A System and Method for Monitoring Underground Fluid Distribution Based on Active Heating Fiber Optic System

Abstract

This invention belongs to the field of fiber optic logging and reservoir evaluation technology, and relates to an underground downhole fluid distribution monitoring system and method based on an active heating fiber optic system. A first armored active heating fiber optic cable is fixed outside the casing, and a second armored active heating fiber optic cable is deployed inside the oil and gas tubing string. Near the wellhead, the multimode fiber inside the armored active heating fiber optic cable is connected to an AH-DTS modem instrument of the surface active heating fiber optic system, forming an underground downhole fluid distribution monitoring system based on the active heating fiber optic system. This invention utilizes the first armored active heating fiber optic cable fixed outside the metal casing to construct an external real-time monitoring unit for the distribution and changes of fluids in underground oil and gas reservoirs. The second armored active heating fiber optic cable deployed inside the oil and gas tubing string serves as an in-well sensing unit for long-term dynamic monitoring of the production profile or water absorption profile of oil and gas production wells, water injection wells, steam injection wells, carbon dioxide injection wells, or polymer injection wells, thereby achieving scientific management of oil and gas reservoirs and improving recovery rates.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic logging and reservoir evaluation technology, specifically relating to a system and method for monitoring the distribution of underground fluids based on an active heating fiber optic system. Background Technology

[0002] The emergence of the Active Heating Distributed Fiber Optic Temperature Measurement (AH-DTS) system represents a revolution from "measuring the temperature of a medium" to "measuring the thermal properties of a medium." Measuring the thermal properties of a medium, or simply thermal properties, is central to understanding active heating distributed fiber optic temperature sensing technology and many other advanced sensing technologies. AH-DTS is an advanced and novel monitoring technology that combines traditional distributed fiber optic temperature sensing with active heating control. Thermal properties, also known as thermophysical properties, refer to the inherent physical properties of a substance under thermal interaction. They describe the substance's ability to store and transfer heat and are closely related to the type, composition, structure, and state of the substance.

[0003] In engineering and physics, some of the most important thermal property parameters of a medium include:

[0004] (1) Thermal conductivity: A physical quantity that measures the ability of a material to conduct heat. High thermal conductivity means good thermal conductivity.

[0005] (2) Thermal diffusivity: A physical quantity that measures the ability of a material to achieve uniform temperature within the material. It combines thermal conductivity, density, and specific heat capacity to indicate how quickly heat diffuses within the material.

[0006] (3) Specific heat capacity: A physical quantity that measures the ability of a unit mass of a substance to store heat. The greater the specific heat capacity, the more heat is required to raise the temperature by the same amount.

[0007] The fundamental purpose of measuring the thermal properties of a medium is to identify and distinguish substances or states. Absolute temperature tells us "how hot it is here." Thermal properties tell us "what is here, or what state it is in." Because different substances, and even different states of the same substance (such as dry / wet, frozen / thawed), have significantly different thermal property parameters.

[0008] By measuring thermophysical properties, we can achieve the following: Composition identification: Differentiating between water, oil, air, soil, metals, etc. State determination: Determining whether strata or rocks are dry or wet, whether pipes contain liquids or gases, and whether materials are frozen. Structural detection: Detecting cavities, cracks, or inhomogeneities within materials.

[0009] In the field and at engineering sites, we employ an indirect but highly effective method: active thermal excitation. The core idea is to heat an object or medium in a known manner and then observe the change in its temperature response (heating / cooling process) over time. This response curve contains all the information about its thermophysical properties.

[0010] The active thermal excitation method is implemented as follows: A known thermal pulse is applied to the medium under test, which exhibits a specific temperature-time curve (ΔT vs time). The temperature change curve (ΔT vs time) is analyzed to deduce the thermal properties of the medium.

