Seabed shallow casing section heat preservation structure and heat preservation method for polar region supercritical carbon dioxide drilling

Abstract

The invention discloses a seabed shallow casing section thermal insulation structure for polar region supercritical carbon dioxide drilling, which comprises a casing, a thermal insulation coating, a protective coating, an annular cement slurry layer, an electric heating pipe, a sensor module, a wireless conductive module, a ground system and a seabed wireless transmission module, and is characterized in that the electric heating pipe is fixed on the outer wall of the casing through a hoop; the outer wall of the casing pipe is sequentially coated with a heat preservation coating, a protective coating and an annular cement paste layer from inside to outside, the wireless conductive module is integrated at the end of the casing pipe, and the ground system comprises a ground data acquisition system and a ground control center. The sea surface platform is provided with a ground data acquisition system and a ground control center which are connected with the seabed wireless transmission module through an umbilical cable, and temperature and pressure data acquired by the sensor module are uploaded to the ground control center. According to the invention, the problems of rapid heat loss, annular air channeling, casing mechanical property degradation, poor drilling fluid fluidity and the like of the seabed shallow casing section in the polar region extreme low-temperature environment are solved.

Description

Technical Field

[0001] This invention relates to the field of deep-water and polar marine oil and gas drilling engineering technology, and in particular to a thermal insulation structure and method for shallow seabed casing sections used in polar supercritical carbon dioxide drilling. Background Technology

[0002] Conducting supercritical CO2 drilling operations in polar regions faces the dual challenges of an extremely cold environment of -60°C and high marine corrosion. Among them, the shallow casing section on the seabed is in direct contact with low-temperature seawater and low-temperature strata, and is located in a region of strong convection and high heat dissipation 0-5m below the mud surface. The heat loss rate is much higher than in conventional drilling scenarios, making it a key factor restricting drilling safety.

[0003] The physical properties of supercritical CO2 are extremely sensitive to temperature changes: when the temperature of the shallow casing section on the seabed decreases, the viscosity of the CO2 fluid will increase significantly and the density will fluctuate greatly, directly leading to a reduction of more than 30% in its cuttings carrying capacity. This not only reduces drilling efficiency but may also cause complex downhole conditions such as cuttings bed accumulation and incomplete wellbore cleaning. At the same time, sustained low temperatures will degrade the mechanical properties of the casing substrate, such as reduced toughness and increased brittleness, increasing the risk of casing damage by 2-3 times compared to normal temperature environments. In addition, low temperatures will also cause the drilling fluid inside the casing to increase viscosity and decrease fluidity, and in extreme cases, even solidification may occur, further hindering the continuous advancement of drilling operations.

[0004] Currently, conventional drilling insulation solutions have three major drawbacks: First, they rely solely on a single casing coating or a single annular cement slurry for insulation, failing to form a synergistic insulation system, resulting in thermal conductivity generally exceeding 0.15 W / (m²). First, the existing heating elements are inadequate, unable to withstand the strong heat dissipation requirements of polar supercritical CO2 drilling. Second, there is a lack of active heating design adapted to the low temperatures of polar regions. Existing heating elements are prone to unstable heating below -40℃, and power is not adapted to the differences in heat loss of casings of different diameters, which can easily lead to heating blind spots. Third, the monitoring and control system is imperfect, with insufficient sensor density, poor adaptability of wireless transmission modules, and no linkage control logic between temperature and heating power, making it difficult to respond to real-time temperature fluctuations in polar environments.

[0005] The aforementioned conventional solutions cannot effectively meet the unique requirements of integrated "insulation-cementing-heating-monitoring" for shallow subsea casing sections in polar supercritical CO2 drilling. Therefore, there is an urgent need to develop a comprehensive technical solution that is highly targeted, stable in performance, and easy to operate, in order to overcome the bottlenecks of existing technologies. Summary of the Invention

[0006] This invention provides, in one aspect, a thermal insulation structure for shallow subsea casing sections used in polar supercritical carbon dioxide drilling, aiming to solve problems such as rapid heat loss, annular air channeling, deterioration of casing mechanical properties, and poor drilling fluid flowability in shallow subsea casing sections under extreme low-temperature environments in polar regions. This invention also provides a method for thermal insulation of shallow subsea casing sections used in polar supercritical carbon dioxide drilling.

[0007] The first aspect of this invention provides a thermal insulation structure for a shallow subsea casing section used in polar supercritical carbon dioxide drilling, comprising a casing, a thermal insulation coating, a protective coating, an annular cement slurry layer, an electric heating tube, a sensor module, a wireless conductive module, a ground system, and a subsea wireless transmission module. The electric heating tube is fixed to the outer wall of the casing by clamps. The outer wall of the casing is coated with the thermal insulation coating, the protective coating, and the annular cement slurry layer sequentially from the inside out. The protective coating prevents wellbore cuttings from scraping the thermal insulation coating during the drilling process and is biodegradable. The wireless conductive module is integrated at the end of the casing, and the subsea wireless transmission module is integrated on the casing. The ground system includes a ground data acquisition system and a ground control center. The ground data acquisition system is deployed on the surface platform and connected to the subsea wireless transmission module via an umbilical cable. Temperature and pressure data collected by the sensor module are first transmitted to the subsea wireless transmission module, processed by the subsea wireless transmission module, then transmitted to the ground data acquisition system, and finally uploaded to the ground control center in real time.

[0008] The aforementioned insulation structure for shallow subsea casing sections used in polar supercritical carbon dioxide drilling preferably comprises an insulation coating material with a thermal conductivity of 0.015 W / (m²). K) is a polyimide-modified polyurethane material, wherein the polyimide-modified polyurethane material includes a modified sulfoaluminate low-temperature micro-expansion agent.

[0009] The aforementioned insulation structure for the shallow subsea casing section used in polar supercritical carbon dioxide drilling preferably includes a biodegradable polylactic acid coating as the protective coating.

[0010] The aforementioned insulation structure for the shallow subsea casing section used in polar supercritical carbon dioxide drilling preferably comprises, in the form of, 3%-5% nano-aerogel particles with a particle size of 20-50 nm, 2%-3% hollow glass microspheres with a particle size of 50-100 μm, 0.5%-1% low-temperature resistant copolyamide organic fibers with a length of 8-12 mm and a tensile strength of not less than 500 MPa, and the balance being Grade G oil well cement.

[0011] The aforementioned insulation structure for the shallow subsea casing section used in polar supercritical carbon dioxide drilling preferably includes a sensor module comprising a temperature sensor and a pressure sensor. The temperature sensor is fixed to the outer wall of the casing by clamps and is located near the female threaded interface of the casing. The temperature sensor and the pressure sensor first transmit temperature and pressure data to the subsea wireless transmission module, which processes the data before transmitting it to the ground data acquisition system, and finally uploads it to the ground control center in real time.

[0012] The aforementioned insulation structure for the shallow subsea casing section used in polar supercritical carbon dioxide drilling, preferably, includes a wireless conductive module comprising a shell, a high-permeability ferrite core, and a 316L stainless steel protective cover. The high-permeability ferrite core is disposed inside the shell, and the 316L stainless steel protective cover is fitted over the outside of the shell.

[0013] A second aspect of this invention provides a method for insulating a shallow subsea casing section for polar supercritical carbon dioxide drilling, comprising the aforementioned insulating structure for the shallow subsea casing section, specifically including the following steps: Prefabricated sleeves and supporting modules; Connect the sleeves into a sleeve string, insert the sleeve string and fix it to the annulus; Heat is recovered and reused. The wellbore temperature is monitored in real time and continuously by a network of temperature sensors. When the monitored temperature continues to be higher than the safety threshold, the polar supercritical carbon dioxide drilling process is initiated. When the monitored temperature is below the safety threshold, the system immediately and automatically triggers the control mechanism until the temperature rises and stabilizes within the safe range to start the polar supercritical carbon dioxide drilling process.

[0014] The method for insulating the shallow subsea casing section for polar supercritical carbon dioxide drilling, preferably, includes the following steps: The outer wall of the casing is treated with sandblasting to achieve the required surface roughness. After removing oxide scale and oil, impurities are blown away with compressed air. The thermal insulation coating is applied layer by layer using a high-pressure airless thermal spraying process. Apply a protective coating to the surface of the thermal insulation coating; An electric heating element is installed outside the sleeve; Install wireless conductive module; Abrasion-resistant strips are installed on the facing side of the sleeve. A temperature sensor and a pressure sensor are installed in the middle of the sleeve; Protective covers are installed on the outside of the temperature sensor and the pressure sensor, and the power supply cables and signal transmission cables of the temperature sensor and the pressure sensor are fixed along the outer wall of the sleeve using cable brackets. Connect the cable terminals of the temperature sensor and the pressure sensor to the interface of the seabed wireless transmission module. Activate the submarine wireless transmission module and use a portable data acquisition instrument to receive data from the temperature and pressure sensors. Confirm that the temperature error is ≤ ±0.5℃ and the pressure error is ≤ ±0.25% FS. Ensure that the data transmission is stable and uninterrupted or without interference, and complete the prefabrication and acceptance of the single sleeve.

