Formation heat injection system and formation heat injection method

Abstract

The application discloses a stratum heat injection system and a stratum heat injection method, and relates to the technical field of oilfield exploitation. The stratum heat injection system comprises a light collecting device, a light transmission channel and a light-heat conversion device. The light collecting device is arranged on the ground and is used for collecting sunlight and converging the sunlight into a light beam. The light transmission channel is used for transmitting the light beam to a target stratum by taking a hollow optical fiber as a light transmission medium. The light-heat conversion device is arranged at the end of the light transmission channel and is used for converting the light energy of the light beam into heat energy and injecting the heat energy into the target stratum. The application significantly reduces the cumulative loss on the whole energy link and has a high energy utilization rate.

Description

Technical Field

[0001] This application relates to the field of oilfield development technology, and in particular to formation heating systems and methods. Background Technology

[0002] In existing deep formation heating methods in oilfield development, surface steam injection relies on burning fossil fuels to generate steam. During long-distance wellbore transmission, steam suffers significant heat loss due to thermal radiation and conduction, resulting in a substantial decrease in enthalpy at the bottom of the well. While downhole electric heating avoids transmission heat loss, the process of converting electrical energy into heat energy is inefficient compared to the thermal value of directly utilizing solar energy. If photovoltaic power generation is used, it still requires a two-stage conversion between light, electricity, and heat, resulting in low overall energy utilization.

[0003] In summary, existing heat injection methods suffer from significant energy losses at each stage of the process of converting surface energy into thermal energy in the formation. This results in a low proportion of effective thermal power used to heat the formation compared to the original energy input, making it difficult to meet the needs of efficient heating and energy storage in deep formations. Summary of the Invention

[0004] The main purpose of this application is to provide a formation heating system and a formation heating method, which aims to solve the technical problem of low overall energy utilization when heating deep formations.

[0005] To achieve the above objectives, this application proposes a formation heat injection system, which includes a light-collecting device, a light transmission channel, and a photothermal conversion device; The light-collecting device is installed on the ground to collect sunlight and focus it into a beam; The optical transmission channel is used to transmit the light beam to the target stratum using hollow optical fiber as the optical transmission medium. The photothermal conversion device is located at the end of the light transmission channel and is used to convert the light energy of the light beam into heat energy and inject the heat energy into the target formation.

[0006] In one embodiment, the hollow optical fiber is an anti-resonant hollow optical fiber; the core of the hollow optical fiber is filled with inert gas and the core is maintained under a preset positive pressure.

[0007] In one embodiment, the hollow optical fiber is encapsulated in a spiral armored tube, which is disposed in the optical transmission channel; the spiral armored tube is filled with a buffer lubricating material, and the hollow optical fiber has a preset length of allowance inside the spiral armored tube to protect the hollow optical fiber from tension when the spiral armored tube is stretched.

[0008] In one embodiment, an optical fiber bundle is provided inside the spiral armored tube. The optical fiber bundle is composed of a preset number of hollow optical fibers, at least one of which serves as a spare hollow optical fiber. When the primary hollow optical fiber fails, the system automatically switches to the spare hollow optical fiber. When all the hollow optical fibers in the optical fiber bundle reach their service life limit, the optical fiber bundle is replaced with a new optical fiber bundle through ground steel wire operations.

[0009] In one embodiment, beam expanders are connected to both ends of the hollow fiber, which are used to increase the beam spot diameter to reduce the energy density of the beam at the incident and exit ends of the hollow fiber.

[0010] In one embodiment, a bending limiter is provided in the optical transmission channel to constrain the bending radius of the hollow optical fiber to be no less than a preset value.

[0011] In one embodiment, the photothermal conversion device includes a heat-absorbing tube, the heat-absorbing tube having a spiral cavity structure inside, and the spiral cavity structure having blackbody physical properties.

[0012] In one embodiment, the photothermal conversion device further includes a thermal insulation connection structure connected between the heat absorption tube and the light transmission channel; the thermal insulation connection structure has a vacuum cavity inside, the vacuum cavity is filled with multiple layers of radiation reflective screens, and the thermal insulation connection structure is made of a low thermal conductivity material.

[0013] In one embodiment, the light-collecting device includes a filter assembly for limiting the wavelength of the light beam to be introduced into the hollow optical fiber to a near-infrared low-loss window within a preset wavelength range.

[0014] Furthermore, to achieve the above objectives, this application also proposes a formation heating method, which applies the aforementioned formation heating system, the method comprising: Sunlight is collected on the ground using a light-collecting device, and then focused into a beam of light. A longitudinal optical transmission channel is constructed extending from the ground to the target stratum, and the light beam is transmitted to the target stratum through the optical transmission channel, wherein hollow optical fiber is used as the optical transmission medium in the optical transmission channel; At the end of the optical transmission channel, the light energy of the light beam is converted into heat energy by a photothermal conversion device, and the heat energy is injected into the target formation.

[0015] In addition, to achieve the above objectives, this application also proposes a storage medium, which is a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, it implements the steps of the formation heat injection method described above.

[0016] In addition, to achieve the above objectives, this application also provides a computer program product, which includes a computer program that, when executed by a processor, implements the steps of the formation heat injection method described above.

[0017] One or more technical solutions proposed in this application have at least the following technical effects: This application collects sunlight using a ground-based light-collecting device and focuses it into a beam. A hollow-core optical fiber is used as the light transmission medium to form a light transmission channel, directly transmitting the beam to the target formation. A photothermal conversion device is installed at the end of the light transmission channel to convert the light energy of the beam into heat energy, which is then injected into the target formation. Compared to traditional surface steam injection methods that rely on fossil fuel combustion and long-distance wellbore transmission, resulting in significant heat loss along the way, this solution uses light as the energy carrier for low-loss transmission in hollow-core optical fiber. This fundamentally avoids heat radiation and heat conduction losses during the heat transfer process. Furthermore, compared to downhole electric heating methods (especially those involving a two-stage photo-electric-heat conversion via photovoltaic power generation), this solution eliminates the intermediate energy conversion steps of light to electricity and electricity to heat, achieving direct conversion and utilization of sunlight into formation heat energy. This significantly reduces the cumulative losses along the entire energy chain, resulting in a substantial increase in the proportion of effective heat power used to heat the formation relative to the original solar energy input. This effectively solves the technical problems of low energy utilization rates in existing heat injection methods, which are insufficient to meet the demands of efficient heating and energy storage in deep formations. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A schematic diagram of an embodiment of the formation heat injection system of this application Figure 1 ; Figure 2 A schematic diagram of an embodiment of the formation heat injection system of this application Figure 2 ; Figure 3 A schematic diagram of an embodiment of the formation heat injection system of this application Figure 3 ; Figure 4 A schematic flowchart of an embodiment of the formation heating method of this application is provided; Figure 5A schematic diagram of an embodiment of the formation heat injection system of this application Figure 4 ; Figure 6 A schematic diagram of an embodiment of the formation heat injection system of this application Figure 5 ; Figure 7 A schematic diagram of an embodiment of the formation heat injection system of this application Figure 6 .

[0021] Explanation of icon numbers: 10. Lighting devices; 20. Optical transmission channel; 21. Hollow-core optical fiber; 22. Spiral armored tube; 30. Photothermal conversion device.

[0022] The purpose, features, and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0023] It should be understood that the specific embodiments described herein are only used to explain the technical solutions of this application and are not intended to limit this application.