[0011] Distributed fiber optic temperature sensing (DTS) technology measures the distributed temperature changes along the medium of an optical fiber. We can use a linear heat source model to process and interpret DTS data from active thermal excitation methods. A linear heat source model is a mathematical model used to describe the distribution and transfer of heat along a line (or approximately a line). It is often used to simplify the analysis of one-dimensional or approximately one-dimensional heat conduction problems, where the generation or input of heat is mainly concentrated along a line, or where the geometry and boundary conditions of the system make temperature changes along that line the dominant factor. Mathematically, a linear heat source is usually represented by the Dirac delta function or a line integral. For example, for a heat source located on a coordinate axis, the heat flux density can be expressed as (q(x,y,z)= Q δ(x - x_0, y - y_0)), where (Q) is the heat source intensity, and (δ) is the delta function used to describe the concentrated distribution of heat along the line. The heat conduction process follows the heat conduction equation: (kT) + q(x,y,z) = 0, where (k) is the thermal conductivity of the material and (T) is the temperature. The heat conduction equation is a partial differential equation describing the change of temperature with time and space, and is widely used in thermodynamics, diffusion processes, and financial mathematics. This equation is derived from Fourier's law of cooling, and formally uses the Laplace operator to represent the spatial derivative, belonging to the parabolic type of partial differential equation. Its solution has the characteristic of smoothing the initial temperature distribution and tending towards thermal equilibrium.

[0012] For the Active Heating Fiber Optic System (AH-DTS), the measurement results no longer simply report "the temperature at the location of the fiber is 10°C", but rather "the surrounding medium at the location of the fiber has thermal properties similar to natural gas", "thermal properties similar to water", or "thermal properties similar to oil". Combined with the linear heat source model and inversion calculation, it can be fully explained quantitatively. This is the leap from "temperature measurement" to "thermal property measurement". Summary of the Invention

[0013] To obtain information about the distribution of oil, gas, and water in the corresponding underground reservoir and their changes during the production process, various testing instruments are used to conduct downhole testing throughout the entire production process of oil and gas production wells, from commissioning to decommissioning. This includes measuring parameters such as well temperature, pressure, fluid flow rate, and water holdup to understand the production (fluid production) and injection (water absorption) profiles, providing a basis for oil and gas reservoir stimulation. Production logging has become an indispensable tool for the scientific management of oil and gas reservoirs and improving recovery rates. Due to the limitations of conventional production logging instruments operating in high-temperature and high-pressure wells, a low-cost, high-precision, and highly reliable method and technology are needed to understand the production (fluid production) and injection (water absorption) profiles of oil and gas wells.

[0014] The purpose of this invention is to overcome the shortcomings of existing technologies and propose an underground downhole fluid distribution dynamic monitoring system using an Active Heating Fiber Optic System (AH-DTS). This system is formed by fixing a first armored active heating fiber optic cable outside the metal casing and laying a second armored active heating fiber optic cable inside the oil and gas tubing string. Near the wellhead, the multimode fiber inside the armored active heating fiber optic cable is connected to a surface-based AH-DTS modem, thus creating an underground downhole fluid distribution monitoring system based on the active heating fiber optic system. This system establishes an inside-well sensing unit for real-time monitoring of fluid distribution and changes within underground oil and gas reservoirs and long-term dynamic monitoring of the production profile or water absorption profile of oil and gas production wells, water injection wells, steam injection wells, carbon dioxide injection wells, or polymer injection wells, enabling scientific management of oil and gas reservoirs and improving oil recovery.

[0015] Distributed fiber optic sensing technology is the optimal choice for long-term dynamic monitoring downhole and forms the foundation for true information-based and intelligent oil and gas field production. The advantages of distributed downhole fiber optic sensing include:

[0016] 1) It can provide real-time, high-density, multi-parameter parameters for the entire life cycle of oil and gas field development, thereby improving the scientific level and efficiency of decision-making for fine oil and gas reservoir description;

[0017] 2) No production interruption is required for downhole operations, resulting in no production loss, no operating costs, no personnel risks, and no environmental pollution risks;

[0018] 3) It can replace and surpass conventional logging, providing not only more real-time and higher quality data, but also high cost-effectiveness, with a one-time investment yielding lifelong benefits;

[0019] 4) No special equipment is required. It can be easily applied to wells with high deflection and horizontal orientation, and does not affect operations inside the tubing.

[0020] To achieve the above objectives, the specific technical solution of the present invention is as follows:

[0021] The underground fluid distribution monitoring system based on the active heating fiber optic system includes a borehole, a metal casing inside the borehole, an oil and gas tubing string inside the metal casing, a first armored active heating fiber optic cable fixed on the outside of the metal casing, and a second armored active heating fiber optic cable arranged inside the oil and gas tubing string; it also includes an AH-DTS modulator / demodulator instrument with a four-channel active heating fiber optic system placed near the wellhead.