[0015] The method for insulating shallow subsea casing sections for polar supercritical carbon dioxide drilling, preferably, includes the following steps: "connecting the casings into a casing string, lowering the casing string and fixing it to the annulus": The sleeves are connected one by one to form a pre-assembled sleeve string, and the pre-assembled sleeve string is then tested for connection. The pre-assembled sleeve string was subjected to comprehensive performance testing. Preparations are made for the on-site installation of the pre-assembled bushing string. Lower the first casing of the pre-assembled casing string and fix it at the wellhead; The remaining pre-assembled bushings are lowered in sections until the bushings are completely lowered. Preparation of annular cement slurry; Inject the annular two-stage cement grout; After the cement grout is poured, the cement grout is cured and the bonding quality is tested. Clean the submarine cable connectors; Docking underwater wet joints and conducting performance tests; The underwater wet joint was protected and inspected.

[0016] The aforementioned method for heat preservation of shallow subsea casing sections used in polar supercritical carbon dioxide drilling preferably includes the following steps for "heat recovery and heat reuse": Deploy a ground data acquisition system and a ground control center on a sea surface platform, and connect the seabed wireless transmission module to the ground system via an umbilical cable; Configure the software of the ground control center; Test the system's data transmission; Debug the temperature control logic under low-temperature conditions; Debug the temperature control logic under temperature recovery conditions; Simulate system failures and conduct tests; The execution system performs daily monitoring. System maintenance; Perform emergency procedures on the system.

[0017] The beneficial effects are: 1. Synergistic improvement of insulation and cementing quality: The dual passive insulation system of "polyimide modified polyurethane coating on the outer wall of the casing + annular modified cement slurry" is adopted, which significantly improves the heat insulation effect compared with conventional solutions and can block heat loss in shallow casing sections on the seabed. The design of the expansion agent in the modified cement slurry and coating can control the shrinkage rate of cement sheath, fill the micro gaps at the interface, avoid annular air leakage, and at the same time ensure the corrosion protection and long-term insulation of the tubing string.

[0018] 2. Optimization of heating system reliability and adaptability: The nickel-chromium alloy heating tube has both flexibility and corrosion resistance, the wireless conductive module improves transmission efficiency and anti-corrosion heat dissipation capabilities, the heating power is designed according to the tube diameter and redundancy is reserved, and the power interruption rate in low temperature environment is greatly reduced.

[0019] 3. Temperature monitoring accuracy and data integrity assurance: High corrosion resistant sensors extend service life, optimized layout density covers key areas, improve fit and reduce measurement errors; dual protocol transmission adapts to different well depths, and large storage capacity and automatic retransmission function ensure data integrity.

[0020] 4. Enhanced cable connection safety and sealing: High-pressure underwater wet connectors are suitable for deep-water environments, and temperature-resistant seals and signal filtering modules reduce the risk of seal failure and signal distortion. Special sealing components at the openings prevent seawater leakage, significantly reducing the cable connection failure rate.

[0021] 5. Improved efficiency and safety of automated control response: Ground-based automatic control significantly shortens response time and precisely controls wellbore temperature fluctuations; when signals are interrupted, it automatically switches protocols and starts backup power, quickly generates fault reports, improves polar operation efficiency and reduces safety risks. Attached Figure Description

[0022] Figure 1 A schematic diagram of the overall insulation scheme for the shallow subsea casing section of polar supercritical carbon dioxide drilling. Figure 2 A schematic diagram of the thermal insulation scheme for the longitudinal section of the wellbore; Figure 3 This is a schematic diagram of the sleeve structure; Figure 4 This is a schematic diagram of the steps in Example 2.

[0023] In the picture: 1. Sleeve; 2. Thermal insulation coating; 3. Protective coating; 4. Annular cement grout layer; 5. Electric heating element; 6. Copper core live wire for power supply; 7. Copper core neutral wire for power supply; 8. Temperature sensor; 9. Pressure sensor; 10. Sensor power supply cable; 11. Sensor data cable; 12. Wireless conductive module; 13. Electric heating power supply cable; 14. Ground layer; 15. Male connector; 16. Female connector; 17. Induction coil; 18. Radio frequency signal module. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0025] In the description of this invention, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the system or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the use of terms such as "first," "second," etc., to define components is merely for the convenience of distinguishing the aforementioned components; unless otherwise stated, these terms have no special meaning and should not be construed as indicating or implying relative importance.

[0026] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "setting," and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0027] This invention provides a thermal insulation structure for a shallow subsea casing section used in polar supercritical carbon dioxide drilling, comprising a casing, a thermal insulation coating, a protective coating, an annular cement slurry layer, an electric heating element, a sensor module, a wireless conductive module, a surface system, and a subsea wireless transmission module. The electric heating element is fixed to the outer wall of the casing by clamps. The outer wall of the casing is coated with the thermal insulation coating, the protective coating, and the annular cement slurry layer sequentially from the inside out. The protective coating prevents wellbore cuttings from scraping the thermal insulation coating during the drilling process and is biodegradable. The wireless conductive module is integrated at the end of the casing, and the subsea wireless transmission module is integrated into the casing. The surface system includes a surface data acquisition system and a surface control center. The surface platform deploys the surface data acquisition system and the surface control center, which are connected to the subsea wireless transmission module via an umbilical cable. The temperature and pressure data collected by the sensor module are first transmitted to the subsea wireless transmission module, processed by the subsea wireless transmission module, then transmitted to the surface data acquisition system, and finally uploaded to the surface control center in real time. This invention provides an integrated technical solution for insulation, heating, temperature monitoring, cable connection, and automated control of subsea casing strings. It is applicable to oil and gas drilling operations in extreme marine environments such as deep water and polar regions. It solves problems such as heat loss, structural damage, signal transmission interruption, and control failure caused by low temperature, high pressure, and high corrosion in subsea casing strings. It falls under the category of marine oil and gas extraction equipment and supporting technologies, and is particularly suitable for the coordinated operation of intelligent drill pipe systems with subsea wellheads and blowout preventers. This invention constructs a dual passive insulation system, with the outer wall of the casing coated with a polyimide-modified polyurethane coating. This coating has a thermal conductivity of 0.015 W / (m²). K) and contains a low-temperature micro-expansion agent; annular grouting modified cement grout, the thermal conductivity of which is 0.08-0.10 W / (m K), and incorporates nano-aerogel, hollow glass microspheres, and low-temperature resistant fibers, simultaneously addressing insulation and cementing anti-channeling requirements; an active heating system is configured, using nickel-chromium alloy armored electric heating tubes, with power adapted to the casing diameter, and densely arranged in a high heat dissipation zone of 0-5m below the mud surface; a wireless conductive module is integrated at the casing end to achieve continuous power transmission between adjacent casings; a full-link monitoring and control system is established, with temperature and pressure sensors densely arranged in areas, and equipped with a wireless transmission module supporting Bluetooth 5.0 / LoRa dual protocols; an automated control center is deployed on the offshore platform, with a preset wellbore temperature safety threshold of 5℃, automatically adjusting heating parameters through temperature-power linkage logic; in the event of a signal interruption, a backup power supply can be activated and the transmission protocol switched. The following section uses a subsea shallow casing section insulation structure for polar supercritical carbon dioxide drilling as an example to illustrate the entire technical process in detail.

[0028] Example 1 like Figure 1 , Figure 2 and Figure 3 As shown, a shallow subsea casing section insulation structure for polar supercritical carbon dioxide drilling includes a casing 1, an insulation coating 2, a protective coating 3, an annular cement slurry layer 4, an electric heating element 5, a sensor module, a wireless conductive module, a surface system, and a subsea wireless transmission module. The electric heating element 5 is fixed to the outer wall of the casing 1 by clamps. The outer wall of the casing 1 is coated with the insulation coating 2, the protective coating 3, and the annular cement slurry layer 4 sequentially from the inside out. The protective coating 3 prevents wellbore cuttings from scratching the insulation coating during the drilling process, and the protective coating 3 is biodegradable. The wireless conductive module is first integrated and fixed at the end of the casing 1 (i.e., the wireless conductive module is fixed at the outer wall end of the male and female ends (100mm from the port), which avoids the sealing surface of the casing joint and can form an effective sensing distance after adjacent casings are connected), and then it is lowered into the wellbore with the casing 1, and finally surrounded and wrapped by the annular cement slurry layer 4. The subsea wireless transmission module is integrated on the casing 1 (the subsea wireless transmission module is integrated on the outer wall of the female end of the casing, 100mm from the female port, and is fixed by snap-fit, maintaining a distance of ≥100mm from the wireless conductive module at the same end to avoid electromagnetic interference). The ground system includes a ground data acquisition system and a ground control center. The ground data acquisition system deployed on the sea surface platform is connected to the subsea wireless transmission module via an umbilical cable. The temperature and pressure data collected by the sensor module are first transmitted to the subsea wireless transmission module, processed by the subsea wireless transmission module, and then transmitted to the ground data acquisition system, and finally uploaded to the ground control center in real time.