[0024] To better understand the technical solution of this application, a detailed description will be provided below in conjunction with the accompanying drawings and specific implementation methods.

[0025] In the lighting field, there are technologies that use hollow optical fibers to transmit sunlight (such as the daylighting system disclosed in CN115127072A), which uses hollow optical fibers to introduce sunlight into the room for lighting and uses solar energy for illumination. However, in the field of oilfield extraction, the deep geological environment is extremely harsh—including high temperature (up to 150°C or higher), high pressure (up to tens of megapascals), the presence of corrosive fluids (such as hydrogen sulfide, carbon dioxide, mineralized water, etc.), and the severe vibration and bending deformation of the wellbore during drilling and production. Furthermore, light energy needs to be transmitted vertically to a depth of several thousand meters, and ultimately, the light energy needs to be efficiently converted into heat energy and injected into the formation to reduce the viscosity of heavy oil or provide geothermal heating.

[0026] Using conventional hollow-core optical fibers directly presents the following problems: First, the fundamental and bending losses of conventional hollow-core optical fibers increase dramatically over long distances of several kilometers, making it difficult to guarantee sufficient optical power delivery to the bottom of the well. Second, the high-temperature and high-pressure environment downhole can cause a surge in moisture absorption peaks within the fiber, thermal cracking at the end face, and joint seal failure. Third, the stretching, torsion, and formation creep of the wellbore can easily cause micro-bending losses or even mechanical breakage in the optical fiber, while the lighting field does not involve such mechanical reliability issues. Fourth, the lighting field only requires visible light output, while this field requires high photothermal conversion efficiency and long-term heat storage capacity. Therefore, conventional hollow-core optical fibers cannot meet the needs of formation heating.

[0027] Therefore, in response to the special needs of deep formation heating in the oilfield mentioned above, as well as the problems of low energy utilization and high losses in existing formation heating methods (such as huge heat loss along the way caused by surface steam injection and low light-electric-thermal conversion efficiency caused by downhole electric heating), this application designs a formation heating system for special working conditions in the oilfield development field.

[0028] This formation heating system includes: a ground-based light-gathering device for collecting sunlight and focusing it into a high-energy-density beam; a filter assembly for confining the beam wavelength to be introduced into the hollow-core optical fiber within a near-infrared low-loss window; hollow-core optical fiber as the light transmission medium, its core filled with inert gas and maintained under a slight positive pressure; a spiral armored tube encapsulating the hollow-core optical fiber, the tube being filled with buffer lubricating material, and the hollow-core optical fiber having a margin to protect it from tension when the tube is stretched; multiple hollow-core optical fibers bundled together within the spiral armored tube, at least one of which is a spare fiber that can automatically switch in case of failure of the primary fiber; and a complete bundle... After the hollow fiber reaches the end of its lifespan, it can be pulled out as a whole and replaced with a new fiber bundle; the beam expander, connected to both ends of the hollow fiber, is used to increase the beam spot diameter and reduce the end-face energy density; the bend limiter, set in the optical transmission channel, constrains the bending radius of the hollow fiber to be no less than a preset value; the photothermal conversion device, which has a spiral cavity structure of heat-absorbing tube inside, has blackbody physical properties, and is used to efficiently absorb light energy and convert it into heat energy; the thermal insulation connection structure, connected between the heat-absorbing tube and the optical transmission channel, has a vacuum cavity and a multi-layer radiation reflection screen inside, and is made of low thermal conductivity material to prevent heat loss to the upper part.

[0029] Through the synergistic effect of the above-mentioned technical features, the formation heat injection system of this application can transmit sunlight from the ground to underground thousands of meters deep with extremely low loss, and achieve high-efficiency photothermal conversion at the bottom of the well, injecting heat energy into the formation for heavy oil viscosity reduction, cross-seasonal energy storage, or online heat replenishment of geothermal wells.

[0030] Based on this, embodiments of this application provide a formation heat injection system, referring to... Figure 1 The formation heating system includes a light-collecting device (10), a light transmission channel (20), and a photothermal conversion device (30). The light-collecting device (10) is installed on the ground and is used to collect sunlight and converge the sunlight into a beam; The optical transmission channel (20) is used to transmit the light beam to the target stratum using hollow optical fiber as the optical transmission medium. The photothermal conversion device (30) is disposed at the end of the light transmission channel and is used to convert the light energy of the light beam into heat energy and inject the heat energy into the target stratum.

[0031] It should be noted that formation heating systems can be applied to (but are not limited to) the following scenarios: thermal exploitation of deep and ultra-deep heavy oil reservoirs, and development of reservoirs where existing steam huff and puff / steam drive technologies are not economically viable; long-term stable production and thermal reservoir restoration of hydrothermal geothermal systems and hot dry rock geothermal systems; reuse of abandoned or low-yield wells, transforming them into solar underground thermal storage wells to achieve cross-seasonal energy storage; and winter stable production and viscosity reduction operations in oil and gas fields in high-altitude or significantly seasonally temperature-different regions.

[0032] Optionally, a light-collecting device (10) is installed on the ground to collect sunlight and converge it into a high-energy-density beam. The light-collecting device includes a large-aperture Fresnel lens group or a dish-type concentrator and is equipped with a dual-axis automatic tracking device to track the sun's trajectory in real time, converge parallel sunlight into a high-energy-density spot or parallel beam, and ensure the stability of the converged beam.

[0033] Optionally, the optical transmission channel (20) is a longitudinal path extending from the ground to the target stratum, and its transmission medium is hollow optical fiber (also simply referred to as optical fiber). Hollow optical fiber is an optical fiber with an air or gas medium in its core. Light mainly propagates in the hollow region. Compared with solid optical fiber, it can significantly reduce material absorption and scattering losses, and is especially suitable for long-distance, high-power laser or sunlight transmission.

[0034] Optionally, this application preferentially uses anti-resonant hollow fiber, such as nodeless single-ring anti-resonant hollow fiber. Its core diameter is typically 30μm to 50μm, thereby achieving a fundamental confinement loss of less than 1dB / km over distances of several kilometers.

[0035] Optionally, the target formation is an underground rock formation that needs to be heated, which may include: oil-bearing layers of heavy oil reservoirs, geothermal well reservoirs (such as hot dry rock or hydrothermal reservoirs), and abandoned wells or geothermal reservoirs used for cross-seasonal energy storage.

[0036] Optionally, a photothermal conversion device (30) is installed at the end of the light transmission channel (i.e., the bottom of the well) to convert light energy into heat energy and inject the heat energy into the target formation. It includes a heat absorber tube with a spiral cavity inside, which has blackbody properties, allowing the incident light beam to be efficiently absorbed after multiple reflections and diffusions on the inner wall.

[0037] Optionally, the heat generated by the photothermal conversion device can be transferred to the rock skeleton and pore fluid of the target formation through heat conduction, heat convection or heat radiation to inject thermal energy, thereby achieving the purpose of formation heating, heavy oil viscosity reduction or thermal energy storage.

