Photoelectric composite logging cable, master-slave distributed intelligent transmission system with same and oil well underground monitoring method

Abstract

The invention discloses a photoelectric composite logging cable, a master-slave distributed intelligent transmission system with the photoelectric composite logging cable and an oil well underground monitoring method, the photoelectric composite logging cable comprises a cable core, a waterproof layer, an inner sheath layer, an armor layer and an outer sheath layer which are sequentially arranged from inside to outside, and the cable core comprises an anti-torsion center framework and a core transmission unit. According to the invention, the non-circular anti-torsion central skeleton and the non-pitch synchronously twisted core transmission unit are adopted, torque can be offset from the inside, the torque balance tension-bearing armor layer with opposite rotation directions can compensate torsion stress from the outside, multiple anti-twist design is formed, and the twist risk of the cable body in laying and using is fundamentally eliminated; the system bus unit, the underground self-healing unit and the ground main control unit work cooperatively, real-time monitoring of the health state of a cable body and accurate fault positioning can be achieved, when a fault occurs, automatic switching can be achieved to guarantee operation, the position of a fault point can be reported immediately, the maintenance and troubleshooting time is greatly shortened, and production halt loss is reduced.

Description

Technical Field

[0001] This invention belongs to the field of oil well cable technology, specifically relating to a photoelectric composite logging cable and its master-slave distributed intelligent transmission system and oil well downhole monitoring method. Background Technology

[0002] With the development of smart oilfields, downhole monitoring systems are evolving towards intelligence, real-time capabilities, and multi-dimensionality. Traditional oil well cables have the following main drawbacks: Traditional pure copper cables (power / signal) or coaxial cables have bottlenecks such as low transmission bandwidth, large signal attenuation, susceptibility to electromagnetic interference, and inability to achieve long-distance high-definition video and massive sensor data transmission. While fiber optic cables offer superior transmission performance, they cannot directly power downhole instruments such as sensors, actuators, and cameras. Existing optical fiber composite cables typically have only a single main optical fiber. If damaged under harsh conditions, it will lead to a complete interruption of high-data communication, lacking effective signal backup and self-healing mechanisms. Traditional cables are prone to kinking or plastic deformation under complex stresses (such as tension, torsion, and lateral pressure). Although steel wire armor can provide some protection, it is heavy and has limited ability to compensate for torsional imbalance. Its airtightness and fatigue resistance need to be improved. Traditional cables are merely "passive transmission conduits," lacking status awareness and diagnostic capabilities. Their operation and maintenance are not intelligent enough, making it difficult to locate faults and time-consuming to troubleshoot, leading to unplanned production stoppages and huge economic losses. Summary of the Invention

[0003] To address the problems in the prior art, the present invention aims to provide a photoelectric composite logging cable and a master-slave distributed intelligent transmission system thereon, as well as a method for monitoring downhole oil wells.

[0004] To achieve the above objectives and technical effects, the technical solution adopted by this invention is as follows: A photoelectric composite logging cable includes a cable core, a water-blocking layer, an inner sheath, an armor layer, and an outer sheath arranged sequentially from the inside out. The cable core includes an anti-torsion central skeleton and a core transmission unit.

[0005] Furthermore, the core transmission unit includes several main optical units, main power units, backup optical units, backup power units, and system bus units. The main optical units and main power units are twisted together and separated by an anti-torsion central frame to form a first twisted layer. The backup optical units, backup power units, and system bus units are twisted outside the first twisted layer and separated by an anti-torsion central frame to form a second twisted layer.

[0006] Furthermore, there is one main optical unit and one main power unit, which are respectively embedded in two opposite grooves of the anti-torsion center frame and are twisted together with a first twisting direction and a first twisting pitch P1. The backup optical unit, backup power unit and system bus unit are twisted together with a second twisting direction and a second twisting pitch P2, wherein the first twisting direction is opposite to the second twisting direction.

[0007] Furthermore, the ratio of P1 to P2 is 1.2 to 1.8:1.