[0029] The sleeve 1 includes a male connector 15, a female connector 16, an induction coil 17, a radio frequency signal module 18, and a temperature sensor 8. The male connector 15 and the female connector 16 are connected by threads. The outer wall of the male connector 15 (non-threaded area) and the outer wall of the female connector 16 (non-threaded area) are coated with a thermal insulation coating 2, a protective coating 3, and an annular cement slurry layer 4 from the inside out. The induction coil 17 is connected at the threaded joint. The radio frequency signal module 18 is installed on the induction coil 17, and the temperature sensor 8 is installed on the female connector 16.

[0030] The induction coil 17 relies on the principle of electromagnetic induction to realize wireless power transmission (powering electric heating tubes, sensors, etc.) and bidirectional operating condition signal transmission at the docking point of the male connector 15 and the female connector 16.

[0031] The radio frequency signal module 18 receives the signal from the sensor / induction coil 17 and converts it into an anti-interference radio frequency signal, which is then transmitted over a long distance to the seabed wireless transmission module and then uploaded to the ground. At the same time, it receives and demodulates the ground control commands, thus realizing closed-loop transmission of data and commands.

[0032] Temperature sensor 8 is designed for the weak area of ​​the bushing 1 joint. Due to special circumstances such as thread gaps and heat dissipation of the wireless conductive module at the joint, a separate temperature sensor 8 is set up to accurately capture the temperature of this local area, forming a supplementary unit for "intensified monitoring of key areas". One set is arranged at the female end 16 of each bushing joint.

[0033] The material of the thermal insulation coating 2 has a thermal conductivity of 0.015 W / (m²). K) is a polyimide-modified polyurethane material, wherein the polyimide-modified polyurethane material includes a modified sulfoaluminate-based low-temperature micro-expansion agent. The modified sulfoaluminate-based low-temperature micro-expansion agent is incorporated at a proportion controlled at approximately 8%-10% of the total material. In preparation, the micro-expansion agent is first pretreated, then added together with additives to the polyimide-modified polyurethane prepolymer and dispersed to form a coating slurry. The slurry is then sprayed onto the outer wall of the casing and pre-cured at room temperature. After the casing is lowered, the micro-expansion agent is activated by the exothermic hydration of the annular cement slurry, simultaneously completing the final curing of the resin, thus obtaining the target polyimide-modified polyurethane material.

[0034] In cementing operations, the traditional casing 1 coating, due to its smooth surface and reliance on physical contact for interfacial bonding with cement slurry, is prone to forming micro-cracks, leading to an increased risk of annular gas channeling. To prevent the coating from affecting cementing gas channeling, the outer wall coating of casing 1 uses a thermal conductivity as low as 0.015 W / (m²). The polyimide-modified polyurethane material (K) maintains stable physicochemical properties in the temperature range of -60℃ to 150℃ and has excellent resistance to seawater corrosion. It is coated using a high-pressure airless thermal spraying process, with the spraying temperature controlled at 80-120℃ to avoid damaging the substrate of the sleeve 1. The spraying pressure is 0.8-1.2MPa, and it is sprayed in 3-4 layers. After each layer is sprayed, it is cured at a low temperature of 60-80℃ for 2 hours to finally form a continuous thermal insulation layer with a thickness of 3-5mm.

[0035] To address the gas channeling issue caused by micro-gaps at the interface between the casing 1 coating and the cement slurry, a modified sulfoaluminate-based low-temperature micro-expansion agent was introduced into the polyimide-modified polyurethane coating formulation. This modified sulfoaluminate-based low-temperature micro-expansion agent maintains stable hydration activity at low temperatures of 4-10℃. During coating curing, a slow hydration reaction occurs, resulting in a volume expansion of 0.1%-0.3% to prevent coating cracking. Simultaneously, it forms an "active extrusion" effect upon contact with the cement slurry, filling the interfacial micro-gaps. Furthermore, the hydration products of the expansion agent can interweave with the hydration products of the cement slurry, further enhancing interfacial density and ensuring the long-term thermal insulation and corrosion resistance of the tubing.

[0036] The protective coating 3 is a biodegradable polylactic acid (PLA) coating. The coating thickness is 0.5-1 mm. The biodegradable PLA coating prevents rock cuttings from scraping the insulation coating 2 during casing 1 installation. After casing 1 is installed, the biodegradable PLA coating can be naturally degraded by drilling fluid.

[0037] The annular cement slurry layer 4 includes 3%-5% nano-aerogel particles with a particle size of 20-50nm, 2%-3% hollow glass microspheres with a particle size of 50-100μm, 0.5%-1% copolyamide low-temperature resistant organic fibers with a length of 8-12mm and a tensile strength of not less than 500MPa, and the balance being G-grade oil well cement.

[0038] Specifically, based on conventional Grade G oil well cement, 3%-5% of nano-aerogel particles with a particle size of 20-50 nm and 2%-3% of hollow glass microspheres with a particle size of 50-100 μm are added. After compounding, the thermal conductivity of the cement slurry is reduced to 0.08-0.10 W / (m²). Below K), it reduces the amount of cement by more than 70% compared to conventional G-grade cement, significantly improving the thermal insulation effect; at the same time, it adds 0.5%-1% of copolyamide low-temperature resistant organic fibers with a length of 8-12mm and a tensile strength of not less than 500MPa to ensure that the cement ring shrinkage rate does not exceed 0.06% at -40℃, avoiding low-temperature shrinkage cracking.

[0039] like Figure 2 As shown, the sensor module includes a temperature sensor 8 and a pressure sensor 9. The temperature sensor 8 and the pressure sensor 9 are fixed to the outer wall of the sleeve 1 by clamps and are located at the threaded opening near the female head 16. The temperature sensor 8 and the pressure sensor 9 first transmit temperature and pressure data to the seabed wireless transmission module. After being processed by the seabed wireless transmission module, the data is then transmitted to the ground data acquisition system and finally uploaded to the ground control center in real time.

[0040] Temperature sensor 8 is paired with electric heating tube 5, power supply copper core live wire 6 / neutral wire 7, and wireless conductive module 11. Its core function is to monitor the temperature of the entire area of ​​the sleeve 1 body and the surrounding annular cement slurry. It is a basic monitoring unit in the "full-link temperature monitoring" and is arranged at a density of "one group every 2m and one group every 0.5m in high heat dissipation area", covering most of the main body of sleeve 1.

[0041] Among them, a nickel-chromium alloy armored electric heating tube 5 is selected as the core heating element. Its heating core is a high-resistance nickel-chromium alloy wire, which has good flexibility, corrosion resistance and low-temperature stable heating capability. In order to adapt to the heating requirements of different specifications of sleeves 1, the power of a single electric heating tube 5 is precisely matched according to the diameter of the sleeve 1, and a wireless conductive module is integrated at the end of the sleeve 1. This module is the core unit to ensure the continuous power supply of the electric heating tube 5, and its structure and performance design are fully adapted to the heating scenario requirements of the sleeve 1.

[0042] The wireless conductive module 12 includes a housing, a high-permeability ferrite core, and a 316L stainless steel protective cover. The high-permeability ferrite core is housed inside the housing, and the 316L stainless steel protective cover is fitted over the outside of the housing. Specifically: (1) Module body design: The outer shell is made of 316L stainless steel. After solution treatment, the tensile strength is ≥515MPa and the yield strength is ≥205MPa. It has excellent resistance to marine salt spray corrosion and can resist corrosive media in seawater and soil. It also has good impact resistance and can withstand the impact of gravel on the well wall. The internal high permeability ferrite core has an initial permeability ≥5000μH / m and a saturation magnetic flux density ≥0.45T, which can effectively reduce magnetic leakage loss. It also has a high purity oxygen-free copper coil with a coil purity ≥99.95% and conductivity ≥58MS / m. Compared with ordinary copper coils, it can reduce resistance loss by 3%-5%. The synergistic effect of the two greatly improves the power transmission efficiency. (2) External protective structure: The module is fitted with a hollow 316L stainless steel protective cover, which is processed by laser cutting technology. The hole diameter is precisely controlled at 3-5 mm, taking into account both "wear prevention" and "heat dissipation": the minimum hole diameter of 3 mm can block gravel and mud with a diameter > 3 mm in the well, avoiding scratching the internal components; the maximum hole diameter of 5 mm can quickly dissipate working heat. According to thermal simulation test, under the maximum transmission power of 22 W / m, the internal temperature of the module can be controlled below 65℃, which is far below the tolerance limit of ferrite core (temperature resistance 120℃) and copper coil (temperature resistance 150℃).