[0038] This embodiment provides a formation heat injection system. It collects sunlight using a surface-mounted light-collecting device and focuses it into a beam. A hollow optical fiber serves as the light transmission medium, forming a light transmission channel that directly transmits the beam to the target formation. At the end of the light transmission channel, a photothermal conversion device converts the light energy of the beam into heat energy, which is then injected into the target formation. Compared to traditional surface steam injection methods that rely on fossil fuel combustion and long-distance wellbore transmission, resulting in significant heat loss along the way, this solution uses light as the energy carrier for low-loss transmission in hollow optical fibers. This fundamentally avoids heat radiation and conduction losses during heat fluid transmission. Furthermore, compared to downhole electric heating methods (especially those involving a two-stage photo-electric-thermal conversion via photovoltaic power generation), this solution eliminates the intermediate energy conversion steps of light to electricity and electricity to heat, achieving direct conversion and utilization of sunlight into formation heat energy. This significantly reduces accumulated losses along the entire energy chain, resulting in a substantial increase in the proportion of effective heat power used to heat the formation relative to the original solar energy input. This effectively solves the technical problems of low energy utilization rates in existing heat injection methods, which are insufficient to meet the demands of efficient heating and energy storage in deep formations.

[0039] In one feasible implementation, the hollow optical fiber (21) is an anti-resonant hollow optical fiber; the core of the hollow optical fiber is filled with inert gas and the core is maintained under a preset positive pressure.

[0040] It should be noted that the core diameter of anti-resonant hollow fiber (such as anti-resonant hollow fiber with nodeless single-ring structure) can be 30μm to 50μm, which can achieve a lower fundamental confinement loss and thus support long-distance transmission.

[0041] Additionally, it should be noted that during long-distance transmission over thousands of meters underground, water molecules in the air will produce strong absorption peaks at specific wavelengths (such as 1383nm). If air or moisture is present inside the core of the hollow optical fiber, this absorption effect will accumulate over long distances, leading to a sharp decrease in optical power. Therefore, this embodiment fills the core with a high-purity (≥99.999%) inert gas (such as argon or high-purity nitrogen) and installs a high-pressure drying and circulating filtration system on the ground to maintain the gas pressure inside the core at a slightly positive pressure of 0.2MPa to 0.5MPa, while ensuring the dew point is below -70°C, thereby completely expelling air and eliminating trace amounts of moisture.

[0042] Understandably, because the fiber core is filled with inert gas and maintains a preset positive pressure, it can effectively expel air and moisture from the fiber core, preventing moisture from generating strong absorption peaks in characteristic bands. This significantly reduces the accumulation of absorption loss during long-distance transmission and improves the delivery efficiency of optical energy in deep well transmission channels thousands of meters deep.

[0043] In one feasible implementation, the hollow optical fiber is encapsulated in a spiral armor tube (22), which is disposed in the optical transmission channel; the spiral armor tube is filled with a buffer lubricating material, and the hollow optical fiber is reserved with a preset length of allowance in the spiral armor tube to protect the hollow optical fiber from tension when the spiral armor tube is stretched.

[0044] It should be noted that the spiral armored tube (also known as the armored tube) is usually a spiral armored protective tube made of stainless steel. The buffer lubricating material inside is a high-viscosity, high-temperature resistant (e.g., greater than or equal to 300℃) damping silicone grease or fluorosilicone grease, which is used to reduce the friction between the hollow optical fiber and the tube wall of the spiral armored tube and provide a buffering effect.

[0045] Optionally, the preset length margin refers to the fact that the hollow fiber is not completely straightened in the armored tube, but maintains a spiral geometric margin of 0.5% to 1.0% (i.e., the fiber length is slightly longer than the armored tube length), so that the fiber is in a relaxed state in the armored tube.

[0046] It's also important to note that in downhole operations at depths of several thousand meters, lowering the optical transmission channel into the wellbore requires a downhole tubing string. This string undergoes axial tensile deformation due to its own weight. Furthermore, it is subject to expansion, contraction, or bending deformation due to formation creep, impacts during tripping in and out of the well, and vibrations from downhole fluids. If the hollow fiber is completely bonded to or stretched taut within the armored tube, the tensile deformation of the downhole tubing string will be directly transmitted from the armored tube to the hollow fiber, subjecting it to excessive axial tension. This can result in micro-bending loss leading to reduced optical power, or even breakage of the hollow fiber. By encapsulating the hollow fiber within the armored tube with allowance and filling it with buffering and lubricating material, the armored tube can bear the main tensile force, while the hollow fiber slides freely within the tube, effectively isolating it from external tensile forces.

[0047] Understandably, because the hollow fiber has a pre-set length of allowance inside the spiral armor tube, and the spiral armor tube is filled with buffer lubricating material, when the spiral armor tube is stretched or deformed by thermal expansion and contraction, the hollow fiber will not directly bear the tensile or shear force. Instead, it will absorb the deformation through sliding and the allowance, thereby avoiding micro-bending loss or mechanical breakage of the hollow fiber due to force, which significantly improves the reliability of the downhole optical transmission channel and the service life of the hollow fiber.

[0048] In one feasible implementation, the spiral armored tube contains an optical fiber bundle, which is composed of a preset number of hollow optical fibers, at least one of which serves as a spare hollow optical fiber. When the primary hollow optical fiber fails, the system automatically switches to the spare hollow optical fiber. When all the hollow optical fibers in the optical fiber bundle reach their service life limit, the optical fiber bundle is replaced with a new optical fiber bundle through ground steel wire operations.

[0049] It should be noted that in the downhole environment thousands of meters deep, hollow optical fibers are subjected to high temperatures, high pressures, formation creep, and fluid corrosion over long periods, posing a risk of fatigue fracture or degradation of optical performance. If only a single hollow optical fiber is used, the entire downhole tubing must be pulled out for replacement if it fails, resulting in extremely high operating costs, long construction periods, and potentially interruption of the heating operation. Therefore, this embodiment uses a predetermined number of hollow optical fibers (e.g., 3 to 4 fibers) to run in parallel within the same spiral armored tube (i.e., the spiral armored tube contains a fiber bundle), with at least one fiber serving as a spare redundant fiber.

[0050] Optionally, the output optical power is monitored in real time on the ground. When the main hollow fiber breaks or liquid enters, causing a sudden drop in output optical power, the steering reflector in the light-collecting device automatically deflects within microseconds, couples the beam, and cuts into the backup hollow fiber.

[0051] Furthermore, when all spare hollow optical fibers reach the end of their lifespan, there is no need to remove the heavy metal heating pipes underground. The old fiber bundle can be pulled out of the armored pipe as a whole using surface steel wire operations (by lowering a special replacement tool with a steel wire rope), and the new fiber bundle can be redeployed and sunk to the bottom of the well. Blind coupling is achieved through a high-pressure wet optical plug-in connector pre-installed at the upper end of the heat absorption pipe at the bottom of the well. The high-pressure wet optical plug-in connector is used to automatically guide the end of the hollow optical fiber to align, seal, and lock with the positioning guide structure inside the high-pressure wet optical plug-in connector in a humid environment filled with liquid (such as mud, water, or crude oil) in the well, thus completing the low-loss connection of the optical path.

[0052] By pre-installing a high-pressure wet optical plug-in connector at the bottom of the well, the fiber optic bundle is structurally separated from the downhole tubing, meaning the downhole tubing remains permanently in the well, and only the internal fiber optic bundle is replaced. Without this high-pressure wet optical plug-in connector, replacing the fiber optic bundle would require retrieving the entire downhole tubing (including coiled tubing, packers, etc.) from the wellbore to the surface, threading the new hollow optical fibers, and then re-running it. This process requires large workover equipment, takes several days to several weeks, is extremely expensive, and would interrupt formation heating and energy storage operations for an extended period.