[0008] Furthermore, the main optical unit uses a loose-tube single-mode optical fiber in a stainless steel tube, and the backup optical unit uses a loose-tube multimode optical fiber in a stainless steel tube. The surface of the single-mode or multimode optical fiber is coated with a high-temperature resistant polyimide coating and placed in a precision-welded stainless steel tube filled with high-temperature silicone gel.

[0009] Furthermore, the main power unit uses tightly stranded copper conductors as the core, and is surrounded by multiple layers of composite insulation. The composite insulation layer includes a high-temperature resistant cross-linked polyethylene base layer or an ethylene propylene rubber base layer and a fluoropolymer outer layer arranged sequentially from the inside to the outside; the backup power unit uses shielded twisted pair cable.

[0010] Furthermore, the system's total electrical unit includes transmission line pairs and power supply line pairs, and the entire unit needs to be longitudinally shielded with aluminum-plastic composite tape and tinned copper wire braided to form a complete electromagnetic shielding layer to prevent strong electromagnetic interference downhole.

[0011] Furthermore, the armor layer includes a high-strength compressive armor layer made of metal strip wrapping and a torque-balancing tensile armor layer made of at least two layers of steel wires with opposite directions of rotation.

[0012] This invention also discloses a master-slave distributed intelligent transmission system, comprising: The above-mentioned photoelectric composite logging cable; The ground control unit is used for system control, power supply, data reception and processing; The downhole instruments are connected to the surface main control unit via a photoelectric composite logging cable; The downhole self-healing unit is integrated into the key nodes or ends of the photoelectric composite logging cable and connected to the system bus unit. It is used to monitor the communication status between the main optical unit and the backup optical unit, and between the main power unit and the backup power unit. When the main optical channel fails, it performs automatic switching to the backup power channel or the backup optical channel. When a channel switch occurs, it reports the fault information and location information to the ground main control unit.

[0013] Furthermore, the downhole self-healing unit is connected to the system bus unit and is used to report fault information and location information to the ground main control unit when a channel switch occurs.

[0014] Furthermore, the downhole self-healing unit includes a monitoring module for monitoring the quality of the main signal channel, a switch matrix for performing signal path switching, a photoelectric / electro-optical conversion module for converting optical signals to electrical signals, and a microcontroller for controlling the coordinated operation of the above modules. Multiple self-healing units are interconnected via a system bus unit and mechanically and electrically connected to the preceding and following cable sections via armored locking connectors, becoming part of the cable body and enabling communication with the surface main control unit.

[0015] This invention also discloses a downhole monitoring method for oil wells, applied to a master-slave distributed intelligent transmission system as described above, comprising the following steps: System initialization: The ground control unit establishes communication with the downhole instruments and the downhole self-healing unit. During the descent of the downhole instrument following the photoelectric composite logging cable, the status and descent parameters of the photoelectric composite logging cable are monitored in real time. During the data acquisition phase, high-speed data is uploaded via the primary optical channel; When the downhole self-healing unit detects an interruption in the primary optical channel, it automatically switches the communication link to the backup electrical channel or backup optical channel and reports the fault event, thus achieving uninterrupted monitoring.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) High reliability and self-healing capability of communication: The main optical unit, main power unit, backup optical unit, backup power unit and system bus unit are physically isolated by a non-circular anti-torsion central skeleton. When the downhole self-healing unit detects that the main optical channel is interrupted, it automatically switches the communication link to the backup power channel (including the backup power unit) or the backup optical channel (including the backup optical unit) and reports the fault event to achieve uninterrupted monitoring. The cable itself is not only a passive transmission medium, but also an intelligent carrier with active diagnosis and self-healing capabilities. 2) Anti-kink: The non-circular anti-torsion central skeleton and the non-pitch synchronously twisted core transmission unit can offset the torque from the inside. The torque-balancing tension armor layer with opposite rotation direction can compensate for torsional stress from the outside, forming a multi-layer anti-kink design, which fundamentally eliminates the risk of kinking in the cable during laying and use. 3) Intelligent operation and maintenance: The system bus unit works in collaboration with the downhole self-healing unit and the ground main control unit to realize real-time monitoring of the cable's health status and accurate fault location. When a fault occurs, it can not only automatically switch to ensure operation, but also immediately report the location of the fault point, greatly shortening the maintenance and troubleshooting time and reducing downtime losses. 4) Environmental adaptability: The high-temperature resistant materials (such as polyimide coating and fluoropolymer insulation) and water-blocking structure used in each unit ensure long-term stable operation of the cable in extreme downhole environments with high temperature, high pressure and humidity. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a schematic diagram of the master-slave distributed intelligent transmission system of the present invention; The components include: 1. Anti-torsion central frame; 2. Core transmission unit; 2-1. Main optical unit; 2-2. Main power unit; 2-3. Backup optical unit; 2-4. Backup power unit; 2-5. System bus unit; 3. Water-blocking layer; 4. Inner sheath layer; 5. Armor layer; 6. Outer sheath layer. Detailed Implementation