[0043] The module is externally fitted with a perforated 316L stainless steel protective cover, processed using laser cutting technology, with the aperture precisely controlled within 3-5 mm. This ensures both wear resistance and heat dissipation without affecting the transmission of radio magnetic fields. (1) Anti-wear and impurity isolation: The minimum aperture of 3mm can block gravel and mud with a diameter of >3mm in the well, avoid the magnetic field deviation caused by impurities scraping the internal magnetic core and coil, and ensure the stable coupling distance of radio transmission. (2) Heat dissipation and temperature control: The maximum aperture of 5mm can quickly dissipate the heat of the module. According to thermal simulation test, under the maximum transmission power of 22W / m, the internal temperature of the module can be controlled below 65℃, which is far below the tolerance limit of ferrite core and copper coil. Temperature stability can avoid the magnetic permeability of the core from decreasing due to high temperature, ensuring that the radio transmission power does not decrease, and solving the problem of unstable radio power supply caused by high temperature in traditional modules.

[0044] Meanwhile, the protective cover and other key components of the sleeve 1 (such as anti-abrasion strips and positioning brackets) adopt the same anti-corrosion process: first, they are sandblasted to achieve a surface roughness of Ra6.3-12.5μm, then coated with a 2mm thick polyimide-modified polyurethane coating, and finally wrapped with low-temperature resistant fiberglass cloth to ensure that the protective cover will not rust in the marine environment for a long time, forming a "double protection" with the module shell, which not only extends the service life of the module, but also avoids interference to radio transmission caused by the magnetic properties of the anti-corrosion layer.

[0045] To ensure that radio transmission can fully meet the power requirements of electric heating tubes 5 under different pipe diameters and operating conditions, the module has been specifically optimized in three core dimensions of radio transmission: "power adaptation", "distance compatibility" and "anti-interference". (1) Power graded adaptation: The module radio transmission power is designed according to the pipe diameter of sleeve 1, which is precisely matched with the power of the single group of electric heating tube 5 and reserved for redundancy: In the small pipe diameter scenario (pipe diameter ≤ 200mm), the transmission power is not less than 12W / m and can be expanded to 15W / m, corresponding to the electric heating tube 5 requirement of 8-12W / m; In the medium pipe diameter scenario (200mm < pipe diameter ≤ 350mm), the transmission power is increased to 15-18W / m, corresponding to the electric heating tube 5 requirement of 12-15W / m; In the large pipe diameter scenario (pipe diameter > 350mm), the transmission power is further increased to 18-22W / m, corresponding to the electric heating tube 5 requirement of 15-18W / m. Taking the 168mm sleeve 1 as an example, its electric heating tube 5 has a power of 12W / m. When the module's radio transmission power is 15W / m, after deducting ≤10% transmission loss, the actual power supply can reach 13.5W / m, which fully covers the heating requirements and reserves 12.5% ​​redundancy, and can cope with extreme working conditions such as low temperature and high heat dissipation. (2) Sensing distance compatibility: The sensing distance of radio transmission is designed to be 5-10mm, which is highly compatible with the installation accuracy of the positioning bracket. The positioning bracket slot tolerance is ±0.5mm and the heating tube spacing deviation is ±3mm. Even if there is a slight deviation in the installation of sleeve 1, the 2mm thick methyl vinyl silicone rubber pad on the inner side of the bracket can compensate for the error through elastic deformation. Moreover, the silicone rubber is a non-magnetic material, which ensures that the sensing distance between the module and the adjacent sleeve 1 is stable within the range of 5-10mm. This avoids the magnetic core saturation and transmission power drop due to the distance being too close, or the efficiency drop due to the distance being too far. The efficiency drops by about 3% for every 1mm increase in distance, ensuring the continuous stability of radio transmission. (3) Anti-interference design: The module has a built-in electromagnetic shielding layer, which uses high-purity aluminum foil with a shielding effectiveness of ≥60dB. It can block electromagnetic interference generated by other metal parts in the well (such as anti-wear strips and clamps) and avoid distortion of radio transmission signals. At the same time, the distance between the module and the anti-wear strip on the facing side of the casing 1 is ≥40mm and the distance between the module and other functional modules is ≥100mm. After electromagnetic compatibility testing, it was verified that this distance can control the impact of external electromagnetic interference on radio transmission efficiency to within 2%, ensuring that the module can still supply power stably in complex electromagnetic environments.

[0046] In addition, the module also has a radio dynamic power compensation function: the built-in power detection chip can monitor the radio transmission efficiency and the actual power consumption of the electric heating tube 5 in real time. When it is detected that the transmission efficiency drops by more than 5% due to external interference, the chip will automatically trigger the compensation mechanism to increase the radio transmission power by 5%-8% by adjusting the coil excitation current, so as to quickly make up for the loss.

[0047] The arrangement and fixing design of electric heating element 5 revolves around "improving heating efficiency and ensuring installation accuracy": (1) Spacing: The spacing between the foundations is 1 meter per group, and the heat dissipation area 0-5 meters below the mud surface is reduced to 0.8 meters per group. The heating coverage density is increased by 20% by increasing the density of the arrangement to make up for the temperature loss caused by high heat dissipation.

[0048] (2) Fixing method: All heating tubes are fixed by 316L stainless steel clamps and installed by an integrated 316L stainless steel positioning bracket that matches the curvature of sleeve 1. A 2mm thick methyl vinyl silicone rubber pad is pre-attached to the inside of the bracket. The temperature range of this silicone rubber is -60℃ to 120℃. At -60℃, the Shore hardness is ≤60HA. It has both low temperature elasticity and high temperature aging resistance. It can fit tightly with sleeve 1 and heating tubes to reduce heat loss between gaps.

[0049] (3) Precision control: The bracket is pre-set with a slot that matches the outer diameter of the heating tube, with a tolerance of ±0.5 mm, to ensure that the spacing deviation of each heating tube is ≤±3 mm; when fixing, use a wrench with a torque indicator corresponding to the tube diameter to tighten the bolts. When the tube diameter is ≤350 mm, the torque is controlled at 25-30 Nm, and when the tube diameter is >350 mm, the torque is controlled at 30-35 Nm.

[0050] To protect critical components of casing 1 during well insertion, 316L stainless steel anti-wear strips are added to the facing surfaces prone to scraping against the well wall (such as the rotational stress side of casing 1). These anti-wear strips are 50-80 mm wide and 2-3 mm thick, installed axially along casing 1 with 5 mm rounded ends to reduce frictional resistance during insertion and prevent damage to sharp edges. The installation position must maintain a distance of ≥40 mm from the electric heating element 5 and ≥40 mm from the wireless conductive module, ensuring neither affecting heat dissipation from the heating element nor interfering with the module's power transmission. The anti-wear strips are fixed to the outer wall of casing 1 using 316L stainless steel snap-on brackets, eliminating the need for on-site welding and preventing high-temperature damage to the casing 1 coating or module components. The bracket bolt tightening torque is controlled at 20-25 Nm, balancing fixing strength and installation convenience. The connection point between the bracket and casing 1 also employs the aforementioned unified anti-corrosion process to prevent corrosion in the marine environment and ensure the functionality of the wireless conductive module is not affected.

[0051] Equipped with a low-temperature pressure-type temperature sensor 8, which features a Pt100 platinum resistance core, a measurement range of -80℃ to 150℃, and an accuracy of ±0.5℃, the sensor uses a 316L stainless steel shell with a seawater corrosion resistance rating of ≥C4, enabling stable operation in harsh polar environments and maintaining the same weather resistance as the main body material of the sleeve 1. The temperature sensors 8 are arranged at a specific density, with at least one set on each sleeve 1, preferably placed in the middle position. The basic arrangement standard is one set every 2m. For the high heat dissipation area with strong convection at low temperatures 0-5m below the mud surface, the spacing is reduced to one set every 1.5m to enhance the monitoring density. An additional set is added near weak points such as joints and welds of sleeve 1 to monitor temperature changes around the weak points in real time and provide early warning of abnormal heat loss.

[0052] All temperature sensors 88 are fixed to the outer wall of sleeve 1 using 316L stainless steel clamps. During installation, a pre-installed 316L stainless steel positioning bracket with a silicone rubber pad matching the curvature of sleeve 1 is used. The bracket has pre-set mounting slots that match the sensor dimensions, ensuring that the spacing deviation between each sensor is ≤±5mm. A 2mm thick low-temperature silicone rubber pad, consistent with the installation specifications of the electric heating element 55, is pre-attached to the inside of the bracket. During fixing, the bolts are tightened to 25-35N using a torque wrench. To ensure a tight fit between the sensor probe and the outer wall of casing 1, preventing loosening or displacement, the installation must strictly avoid weak points such as joints and welds on casing 1. Simultaneously, the sensor cable should be fixed along the outer wall of casing 1 and finally connected to the subsea wireless transmission module interface at the end of casing 1. To address potential well wall scratches during casing 1 installation, a 316L stainless steel protective cover is fitted over the sensor probe. This cover has a perforated structure with a 3-5mm diameter hole, a 1.5-2mm wall thickness, and a length exceeding the probe by 20-30mm. It connects to the sensor housing using a snap-fit ​​method, with a built-in nitrile rubber sealing ring at the snap-fit ​​point to enhance the sealing effect, eliminating the need for PTFE tape. The sensor cable uses the same anti-abrasion protection measures as the electric heating tube 5, namely, an integrated low-temperature resistant nylon anti-abrasion tube wrapped with factory-prefabricated outer tape, ensuring the safe installation of the temperature monitoring element without affecting the stability of the connection with the subsea wireless transmission module.