[0053] Understandably, the pre-installed high-pressure wet optical plug-in connector at the top of the bottom heat absorber allows for rapid, maintenance-free replacement of the downhole optical transmission medium: the old fiber bundle automatically detaches from the connector when pulled out as a whole by the wireline operation, and the new fiber bundle is automatically blind-coupled by gravity or a pushing tool when it is deployed and lowered. This reduces replacement time from several days to several hours, avoiding high well workover costs and prolonged heat injection interruptions, significantly reducing the system's total lifecycle maintenance costs. It is particularly suitable for scenarios where well workover operations are extremely difficult, such as deep wells (greater than or equal to 3000 meters) and offshore platforms.

[0054] Understandably, because multiple hollow optical fibers are bundled together in the same armored tube and spare hollow optical fibers are reserved, and all hollow optical fibers can be replaced as a whole through wire work after the end of their lifespan, the optical transmission capability can be quickly restored without lifting or repairing the well, avoiding expensive overhaul operations, significantly reducing the full life cycle maintenance cost of the formation heating system, and ensuring the continuity and reliability of formation heating and energy storage operations.

[0055] In one feasible implementation, beam expanders are connected to both ends of the hollow fiber, which are used to increase the beam spot diameter to reduce the energy density of the beam at the incident and exit ends of the hollow fiber.

[0056] It should be noted that in optical transmission at depths of several kilometers, the light beam output from the ground-based light-gathering device has extremely high energy density (e.g., the power of the converged beam can reach several kilowatts to tens of kilowatts), while the core diameter of hollow optical fiber is only tens of micrometers (e.g., 30μm to 50μm). If this high-power beam is directly coupled into or out of the end face of the hollow optical fiber, extremely high local optical power density will be generated at the glass-air interface of the end face, which can easily lead to thermal self-focusing effect, thermal stress cracking of the end face, or even instantaneous burn-out. This problem is more prominent at the incident end (at the ground) and the exit end (downhole) of the hollow optical fiber. Therefore, this embodiment connects a beam expander to each end of the hollow optical fiber.

[0057] It should also be noted that the beam expander can be made of a large-diameter coreless quartz glass rod, with a diameter designed to be 5 to 10 times the core diameter of the hollow fiber (e.g., 300μm to 500μm) and a length of 5 to 10 mm. This beam expander is tightly connected to the end face of the hollow fiber using high-voltage fusion splicing technology, without an internal core structure. When a high-power beam enters the beam expander at the incident end of the hollow fiber, because the refractive index of the glass rod is higher than that of the outside air, the light undergoes multiple total internal reflections at the interface between the glass wall and the air, thus being confined within the glass rod and propagating forward. During propagation, the beam gradually fills the entire cross-section of the glass rod, dispersing the energy originally concentrated in a small spot over a larger area, thereby expanding the beam diameter. When the light beam exits from the other end of the glass rod, its beam spot diameter has expanded to nearly the diameter of the glass rod. This reduces the local optical power density before it enters the micron-sized core of the hollow fiber by at least two orders of magnitude (greater than or equal to 100 times), preventing localized overheating and ablation of the incident end of the hollow fiber due to the tiny beam spot. Similarly, at the exit end at the bottom of the well, after the light beam exits from the hollow fiber, it first passes through a beam expander to further expand the beam spot before irradiating the heat absorber tube of the photothermal conversion device. This also prevents localized overheating and ablation of the exit end of the hollow fiber or the surface of the heat absorber tube due to the tiny beam spot.

[0058] Furthermore, when a high-power beam directly illuminates the tiny end face of a hollow fiber, there may be tiny impurity particles or local air defects on the end face. These particles may absorb extremely high density of light energy, forming local hot spots that trigger a nonlinear thermal self-focusing effect. This causes the energy to concentrate further and burn through the end face of the hollow fiber instantly. However, after the beam expander enlarges the beam spot and reduces the energy density, even if there are impurity particles on the end face, the light power received per unit area is far below the threshold that triggers thermal self-focusing, thus fundamentally avoiding the problem of thermal breakage of the end face of the hollow fiber.

[0059] Understandably, by setting beam expanders at both ends of the hollow fiber, the optical power density at the end face of the hollow fiber is significantly reduced by increasing the beam spot diameter by 5 to 10 times. This effectively avoids the thermal self-focusing effect, thermal stress cracking, and end face burn-out caused by high-power beams at the incident and exit ends. It significantly improves the upper limit of the power tolerance of the hollow fiber end face and the reliability of the long-term operation of the formation heat injection system, and realizes the deep well transmission of kilowatt-level solar energy.

[0060] In one feasible implementation, a bending limiter is provided in the optical transmission channel to constrain the bending radius of the hollow optical fiber to be no less than a preset value.

[0061] It should be noted that although hollow-core optical fiber has low transmission loss, its light guiding principle relies on the confinement of light by an anti-resonant structure. Since the optical transmission channel extends from the ground to the target formation thousands of meters deep, the distance is extremely long. Therefore, hollow-core optical fiber will inevitably be subjected to tension, torsion, and bending during installation in the well and subsequent applications, especially at the wellhead turning section and the bends of the downhole tubing, where bending deformation is likely to occur.

[0062] When a hollow optical fiber bends, the direction of light travels changes at the bend, causing some light rays to strike the fiber wall at a larger angle. If this angle exceeds the effective reflection range of the anti-resonance layer, the photonic barrier is breached, and light leaks out from the outside of the bend. The smaller the bend radius, the larger the angle at which light strikes the fiber wall, resulting in more energy leakage and greater bending loss. Furthermore, an excessively small bend radius can generate mechanical stress within the fiber wall, potentially leading to microscopic cracks or even breakage over time. In deep-well optical transmission channels, hollow optical fibers need to be lowered into the wellbore from surface equipment via wellhead bogies, coiled tubing guide wheels, and other points, all of which involve varying degrees of bending. Without restraint, the fiber may experience a sharp increase in transmission loss at these bends, or even be damaged directly.

[0063] It should also be noted that bending limiters are installed at critical locations such as the surface wellhead inlet section, the steering pulley block, and bends in the downhole tubing. The specific form of the bending limiter can be an arc-shaped limiting groove, a rigid guide elbow, or a limiting pulley block with a curved surface; the radius of its internal curved surface is the preset value of the constrained bending radius. Based on the mechanical and optical properties of hollow optical fibers, this preset value is typically not less than 300 mm. Under this bending radius constraint, the single-turn bending loss of the hollow optical fiber can be limited to below 0.05 dB, while the bending stress within the hollow optical fiber wall is lower than the fatigue limit of the material used to manufacture the hollow optical fiber, thus preventing mechanical damage.

[0064] Understandably, because a bending limiter is installed at the bending point in the optical transmission channel, the actual bending radius of the hollow fiber is always constrained to be no less than 300mm. This can simultaneously avoid: firstly, preventing a surge in optical energy leakage due to excessive bending, thus ensuring high optical power delivery efficiency over long distances; and secondly, preventing mechanical cracks or breaks in the hollow fiber due to excessive bending, thus ensuring the mechanical reliability of the formation heating system at depths of several thousand meters and over a long period.

