea riser's status. The diverse inner layer of sensors, arranged in a circular pattern, covers all directions of the riser, ensuring rapid response to subtle changes. The outer layer's dual-grating array arrangement provides redundant data acquisition, enhancing the cable's monitoring accuracy for offshore oil and gas risers.

[0005] The present invention provides a multi-parameter optical fiber sensing submarine cable for deep-sea riser safety monitoring, comprising a central strengthening core and an inner cladding, an inner sheath, an outer cladding and an outer sheath sequentially covering the outer periphery of the central strengthening core from the inside to the outside, wherein:

[0006] The inner cladding includes a plurality of inner layer sensing units, which are distributed in a ring array. The inner layer sensing units include any one of a single-mode optical fiber, a weak grating array, and a multi-mode optical fiber. The single-mode optical fiber, the weak grating array, and the multi-mode optical fiber are all coated with a first fiber gel layer, and the first fiber gel layer is coated with a first stainless steel tube.

[0007] The outer cladding includes multiple outer layer sensing units and multiple armored steel wires, and the multiple outer layer sensing units and the multiple armored steel wires are distributed in a ring array. Multiple armored steel wires are arranged between any two adjacent outer layer sensing units. The outer layer sensing unit includes a first fiber grating array and a second fiber grating array. The first fiber grating array is arranged on the central axis of the outer layer sensing unit, and the second fiber grating array is arranged in parallel with the first fiber grating array.

[0008] On the basis of the above technical solution, preferably, the inner cladding layer includes a first inner layer sensing unit, a second inner layer sensing unit and a third inner layer sensing unit, wherein:

[0009] The first inner layer sensing unit includes the single-mode optical fiber and the first fiber jelly layer and the first stainless steel tube sequentially covering the outer circumference of the single-mode optical fiber from the inside to the outside;

[0010] The second inner layer sensing unit includes the weak grating array and the first fiber paste layer and the first stainless steel tube sequentially covering the outer periphery of the weak grating array from the inside to the outside;

[0011] The third inner layer sensing unit includes the multimode optical fiber and the first fiber jelly layer and the first stainless steel tube sequentially covering the outer circumference of the multimode optical fiber from the inside to the outside.

[0012] On the basis of the above technical solution, preferably, the first inner layer sensing unit or the third inner layer sensing unit is arranged between any two adjacent second inner layer sensing units.

[0013] Further preferably, the weak grating array includes a first debugging area, a first measurement area and a second debugging area connected in sequence, the first debugging area and the second debugging area are both single-mode optical fibers, the first measurement area is a weak grating measurement area, and the first debugging area and the second debugging area have the same length.

[0014] More preferably, the angle formed between the central axes of the first fiber grating array and the second fiber grating array in any two adjacent outer sensing units is 120°.

[0015] More preferably, the first fiber Bragg grating array includes a third debugging area, a first demodulation area, a second measurement area, a second demodulation area, and a fourth debugging area connected in sequence; the second fiber Bragg grating array includes a fifth debugging area, a third demodulation area, a third measurement area, a fourth demodulation area, and a sixth debugging area connected in sequence; the third debugging area, the fourth debugging area, the fifth debugging area, the sixth debugging area, the first demodulation area, the second demodulation area, the third demodulation area, and the fourth demodulation area are all single-mode optical fibers, and the second measurement area and the third measurement area are both strong grating measurement areas.

[0016] More preferably, the third debugging area, the fourth debugging area, the fifth debugging area and the sixth debugging area are all the same length, and 12 evenly distributed strong gratings are engraved in the second measurement area and the third measurement area, and the center wavelength interval of each adjacent strong grating is 3nm.

[0017] More preferably, the first fiber grating array and the second fiber grating array have the same length, and the weak grating array has a length greater than that of the first fiber grating array.

[0018] In a second aspect of the present application, a multi-parameter optical fiber sensing submarine cable monitoring system for deep-sea riser safety monitoring is provided, comprising a floating platform, a riser articulated to the floating platform, and a multi-parameter optical fiber sensing submarine cable as described above and arranged inside the riser.

[0019] More preferably, the riser includes a suspension area, a catenary midsection and a ground contact section, the first fiber grating array and the second fiber grating array are located in the suspension area, and the single-mode optical fiber, the weak grating array and the multi-mode optical fiber are all located in the suspension area, the catenary midsection and the ground contact section.