[0018] The present invention will now be described in detail so that its advantages and features can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0019] The following provides a brief overview of one or more aspects to offer a basic understanding of them. This overview is not an exhaustive summary of all conceived aspects, nor is it intended to identify key or decisive elements of all aspects, nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form to prepare for the more detailed descriptions that follow.

[0020] like Figure 1 As shown, the present invention discloses a photoelectric composite logging cable, comprising a cable core, a water-blocking layer 3, an inner sheath layer 4, an armor layer 5, and an outer sheath layer 6 arranged sequentially from the inside to the outside. The cable core includes an anti-torsion central skeleton 1 and a core transmission unit 2. The core transmission unit 2 is wrapped around the anti-torsion central skeleton 1 in a non-pitch synchronous stranding manner and adopts a layered stranding method.

[0021] In some embodiments, the cross-section of the anti-torsion central frame 1 is a non-circular profile, such as a cross shape or a star shape.

[0022] In some embodiments, the core transmission unit 2 includes several main optical units 2-1, main power units 2-2, backup optical units 2-3, backup power units 2-4, and system bus units 2-5. The main optical units 2-1 and main power units 2-2 are twisted together and separated by the anti-torsion central frame 1 to form a first twisted layer. The backup optical units 2-3, backup power units 2-4, and system bus units 2-5 are twisted together outside the first twisted layer and separated by the anti-torsion central frame 1 to form a second twisted layer.

[0023] In some embodiments, there is one main optical unit 2-1 and one main electrical unit 2-2, which are respectively embedded in two opposite grooves of the anti-torsion center frame 1 and are twisted in a first twisting direction (e.g., S-direction) and a first twisting pitch P1.

[0024] In some embodiments, the backup light unit 2-3, the backup power unit 2-4, and the system bus unit 2-5 are twisted together with a second twisting direction (e.g., Z-direction) and a second twisting pitch P2, wherein the first twisting direction is opposite to the second twisting direction.

[0025] In some implementations, the ratio of P1 to P2 is 1.2 to 1.8:1, for example, P1 = 150 mm and P2 = 100 mm. This differentiated pitch ratio is key to eliminating periodic resonance. This method creates two stranded layers with opposite directions and different pitches, producing a torsion balance effect and physically isolating the primary and backup systems.

[0026] In some implementations, the main optical unit 2-1 uses loose-tube single-mode fiber in a stainless steel tube, while the backup optical unit 2-3 uses loose-tube multimode fiber in a stainless steel tube. Multimode fiber has lower alignment requirements for connectors, making it easier to establish a connection in emergency situations. The surface of the single-mode or multimode fiber is coated with a high-temperature resistant (>200°C) polyimide coating and placed within a precision-welded stainless steel tube filled with high-temperature silicone gel, providing the fiber with a physical barrier against pressure and bending, as well as excellent temperature isolation.