[0053] The underwater wireless transmission module at the end of casing 1 supports either Bluetooth Low Energy 5.0 or LoRa protocols. Bluetooth Low Energy 5.0 is suitable for drilling scenarios with a depth ≤ 500m, while LoRa is suitable for drilling scenarios with a depth > 500m. Both protocols can meet the stable transmission requirements of sensor data in polar environments. The module's signal transmission rate is ≥ 0.8Mbps, and the starting voltage is 3.3V in extremely cold environments down to -60℃. It also features a built-in coil for both signal and low-voltage transmission, allowing simultaneous transmission of sensor data and low-voltage signals. The module is powered by a 12V DC waterproof power supply with a battery life ≥ 72 hours. It also has a built-in backup battery with a battery life ≥ 48 hours for temporary power supply in case of main power failure. The power cables and signal transmission cables for temperature sensor 8 and pressure sensor 9 must be directly connected to the corresponding interfaces on the module to ensure that monitoring data is directly transmitted to the module for processing and forwarding. The module and the end of casing 1 are connected by a snap-fit ​​mechanism, with the tightening torque controlled at 15-20N. When adjacent bushings 1 are connected, the module automatically identifies and pairs them through a preset ID. The pairing is completed within 3 seconds after connection, ensuring continuous data and power transmission. To ensure the sealing and corrosion resistance of the interface in the harsh polar and marine environment, a triple protection measure is adopted for the module interface: First, butyl rubber waterproof tape is tightly wrapped around the interface and cable connection to form a basic waterproof barrier. Then, epoxy resin is evenly coated on the outside of the tape. After it is fully cured, a second layer of sealing protection is formed to further prevent seawater intrusion. Finally, an engineering plastic waterproof box is installed on the outside of the epoxy resin. Through physical protection and sealing structure, the overall waterproof rating of the interface reaches the IP68 standard, effectively resisting the effects of long-term seawater immersion and low-temperature freeze-thaw. In addition, the outer surface of the module needs to be sandblasted to achieve a surface roughness of Ra 6.3-12.5μm, which enhances the bonding force with the annular cement grout. At the same time, a cement grout flow channel with a width of 25-30mm is reserved around the module to ensure that the cement grout is evenly distributed near the module and avoids the formation of local heat loss channels.

[0054] The signal cables for temperature sensor 8 and pressure sensor 9 use two-core or four-core tinned copper mesh shielded cables with an anti-interference level of EMC Class B, ensuring uninterrupted data transmission with the intelligent drill pipe wireless signal transmission module. The power cable is an RVV type PVC insulated cable with a temperature range of -30℃ to 70℃. For the intertidal zone, a double-sheathed cable with an inner PVC layer and an outer neoprene rubber layer is used to further enhance weather resistance and corrosion resistance.

[0055] Regarding cable termination and connector protection, to ensure consistent overall sealing performance and uniformity with the interface protection of the intelligent drill rod signal module, at the cable and monitoring cable termination joints under normal conditions, firstly, use at least three layers of 50mm wide butyl rubber waterproof tape to tightly wrap the base layer for waterproofing, then evenly coat the outside with epoxy resin to form a sealing layer for reinforcement. At the same time, install silicone rubber sealing rings and corrosion-resistant engineering plastic waterproof boxes to achieve double physical protection, thus constructing a four-fold protection system of waterproofing, corrosion prevention, and mechanical damage prevention.

[0056] In the high-pressure and highly corrosive environment of the seabed, the cable joints and communication cable joints on the outer wall of casing 1 are connected to the corresponding cables at the underwater blowout preventer via underwater wet connectors operated by ROV (Remotely Operated Vehicle). The selected underwater wet plug connectors have a pressure rating of 30MPa and are compatible with the ISO 13628-8 standard ROV robotic arm interface. The main body is made of seawater-resistant 316L stainless steel, and the seals are made of perfluoroelastomer rubber with a temperature range of -20℃ to 200℃. An internal signal filtering module is also integrated to filter seabed electromagnetic interference, ensuring stable power and signal transmission and providing a reliable link for communication between the intelligent drill pipe and the ground system.

[0057] From a structural layout perspective, the subsea wellhead is located above the mud outlet end of casing 1. The mud outlet end of casing 1 is typically 1-1.5m above the seabed mud surface, and the connections above it follow the sequence of "mud outlet end of casing 1 - subsea wellhead - subsea blowout preventer". Based on this layout, the opening is determined to be located at the mud outlet end of casing 1 below the subsea wellhead. This location avoids the squeezing and abrasion of casing 1 by the mud layer, and its proximity to the subsea blowout preventer significantly shortens the connection distance between the cable and the blowout preventer connector, reducing potential failure points and laying the foundation for a stable connection later. After the hole is drilled, the next step is to lead out and connect the cables: (1) Pre-treat the lead-out ends of the heating cable and monitoring cable, remove excess insulation and check the integrity of the core wire to eliminate the risk of damage and short circuit; (2) With the assistance of the ROV robotic arm, the pre-treated cable is slowly led out from the opening to avoid friction damage between the cable and the edge of the opening; (3) After the cable lead-out length meets the docking requirements, fix its position to prevent water flow from impacting and displacing it; (4) Use a dedicated underwater wet connector for connection: First, align and tighten the cable end with the cable interface of the wet connector, and then use ROV to accurately connect the wet connector equipment end with the underwater blowout preventer assembly connector. Follow the ISO 13628-8 standard throughout the process to ensure that the connector is properly fastened and the seal is properly fitted. (5) Use ROV testing equipment to preliminarily check the opening seal and joint connection status, check for leakage and signal interruption problems, and adjust to meet the standard in time if there are any abnormalities.

[0058] In addition, to ensure the long-term pressure-resistant sealing performance of the opening, a special pressure-resistant sealing component needs to be installed at the opening gap after the opening and cable lead-out. This component has a shell of 316L stainless steel that is resistant to seawater corrosion, and a perfluoroether rubber sealing gasket with a temperature range of -20℃ to 200℃ is embedded inside. The sealing component is fixed to the opening of the sleeve 1 by bolt fastening, so that the sealing gasket fits tightly against the outer wall of the sleeve 1 and the outer sheath of the cable, forming a double sealing structure. This further prevents seawater from entering the sleeve 1 from the opening gap, while enhancing the structural strength of the opening area and resisting the squeezing effect of the high pressure environment on the opening.

[0059] Temperature and pressure data collected by temperature sensor 8 and pressure sensor 9 are first transmitted to the submarine wireless transmission module integrated in the casing 1. After processing by the module, the data is then transmitted to the ground data acquisition system on the surface platform via cable and underwater wet connector, and finally uploaded to the ground control center in real time. The submarine wireless transmission module integrated in the casing 1 has a preset data storage unit with a storage capacity of ≥16GB, which can cache at least 100,000 sets of temperature / pressure data and retain the data for ≥72 hours. When a momentary signal interruption occurs, the monitoring data can be temporarily stored, and the interrupted data can be automatically prioritized and retransmitted after the signal is restored to ensure data integrity.

[0060] The control process relies entirely on the automated control of the power supply end of the umbilical cable of the underwater blowout preventer from the surface platform: the preset safe threshold for wellbore temperature is 5℃. When the wellbore temperature is detected to be below 5℃, the system automatically sends a command to the power supply end of the umbilical cable. By adjusting the switch status of the power supply end and the input current and voltage parameters (such as increasing the current from 10A to 15A), the power input of the electric heating tube 5 on the outer wall of the duct is increased, thereby increasing the heating power. If the temperature remains below 5℃ and there is no upward trend within 10 minutes, the current and voltage ratio is further optimized to ensure that the heating efficiency is accurately matched with the wellbore temperature rise requirements. When the temperature is detected to rise back to the safe range of 5-8℃, the system automatically adjusts the power supply parameters, reducing the power input to a sustaining heating level to avoid energy waste. If abnormal pressure or signal abnormality occurs in the integrated submarine wireless transmission module of casing 1, the system immediately triggers an early warning signal. If the signal interruption exceeds 5 minutes, the module's built-in backup battery is automatically activated and the LoRa protocol is switched (originally using Bluetooth 5.0 protocol). At the same time, the ground system generates a fault location report to assist operators in quickly troubleshooting the cause of the abnormality. No additional underwater operations are required throughout the process, adapting to the operational limitations of polar and marine environments and ensuring the safe and stable progress of drilling operations.