[0065] In one feasible implementation, in a downhole optical transmission channel thousands of meters deep, the length of a single hollow-core optical fiber cannot completely cover the entire longitudinal distance from the surface to the target formation. Therefore, multiple hollow-core optical fiber segments need to be connected end-to-end. Specifically, at the connection point between two hollow-core optical fibers, the output end face of the preceding segment is fused to the input end face of the following segment, allowing the light beam to be continuously transmitted from the previous segment to the next. To avoid the collapse of microscopic air holes in the hollow-core optical fiber caused by conventional arc fusion splicing, a non-mechanically contactless carbon dioxide laser photothermal fusion splicing technique is used at this connection point. Simultaneously, a 1mm–2mm long yttrium aluminum garnet (YAG) support crystal with an antireflection coating is fused to the end faces of the two hollow-core optical fiber segments to be connected as a transition. The YAG crystal is tightly sealed to the end faces of the hollow-core optical fibers, controlling the insertion loss at the connection point to below 0.1dB and preventing high-power thermal damage in the fusion splice area.

[0066] In one feasible implementation, a convection heat exchange cooling jacket is provided around the emitting end (i.e., the bottom-of-well emitting end) of the hollow optical fiber.

[0067] It should be noted that even though hollow-core optical fibers have very low overall loss during transmission, some light energy will still be absorbed or scattered by the fiber walls over a length of several kilometers, converting into heat. Simultaneously, at the output end face of the hollow-core optical fiber at the bottom of the well, even with a beam expander to reduce energy density, a small amount of reflected light, scattered light, and residual absorption from the end face itself are unavoidable. These sporadic dissipated light and heat will accumulate locally at the transmitting end. Because the environment at the bottom of the well is inherently high-temperature (reaching over 150°C) and has poor heat dissipation, if local heat continues to accumulate, the temperature may rapidly rise below the softening point of the quartz material used to make the hollow-core optical fiber (approximately 1500°C). While it will not immediately melt, prolonged high temperatures will accelerate material fatigue, generate thermal stress, and may even cause the end face to crack. Therefore, active cooling of this localized area is necessary.

[0068] It should also be noted that the convection heat exchange cooling jacket is installed around the emitting end of the hollow fiber, and its interior contains fluid channels. This cooling jacket does not require an additional independent cooling system; instead, it directly utilizes the existing flowing medium within the wellbore. For example, in heavy oil thermal recovery injection wells, cold or hot water injected from the surface flows upwards through the wellbore annulus; in geothermal wells, extracted geothermal fluid flows upwards through the annulus between the central tube and the casing. During this flow, these fluids naturally pass over the outer wall of the cooling jacket, and through forced or natural thermal convection, promptly remove the heat dissipation generated at the emitting end of the hollow fiber. The cooling jacket can be made of a metal with good thermal conductivity (such as stainless steel or copper alloy), and its outer wall can be finned to enhance the heat exchange area.

[0069] Understandably, by installing a convective heat exchange cooling jacket around the transmitter at the bottom of the well and utilizing the existing flowing medium within the wellbore for passive cooling, the local temperature at the output end of the hollow optical fiber can be effectively controlled below the long-term safe operating temperature of the quartz material used to manufacture the hollow optical fiber. This prevents localized heat buildup exceeding the softening point of the quartz skeleton of the hollow optical fiber, avoiding end-face thermal damage, and thus ensuring long-term, stable output of high-power optical energy under high-temperature and high-pressure conditions at the bottom of the well. Furthermore, this cooling method does not rely on external power or an independent circulation system, and its structure is simple and highly reliable.

[0070] For example, to help understand formation heat injection systems, please refer to Figure 2 , specifically: Figure 2 The cross-sectional structure of the optical transmission channel is shown. 20 is the optical transmission channel used to construct the longitudinal optical path extending from the ground to the target stratum, and to carry and protect the internal components. 21 is a hollow optical fiber (which can be a bundle of multiple anti-resonant hollow optical fibers) used as the optical transmission medium to transmit the light beam over long distances to the bottom of the well with extremely low loss. 22 is a spiral armored tube used to encapsulate and protect 21 (hollow optical fiber), located in 20 (optical transmission channel).

[0071] Based on the above embodiments of this application, in another embodiment of this application, the same or similar content as the above embodiments can be referred to the above description, and will not be repeated hereafter. In addition, the photothermal conversion device includes a heat-absorbing tube, the heat-absorbing tube having an internal spiral cavity structure, and the spiral cavity structure possessing blackbody physical properties.

[0072] It should be noted that after the light energy is transmitted through thousands of meters of hollow optical fiber to the bottom of the well, it needs to be efficiently converted into heat energy and injected into the formation. Conventional flat-plate or simple tubular heat absorption structures have two problems in the closed, high-pressure environment downhole: first, the single absorption rate is limited, and some light energy will be reflected back to the optical fiber or lost; second, the local heat flux density is extremely high, which can easily cause material ablation or thermal fatigue. To address this, this embodiment designs the heat absorption tube with a spiral cavity structure. Specifically, this spiral cavity can adopt a tapered spiral flow channel, that is, the cross-section of the flow channel gradually decreases along the incident direction of the light beam. After the high-power light beam emitted from the emitting end of the hollow optical fiber enters the spiral cavity, it will undergo multiple (no less than 5) overlapping diffuse reflections and geometric absorptions on the inner wall of the spiral. Each reflection captures a portion of the light energy by the wall surface. Due to the geometric constraints of the spiral structure, the light beam cannot directly escape from the cavity, which is equivalent to forming an optical blackbody. The incident light is repeatedly absorbed in the spiral cavity, and the final overall equivalent geometric light absorption rate can reach more than 98%, which is much higher than the absorption rate of ordinary metal surfaces.

[0073] It should also be noted that high absorption rates based solely on the geometric structure are insufficient to cope with the harsh working conditions downhole. This is because the heat absorber tube undergoes drastic temperature changes during frequent injection and shutdown cycles (e.g., rapidly rising from ambient temperature of 20°C to over 350°C and then cooling back to room temperature). If the thermal expansion coefficients of the heat absorber tube material or surface coating do not match those of the substrate, thermal stress can easily occur, leading to coating peeling and substrate cracking. To address this, this embodiment further employs the following design: the substrate of the heat absorber tube is made of Inconel nickel alloy (such as Inconel 625), which possesses excellent high-temperature resistance, high-pressure resistance, and thermal shock resistance. A nano-spectrally selective absorption coating, such as a nickel / metal-ceramic composite coating (Ni-Al2O3 or W-Al2O3), is deposited on the inner wall surface of the spiral cavity using a plasma spraying process. This absorption coating exhibits extremely high absorptivity in the near-infrared band and low emissivity in the infrared radiation band, which helps to retain absorbed light energy as heat energy rather than radiating it back into the air. A nickel-chromium alloy transition bonding layer is also provided between the absorption coating and the substrate to ensure a smooth transition of the thermal expansion coefficient, preventing coating peeling or microcracks due to expansion differences. Testing has shown that the above-mentioned heat absorber tube structure can withstand at least 10,000 severe thermal cycles from 20°C to 350°C and back to 20°C, without any peeling, flaking, or microcrack propagation of the absorption coating.

[0074] Understandably, the helical cavity structure with blackbody physical properties inside the heat absorber allows the incident light beam to be reflected and absorbed multiple times within the helical cavity, achieving an equivalent absorption rate of over 98%. Combined with the thermal shock resistant design of the Inconel alloy substrate, spectrally selective absorption coating, and transition bonding layer, it can achieve high-efficiency photothermal conversion and ensure long-term structural stability under harsh conditions of high temperature, high pressure, and frequent thermal cycling downhole, thus providing a reliable and efficient heat source for storing thermal energy in deep formations.