[0022] The structure of the first armored active heating optical cable and the second armored active heating optical cable includes two high-temperature resistant, hydrogen loss resistant, high-sensitivity multimode optical fibers, a thin stainless steel tube, a carbon fiber heating or copper mesh heating resistance wire mesh sleeve, a high-temperature resistant, high-strength, flexible insulating composite material sheath, and a stainless steel wire outer armored optical cable sheath.

[0023] Both the first armored active heating optical cable and the second armored active heating optical cable are armored optical cables. Each of the first armored active heating optical cable and the second armored active heating optical cable includes two multimode optical fibers. The multimode optical fibers are encapsulated in sequence by a thin stainless steel tube, a carbon fiber heating or copper mesh heating resistance wire mesh sleeve, a high temperature and high strength flexible insulating composite material sheath, and a stainless steel wire outer armored optical cable sheath.

[0024] It also includes a ring-shaped metal clip, which is installed and fixed at each metal sleeve shoe to secure the first armored active heating optical cable.

[0025] The two multimode optical fibers within the first and second armored active heating optical cables are fused into a U-shape at the cable ends for high-precision dual-ended input DTS measurements. The second armored active heating optical cable is connected to a high-density metal counterweight rod at its end and is installed within the oil and gas pipeline.

[0026] The first and second channels of the four-channel active heating fiber optic system AH-DTS modem are connected to the two multimode fibers at the beginning of the first armored active heating fiber optic cable, and the third and fourth channels of the AH-DTS modem are connected to the two multimode fibers at the beginning of the second armored active heating fiber optic cable.

[0027] The AH-DTS modem also includes two heating source channels, which are respectively connected to the first armored active heating optical cable and the second armored active heating optical cable carbon fiber heating or copper mesh heating resistance wire mesh sleeve.

[0028] The monitoring method for an underground fluid distribution monitoring system based on an active heating fiber optic system is characterized by the following steps:

[0029] (a) After drilling is completed, the metal sleeve and the first armored active heating optical cable are simultaneously and slowly lowered into the drilled hole.

[0030] (b) Install the annular metal clip at the wellhead at the connecting shoe of the two metal casings to fix and protect the first armored active heating optical cable from rotation, movement and / or damage during the casing lowering process;

[0031] (c) Use a high-pressure pump truck to pump cement slurry from the bottom of the well, so that the cement slurry returns from the bottom of the well to the wellhead along the annulus between the outer wall of the metal casing and the borehole. After the cement slurry solidifies, it permanently fixes the metal casing, the first armored active heating optical cable and the formation rock together.

[0032] (d) The two multimode optical fibers in the first armored active heating optical cable and the second armored active heating optical cable are spliced ​​into a U-shape at the end of the optical cable for high-precision dual-ended input DTS measurement.

[0033] (e) Connect the two multimode optical fibers in the first armored active heating optical cable and the two multimode optical fibers in the second armored active heating optical cable to the four DTS signal input terminals of the AH-DTS modem at the wellhead.

[0034] (f) Run the oil and gas tubing string into the cemented and completed metal casing well, and then slowly lay the second armored active heating fiber optic cable through the high specific gravity metal counterweight rod connected to the tail end inside the oil and gas tubing string until the bottom of the well.

[0035] (g) At the wellhead, connect the carbon fiber heating or copper mesh heating resistance wire sleeves inside the first armored active heating optical cable and the second armored active heating optical cable to the two heating source channels of the AH-DTS modem.

[0036] (h) During oil and gas production, the carbon fiber heating or copper mesh heating resistance wire mesh sleeve of the first armored active heating optical cable and the second armored active heating optical cable are powered through the two heating source channels of the AH-DTS modulator placed next to the wellhead to power the formation and fluid in the oil and gas tubing around the heating optical cable. Then, the DTS signal of the multimode optical fiber in the first armored active heating optical cable outside the metal casing and the second armored active heating optical cable inside the oil and gas tubing is continuously monitored and measured.

[0037] (i) Modulate and demodulate the DTS signal continuously measured by the AH-DTS modulator and demodulator to obtain the temperature rise curve (ΔT vs time) of the fluid around the multimode fiber in the first armored active heating optical cable outside the metal sheath and the second armored active heating optical cable inside the oil and gas pipeline during the heating process.