[0020] The multi-parameter optical fiber sensing submarine cable and monitoring system for deep-sea riser safety monitoring provided by the present invention have the following beneficial effects compared with the prior art:

[0021] (1) By setting up two different sets of inner and outer sensing units in the multi-parameter fiber optic sensing cable, namely single-mode fiber, weak grating array, multi-mode fiber and multiple groups of fiber grating array, multiple parameters can be monitored simultaneously to achieve comprehensive safety monitoring of the overall status of the deep-sea riser. In addition, the inner and outer sensing units use different sensing technologies. The diversified sensors in the inner layer can cover all directions of the riser under a ring distribution, ensuring a rapid response to small changes. The outer double grating array arrangement provides redundant data acquisition, which helps to improve the monitoring accuracy of the submarine cable and achieve high-precision monitoring of the key sections of the marine riser and overall shape monitoring. At the same time, the submarine cable structure includes a central reinforcement core and multi-layer protection, plus the setting of armored steel wire, thus forming a structural system that can resist deep-sea high pressure, corrosion and prevent mechanical damage, ensuring the long-term stable operation of the sensing unit in harsh deep-sea environment.

[0022] (2) By distributing the outer layer sensing units and multiple armored steel wires in a circular array and arranging armored steel wires between any two adjacent outer layer sensing units, a redundant arrangement is achieved. Even if some sensing units or armored steel wires are damaged, the remaining units can still work normally, and the reliability and stability of submarine cable monitoring are greatly improved. The first and second fiber grating arrays are configured in the outer layer sensing units at the same time, and the first fiber grating array is arranged on the central axis. The second fiber grating array is arranged in parallel with the first fiber grating array, so that monitoring data can be collected in multiple parameters and directions, realizing multi-point collaborative monitoring and data complementarity, and improving the sensitivity of the submarine cable to external changes. The angle formed by the connecting line of the two grating arrays in any two adjacent outer layer sensing units is 120°, which helps to ensure that the monitoring signal is evenly distributed in the entire outer cladding, strengthen the capture and positioning of parameters such as vibration or stress, and thus improve monitoring accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only 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.

[0024] Figure 1 A schematic cross-sectional view of the multi-parameter optical fiber sensing submarine cable provided by the present invention;

[0025] Figure 2 A schematic cross-sectional view of the multi-parameter optical fiber sensing submarine cable provided by the present invention;

[0026] Figure 3 A grating layout diagram of a weak grating array provided by the present invention;

[0027] Figure 4A grating layout diagram of a first fiber grating array and a second fiber grating array provided by the present invention;

[0028] Figure 5 This is a structural schematic diagram of the multi-parameter optical fiber sensing submarine cable monitoring system provided by the present invention.

[0029] Explanation of the accompanying symbols: 1. Central reinforcing core; 2. Inner cladding; 21. Inner sensing unit; 211. First stainless steel tube; 212. First fiber grease layer; 213. Single-mode optical fiber; 214. Weak grating array; 215. Multimode optical fiber; 3. Inner sheath; 4. Outer cladding; 41. Outer sensing unit; 411. Second stainless steel tube; 412. Second fiber grease layer; 413. First fiber grating array; 414. Second fiber grating array; 42. Armored steel wire; 5. Outer sheath. DETAILED DESCRIPTION

[0030] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the usual meanings understood by persons of ordinary skill in the field to which the present invention belongs. The words "first", "second" and similar terms used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, words such as "one" or "a" do not indicate a quantity limitation, but rather indicate the existence of at least one. Words such as "connected" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship also changes accordingly.

[0032] like Figure 1 and Figure 2 As shown, the present invention provides a multi-parameter optical fiber sensing submarine cable for deep-sea riser safety monitoring, comprising a central strengthening core 1 and an inner cladding 2, an inner sheath 3, an outer cladding 4 and an outer sheath 5 sequentially covering the outer periphery of the central strengthening core 1 from the inside to the outside, wherein:

[0033] The inner cladding 2 includes a plurality of inner layer sensing units 21, which are distributed in a ring array. The inner layer sensing units 21 include any one of a single-mode optical fiber 213, a weak grating array 214, and a multi-mode optical fiber 215. The outer peripheries of the single-mode optical fiber 213, the weak grating array 214, and the multi-mode optical fiber 215 are all coated with a first fiber gel layer 212, and the outer periphery of the first fiber gel layer 212 is coated with a first stainless steel tube 211.