[0075] In one feasible embodiment, the photothermal conversion device further includes an insulating connection structure connected between the heat absorption tube and the light transmission channel; the insulating connection structure has a vacuum cavity inside, the vacuum cavity is filled with multiple layers of radiation reflective screens, and the insulating connection structure is made of a low thermal conductivity material.

[0076] It should be noted that after the heat absorber converts light energy into heat energy at the bottom of the well, the outer wall temperature of the heat absorber can reach over 350°C. If the heat absorber is directly connected to the upper optical transmission channel by metal, a large amount of heat will be lost upwards along the metal wall through heat conduction. This not only reduces the effective heat power injected into the formation but also causes the temperature of the downhole tubing and optical transmission medium supporting the optical transmission channel to rise, accelerating the aging of the hollow optical fiber and even causing failure. To block this upward axial heat conduction path, this embodiment adds a heat-insulating connection structure between the heat absorber and the optical transmission channel.

[0077] Specifically, the thermal insulation connection structure can adopt a double-layer stainless steel jacket, with the inside of the jacket evacuated to a high vacuum (vacuum degree less than or equal to) To eliminate convective heat transfer, the vacuum chamber is also filled with multiple layers of radiation reflective screens (such as aluminum foil or stainless steel foil) to reflect infrared radiation, further reducing radiative heat transfer. Simultaneously, this thermal insulation connection structure employs structural ceramics with low thermal conductivity (such as high-strength zirconia). This ensures connection strength while maximizing the prevention of upward heat conduction.

[0078] It is understandable that, due to the thermal insulation connection structure with a vacuum cavity, multi-layer radiation reflector and low thermal conductivity ceramic material set between the heat absorption tube and the optical transmission channel, the high temperature heat generated at the bottom of the well can be effectively blocked from being conducted upward axially, forcing the heat to diffuse radially towards the formation, thereby greatly improving the utilization efficiency of heat energy injected into the formation, while protecting the upper optical transmission channel and hollow optical fiber from high temperature damage.

[0079] For example, to help understand formation heat injection systems, please refer to Figure 3 , specifically: Figure 3This demonstrates the top-to-bottom series connection between the optical transmission channel, the thermal insulation structure, and the heat absorber. The thermal insulation structure plays a crucial role in heat insulation. Located between the optical transmission channel and the heat absorber, the thermal insulation structure contains a vacuum cavity, multiple layers of radiation reflectors, and is made of low thermal conductivity material. It prevents the heat generated at the bottom of the well from being conducted upwards axially, thus forcing heat to diffuse primarily radially towards the formation. This improves the efficiency of heat energy injection into the formation and protects the upper optical transmission channel.

[0080] Based on the above embodiments of this application, in another embodiment of this application, the same or similar content as the above embodiments can be referred to the above description, and will not be repeated hereafter. In addition, the light-collecting device includes a filter component for limiting the wavelength of the light beam to be introduced into the hollow optical fiber to a near-infrared low-loss window within a preset wavelength range.

[0081] It should be noted that sunlight has an extremely wide spectral range, distributed from the ultraviolet (approximately 200 nm) to the mid-infrared (above approximately 2500 nm). However, the transmission loss of hollow-core optical fibers varies greatly across different wavelengths: in the near-infrared range of 1000 nm to 1600 nm, the basic confinement loss can be reduced to below 1 dB / km through anti-resonant structure design and core gas drying; but in the ultraviolet band (<400 nm), the scattering loss of the glass material (the material used to make hollow-core optical fibers) is extremely high; in the mid-infrared band (>2000 nm), the absorption peaks of water molecules and carbon dioxide are significantly enhanced; in addition, the OH groups near 1383 nm... - Even trace amounts of moisture can cause severe attenuation in absorption peaks. If full-spectrum sunlight is directly introduced into hollow-core optical fibers, ultraviolet light will accelerate fiber material aging, while mid-infrared and moisture absorption bands will significantly increase cumulative loss over long distances, and may even damage the fiber due to localized overheating. Therefore, band selection is necessary before the light beam enters the hollow-core optical fiber.

[0082] It should also be noted that the filtering component is positioned between the focusing system of the ground-based solar collector and the incident end of the hollow-core optical fiber. Specifically, it may include an infrared / ultraviolet filter, a dichroic beam splitter, or a bandpass filter. Its function is to reflect or absorb wavelengths of sunlight outside the 1000nm–1600nm near-infrared low-loss window (such as ultraviolet, short-wavelength visible light, mid-infrared, and light near the strong absorption band of water), allowing only light beams within this low-loss window to pass through and couple into the hollow-core optical fiber. The filtered wavelengths can be guided to auxiliary photovoltaic cells or collectors for secondary utilization (such as powering ground-based equipment) to improve the overall utilization rate of solar energy.

[0083] Understandably, because a filter component is installed in the light-collecting device, the wavelength of the beam introduced into the hollow fiber is strictly limited to the near-infrared low-loss window of 1000nm to 1600nm. This effectively avoids damage to the hollow fiber material from ultraviolet light, eliminates additional transmission losses caused by mid-infrared and moisture absorption bands, ensures that the hollow fiber maintains low-loss transmission characteristics over long distances of several kilometers, thereby ensuring that sufficient solar power is delivered to the bottom of the well, and extending the service life of the hollow fiber.

[0084] Based on the above embodiments of this application, in another embodiment of this application, the same or similar content as the above embodiments can be referred to the above description, and will not be repeated hereafter. Based on this, refer to... Figure 4 A formation heating method is proposed, which applies the formation heating system described in the above embodiments. The method includes: Step S1: Collect sunlight on the ground using a light-collecting device and focus the sunlight into a beam; It should be noted that the purpose of this step is to convert raw solar energy into a high-energy-density directional beam, providing a sufficient power source for subsequent long-distance light transmission. This is because the intensity of solar radiation is relatively low (approximately...). Direct irradiation cannot meet the energy density required for heating deep strata, so it is necessary to concentrate the light through a light-gathering device.

[0085] Optionally, the light-collecting device is installed on the ground to collect sunlight and focus it into a beam.

[0086] Alternatively, sunlight from a large area can be focused onto a small area to form a high-power-density light spot, for example from... It is concentrated to several kilowatts per square centimeter.

[0087] Optionally, the light-collecting device also includes a filter assembly for limiting the wavelength of the beam to be introduced into the hollow fiber to a near-infrared low-loss window of 1000nm to 1600nm, so as to match the lowest transmission loss wavelength of the subsequent hollow fiber.

[0088] Understandably, this step enables high-magnification solar energy collection and transformation, providing feasible light source conditions for subsequent low-loss transmission over several kilometers.

[0089] Step S2: Construct a longitudinal optical transmission channel extending from the ground to the target stratum, and transmit the light beam to the target stratum through the optical transmission channel, wherein hollow optical fiber is used as the optical transmission medium in the optical transmission channel; It should be noted that the purpose of this step is to transmit a high-power beam focused on the ground to the target formation thousands of meters underground with extremely low energy loss. Because traditional hot fluids (steam, hot water) suffer huge heat loss along the way during long-distance wellbore transmission, hollow optical fibers, which utilize the principle of light propagation in an air core, produce almost no heat conduction loss and are therefore used as the transmission medium.

[0090] Optionally, constructing an optical transmission channel refers to laying a longitudinal path extending from the surface wellhead to the target formation depth. This path is encapsulated with hollow optical fibers, which are placed in a spiral armored tube inside the wellbore. Alternatively, the optical fibers can be placed in coiled tubing or a downhole tubing string.