[0038] (j) Based on the temperature rise curve (ΔT vs time) of the reservoir fluid obtained by monitoring and measuring the first armored active heating optical cable outside the metal casing in step (i), the distribution and saturation of water or saline water, oil and natural gas in the pores of the formation and rock strata outside the metal casing are calculated and interpreted by combining the linear heat source model of different fluids (water, oil and gas). This provides the distribution law of oil, gas and water in the pores of the formation and rock strata around the borehole and its changes over time, thereby realizing long-term dynamic monitoring of the development and production process of oil and gas wells and its changing law, optimizing the underground oil and gas resource extraction methods and production system, and improving the recovery rate of underground oil and gas resources.

[0039] (k) Based on the temperature rise curve (ΔT vs time) of the fluid in the oil and gas pipeline obtained by the second armored active heating optical cable in step (i), the distribution and migration patterns and characteristics of water or saline water, oil or oil bubbles and natural gas or natural gas bubbles in the oil and gas pipeline are analyzed and interpreted by combining the linear heat source model of different fluids (water, oil, gas) and inversion calculation. The flow rate, velocity and variation of the fluid in the oil and gas pipeline are also analyzed. This enables long-term dynamic monitoring of the distribution, flow rate, velocity, water holding capacity and variation of water, oil or oil bubbles and natural gas or gas bubbles in the oil and gas pipeline during the production process. This optimizes the underground oil and gas resource extraction methods and production system, and ultimately improves the recovery rate of underground oil and gas resources.

[0040] This invention provides a downhole fluid distribution monitoring system based on an active heating fiber optic system, along with its data acquisition, processing, and interpretation method. This represents a low-cost, high-precision, and highly reliable method and technology for dynamic comprehensive monitoring of downhole fluid distribution. The invention proposes fixing a first armored active heating fiber optic cable outside the metal casing and deploying a second armored active heating fiber optic cable inside the oil and gas tubing string. Near the wellhead, the multimode fiber within the armored active heating fiber optic cable is connected to an AH-DTS modem instrument of the surface active heating fiber optic system, thus constructing a downhole fluid distribution monitoring system based on the active heating fiber optic system. This system enables real-time monitoring of fluid distribution and changes within underground oil and gas reservoirs, as well as long-term dynamic monitoring of the production profile or water absorption profile of oil and gas production wells, water injection wells, steam injection wells, carbon dioxide injection wells, or polymer injection wells. These internal and external sensing units enable scientific management of oil and gas reservoirs and improved oil recovery. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the armored active heating optical cable of the present invention deployed on the outside of the downhole casing and inside the oil and gas tubing string.

[0042] Figure 2 This is a schematic diagram of the armored active heating optical cable structure of the present invention.

[0043] The attached diagram shows the markings and corresponding component names:

[0044] 1-Drilling hole, 2-Metal sleeve, 3-Oil and gas tubing string, 4-First armored active heating optical cable, 5-Second armored active heating optical cable, 6-AH-DTS modem, 7-Multimode optical fiber, 8-Fine stainless steel tube, 9-Carbon fiber heating or copper mesh heating resistance wire mesh sleeve, 10-High temperature resistant, high strength, flexible insulating composite material sheath, 11-Stainless steel wire outer armored optical cable sheath, 12-Ring metal clip, 13-High specific gravity metal counterweight rod. Detailed Implementation

[0045] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. However, these embodiments do not constitute a limitation of the present invention and are merely examples. The advantages of the present invention will become clearer and easier to understand by describing them.

[0046] A specific embodiment of the downhole fluid distribution dynamic monitoring system based on distributed optical fiber sensing according to the present invention is as follows:

[0047] like Figure 1 The schematic diagram of the armored active heating optical cable of the present invention on the outside of the downhole casing and inside the oil and gas tubing string is shown. The downhole fluid distribution dynamic monitoring system based on distributed optical fiber sensing includes a borehole 1, a metal casing 2, an oil and gas tubing string 3 built into the metal casing 2, a first armored active heating optical cable 4 fixed on the outside of the metal casing 2, and a second armored active heating optical cable 5 arranged inside the oil and gas tubing string 3; it also includes a four-channel active heating optical fiber system AH-DTS modulation and demodulation instrument 6 placed near the wellhead.