[0034] The inner cladding 2 includes a first inner sensing unit, a second inner sensing unit, and a third inner sensing unit. The first inner sensing unit includes a single-mode optical fiber 213 and a first fiber grease layer 212 and a first stainless steel tube 211 sequentially covering the outer circumference of the single-mode optical fiber 213 from the inside out. The second inner sensing unit includes a weak grating array 214 and a first fiber grease layer 212 and a first stainless steel tube 211 sequentially covering the outer circumference of the weak grating array 214 from the inside out. The third inner sensing unit includes a multi-mode optical fiber 215 and a first fiber grease layer 212 and a first stainless steel tube 211 sequentially covering the outer circumference of the multi-mode optical fiber 215 from the inside out. The single-mode optical fiber 213 is used for vibration monitoring in a distributed acoustic sensing (DAS) system, the multi-mode optical fiber 215 is used for temperature monitoring in a distributed temperature sensing system, the weak grating array 214 is used for distributed measurement of the overall strain of the riser, and the fiber Bragg grating is used for strain monitoring in key areas.

[0035] In one example, a first inner layer sensing unit or a third inner layer sensing unit is disposed between any two adjacent second inner layer sensing units. The central reinforcing core 1 provides core support and mechanical strength for the optical cable. The inner layer sensing unit 21 includes two first inner layer sensing units, three second inner layer sensing units and one third inner layer sensing unit. Single-mode optical fiber 213 is arranged in the first inner layer sensing unit, weak fiber grating array is arranged in the second inner layer sensing unit, and multi-mode optical fiber 215 is arranged in the first inner layer sensing unit. The first inner layer sensing unit, the second inner layer sensing unit and the third inner layer sensing unit provide overall strain, temperature and vibration data monitoring of the riser. The first inner layer sensing unit, the second inner layer sensing unit and the third inner layer sensing unit are all filled with fiber paste to improve their water resistance and hydrogen loss resistance. After the first inner layer sensing unit, the second inner layer sensing unit and the third inner layer sensing unit are formed, a layer of wrapping tape is wrapped around them to ensure their structural stability. The sensing units used for overall distributed monitoring of the submarine cable are arranged inside the inner sheath 3 to ensure the reliability of the sensors.

[0036] Fiber grease—the fiber-filling grease—is the primary protective layer for the optical fibers in the first, second, and third inner sensing units. It protects the fibers from moisture and mitigates external mechanical forces such as vibration, impact, and bending. The fiber grease maintains a free, low-stress state within the loose tube, minimizing microbend losses and corrosion from stress, moisture, and humidity. Therefore, fiber grating arrays and weak fiber grating arrays require a tight-buffered structure to increase the stress they are subjected to and mitigate the low-stress state created by the fiber grease.

[0037] like Figure 3 As shown, the weak grating array 214 includes a first debugging area, a first measurement area and a second debugging area connected in sequence. The first debugging area and the second debugging area are both single-mode optical fibers 213. The first measurement area is a weak grating measurement area. The lengths of the first debugging area and the second debugging area are the same.

[0038] In one example, a 4000-meter-long 200kpsi-screened single-mode optical fiber 213, a multimode optical fiber 215, and a weak grating array 214 are used. The spatial resolution of the test equipment is 0.966 meters, combined with the submarine cable twisting angle and the test equipment. Three weak gratings of different wavelengths are written on the 200kpsi-screened single-mode optical fiber 213. The grating writing spacing is set in combination with the submarine cable twisting angle of 15° to ensure that the grating measurement points are in the same plane and the measurement point spacing is 1.2m. The length of a single weak grating is 4000 meters, and the grating is not written in the first 450 meters and the last 500 meters. Afterwards, a tight-wrapped sheath is extruded on the outside, and a mark is made on the outside of the tight-wrapped optical fiber at the grating area position. It can be understood that the total length of the weak grating array 214 is 4000 meters, 3000 meters of which is used as a monitoring section and a 20-meter debugging section. The remaining section is not written with gratings, which is used as a debugging loss.

[0039] In this embodiment, by introducing single-mode optical fiber 213, weak grating array 214, and multimode optical fiber 215, first, second, and third inner-layer sensing units are constructed, enabling multi-angle joint monitoring of different physical quantities (such as strain and temperature), improving monitoring coverage and sensitivity. The placement of a first or third inner-layer sensing unit between any two adjacent second-layer sensing units provides the system with redundancy in key monitoring areas, ensuring reliable data acquisition and monitoring capabilities even if some sensing units fail. In the design of weak grating array 214, single-mode optical fiber 213 is used in the first and second debugging zones, and both are of the same length. This facilitates high-precision calibration and compensation, enhancing the stability and accuracy of data in the weak grating measurement area. Each sensing unit is sequentially covered with a first fiber gel layer 212 and a first stainless steel tube 211. This layered protective structure not only ensures sensor performance, but also improves the overall connection's robustness and resistance to complex marine environments (such as high pressure and corrosion).