[0061] Example 2 like Figure 4 As shown, a method for insulating shallow subsea casing sections for polar supercritical carbon dioxide drilling includes the shallow subsea casing section insulation structure for polar supercritical carbon dioxide drilling described in Example 1, specifically including the following steps: S1: Prefabricated sleeves and supporting modules.

[0062] S2: Connect the sleeves into a sleeve string, lower the sleeve string and fix it to the annulus.

[0063] S3: To recover and reuse heat.

[0064] S4: The wellbore temperature is monitored in real time and continuously through a network of temperature sensors. When the monitored temperature continues to be higher than the safety threshold, the polar supercritical carbon dioxide drilling process is initiated.

[0065] When the temperature is abnormally higher than the safe range, the system will first stop or significantly reduce heating, monitor the temperature drop trend, and trigger an alarm if necessary. The entire process of "monitoring-judgment-control-re-monitoring" forms an intelligent closed loop.

[0066] S5: When the monitored temperature is below the safety threshold, the system will immediately and automatically trigger the control mechanism until the temperature rises and stabilizes within the safe range to start the polar supercritical carbon dioxide drilling process.

[0067] Specifically, step S1 includes the following steps: Step 1: Use sandblasting to treat the outer wall of the casing to achieve the required surface roughness. After removing the oxide scale and oil, blow away the impurities with compressed air.

[0068] The first step specifically involves: using sandblasting to treat the outer wall of the sleeve to achieve a surface roughness of Ra 6.3-12.5μm, removing oxide scale and oil stains, and then blowing away impurities with 0.6MPa compressed air; focusing on grinding the 100mm range at the end of the sleeve to improve the fit of subsequent module installation and lay the foundation for coating construction.

[0069] Before step 1, the selection and performance verification of core materials are carried out.

[0070] Specifically, referring to the API SPEC 5CT casing specification and the requirements for corrosion protection and low temperature resistance in polar and marine drilling, insulation materials (polyimide modified polyurethane coating, modified annular cement slurry, etc.), heating elements (nickel-chromium alloy armored electric heating tubes and matching brackets), and monitoring and connection components (Pt100 temperature sensor, diffused silicon pressure sensor, dual-protocol wireless transmission module, etc.) were selected. The performance was verified by conducting a 72-hour performance test in a -60℃ low temperature environment chamber and a 5% NaCl salt spray test chamber to ensure that the materials are suitable for polar working conditions.

[0071] Step 2: Apply the insulation coating layer by layer using a high-pressure airless thermal spraying process.

[0072] Specifically, a high-pressure airless thermal spraying process is adopted, and the thermal insulation coating is sprayed in 3-4 layers at 80-120℃ and 0.8-1.2MPa, with each layer being 1-1.5mm thick. After spraying, the coating is cured in a low-temperature oven at 60-80℃ for 2 hours, ultimately forming a continuous coating with a thickness of 3-5mm. After curing, the uniformity is checked with a coating thickness gauge, and the adhesion is tested by the cross-cut test (≥5MPa) to ensure that the coating performance meets the standards.

[0073] Step 3: Spray a protective coating onto the surface of the insulation coating.

[0074] Specifically, a 0.5-1mm thick biodegradable polylactic acid coating is uniformly applied to the surface of the insulation coating at a pressure of 0.5MPa and a temperature of 60℃, fully covering the outer wall of the casing without any gaps. This coating is used to protect the insulation coating during the casing installation process and can be naturally degraded by the drilling fluid after the casing installation is completed.

[0075] Step 4: Install the electric heating element on the outside of the sleeve.

[0076] Specifically, the nickel-chromium alloy armored electric heating tubes are fixed to the positioning brackets on the outer wall of the casing using 316L stainless steel clamps at intervals of "1m / set for the foundation and 0.8m / set for the heat dissipation area 0-5m below the mud surface". Silicone rubber pads are pre-attached to the inner side of the brackets, and the bolts are tightened using a torque wrench corresponding to the casing diameter (25-30N for ≤350mm). When m > 350mm, 30-35N m), attach gap test paper to confirm that the gap between the heating tube and the sleeve is ≤1mm.

[0077] Step 5: Install the wireless conductive module.

[0078] Specifically, a wireless conductive module with a 316L stainless steel shell is installed 100mm from the port at both ends of the sleeve, and an external 316L stainless steel protective cover with a 3-5mm perforated hole is fitted on the outside; the distance between the control module and the anti-wear strip is ≥40mm, and the distance between it and other modules is ≥100mm, using 15-20N. The torque snap-fit ​​fixing method and the pre-connection test between adjacent sleeves ensure a sensing distance of 5-10mm, a transmission efficiency of ≥90%, and no electromagnetic interference.

[0079] Step 6: Install the anti-wear strip facing the sleeve.

[0080] Specifically, on the face of the casing during rotational stress at the wellhead, install a 50-80mm wide and 2-3mm thick 316L stainless steel anti-wear strip with 5mm rounded transitions at both ends; use a snap-on bracket with 20-25N... The torque is fixed, and the connection point between the bracket and the sleeve is treated with sandblasting (Ra6.3-12.5μm), coating with a 2mm thick polyimide coating, and wrapping with low-temperature resistant glass fiber cloth to enhance corrosion resistance.

[0081] Step 7: Install temperature and pressure sensors in the middle of the casing.

[0082] Specifically, a temperature sensor is installed 5m from the middle of each casing, and a pressure sensor is installed 1m from the end. For the first casing (corresponding to 0-5m below the mud surface), additional temperature sensors are installed at 2.5m and 5m, and an additional temperature sensor is installed near weak points such as welds. The sensors are fixed to positioning brackets with silicone rubber pads (groove tolerance ±0.5mm) using 316L stainless steel clamps, and subjected to 25-35N pressure. Tighten the bolts with torque m to ensure that the gap between the probe and the sleeve is ≤0.5mm.

[0083] Step 8: Install protective covers on the outside of the temperature and pressure sensors, and fix the cables along the outer wall of the sleeve with cable brackets.

[0084] Specifically, a 316L stainless steel perforated protective cover with a diameter of 3-5mm, a wall thickness of 1.5-2mm, and extending 20-30mm beyond the sensor probe is fitted over the sensor probe. It is connected by a snap-fit ​​and has an internal nitrile rubber sealing ring. The sensor cable is a two-core tinned copper mesh shielded cable with EMC Class B anti-interference, and is fixed along the outer wall of the sleeve with a 316L stainless steel cable bracket with a spacing of 500mm.

[0085] Step 9: Connect the cable terminals of the temperature sensor and the pressure sensor to the interface of the submarine wireless transmission module.

[0086] Specifically, the sensor cable terminal is connected to the interface of the submarine wireless transmission module. The interface is wrapped with three layers of butyl rubber tape, sealed with epoxy resin, and then an engineering plastic waterproof box is installed to achieve an IP68 waterproof rating, ensuring sealing and corrosion protection in the polar marine environment.

[0087] Step 10: Activate the seabed wireless transmission module and use a portable data acquisition instrument to receive data from the temperature and pressure sensors. Confirm that the temperature error is ≤ ±0.5℃ and the pressure error is ≤ ±0.25%FS. Ensure that the data transmission is stable without interruption or interference. Complete the prefabrication and acceptance of the single sleeve.

[0088] Step S2 specifically includes the following steps: Step 1: Connect the sleeves one by one to form a pre-assembled sleeve string, and then perform a connection test on the pre-assembled sleeve string.

[0089] Specifically, taking 128 casings as an example, they are connected one by one in the order of being run from the wellhead to a depth of 1280 meters to ensure that the wireless conductive module completes automatic ID pairing within 3 seconds, and that the heating tube is powered by 12VDC without voltage drop and the sensor data is transmitted continuously. The joints are tightened according to the casing specifications to ensure sealing performance.

[0090] Step 2: Perform comprehensive performance testing on the pre-assembled sleeve string.

[0091] Specifically, after pre-assembly, a bore gauge with an inner diameter of 85% of the casing is used to conduct a bore test to ensure that the inner diameter is unobstructed; the insulation resistance between the heating tube and the casing is tested and must reach more than 100MΩ; the casing internal pressure is tested at 1.2 times the design pressure and stabilized for 30 minutes without leakage; the facing side of each casing and the sensor position are marked to facilitate alignment with the wellbore trajectory during on-site installation.

[0092] Step 3: Prepare for the on-site installation of the pre-assembled bushing string.

[0093] Specifically, a guide device is installed at the subsea wellhead, and a ROV is used to remove large pieces of rock debris from the wellbore; the rated load of the marine crane is checked and must be no less than 1.5 times the weight of the casing, and the wear of the wire rope is checked to eliminate potential safety hazards during lifting.

[0094] Step 4: Lower the first casing of the pre-assembled casing string and fix it to the wellhead.

[0095] Specifically, the first casing is lifted to the seabed wellhead, aligned with the wellhead flange with the assistance of an ROV, and the bolts are tightened to the appropriate torque according to the wellhead specifications to complete the fixing of the first casing.