[0027] In some implementations, the main electrical unit 2-2 uses a tightly stranded copper conductor as the core, and is surrounded by a multi-layer composite insulation layer. The composite insulation layer includes a high-temperature resistant cross-linked polyethylene base layer or an ethylene propylene rubber base layer and a fluoropolymer outer layer arranged sequentially from the inside to the outside, to ensure insulation performance and mechanical strength under high temperature, high pressure and humid environments.

[0028] In some implementations, there are two backup power units 2-4, which use shielded twisted-pair cables.

[0029] Traditional hybrid cables for oil wells have a relatively simple function, serving merely as a "pipeline." This invention upgrades the cable into a downhole network neural network with intelligence, path redundancy, and signal self-adaptation capabilities. While retaining the original high-performance single-mode fiber (used for high-speed backbone data), an additional pair of independent transmission units is added: multimode fiber serves as a transmission unit for backup signal transmission in emergencies, and a pair of shielded twisted-pair cables serves as an electrical backup channel specifically for transmitting low-speed digital or analog modulated signals.

[0030] In some implementations, the system's main electrical unit 2-5 includes transmission line pairs and power supply line pairs, and the entire unit needs to be longitudinally shielded with aluminum-plastic composite tape and tinned copper wire braided to form a complete electromagnetic shielding layer to prevent strong electromagnetic interference downhole.

[0031] In some embodiments, the armor layer 5 includes a high-strength compressive armor layer made of metal strip wrapping and a torque-balancing tensile armor layer made of at least two layers of steel wires with opposite directions of rotation.

[0032] In some embodiments, the water-blocking layer 3, the inner sheath layer 4, and the outer sheath layer 6 are all made of conventional materials that enable the cable to operate in extreme environments, which will not be described in detail here.

[0033] This invention also discloses a master-slave distributed intelligent transmission system with downhole autonomous survival and repair capabilities, which can be applied downhole to achieve photoelectric conversion in extreme environments, such as... Figure 2 As shown, it includes: The aforementioned photoelectric composite logging cable; The ground control unit is the command and control center of the entire system. It includes a human-machine interface, a main control computer, an optical line terminal, a high-voltage power supply system, and a database server. The human-machine interface is connected to the main control computer, and the main control computer is connected to the database server through the optical line terminal and the high-voltage power supply system. The downhole instruments are connected to the surface main control unit via a photoelectric composite logging cable. These instruments include a data acquisition unit and connected temperature and pressure sensors, electromagnetic flow meters, high-definition cameras, electric control valves, fiber optic sensor arrays, etc. The data acquisition unit collects data and uploads it to the surface main control unit. The downhole self-healing unit is integrated into the key nodes or ends of the photoelectric composite logging cable. It is used to monitor the communication status between the main optical unit 2-1 and the backup optical unit 2-3, and between the main power unit 2-2 and the backup power unit 2-4. When the main optical channel fails, it automatically switches to the backup power channel or the backup optical channel. The downhole self-healing unit is connected to the system bus unit 2-5 and is used to report the fault information and location information to the surface main control unit when a channel switch occurs.

[0034] In some implementations, the downhole self-healing unit includes a monitoring module for monitoring the quality of the main signal channel, a switch matrix for performing signal path switching, a photoelectric / electro-optical conversion module for converting optical signals to electrical signals, and a microcontroller for controlling the coordinated operation of the above modules. Multiple downhole self-healing units are interconnected via system bus units 2-5, and mechanically and electrically connected to the preceding and following cable sections via armored locking connectors, becoming part of the cable body and enabling communication with the surface main control unit.

[0035] This invention also discloses a downhole monitoring method for oil wells, applied to a master-slave distributed intelligent transmission system as described above, comprising the following steps: System initialization: The ground control unit establishes communication with the downhole instruments and the downhole self-healing unit. During the descent of the downhole instrument following the photoelectric composite logging cable, the status and descent parameters of the photoelectric composite logging cable are monitored in real time. During the data acquisition phase, high-speed data is uploaded through the main optical channel (including optical line terminal, main optical unit 2-1, etc.); When the downhole self-healing unit detects an interruption in the main optical channel, it automatically switches the communication link to the backup electrical channel (including backup electrical units 2-4, etc.) or the backup optical channel (including backup optical units 2-3, etc.) and reports the fault event to achieve uninterrupted monitoring.