[0040] The outer cladding 4 includes multiple outer sensing units 41 and multiple armored steel wires 42. The multiple outer sensing units 41 and the multiple armored steel wires 42 are arranged in a ring array. Multiple armored steel wires 42 are disposed between any two adjacent outer sensing units 41. The outer sensing units 41 include a first fiber grating array 413 and a second fiber grating array 414. The first fiber grating array 413 is disposed on the central axis of the outer sensing unit 41, and the second fiber grating array 414 is disposed parallel to the first fiber grating array 413. The first and second fiber grating arrays 413 and 414 are both coated with a second fiber grease layer 412, the outer periphery of which is covered with a second stainless steel tube 411.

[0041] In one example, the angle formed between the central axes of the first fiber grating array 413 and the second fiber grating array 414 in any two adjacent outer sensing units 41 is 120°. The first fiber grating array 413 and the second fiber grating array 414 are used for distributed measurement of the riser's overall strain. Combined with a shape inversion algorithm, this achieves inversion of the riser's overall shape and primarily monitors the strain characteristics of the deep-sea riser at the bottom. The submarine cable is designed to have 15 armored steel wires 42 and contain sensing units with a diameter of 2.3 mm. The three armored steel wires 42 distributed at 120° are replaced with outer sensing units 41 with a diameter of 2.2 mm, ensuring the stranding performance while reducing the shear force it receives.

[0042] In this embodiment, the outer layer sensing units 41 and the multiple armored steel wires 42 are arranged in a circular array, and an armored steel wire 42 is provided between any two adjacent outer layer sensing units 41, achieving a redundant arrangement. Even if some sensing units or armored steel wires 42 are damaged, the remaining units can still operate normally, greatly improving the reliability and stability of the overall monitoring system. The outer layer sensing units 41 are simultaneously configured with first and second fiber grating arrays 414, wherein the first fiber grating array 413 is arranged on the central axis, and the second fiber grating array 414 is arranged in parallel with the first fiber grating array 413. This allows monitoring data to be collected from multiple parameters and directions, achieving multi-point coordinated monitoring and data complementarity, and improving the submarine cable's sensitivity to external changes. The angle formed by the line connecting the central axes of the two grating arrays in any two adjacent outer layer sensing units 41 is 120°, which helps ensure that the monitoring signal is evenly distributed throughout the outer cladding 4, enhances the capture and positioning of parameters such as vibration or stress, and thus improves monitoring accuracy. The outer layer 4 structural design not only provides high-precision sensor data acquisition, but also enhances the overall mechanical strength and resistance to external interference through the reasonable layout of the armored steel wire 42 and the sensor unit, allowing the equipment to operate stably in the harsh environment of the deep sea.

[0043] like Figure 4As shown, the first fiber Bragg grating array 413 includes a third debugging zone, a first demodulation zone, a second measurement zone, a second demodulation zone, and a fourth debugging zone, which are connected in sequence. The second fiber Bragg grating array 414 includes a fifth debugging zone, a third demodulation zone, a third measurement zone, a fourth demodulation zone, and a sixth debugging zone, which are connected in sequence. The third debugging zone, the fourth debugging zone, the fifth debugging zone, the sixth debugging zone, the first demodulation zone, the second demodulation zone, the third demodulation zone, and the fourth demodulation zone are all single-mode optical fibers 213. The second and third measurement zones are both strong grating measurement zones. The third debugging zone, the fourth debugging zone, the fifth debugging zone, the sixth debugging zone, the first demodulation zone, the second demodulation zone, the third demodulation zone, and the fourth demodulation zone are all the same length. The second and third measurement zones are each inscribed with 12 evenly distributed strong gratings, with the center wavelength interval between adjacent strong gratings being 3 nm. The first fiber Bragg grating array and the second fiber Bragg grating array 414 are the same length, and the weak grating array 214 is longer than the first fiber Bragg grating array 413.