[0096] Step 5: Insert the remaining pre-assembled bushings in sections until the bushings are completely inserted.

[0097] Specifically, casing sections 2-128 were lowered and connected in stages for confirmation. Subsequent casing sections were then lifted one by one. During the lowering process, the casing attitude was adjusted using a wellbore trajectory monitoring system with an accuracy of ±0.1° to prevent the anti-abrasion strips from scraping against the well wall. Work was paused every 10 casing sections to allow the ROV to inspect the anti-abrasion strips and protective covers on the front casing. If the wear thickness exceeded 0.5 mm, the casing was replaced immediately. After each casing was lowered to the designated depth, the wireless conductive modules and transmission modules at both ends were confirmed to be successfully paired. The power connectivity of the heating element and the sensor signal transmission were tested. Lowering continued only after all tests were completed.

[0098] Step 6: Prepare annular cement slurry.

[0099] Specifically, the annular cement slurry is prepared in batches. The slurry from the wellhead to 50 meters below the mud surface incorporates 5% nano-aerogel, 3% hollow glass microspheres, and 1% copolyamide fiber. The slurry from 50 meters to 1280 meters below the mud surface incorporates 3% nano-aerogel, 2% hollow glass microspheres, and 0.5% copolyamide fiber. The viscosity of the cement slurry is tested using a rotational viscometer, and the result must not exceed 30 seconds. The thermal conductivity of the cured cement slurry is tested using a thermal conductivity meter and must be controlled within 0.10 W / (m²). K) and below.

[0100] Step 7: Inject the annular two-stage cement grout.

[0101] Specifically, a two-stage cementing process is adopted. The first stage involves injecting cement slurry into the annulus from the wellhead to 50 meters below the mud surface, with the pumping pressure controlled at 2-3 MPa and the rate at 1.2-1.5 m³ / min, ensuring that the cement slurry fills the 10 mm reserved flow channel around the wireless module. The second stage involves injecting cement slurry into the annulus from 50 meters to 1280 meters below the mud surface, with a pumping rate of 1.5-2 m³ / min. The annulus pressure is monitored in real time by a casing pressure sensor to ensure that it does not exceed 80% of the rated internal pressure of the casing and to avoid casing deformation.

[0102] Step 8: After the cement grout is poured, the cement grout is cured and the bonding quality is tested.

[0103] Specifically, after the cement grout is injected, it is cured at 60-80℃ for 48 hours. During the curing period, the temperature change of the cement sheath is monitored by a temperature sensor to ensure that the peak hydration temperature does not exceed 80℃. After the curing is completed, the cement sheath bonding quality is tested with an acoustic logging tool, and the bonding rate must reach more than 90%.

[0104] Step 9: Clean the submarine cable connectors.

[0105] Specifically, use a high-pressure water gun with a pressure of 0.8 MPa to clean the heating cable, sensor cable connectors and corresponding cable connectors of the underwater blowout preventer at the top of the casing to remove seawater and impurities; wipe the sealing surface of the connectors with an alcohol swab to ensure that there is no oil.

[0106] Step 10: Connect the underwater wet joint and conduct performance tests.

[0107] Specifically, the heating cable and sensor cable are connected to the power supply cable and signal cable of the underwater blowout preventer via an underwater wet connector using an ROV robotic arm. The wet connector must be compatible with the ISO13628-8 standard, and the perfluoroether rubber seals must be undamaged during the connection. After connection, the stability of the heating tube power supply current and the sensor data transmission delay are tested, and the delay must be controlled within 1 second.

[0108] Step 11: Protect and inspect the underwater wet joint.

[0109] Specifically, wrap three layers of 50mm wide butyl rubber waterproof tape around the outside of the wet joint, and evenly apply 2mm thick epoxy resin adhesive. After the adhesive has cured, install the engineering plastic waterproof box. The waterproof rating must be consistent with the sleeve module interface. Confirm that there are no omissions in the protection through the ROV underwater camera.

[0110] Step S3 specifically includes the following steps: Step 1: Deploy a ground data acquisition system and a ground control center on the sea surface platform, and connect the seabed wireless transmission module to the ground system via an umbilical cable.

[0111] Specifically, a ground data acquisition system and a ground control center are deployed on the sea surface platform. The data acquisition system must be equipped with a 16-channel data acquisition card and a sampling frequency of not less than 1Hz. The control center includes an industrial computer, a touch screen display, and an alarm device. The submarine wireless transmission module is connected to the ground system via an umbilical cable. The cable laying must avoid bending, and the bending radius must be not less than 10 times the cable diameter.

[0112] Step 2: Configure the software of the ground control center.

[0113] Specifically, monitoring and control software is installed at the ground control center, and data storage parameters are set to ensure that the storage capacity is not less than 16GB and the data retention time is not less than 72 hours; temperature thresholds are set, with a safety threshold of 5℃ and a sustained heating range of 5-8℃; and early warning parameters are configured to trigger an audible and visual alarm when the temperature is below 3℃ or above 10℃, and to trigger a backup power switch when the signal is interrupted for more than 5 minutes.

[0114] Step 3: Test the system data transmission.

[0115] Specifically, the submarine wireless transmission module is activated, and the ground system receives temperature and pressure data from 128 casings. It is confirmed that when casings with a depth of no more than 500 meters use the Bluetooth 5.0 protocol and casings with a depth of more than 500 meters use the LoRa protocol, the data transmission rate is no less than 0.8 Mbps, and the data buffer function can automatically retransmit normally after the signal is interrupted.

[0116] Step 4: Debug the temperature control logic for low-temperature operating conditions.

[0117] Specifically, the sensor temperature is set to 3℃ via software. The test system is then used to automatically send a command to the umbilical cable power supply end to increase the heating tube current from 10A to 15A, and to ensure that the temperature can rise back to above 5℃ within 30 minutes. At the same time, the power adjustment response time is recorded and must be controlled within 10 seconds.

[0118] Step 5: Debug the temperature control logic for the temperature recovery condition.

[0119] Specifically, the sensor temperature was set to 8℃ using software, and the system was tested to see if it automatically reduced the heating tube current to 8A to maintain the temperature in the 5-8℃ range, thus verifying the stability of sustained heating.

[0120] Step 6: Simulate system failures and conduct tests.

[0121] Specifically, disconnect a section of cable to simulate a signal interruption for 5 minutes, and test whether the system automatically starts the module's built-in backup battery and switches to the LoRa protocol. At the same time, the ground control center needs to generate a fault location report. The location error should not exceed 10 meters, and the alarm device should be triggered normally.

[0122] Step 7: Execute the system and perform daily monitoring.

[0123] Specifically, the ground control center displays the temperature and pressure data of each casing in real time and generates an insulation effect report every hour. The report must include temperature curves of key areas and heating power statistics. When the temperature in key areas such as 0-5 meters below the mud surface and 500 meters deep is below 5°C, the system automatically increases the heating power without manual intervention.

[0124] Step 8: System maintenance.

[0125] Specifically, every 3 months, the integrity of the wet joint at the subsea wellhead and the anti-wear strip on the casing facing side is checked by ROV. If the wear of the anti-wear strip exceeds 1 mm, it is replaced in time. Every 6 months, the capacity of the backup battery of the wireless transmission module is checked. When it is lower than 80% of the rated capacity, it is replaced. Every year, the sensors are calibrated at low temperature, with a calibration range of -60℃ to 20℃. A calibration point is set every 10℃ to ensure that the sensor accuracy meets the standard.

[0126] Step 9: Perform emergency procedures on the system.

[0127] Specifically, if the heating tube of a casing fails, the ground system automatically controls the wireless conductive module of the adjacent casing to divert power, temporarily increasing the power of the adjacent heating tube by 10% to maintain the basic temperature of the fault area; if the sensor fails, the module’s built-in data caching function is immediately activated to save the data of the 30 minutes before the failure, and at the same time, the ROV is arranged to go down into the well to replace the sensor, with the replacement time controlled within 2 hours to ensure continuous operation of the system.

[0128] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A subsea shallow casing section thermal insulation structure for polar supercritical carbon dioxide drilling, characterized by, The application relates to a heat preservation structure of a subsea shallow casing section for polar supercritical carbon dioxide drilling, which comprises a casing, a heat preservation coating, a protective coating, an annular cement slurry layer, an electric heating pipe, a sensor module, a wireless conductive module, a ground system and a subsea wireless transmission module, the electric heating pipe is fixed on the outer wall of the casing through a clamp, the outer wall of the casing is coated with the heat preservation coating, the protective coating and the annular cement slurry layer from inside to outside, the protective coating prevents the heat preservation coating from being scraped by well wall cuttings in the process below the casing, and the protective coating can be naturally degraded, the wireless conductive module is integrated at the end of the casing, the subsea wireless transmission module is integrated on the casing, the ground system comprises a ground data acquisition system and a ground control center, the sea platform is connected with the subsea wireless transmission module through an umbilical cable, temperature and pressure data collected by the sensor module are first transmitted to the subsea wireless transmission module, then transmitted to the ground data acquisition system after being processed by the subsea wireless transmission module, and finally uploaded to the ground control center in real time.