[0036] The specific work process is as follows: The system initializes, the ground main control unit powers on and performs a self-test, and queries the status of the downhole self-healing unit through system bus units 2-5; the downhole instruments are powered on, the sensors are initialized, the ready status is reported, and the well logging data (sampling rate, transmission mode, etc.) are set on the ground. The photoelectric composite logging cable carries downhole instruments into the well, and the downhole self-healing unit provides real-time feedback on the status, continuously monitoring the health of the cable; the descent curve and cable status are displayed on the ground in real time. The ground control unit issues a "start acquisition command (optical signal)". The downhole instruments receive the command, activate all sensors, and acquire data at the set sampling rate. During normal acquisition, data is uploaded via the main optical unit 2-1. If a section of the main optical unit 2-1 breaks, the nearest downhole self-healing unit detects the loss of optical signal and immediately switches communication to the backup power unit 2-4. It also sends an alarm and reports the fault location coordinates to the ground via the system bus unit 2-5. The ground control unit automatically adjusts the communication protocol, and the downhole instrument data continues to be uploaded via the backup channel, achieving seamless switching and continuous monitoring.

[0037] Example 1

[0038] like Figure 1 As shown, a photoelectric composite logging cable includes a cable core, a water-blocking layer 3, an inner sheath layer 4, an armor layer 5, and an outer sheath layer 6 arranged sequentially from the inside to the outside. The cable core includes an anti-torsion central skeleton 1 and a core transmission unit 2. The core transmission unit 2 is wrapped around the anti-torsion central skeleton 1 in a non-pitch synchronous stranding manner and adopts a layered stranding method.

[0039] The cross-section of the anti-torsion center frame 1 is cross-shaped.

[0040] The core transmission unit 2 includes a main optical unit 2-1, a main power unit 2-2, a backup optical unit 2-3, a backup power unit 2-4, and a system bus unit 2-5. The main optical unit 2-1 and the main power unit 2-2 are twisted together and separated by the anti-torsion central frame 1 to form a first twisted layer. The backup optical unit 2-3, the backup power unit 2-4, and the system bus unit 2-5 are twisted together outside the first twisted layer and separated by the anti-torsion central frame 1 to form a second twisted layer.

[0041] There is one main optical unit 2-1 and one main electrical unit 2-2, which are respectively embedded in two opposite grooves of the anti-torsion center frame 1 and twisted in the first twisting direction (S direction) and the first twisting pitch P1.

[0042] The backup light unit 2-3 (one), the backup power unit 2-4 (two), and the system bus unit 2-5 (one) are twisted together in the second twisting direction (Z direction) and the second twisting pitch P2, with the first twisting direction being opposite to the second twisting direction.

[0043] The ratio of P1 to P2 is 1.5:1, with P1 = 150 mm and P2 = 100 mm. This differentiated pitch ratio is key to eliminating periodic resonance. This method creates two stranded layers with opposite directions and different pitches, producing a torsion balance effect and physically isolating the primary and backup systems.

[0044] The main optical unit 2-1 uses loose-tube single-mode fiber in a stainless steel tube, while the backup optical unit 2-3 uses loose-tube multimode fiber in a stainless steel tube. Multimode fiber has lower alignment requirements for connectors, making it easier to establish a connection in emergencies. The surface of the single-mode or multimode fiber is coated with a high-temperature resistant (>200℃) polyimide coating and placed within a precision-welded stainless steel tube filled with high-temperature silicone gel, providing the fiber with a physical barrier against pressure and bending, as well as excellent temperature isolation.

[0045] The main electrical unit 2-2 uses tightly stranded copper conductors as the core, and is surrounded by multiple layers of composite insulation. The composite insulation includes a high-temperature resistant cross-linked polyethylene base layer and a fluoropolymer outer layer arranged sequentially from the inside to the outside, to ensure insulation performance and mechanical strength under high temperature, high pressure and humid environments.