[0044] In this example, 12 evenly distributed strong gratings were inscribed on a single optical fiber, with a center wavelength spacing of 3nm. The grating spacing was set to 0.3107m based on the 15° twist angle of the submarine cable, ensuring that the grating measurement points were coplanar and 0.3m apart. Two tight-buffered fiber Bragg gratings were placed in a sensing unit to accurately measure strain across a 7.2-meter platform connection. The fiber Bragg gratings were inscribed in the middle of a 10-meter fiber segment. After testing, 500-meter and 510-meter dyed and 200kpsi screened single-mode optical fibers 213 were fused at each end for connection and production loss testing. Two colored jackets were then extruded onto the outer surface of the fiber Bragg gratings to distinguish their placement. Finally, the grating area was marked on the outside of the tight-buffered fiber. The total length of the fiber Bragg grating array is 1,157.46 meters, with 7.46 meters of the grating area, 150 meters of which were used for communication connections to the demodulation equipment, and the remaining length for loss testing.

[0045] In one example, after the weak grating array 214 and the fiber Bragg grating array are inscribed, a tightly wrapped protective material (e.g., polyethylene) is placed around the fiber core. This tight wrapping effectively reduces slippage between the fiber paste and the fiber, increasing the fiber's sensitivity to external strain. Furthermore, the protective layer effectively strengthens the fiber and improves its resistance to marine environments.

[0046] In this embodiment, by providing two different sets of inner and outer sensing units within the multi-parameter fiber optic sensing submarine cable, namely, a single-mode optical fiber 213, a weak grating array 214, a multi-mode optical fiber 215, and multiple sets of fiber grating arrays, multiple parameters can be monitored simultaneously, thereby achieving comprehensive and safe monitoring of the overall status of the deep-sea riser. In addition, the inner sensing unit 21 and the outer sensing unit 41 use different sensing technologies. The diversified inner sensors can cover all directions of the riser in a ring-shaped distribution, ensuring rapid response to minor changes. The outer dual grating array arrangement provides redundant data acquisition, which helps to improve the submarine cable's monitoring accuracy of marine oil and gas risers and achieve high-precision monitoring of key sections and overall shape monitoring of marine risers. At the same time, the submarine cable structure includes a central reinforcement core 1 and multiple layers of protection, plus the arrangement of armored steel wires 42, thereby forming a structural system that can withstand deep-sea high pressure, corrosion, and mechanical damage, ensuring the long-term and stable operation of the sensing units in harsh deep-sea environments.

[0047] Based on the above multi-parameter optical fiber sensing submarine cable, the embodiment of the present application discloses a multi-parameter optical fiber sensing submarine cable monitoring system for deep-sea riser safety monitoring, such as Figure 5 As shown, it includes a floating platform, a riser articulated with the floating platform, and a multi-parameter fiber optic sensing submarine cable arranged inside the riser. The riser includes a suspension area, a catenary middle section, and a ground contact section. The first fiber grating array 413 and the second fiber grating array 414 are located in the suspension area. The single-mode optical fiber 213, the weak grating array 214, and the multi-mode optical fiber 215 are all located in the suspension area, the catenary middle section, and the ground contact section.

[0048] In one example, a high-density fiber Bragg grating array (FBG) was used in the riser's suspension zone to monitor real-time changes in tension and stress in the high-stress suspension zone connecting the riser to the platform. Because the forces on deep-sea risers are most pronounced and complex in the suspension zone, they are subject to significant tensile and bending forces due to factors such as their own weight, the interaction between the riser and the floating platform, the interaction between risers, and water flow, making them highly susceptible to damage and requiring intensive monitoring. This intensive monitoring approach utilizes FBGs to increase the density of sensing points in this area, enabling a sensor spacing of 0.3m within a 7-meter interval (FBG arrays are primarily limited by the number of points, and their sensor spacing can be flexibly set).

[0049] Furthermore, single-mode optical fiber 213 and multi-mode optical fiber 215 are used in the middle section of the riser catenary to monitor the vibration and temperature signals of the pipeline in operation. Combined with the vibration and temperature characteristics of the pipeline under different internal flow velocities during transportation under normal conditions, the stability of the riser's operating state is determined to prevent pipeline instability and fatigue caused by internal flow, vortex-induced vibration, etc. A weak fiber grating array is used in the riser's ground-touching section to monitor the strain characteristics of the large-scale high-stress area of the riser at the bottoming point to prevent damage caused by factors such as ground wear, erosion, and internal flow in the pipeline. Single-mode optical fiber 213 and multi-mode optical fiber 215 are set throughout the riser, but they are mainly used for distributed temperature and vibration monitoring of the middle section of the riser's catenary. This section is mainly affected by water flow impact and vortex-induced vibration. If any damage occurs, it will show obvious changes in temperature and vibration signals. A weak fiber Bragg grating array (FBG) is deployed throughout the entire riser section, enabling overall shape inversion. This also allows for monitoring the riser's ground contact section, which is variable. FBG sensors cannot guarantee that the sensing section will touch the bottom, making FBG arrays more effective for monitoring this section. By combining multiple sensing technologies and targeting the overall structural characteristics of deep-sea risers, distributed real-time monitoring is achieved.