2. The subsea shallow casing section thermal insulation structure for polar supercritical carbon dioxide drilling of claim 1, wherein, The material of the heat preservation coating is a polyimide modified polyurethane material with a thermal conductivity of 0.015 W / (m K), which includes a modified sulfoaluminate low-temperature micro-expanding agent.

3. The subsea shallow casing section thermal insulation structure for polar supercritical carbon dioxide drilling of claim 2, wherein, The protective coating is a degradable polylactic acid coating.

4. The subsea shallow casing section thermal insulation structure for polar supercritical carbon dioxide drilling of claim 3, characterized in that, The annular cement slurry layer comprises 3%-5% nanometer aerogel particles with a particle size of 20-50 nm, 2%-3% hollow glass microbeads with a particle size of 50-100 mu m, 0.5%-1% copolyamide low-temperature-resistant organic fibers with a length of 8-12 mm and a breaking strength not lower than 500 MPa, and the rest is G-grade oil well cement.

5. The subsea shallow casing section thermal insulation structure for polar supercritical carbon dioxide drilling of claim 4, wherein, The sensor module comprises a temperature sensor and a pressure sensor, the temperature sensor is fixed on the outer wall of the casing through a clamp and arranged close to a female threaded interface of the casing, the temperature sensor and the pressure sensor first transmit temperature and pressure data to the subsea wireless transmission module, then transmit the data to the ground data acquisition system after being processed by the subsea wireless transmission module, and finally upload the data to the ground control center in real time.

6. The subsea shallow casing section thermal insulation structure for polar supercritical carbon dioxide drilling of claim 5, wherein, The wireless conductive module comprises a shell, a high-permeability ferrite core and a 316L stainless steel protective cover, the high-permeability ferrite core is arranged in the shell, and the 316L stainless steel protective cover is sleeved outside the shell.

7. A method for insulating a subsea shallow casing section for polar supercritical carbon dioxide drilling, characterized by, The application relates to a heat preservation structure of a subsea shallow casing section for polar supercritical carbon dioxide drilling, which comprises a casing, a heat preservation coating, a protective coating, an annular cement slurry layer, an electric heating pipe, a sensor module, a wireless conductive module, a ground system and a subsea wireless transmission module, the electric heating pipe is fixed on the outer wall of the casing through a clamp, the outer wall of the casing is coated with the heat preservation coating, the protective coating and the annular cement slurry layer from inside to outside, the protective coating prevents the heat preservation coating from being scraped by well wall cuttings in the process below the casing, and the protective coating can be naturally degraded, the wireless conductive module is integrated at the end of the casing, the subsea wireless transmission module is integrated on the casing, the ground system comprises a ground data acquisition system and a ground control center, the sea platform is connected with the subsea wireless transmission module through an umbilical cable, temperature and pressure data collected by the sensor module are first transmitted to the subsea wireless transmission module, then transmitted to the ground data acquisition system after being processed by the subsea wireless transmission module, and finally uploaded to the ground control center in real time. The application relates to a heat preservation structure of a subsea shallow casing section for polar supercritical carbon dioxide drilling, which comprises a casing, a heat preservation coating, a protective coating, an annular cement slurry layer, an electric heating pipe, a sensor module, a wireless conductive module, a ground system and a subsea wireless transmission module, the electric heating pipe is fixed on the outer wall of the casing through a clamp, the outer wall of the casing is coated with the heat preservation coating, the protective coating and the annular cement slurry layer from inside to outside, the protective coating prevents the heat preservation coating from being scraped by well wall cuttings in the process below the casing, and the protective coating can be naturally degraded, the wireless conductive module is integrated at the end of the casing, the subsea wireless transmission module is integrated on the casing, the ground system comprises a ground data acquisition system and a ground control center, the sea platform is connected with the subsea wireless transmission module through an umbilical cable, temperature and pressure data collected by the sensor module are first transmitted to the subsea wireless transmission module, then transmitted to the ground data acquisition system after being processed by the subsea wireless transmission module, and finally uploaded to the ground control center in real time. The application relates to a heat preservation structure of a subsea shallow casing section for polar supercritical carbon dioxide drilling, which comprises a casing, a heat preservation coating, a protective coating, an annular cement slurry layer, an electric heating pipe, a sensor module, a wireless conductive module, a ground system and a subsea wireless transmission module, the electric heating pipe is fixed on the outer wall of the casing through a clamp, the outer wall of the casing is coated with the heat preservation coating, the protective coating and the annular cement slurry layer from inside to outside, the protective coating prevents the heat preservation coating from being scraped by well wall cuttings in the process below the casing, and the protective coating can be naturally degraded, the wireless conductive module is integrated at the end of the casing, the subsea wireless transmission module is integrated on the casing, the ground system comprises a ground data acquisition system and a ground control center, the sea platform is connected with the subsea wireless transmission module through an umbilical cable, temperature and pressure data collected by the sensor module are first transmitted to the subsea wireless transmission module, then transmitted to the ground data acquisition system after being processed by the subsea wireless transmission module, and finally uploaded to the ground control center in real time. The application relates to a heat preservation structure of a subsea shallow casing section for polar supercritical carbon dioxide drilling, which comprises a casing, a heat preservation coating, a protective coating, an annular cement slurry layer, an electric heating pipe, a sensor module, a wireless conductive module, a ground system and a subsea wireless transmission module, the electric heating pipe is fixed on the outer wall of the casing through a clamp, the outer wall of the casing is coated with the heat preservation coating, the protective coating and the annular cement slurry layer from inside to outside, the protective coating prevents the heat preservation coating from being scraped by well wall cuttings in the process below the casing, and the protective coating can be naturally degraded, the wireless conductive module is integrated at the end of the casing, the subsea wireless transmission module is integrated on the casing, the ground system comprises a ground data acquisition system and a ground control center, the sea platform is connected with the subsea wireless transmission module through an umbilical cable, temperature and pressure data collected by the sensor module are first transmitted to the subsea wireless transmission module, then transmitted to the ground data acquisition system after being processed by the subsea wireless transmission module, and finally uploaded to the ground control center in real time. ​ ​ 8. The method for insulating a subsea shallow casing section for polar supercritical carbon dioxide drilling according to claim 7, characterized in that, ​ ​ ​ Apply a protective coating to the surface of the thermal insulation coating; An electric heating element is installed outside the sleeve; Install wireless conductive module; Abrasion-resistant strips are installed on the facing side of the sleeve. A temperature sensor and a pressure sensor are installed in the middle of the sleeve; Protective covers are installed on the outside of the temperature sensor and the pressure sensor, and the power supply cables and signal transmission cables of the temperature sensor and the pressure sensor are fixed along the outer wall of the sleeve using cable brackets. Connect the cable terminals of the temperature sensor and the pressure sensor to the interface of the seabed wireless transmission module. Activate the seabed wireless transmission module and use a portable data acquisition instrument to receive data from the temperature sensor and the pressure sensor. Confirm that the temperature error is ≤ ±0.5℃ and the pressure error is ≤ ±0.25% FS. Ensure that the data transmission is stable without interruption or interference. Complete the prefabrication and acceptance of the single sleeve.

9. The method for insulating a subsea shallow casing section for polar supercritical carbon dioxide drilling according to claim 7, characterized in that, The process of "connecting the sleeves into a sleeve string, inserting the sleeve string and fixing it to the annulus" specifically includes the following steps: The sleeves are connected one by one to form a pre-assembled sleeve string, and the pre-assembled sleeve string is then tested for connection. The pre-assembled sleeve string was subjected to comprehensive performance testing. Preparations are made for the on-site installation of the pre-assembled bushing string. Lower the first casing of the pre-assembled casing string and fix it at the wellhead; The remaining pre-assembled bushings are lowered in sections until the bushings are completely lowered. Preparation of annular cement slurry; Inject the annular two-stage cement grout; After the cement grout is poured, the cement grout is cured and the bonding quality is tested. Clean the submarine cable connectors; Docking underwater wet joints and conducting performance tests; The underwater wet joint was protected and inspected.

10. The method for insulating a subsea shallow casing section for polar supercritical carbon dioxide drilling according to claim 7, characterized in that, "Recovering and reusing heat" specifically includes the following steps: Deploy a ground data acquisition system and a ground control center on a sea surface platform, and connect the seabed wireless transmission module to the ground system via an umbilical cable; Configure the software of the ground control center; The data transmission of a complete temperature control monitoring system consisting of subsea equipment and a ground system was tested. Debug the temperature control logic under low-temperature conditions; Debug the temperature control logic under temperature recovery conditions; Simulate system failures and conduct tests; The execution system performs daily monitoring. System maintenance; Perform emergency procedures on the system.

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