[0048] like Figure 2 As shown in the schematic diagram of the armored active heating optical cable structure of the present invention, the structure of the first armored active heating optical cable 4 and the second armored active heating optical cable 5 includes two high-temperature resistant, hydrogen loss resistant, and highly sensitive multimode optical fibers 7, a thin stainless steel tube 8, a carbon fiber heating or copper mesh heating resistance wire mesh sleeve 9, a high-temperature resistant, high-strength, flexible insulating composite material sheath 10, and a stainless steel wire outer armored optical cable sheath 11.

[0049] The first armored active heating optical cable 4 and the second armored active heating optical cable 5 are both armored optical cables. Both the first armored active heating optical cable 4 and the second armored active heating optical cable 5 contain two multimode optical fibers 7. The multimode optical fibers 7 are encapsulated by a thin stainless steel tube 8, a carbon fiber heating or copper mesh heating resistance wire mesh sleeve 9, a high temperature and high strength flexible insulating composite material sheath 10, and a stainless steel wire outer armored optical cable sheath 11.

[0050] The two multimode optical fibers 7 in the first armored active heating optical cable 4 and the second armored active heating optical cable 5 are fused into a U-shape at the end of the optical cable for high-precision dual-ended input DTS measurement.

[0051] It also includes annular metal clips 12, which are installed and fixed at the shoe of each metal sleeve 2 to secure the first armored active heating optical cable 4. The tail end of the second armored active heating optical cable 5 is connected to a high-density metal counterweight rod 13 and is laid inside the oil and gas pipeline 3.

[0052] The first and second channels of the four-channel active heating fiber optic system AH-DTS modem 6 are connected to the two multimode fibers 7 at the beginning of the first armored active heating optical cable 4, and the third and fourth channels of the AH-DTS modem 6 are connected to the two multimode fibers 7 at the beginning of the second armored active heating optical cable 5.

[0053] The AH-DTS modem 6 also includes two heating source channels, which are respectively connected to the first armored active heating optical cable 4 and the second armored active heating optical cable 5 carbon fiber heating or copper mesh heating resistance wire mesh sleeve 9.

[0054] The monitoring method for an underground fluid distribution monitoring system based on an active heating fiber optic system includes the following steps:

[0055] (1) After drilling hole 1 is completed, the metal sleeve 2 and the first armored active heating optical cable 4 are simultaneously and slowly lowered into the completed drilling hole 1.

[0056] (2) Install the annular metal clip 12 at the wellhead at the connecting shoe of the two metal sleeves 2 to fix and protect the first armored active heating optical cable 4 from rotation or movement and / or damage during the lowering of the sleeve.

[0057] (3) Use a high-pressure pump truck to pump cement slurry from the bottom of the well, so that the cement slurry returns from the bottom of the well to the wellhead along the annulus between the outer wall of the metal casing 2 and the borehole 1. After the cement slurry solidifies, it permanently fixes the metal casing 2, the first armored active heating optical cable 4 and the formation rock together.

[0058] (4) The two multimode optical fibers 7 in the first armored active heating optical cable 4 and the second armored active heating optical cable 5 are spliced ​​into a U-shape at the end of the optical cable for high-precision dual-end input DTS measurement.

[0059] (5) At the wellhead, connect the two multimode optical fibers 7 in the first armored active heating optical cable 4 and the two multimode optical fibers 7 in the second armored active heating optical cable 5 to the four DTS signal input terminals of the AH-DTS modem 6 respectively.

[0060] (6) The oil and gas tubing string 3 is lowered into the cemented metal casing 2 well, and then the second armored active heating optical cable 5 is slowly laid in the oil and gas tubing string 3 through the high specific gravity metal counterweight rod 13 connected to the tail end until the bottom of the well.

[0061] (7) At the wellhead, connect the carbon fiber heating or copper mesh heating resistance wire sleeve 9 at the head end of the first armored active heating optical cable 4 and the second armored active heating optical cable 5 to the two heating source channels of the AH-DTS modem 6 respectively.

[0062] (8) During oil and gas production, the carbon fiber heating or copper mesh heating resistance wire mesh sleeve 9 of the first armored active heating optical cable 4 and the second armored active heating optical cable 5 are supplied with power through the two heating source channels of the AH-DTS modulator 6 placed next to the wellhead to heat the formation around the optical cable and the fluid in the oil and gas pipeline 3. Then, the DTS signal of the multimode optical fiber 7 in the first armored active heating optical cable 4 outside the metal casing 2 and the second armored active heating optical cable 5 inside the oil and gas pipeline 3 is continuously monitored and measured.