[0050] Based on the above-mentioned multi-parameter optical fiber sensing submarine cable, the embodiment of the present application also discloses a method for preparing a multi-parameter optical fiber sensing submarine cable, which includes optical fiber preparation, sensing unit metal tube processing, inner layer sensing unit 21 twisting, inner sheath 3 extrusion, armor twisting, and outer sheath 5 extrusion and other processes.

[0051] Processing of the sensor unit metal tube: The optical fiber is processed into the sensor unit according to the designed distribution, and the interior of the sensor unit is filled with fiber paste to improve the water-blocking performance. The weak grating array 214 and the fiber grating array need to be laid out according to the specified tensile tension. Different from the processing of ordinary submarine cable sensor units, the tensile tension cannot be too large, which will cause excess length and fusion fracture.

[0052] During this step, the fabrication of the sensing submarine cable requires strict alignment of the colored areas to prevent significant deviations in the grid area position. During the three processes of extruding the inner sheath (three sets) and the outer sheath (five sets) of the sensing unit metal tube, the positions of the initial five grid points must be calibrated and marked in conjunction with the positions displayed by the demodulation equipment for the weak grating array 214. After cable assembly, a probe is used to perform a destructive test on the reserved test area for the weak grating area to determine its precise position and uniformity of distribution, achieving a positioning accuracy of less than 5 cm for the weak grating array 214 and the fiber grating array.

[0053] Twisting the inner layer sensing unit 21: Using a twisting machine, the processed sensing unit and the reinforcement are twisted together. The twisting head twists the sensing unit and the reinforcement together at a certain speed and rotation direction to form the inner layer sensing unit 21;

[0054] Inner sheath 3 extrusion: Add a layer of plastic sheath to the outside of the optical cable to provide physical protection and improve waterproof performance;

[0055] Armor twisting: Twist the armor steel wire 42, the outer layer sensor unit 41 and the cable core together, maintaining appropriate tension to ensure that the armor material is evenly wound on the optical cable to achieve the tightness and stability of the armor. An anti-corrosion layer should also be added outside the armor layer to resist corrosion from seawater, and finally a wrapping tape is wrapped around it to ensure its structural stability.

[0056] Outer Jacket Extrusion: The submarine cable's outer jacket is made of high-density polyethylene. During the extrusion process, the molten material is evenly extruded and coated onto the cable core. The coating process requires precise control to ensure consistent jacket thickness. The final cable diameter is 20.8mm. After cable assembly, the product model is marked every 1.2 meters at the initial grid point.

[0057] In one example, the sensing unit (single-mode optical fiber 213), the sensing unit (weak grating array 214), the sensing unit (multi-mode optical fiber 215), and the sensing unit (fiber grating array) are processed separately. A steel sheet is selected as the material for the sensing unit. The corresponding optical fibers are placed on the steel sheet, twisted, and then laser welded. The loose tube is then filled with water-blocking glue to waterproof and provide additional protection. The metal tube is then sealed to ensure a good seal.

[0058] After the sensor unit is machined, the central reinforcement is rewound. 2.3mm steel wire is used as the reinforcement material and introduced through the rewinder's pay-off mechanism. Winding is performed according to pre-set parameters, controlling factors such as tension, winding angle, and speed to ensure that the reinforcement is evenly wrapped around the sensor unit assembly, which has been loosened from the metal tube. After completion, the rewound structure is quality-checked to ensure that the reinforcement winding meets the required quality.

[0059] The assembly containing the sensor unit and reinforcement is placed on the pay-off frame of the stranding machine for cable core stranding. Concentric stranding is employed, and the tension, pitch, and direction of the strands are controlled to ensure uniform distribution of the strands within the cable core. Insulation and shielding layers are added to the exterior of the stranded cable to isolate it from the external environment and electromagnetic interference. Online testing and monitoring of the stranded cable core ensures timely identification and resolution of any potential problems.