[0091] Optionally, the target formation refers to the underground rock formation that needs to be heated, including oil-bearing layers of heavy oil reservoirs, geothermal well reservoirs (such as hot dry rock or hydrothermal reservoirs), and abandoned wells or geothermal reservoirs used for cross-seasonal energy storage.

[0092] Optionally, hollow-core optical fiber is used as the optical transmission medium, specifically anti-resonant hollow-core optical fiber (such as nodeless single-ring anti-resonant hollow-core optical fiber). Its core diameter is typically 30μm–50μm, and the core is filled with a high-purity inert gas (such as argon or high-purity nitrogen) and maintained at a slight positive pressure of 0.2MPa–0.5MPa to expel moisture and eliminate OH groups. - Absorption peak.

[0093] Optionally, to prevent damage to the optical fiber when stretched or bent downhole, the hollow optical fiber is encapsulated in a spiral armored tube filled with buffer lubricating material and the optical fiber is reserved with a margin; a bend limiter is also provided in the optical transmission channel to constrain the bending radius of the hollow optical fiber to not less than 300mm; beam expanders (such as large-diameter coreless quartz glass rods) are connected to both ends of the hollow optical fiber to expand the beam spot diameter and reduce the end face energy density.

[0094] Optionally, transmitting the light beam to the target formation via an optical transmission channel means that the light beam is coupled from the ground into a hollow optical fiber, propagates longitudinally along the hollow optical fiber for several kilometers, and then exits from the bottom of the well.

[0095] Understandably, this step utilizes the low-loss characteristics of hollow optical fibers to achieve long-distance, high-efficiency transmission of sunlight from the ground to deep strata, avoiding heat loss along the way in traditional heat injection methods.

[0096] Step S3: At the end of the optical transmission channel, the light energy of the light beam is converted into heat energy by a photothermal conversion device, and the heat energy is injected into the target formation.

[0097] It should be noted that the purpose of this step is to efficiently convert the light energy transmitted to the bottom of the well into heat energy and prevent the heat from dissipating upwards, ensuring that the heat is absorbed by the target formation to achieve viscosity reduction of heavy oil, thermal energy storage, or geothermal heat replenishment.

[0098] Optionally, the end of the optical transmission channel, i.e. the output end of the hollow optical fiber, is located at a depth close to the target formation at the bottom of the well.

[0099] Optionally, the photothermal conversion device includes a heat absorber tube with a spiral cavity structure inside. This cavity structure has blackbody physical properties, which allows the incident light beam to undergo multiple diffuse reflections and absorptions on the inner wall, resulting in an overall equivalent geometric light absorption rate of over 98%.

[0100] Optionally, the substrate of the heat absorber is made of Inconel nickel alloy, and the inner wall is sprayed with a nickel / metal ceramic nano-spectrally selective absorption coating. A nickel-chromium alloy transition bonding layer is provided between the coating and the substrate to withstand severe thermal cycling.

[0101] Optionally, an insulating connection structure is provided between the heat absorption tube and the upper light transmission channel. The structure has a vacuum chamber inside, which is filled with multiple layers of radiation reflective screens and uses high-strength zirconia ceramic with low thermal conductivity to block axial heat conduction to the upper part.

[0102] Optionally, injecting thermal energy into the target formation refers to transferring the heat generated by the heat absorber to the rock skeleton and pore fluid of the target formation through heat conduction, heat convection or heat radiation, thereby achieving formation heating, heavy oil viscosity reduction, cross-seasonal energy storage or geothermal well thermal reservoir recovery.

[0103] Optionally, a convective heat exchange cooling jacket is also provided around the output end of the hollow fiber, using the injected water or geothermal fluid flowing back from bottom to top in the wellbore to cool the output end and prevent local overheating.

[0104] Understandably, this step achieves efficient conversion of light energy into heat energy at the bottom of the well, and utilizes insulation design to inject heat into the target formation to the maximum extent, ultimately completing a clean and efficient energy storage process from ground solar energy to formation thermal energy.

[0105] In one feasible embodiment, the application of the formation heat injection system of this application may include the following: like Figure 5As shown, the formation heating system of this application can be applied to well network layouts for heavy oil thermal recovery or geothermal energy storage development, specifically adopting a "multi-well heating, single-well oil production" well layout pattern. Abandoned or low-production wells in the oilfield are used as heating wells, which are then modified to install the light-collecting device, light transmission channel (including hollow optical fiber, etc.), and photothermal conversion device described in this application. In these heating wells, the surface light-collecting device focuses the collected sunlight into a beam, which is then transmitted with low loss through hollow optical fiber to the bottom of the well thousands of meters deep. The light is then efficiently converted into heat energy through the heat-absorbing tube, continuously injecting heat energy into the formation surrounding the oil well. Specifically, in the heating well, the photothermal conversion device converts light energy into heat energy, heating the water medium injected into the wellbore (such as cold water injected from the surface) to form high-temperature water or steam. The heated heat carrier medium enters the deep reservoir through the heating port, reducing the viscosity of the surrounding heavy oil through heat conduction and forming a thermal flooding front, driving the crude oil towards the central production well. In this process, the surrounding formation rocks act as a huge natural thermal reservoir, mitigating diurnal fluctuations in solar energy and enabling continuous oil displacement. The central production wells are responsible for extracting the crude oil after viscosity reduction and displacement. This forms a well network-assisted heavy oil thermal recovery and storage system of "surrounding heating and central production".

[0106] like Figure 6 As shown, the formation heating system of this application can be applied to single-well cross-seasonal energy storage and oil production. Figure 6 This specifically demonstrates two working states of the same well under different seasons: such as Figure 6 As shown in (a), during the thermal storage period, i.e., summer or a period of abundant sunshine, oil production is stopped and the thermal storage mode is activated. In the summer with abundant sunshine, the ground-based lighting device focuses the collected sunlight into a beam, which is then transmitted with low loss to the bottom of the well thousands of meters deep via hollow optical fibers. Figure 6 (As indicated by the downward arrow in (a)), the heat is efficiently converted into thermal energy through the heat absorber and injected into the formation. This thermal energy radiates to the surrounding deep reservoir rocks and fluids. The heat continuously accumulates in the surrounding strata, forming a heat storage zone that converts a large amount of solar energy into and stores it as ground thermal energy. For example... Figure 6 As shown in (b), during the oil production period, i.e., winter or periods of insufficient sunlight, the light guide is stopped and the oil production mode is activated. After entering winter, due to the continued effect of the heat energy stored during the summer, the rocks and pore fluids near the wellbore remain at a high temperature. Heat is conducted from the formation towards the wellbore, relying on the enormous heat energy stored in the formation to reduce the viscosity of the crude oil and prevent wax deposition in the wellbore. At this time, the crude oil has good fluidity and is pumped to the surface through the wellbore ( Figure 6 (b) The large upward arrow indicates that efficient mining can be achieved. This application method makes full use of the seasonal fluctuations in solar energy and successfully solves the industry pain points of low utilization rate of conventional heat injection energy in deep strata and high difficulty of mining in winter.