[0063] (9) Modulate and demodulate the DTS signal continuously measured by the AH-DTS modulator and demodulator 6 to obtain the temperature rise curve (ΔT vs time) of the fluid around the first armored active heating optical cable 4 outside the metal sleeve 2 and the multimode optical fiber 7 inside the second armored active heating optical cable 5 inside the oil and gas pipe column 3 during the heating process.

[0064] (10) Based on the temperature rise curve (ΔT vs time) of the reservoir fluid monitored and measured by the first armored active heating optical cable 4 outside the metal casing 2 obtained in step (9), the distribution and saturation of water or saline water, oil and natural gas in the pores of the formation and rock outside the metal casing 2 are calculated and interpreted by combining the linear heat source model of different fluids (water, oil and gas). This provides the distribution law of oil, gas and water in the pores of the formation and rock around borehole 1 and its changes over time, thereby realizing long-term dynamic monitoring of the development and production process of oil and gas wells and its changing law, optimizing the underground oil and gas resource extraction method and production system, and improving the recovery rate of underground oil and gas resources.

[0065] (11) Based on the temperature rise curve (ΔT vs time) of the fluid in the oil and gas pipeline 3 obtained by the second armored active heating optical cable 5 in step (9), the distribution and migration patterns and characteristics of water or saline water, oil or oil bubbles and natural gas or natural gas bubbles in the oil and gas pipeline 3, the flow rate, flow velocity and their variation patterns of the fluid in the oil and gas pipeline 3 are explained by combining the linear heat source model of different fluids (water, oil, gas) and inversion calculation. This enables long-term dynamic monitoring of the distribution, flow rate, flow velocity, water holding capacity and their variation patterns of water, oil or oil bubbles and natural gas or gas bubbles in the oil and gas pipeline 3 during the production process. This optimizes the underground oil and gas resource extraction methods and production system, and ultimately achieves the goal of improving the recovery rate of underground oil and gas resources.