[0060] High-density polyethylene (HDPE) is selected as the material for the inner sheath 3, which has excellent insulation, corrosion resistance, and mechanical strength. The inner sheath 3 material is heated and melted in an extruder and extruded through a die head into a continuous tubular sheath, which is then wrapped around the stranded cable core. A metal sheath is then applied to the outer sheath to provide physical protection and enhance waterproofing. After extrusion, the extruded inner sheath 3 is cooled using water to solidify and maintain a stable shape.

[0061] Steel wire is selected as the armor material. The armor material is placed on a pay-off stand and introduced into a stranding machine via a guide pulley. The stranding machine twists the armor material around the inner sheath 3 at a specific speed and rotation direction, forming the armor layer. The twisting angle is 15°. Proper tension is maintained to ensure that the armor material is evenly wound around the sheath, ensuring tightness and stability of the armor. A polyethylene anti-corrosion layer is also applied to the armor layer to resist seawater corrosion.

[0062] The outer sheath 5 is made of the same material as the inner sheath 3 and is extruded in a similar manner to the inner sheath 3. The difference is that the continuous tubular sheath extruded by the die is wrapped around the armor layer. The extruder process parameters are different to ensure the wall thickness, outer diameter, and other dimensions of the outer sheath 5. The outer sheath 5 is cooled to solidify and maintain a stable shape.

[0063] Furthermore, the fiber Bragg grating (FBG) and weak fiber Bragg grating (WFBG) grating areas are marked. The optical fiber is then loosely twisted in a metal tube, and the grating area position is calibrated and sprayed on the surface of the tube. After multiple twisting processes, the existence of tension produces an excess length of about 0.03%, and the grating area has a certain offset, so it is necessary to use a probe to calibrate the grating position again after the submarine cable is formed. The riser deformation algorithm based on the Frenet framework is used to monitor the riser shape. It measures the strain at the corresponding point through the change of the fiber Bragg grating center wavelength, and calculates its curvature and deflection in combination with the submarine cable structure data. The interpolation method is used to complete the supplement of the curvature of each point to achieve the inversion of the submarine cable shape. Since the riser and submarine cable are closely connected, the deformation of the submarine cable can reflect the deformation and stress state of the riser to a certain extent. By fully integrating the data from the sensing submarine cable, the results of the riser deformation inversion from the first 14 meters of fiber Bragg grating array testing are used as calibration for the riser deformation measured by the weak grating array 214. The validity and accuracy of the inversion results are determined based on the R2 parameter of the overall inversion curve, effectively reducing the initial error of the Frenet frame. Temperature data measured by the multimode fiber 215 is used as temperature calibration for the weak grating array 214 and the fiber Bragg grating array, eliminating the impact of their differential sensitivity to temperature strain.

[0064] In this embodiment, fiber optic sensing is designed to address the critical mechanical and sensing properties of offshore oil and gas riser monitoring, enabling it to adapt to harsh marine environments and monitor the riser's operating status. A high-density fiber grating (FBG) monitoring zone is designed for the easily damaged platform section of the offshore riser, enabling precise strain measurement in this area. Pipeline deformation data from this zone is used as a benchmark for calibration of the weak grating array 214's overall pipeline deformation monitoring data, improving overall monitoring accuracy and enabling high-precision monitoring of key sections and overall shape of the offshore riser. A single monitoring method can produce excessive errors in complex marine environments, and using only a single type of data is difficult to apply due to background noise. Simultaneous monitoring of multiple parameters is employed to improve the system's accuracy in monitoring the riser's operating status. Multi-parameter fiber optic sensing marine cables offer advantages such as versatility, high performance, structural stability, durability, and flexibility, making them suitable for real-time monitoring in marine environments and providing reliable data support for marine scientific research, resource development, and environmental protection.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A multi-parameter optical fiber sensing submarine cable for deep-sea riser safety monitoring, characterized in that: It comprises a central reinforcing core (1) and an inner cladding (2), an inner sheath (3), an outer cladding (4) and an outer sheath (5) sequentially covering the outer periphery of the central reinforcing core (1) from the inside to the outside, wherein: The inner cladding (2) includes a plurality of inner layer sensing units (21), the plurality of inner layer sensing units (21) are distributed in a ring array, the inner layer sensing units (21) include any one of a single-mode optical fiber (213), a weak grating array (214), and a multi-mode optical fiber (215), the outer peripheries of the single-mode optical fiber (213), the weak grating array (214), and the multi-mode optical fiber (215) are all coated with a first fiber gel layer (212), and the outer periphery of the first fiber gel layer (212) is coated with a first stainless steel tube (211); The outer cladding (4) comprises a plurality of outer layer sensing units (41) and a plurality of armored steel wires (42), wherein the plurality of outer layer sensing units (41) and the plurality of armored steel wires (42) are distributed in a ring array, and a plurality of armored steel wires (42) are arranged between any two adjacent outer layer sensing units (41). The outer layer sensing unit (41) comprises a first fiber grating array (413) and a second fiber grating array (414), wherein the first fiber grating array (413) is arranged on the central axis of the outer layer sensing unit (41), and the second fiber grating array (414) is arranged in parallel with the first fiber grating array (413).