[0046] Backup power units 2-4 use shielded twisted-pair cables.

[0047] Traditional hybrid cables for oil wells have a relatively simple function, serving merely as a "pipeline." This invention upgrades the cable into a downhole network neural network with intelligence, path redundancy, and signal self-adaptation capabilities. While retaining the original high-performance single-mode fiber (used for high-speed backbone data), an additional pair of independent transmission units is added: multimode fiber serves as a transmission unit for backup signal transmission in emergencies, and a pair of shielded twisted-pair cables serves as an electrical backup channel specifically for transmitting low-speed digital or analog modulated signals.

[0048] The armor layer 5 includes a high-strength compressive armor layer made of metal strip wrapping and a torque-balanced tensile armor layer made of two layers of steel wires with opposite directions of rotation.

[0049] The water-blocking layer 3, the inner sheath layer 4, and the outer sheath layer 6 are all made of conventional materials that enable the cable to operate in extreme environments, and will not be described in detail here.

[0050] A master-slave distributed intelligent transmission system with autonomous survival and repair capabilities in downhole wells can be applied to achieve photoelectric conversion in extreme environments, such as... Figure 2 As shown, it includes: The aforementioned photoelectric composite logging cable; The ground control unit is the command and control center of the entire system. It includes a human-machine interface, a main control computer, an optical line terminal, a high-voltage power supply system, and a database server. The human-machine interface is connected to the main control computer, and the main control computer is connected to the database server through the optical line terminal and the high-voltage power supply system. The downhole instruments are connected to the surface main control unit via a photoelectric composite logging cable. These instruments include a data acquisition unit and connected temperature and pressure sensors, electromagnetic flow meters, high-definition cameras, electric control valves, fiber optic sensor arrays, etc. The data acquisition unit collects data and uploads it to the surface main control unit. The downhole self-healing unit is integrated into the key nodes or ends of the photoelectric composite logging cable. It is used to monitor the communication status between the main optical unit 2-1 and the backup optical unit 2-3, and between the main power unit 2-2 and the backup power unit 2-4. When the main optical channel fails, it automatically switches to the backup power channel or the backup optical channel. The downhole self-healing unit is connected to the system bus unit 2-5 and is used to report the fault information and location information to the surface main control unit when a channel switch occurs.

[0051] A method for downhole monitoring of oil wells, applied to a master-slave distributed intelligent transmission system as described above, includes the following steps: System initialization: The ground control unit establishes communication with the downhole instruments and the downhole self-healing unit. During the descent of the downhole instrument following the photoelectric composite logging cable, the status and descent parameters of the photoelectric composite logging cable are monitored in real time. During the data acquisition phase, high-speed data is uploaded through the main optical channel (including optical line terminal, main optical unit 2-1, etc.); When the downhole self-healing unit detects an interruption in the main optical channel, it automatically switches the communication link to the backup electrical channel (including backup electrical units 2-4, etc.) or the backup optical channel (including backup optical units 2-3, etc.) and reports the fault event to achieve uninterrupted monitoring.

[0052] The specific work process is as follows: The system initializes, the ground main control unit powers on and performs a self-test, and queries the status of the downhole self-healing unit through system bus units 2-5; the downhole instruments are powered on, the sensors are initialized, the ready status is reported, and the well logging data (sampling rate, transmission mode, etc.) are set on the ground. The photoelectric composite logging cable carries downhole instruments into the well, and the downhole self-healing unit provides real-time feedback on the status, continuously monitoring the health of the cable; the descent curve and cable status are displayed on the ground in real time. The ground control unit issues a "start acquisition command (optical signal)". The downhole instruments receive the command, activate all sensors, and acquire data at the set sampling rate. During normal acquisition, data is uploaded via the main optical unit 2-1. If a section of the main optical unit 2-1 breaks, the nearest downhole self-healing unit detects the loss of optical signal and immediately switches communication to the backup power unit 2-4. It also sends an alarm and reports the fault location coordinates to the ground via the system bus unit 2-5. The ground control unit automatically adjusts the communication protocol, and the downhole instrument data continues to be uploaded via the backup channel, achieving seamless switching and continuous monitoring.