Claims

1. A method for monitoring the distribution of underground fluids based on an active heating fiber optic system, wherein an underground fluid distribution monitoring system based on an active heating fiber optic system is adopted, the underground fluid distribution monitoring system based on an active heating fiber optic system includes a borehole (1), a metal casing (2) is provided inside the borehole (1), an oil and gas tubing string (3) is built inside the metal casing (2), a first armored active heating fiber optic cable (4) is fixed on the outside of the metal casing (2), and a second armored active heating fiber optic cable (5) is laid inside the oil and gas tubing string (3); It also includes a ring-shaped metal clip (12), which is installed and fixed at the boot of each metal sleeve (2) for fixing the first armored active heating optical cable (4). It also includes an AH-DTS modulator / demodulator (6) with a four-channel active heating fiber optic system placed near the wellhead; The AH-DTS modem (6) also includes two heating source channels, which are respectively connected to the carbon fiber heating or copper mesh heating resistance wire mesh sleeve (9) of the first armored active heating optical cable (4) and the second armored active heating optical cable (5). Its features are, The method includes the following steps: (a) After drilling (1) is completed, the metal sleeve (2) and the first armored active heating optical cable (4) are simultaneously and slowly lowered into the drilled hole (1); (b) Install the annular metal clip (12) at the wellhead at the shoe of the two metal casings (2) to fix and protect the first armored active heating optical cable (4) from rotation, movement and / or damage during the casing process; (c) Use a high-pressure pump truck to pump cement slurry from the bottom of the well, so that the cement slurry returns from the bottom of the well to the wellhead along the annulus between the outer wall of the metal casing (2) and the borehole (1). After the cement slurry solidifies, it permanently fixes the metal casing (2), the first armored active heating optical cable (4) and the formation rock together. (d) The two multimode optical fibers (7) in the first armored active heating optical cable (4) and the second armored active heating optical cable (5) are spliced ​​into a U-shape at the end of the optical cable for high-precision dual-end input DTS measurement. (e) At the wellhead, connect the two multimode optical fibers (7) in the first armored active heating optical cable (4) and the two multimode optical fibers (7) in the second armored active heating optical cable (5) to the four DTS signal input terminals of the AH-DTS modem (6). (f) The oil and gas tubing string (3) is lowered into the cemented metal casing (2) well, and then the second armored active heating optical cable (5) is slowly laid in the oil and gas tubing string (3) through the high specific gravity metal counterweight rod (13) connected to the tail end until the bottom of the well. (g) At the wellhead, connect the carbon fiber heating or copper mesh heating resistance wire mesh sleeve (9) inside the first armored active heating optical cable (4) and the second armored active heating optical cable (5) to the two heating source channels of the AH-DTS modem (6) respectively. (h) During oil and gas production, the carbon fiber heating or copper mesh heating resistance wire mesh sleeve (9) of the first armored active heating optical cable (4) and the second armored active heating optical cable (5) are powered through the two heating source channels of the AH-DTS modem (6) placed next to the wellhead to power the formation around the heating optical cable and the fluid in the oil and gas pipeline (3). Then, the DTS signal of the first armored active heating optical cable (4) outside the metal casing (2) and the multimode fiber (7) inside the second armored active heating optical cable (5) inside the oil and gas pipeline (3) is continuously monitored and measured. (i) Modulate and demodulate the DTS signal continuously measured by the AH-DTS modulator (6) to obtain the temperature rise curve of the fluid surrounding the first armored active heating optical cable (4) outside the metal sleeve (2) and the second armored active heating optical cable (5) inside the oil and gas pipe column (3) during the heating process. (j) Based on the temperature rise curve of the reservoir fluid obtained by monitoring and measuring the first armored active heating optical cable (4) outside the metal casing (2) obtained in step (i), the distribution and saturation of water or saline water, oil and natural gas in the pores of the formation and rock outside the metal casing (2) are calculated and interpreted by combining different fluid linear heat source models and inversion calculations. This provides the distribution law of oil, gas and water in the pores of the formation and rock around the borehole (1) and its changes over time, thereby realizing long-term dynamic monitoring of the development and production process of oil and gas wells and its changing law, optimizing the underground oil and gas resource extraction methods and production system, and improving the recovery rate of underground oil and gas resources. (k) Based on the temperature rise curve of the fluid in the oil and gas pipeline (3) obtained by the second armored active heating optical cable (5) in the oil and gas pipeline (3) obtained in step (i), the distribution and migration patterns and characteristics of water or saline water, oil or oil bubbles and natural gas or natural gas bubbles in the oil and gas pipeline (3), the flow rate, flow velocity and their variation patterns of the fluid in the oil and gas pipeline (3) are analyzed and explained by combining different fluid linear heat source models and inversion calculations. This enables long-term dynamic monitoring of the distribution, flow rate, flow velocity, water holding capacity and their variation patterns of water, oil or oil bubbles and natural gas or gas bubbles flowing in the oil and gas pipeline (3) during the production process.

2. The method for monitoring underground fluid distribution based on an active heating fiber optic system according to claim 1, characterized in that, The first armored active heating optical cable (4) and the second armored active heating optical cable (5) are both armored optical cables. The first armored active heating optical cable (4) and the second armored active heating optical cable (5) each contain two multimode optical fibers (7). The multimode optical fibers (7) are surrounded by a thin stainless steel tube (8), a carbon fiber heating or copper mesh heating resistance wire mesh sleeve (9), a high temperature and high strength flexible insulating composite material sheath (10), and a stainless steel wire outer armored optical cable sheath (11).

3. The method for monitoring underground fluid distribution based on an active heating fiber optic system according to claim 2, characterized in that, The two multimode optical fibers (7) in the first armored active heating optical cable (4) and the second armored active heating optical cable (5) are fused into a U-shape at the end of the optical cable for high-precision dual-ended input DTS measurement.

4. The method for monitoring underground fluid distribution based on an active heating fiber optic system according to claim 2, characterized in that, The tail end of the second armored active heating optical cable (5) is connected to a high specific gravity metal counterweight rod (13) and laid inside the oil and gas pipeline (3).

5. The method for monitoring underground fluid distribution based on an active heating fiber optic system according to claim 2, characterized in that, The first and second channels of the AH-DTS modem (6) are connected to the two multimode optical fibers (7) at the head end of the first armored active heating optical cable (4), and the third and fourth channels of the AH-DTS modem (6) are connected to the two multimode optical fibers (7) at the head end of the second armored active heating optical cable (5).

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