2. The multi-parameter optical fiber sensing submarine cable for deep-sea riser safety monitoring according to claim 1, characterized in that: The inner cladding (2) comprises a first inner layer sensing unit, a second inner layer sensing unit and a third inner layer sensing unit, wherein: The first inner layer sensing unit comprises the single-mode optical fiber (213) and the first fiber jelly layer (212) and the first stainless steel tube (211) sequentially covering the outer periphery of the single-mode optical fiber (213) from the inside to the outside; The second inner layer sensing unit comprises the weak grating array (214) and the first fiber paste layer (212) and the first stainless steel tube (211) sequentially covering the outer periphery of the weak grating array (214) from the inside to the outside; The third inner layer sensing unit comprises the multimode optical fiber (215) and the first fiber jelly layer (212) and the first stainless steel tube (211) sequentially covering the outer periphery of the multimode optical fiber (215) from the inside to the outside.

3. The multi-parameter optical fiber sensing submarine cable for deep-sea riser safety monitoring according to claim 2, characterized in that: The first inner layer sensing unit or the third inner layer sensing unit is arranged between any two adjacent second inner layer sensing units.

4. The multi-parameter optical fiber sensing submarine cable for deep-sea riser safety monitoring according to claim 1, characterized in that: The weak grating array (214) comprises a first debugging area, a first measuring area, and a second debugging area connected in sequence, the first debugging area and the second debugging area are both single-mode optical fibers (213), the first measuring area is a weak grating measuring area, and the first debugging area and the second debugging area have the same length.

5. The multi-parameter optical fiber sensing submarine cable for deep-sea riser safety monitoring according to claim 1, characterized in that: The angle formed between the central axes of the first fiber grating array (413) and the second fiber grating array (414) in any two adjacent outer layer sensing units (41) is 120°.

6. The multi-parameter optical fiber sensing submarine cable for deep-sea riser safety monitoring according to claim 1, characterized in that: The first fiber grating array (413) includes a third debugging area, a first demodulation area, a second measurement area, a second demodulation area, and a fourth debugging area connected in sequence; the second fiber grating array (414) includes a fifth debugging area, a third demodulation area, a third measurement area, a fourth demodulation area, and a sixth debugging area connected in sequence; the third debugging area, the fourth debugging area, the fifth debugging area, the sixth debugging area, the first demodulation area, the second demodulation area, the third demodulation area, and the fourth demodulation area are all single-mode optical fibers (213); and the second measurement area and the third measurement area are both strong grating measurement areas.

7. The multi-parameter optical fiber sensing submarine cable for deep-sea riser safety monitoring according to claim 6, characterized in that: The third debugging area, the fourth debugging area, the fifth debugging area and the sixth debugging area are all of the same length. Twelve evenly distributed strong gratings are engraved in the second measurement area and the third measurement area, and the center wavelength interval of each adjacent strong grating is 3nm.

8. The multi-parameter optical fiber sensing submarine cable for deep-sea riser safety monitoring according to claim 1, characterized in that: The first fiber grating array (413) and the second fiber grating array (414) have the same length, and the weak grating array (214) has a length greater than that of the first fiber grating array (413).

9. A multi-parameter optical fiber sensing submarine cable monitoring system for deep-sea riser safety monitoring, characterized in that: The invention comprises a floating platform, a riser hinged to the floating platform, and a multi-parameter optical fiber sensing submarine cable according to any one of claims 1 to 8 arranged inside the riser.

10. The multi-parameter optical fiber sensing submarine cable monitoring system for deep-sea riser safety monitoring according to claim 9, characterized in that: The riser includes a suspension area, a catenary midsection, and a ground contact section; the first fiber grating array (413) and the second fiber grating array (414) are located in the suspension area; the single-mode optical fiber (213), the weak grating array (214), and the multi-mode optical fiber (215) are all located in the suspension area, the catenary midsection, and the ground contact section.

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