[0107] like Figure 7As shown, the formation heating system of this application can be applied to various scenarios such as online heating replenishment and well network displacement of geothermal wells. Figure 7 This specifically demonstrates two different methods of heat replenishment and production: such as Figure 7 As shown in (a), the same-well, coaxial online heat replenishment is used for deep geothermal wells or producing heavy oil wells. This scheme adopts a "same-well, coaxial" structure. Within the same wellbore, sunlight collected from the ground is transmitted through an optical transmission channel (with built-in hollow optical fiber and...) Figure 7 (a) indicated by the downward arrow) is directly transmitted to the bottom of the well; at the bottom of the well, the photothermal conversion device efficiently converts light energy into heat energy, which radiates to the surrounding deep reservoir rocks and fluids. Simultaneously, another channel within the wellbore ( Figure 7 (a) The upward arrow indicates that the heated fluid (geothermal water or viscosity-reduced crude oil) is continuously extracted. This "extraction-while-illumination" mode can actively compensate for the thermal energy deficit caused by rapid extraction of the formation without interrupting production, maintain a constant bottom hole temperature, effectively prevent thermal exhaustion of the geothermal well, and extend the production cycle of the oil well. Figure 7 As shown in (b), adjacent wells provide auxiliary heating. For oil fields or geothermal fields with large-scale production, this scheme adopts an "adjacent well pair" layout. Figure 7 (b) The left well serves as a solar thermal injection well. The surface continuously collects and gathers sunlight, which is transmitted to the bottom of the well via hollow optical fiber, converted into heat energy, and then injected into the surrounding strata. Figure 7 (b) Indicated by the downward arrow on the left). As heat injection continues, heat is transferred from the deep reservoir to... Figure 7 (b) Right-side transverse conduction and diffusion. Figure 7 (b) The right-side well serves as a production well, utilizing the thermal front and displacement pressure formed by the injection well in the formation to pump heated and viscosity-reduced crude oil or high-temperature geothermal fluid to the surface through the wellbore. Figure 7 (b) Indicated by the upward arrow on the right. This "one injection, one extraction" adjacent well collaborative model can form a large-scale heat displacement effect, significantly improving the recovery rate of deep resources and the long-term stability of the geothermal system.

[0108] In one feasible embodiment, in a deep well scenario at depths of several kilometers, the energy transfer efficiency and loss of the formation heat injection system of this application are as follows: the light collection efficiency of the ground-based light-collecting device is 83%–88%; in the light transmission channel, the cumulative loss per kilometer of hollow-core optical fiber is controlled within 1.2 dB / km, and the transmission efficiency over long distances is 72%–78%; the photothermal conversion and heat injection efficiency of the bottom-of-well heat absorber is 90%–95%; finally, the proportion of the comprehensive thermal power converted from the original solar energy collected from the ground and actually injected into the target formation (i.e., the total thermal efficiency of the formation heat injection system) remains between 55% and 60%. The data shows that, under long-distance deep well transmission conditions, the formation heat injection system of this application can ultimately convert most of the collected solar energy into effective thermal energy injected into the formation, with a total thermal efficiency significantly higher than traditional ground steam injection methods (usually below 30%) and photovoltaic power generation downhole electric heating methods (the combined photoelectric-thermal efficiency is usually below 20%), verifying the high efficiency and feasibility of the technical solution of this application in the field of clean heat injection in deep formations.

[0109] It should be noted that the above examples are only for understanding this application and do not constitute a limitation on the formation heating method of this application. Any simple variations based on this technical concept, such as the interaction and combination of various embodiments, are all within the protection scope of this application.

[0110] The readable storage medium provided in this application is a computer-readable storage medium that stores computer-readable program instructions (i.e., a computer program) for executing the above-described formation heating method, which can solve the technical problem of low overall energy utilization when heating deep formations. Compared with the prior art, the beneficial effects of the computer-readable storage medium provided in this application are the same as the beneficial effects of the formation heating method provided in the above embodiments, and will not be repeated here.

[0111] This application also provides a computer program product, including a computer program that, when executed by a processor, implements the steps of the formation heat injection method as described above.

[0112] The computer program product provided in this application can solve the technical problem of low overall energy utilization when injecting heat into deep formations. Compared with the prior art, the beneficial effects of the computer program product provided in this application are the same as those of the formation heat injection method provided in the above embodiments, and will not be repeated here.

[0113] The above description is only a part of the embodiments of this application and does not limit the patent scope of this application. All equivalent structural transformations made under the technical concept of this application and using the contents of the specification and drawings of this application, or direct / indirect applications in other related technical fields, are included in the patent protection scope of this application.

Claims

1. A formation heat injection system, comprising: The formation heat injection system includes a light-collecting device, a light transmission channel, and a photothermal conversion device; The light-collecting device is installed on the ground to collect sunlight and focus it into a beam; The optical transmission channel is used to transmit the light beam to the target stratum using hollow optical fiber as the optical transmission medium. The photothermal conversion device is located at the end of the light transmission channel and is used to convert the light energy of the light beam into heat energy and inject the heat energy into the target formation.

2. The system as described in claim 1, characterized in that, The hollow optical fiber is an anti-resonant hollow optical fiber; the core of the hollow optical fiber is filled with inert gas and the core is maintained under a preset positive pressure.

3. The system as described in claim 1, characterized in that, The hollow optical fiber is encapsulated in a spiral armored tube, which is disposed in the optical transmission channel. The spiral armored tube is filled with a buffer lubricating material, and the hollow optical fiber has a preset length of allowance inside the spiral armored tube to protect the hollow optical fiber from tension when the spiral armored tube is stretched.

4. The system as described in claim 3, characterized in that, The spiral armored tube contains an optical fiber bundle, which is composed of a preset number of hollow optical fibers, at least one of which serves as a spare hollow optical fiber. When the primary hollow optical fiber fails, the system automatically switches to the spare hollow optical fiber. When all the hollow optical fibers in the bundle reach their service life limit, the bundle is replaced with a new one using ground steel wire operations.

5. The system as described in claim 1, characterized in that, The hollow fiber is connected to beam expanders at both ends. The beam expanders are used to increase the beam spot diameter to reduce the energy density of the beam at the incident and exit ends of the hollow fiber.

6. The system as described in claim 1, characterized in that, The optical transmission channel is equipped with a bending limiter to constrain the bending radius of the hollow optical fiber to be no less than a preset value.

7. The system as described in claim 1, characterized in that, The photothermal conversion device includes a heat-absorbing tube, the inside of which has a spiral cavity structure, and the spiral cavity structure has blackbody physical properties.

8. The system as described in claim 7, characterized in that, The photothermal conversion device further includes an insulating connection structure, which is connected between the heat absorption tube and the light transmission channel; the insulating connection structure has a vacuum cavity inside, which is filled with multiple layers of radiation reflective screens, and the insulating connection structure is made of a low thermal conductivity material.

9. The system as described in claim 1, characterized in that, The light-collecting device includes a filter component for limiting the wavelength of the light beam to be introduced into the hollow optical fiber to a near-infrared low-loss window within a preset wavelength range.

10. A formation heat injection method, characterized in that, The method, employing the formation heat injection system as described in any one of claims 1-9, comprises: Sunlight is collected on the ground using a light-collecting device, and then focused into a beam of light. A longitudinal optical transmission channel is constructed extending from the ground to the target stratum, and the light beam is transmitted to the target stratum through the optical transmission channel, wherein hollow optical fiber is used as the optical transmission medium in the optical transmission channel; At the end of the optical transmission channel, the light energy of the light beam is converted into heat energy by a photothermal conversion device, and the heat energy is injected into the target formation.

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