[0053] Any parts or structures not specifically described in this invention can be made using existing technologies or products, and will not be elaborated upon here.

[0054] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A photoelectric composite logging cable, characterized in that, It includes a cable core, a water-blocking layer, an inner sheath, an armor layer, and an outer sheath, arranged sequentially from the inside out. The cable core includes an anti-torsion central skeleton and a core transmission unit.

2. The photoelectric composite logging cable according to claim 1, characterized in that, The core transmission unit includes several main optical units, main power units, backup optical units, backup power units, and system bus units. The main optical units and main power units are twisted together and separated by an anti-torsion central frame to form a first twisted layer. The backup optical units, backup power units, and system bus units are twisted outside the first twisted layer and separated by an anti-torsion central frame to form a second twisted layer.

3. The photoelectric composite logging cable according to claim 2, characterized in that, Each of the main optical unit and the main power unit is embedded in two opposite grooves of the anti-torsion center frame and is twisted in a first twisting direction and a first twisting pitch P1. The backup optical unit, the backup power unit and the system bus unit are twisted in a second twisting direction and a second twisting pitch P2, wherein the first twisting direction is opposite to the second twisting direction.

4. The photoelectric composite logging cable according to claim 3, characterized in that, The ratio of P1 to P2 is 1.2 to 1.8:

1.

5. The photoelectric composite logging cable according to claim 2, characterized in that, The main optical unit uses a loose-tube single-mode optical fiber in a stainless steel tube, and the backup optical unit uses a loose-tube multimode optical fiber in a stainless steel tube. The surface of the single-mode or multimode optical fiber is coated with a high-temperature resistant polyimide coating and placed in a precision-welded stainless steel tube filled with high-temperature silicone gel.

6. The photoelectric composite logging cable according to claim 2, characterized in that, The main power unit uses tightly twisted copper conductors as the core, and is surrounded by multiple layers of composite insulation. The composite insulation layer includes a high-temperature cross-linked polyethylene base layer or ethylene propylene rubber base layer and a fluoropolymer outer layer arranged sequentially from the inside to the outside. The backup power unit uses shielded twisted pair cables.

7. The photoelectric composite logging cable according to claim 1, characterized in that, The armor layer includes a high-strength compressive armor layer made of metal strip wrapping and a torque-balanced tensile armor layer made of at least two layers of steel wires with opposite directions of rotation.

8. A master-slave distributed intelligent transmission system, characterized in that, include: A photoelectric composite logging cable according to any one of claims 1-7; The ground control unit is used for system control, power supply, data reception and processing; The downhole instruments are connected to the surface main control unit via a photoelectric composite logging cable; The downhole self-healing unit is integrated into the key nodes or ends of the photoelectric composite logging cable and connected to the system bus unit. It is used to monitor the communication status between the main optical unit and the backup optical unit, and between the main power unit and the backup power unit. When the main optical channel fails, it performs automatic switching to the backup power channel or the backup optical channel. When a channel switch occurs, it reports the fault information and location information to the ground main control unit.

9. A master-slave distributed intelligent transmission system according to claim 8, characterized in that, The downhole self-healing unit is connected to the system bus unit and is used to report fault information and location information to the ground main control unit when a channel switch occurs.

10. A method for downhole monitoring of oil wells, characterized in that, An application to a master-slave distributed intelligent transmission system as described in claim 8 or 9 includes the following steps: System initialization: The ground control unit establishes communication with the downhole instruments and the downhole self-healing unit. During the descent of the downhole instrument following the photoelectric composite logging cable, the status and descent parameters of the photoelectric composite logging cable are monitored in real time. During the data acquisition phase, high-speed data is uploaded via the primary optical channel; When the downhole self-healing unit detects an interruption in the primary optical channel, it automatically switches the communication link to the backup electrical channel or backup optical channel and reports the fault event, thus achieving uninterrupted monitoring.

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