Downhole fluid composition monitoring system and method based on fiber optic chemical sensing

Abstract

This invention discloses a downhole fluid composition monitoring system and method based on fiber optic chemical sensing, relating to the field of chemical measurement technology. It can at least partially solve the problem that existing traditional downhole three-phase fluid chemical composition measurement technologies are difficult to perform online measurement and analysis. The downhole fluid composition monitoring system based on fiber optic chemical sensing in this invention includes a composite modulation and demodulation instrument with distributed fiber optic chemical sensing ports, and fiber optic chemical sensing downhole fluid composition measurement and monitoring optical cables deployed inside / outside the casing of open-hole or cased-hole wells, or inside / outside the oil and gas tubing string. The fiber optic chemical sensing downhole fluid composition measurement and monitoring optical cables include chemical sensing optical fibers connected to the distributed fiber optic chemical sensing ports; the chemical sensing optical fibers include distributed chemical sensing optical fibers or arrayed chemical sensing grating optical fibers.

Description

Technical Field

[0001] This invention belongs to the field of chemical measurement technology, specifically relating to a downhole fluid composition monitoring system and method based on fiber optic chemical sensing. Background Technology

[0002] Fiber optic chemical sensors are sensors constructed using the waveguide properties of optical fibers. They are used to measure certain chemical quantities, such as pH values ​​and the concentration of chemical substances. Optical chemical sensors are a type of chemical sensor with optical response. In chemical analysis, optical techniques based on discrete optical systems and spectroscopic methods are widely used. Since the 1980s, due to the rapid development of communication and computer technologies, their combination with spectroscopic techniques has formed a new analytical testing technology—fiber optical chemical sensors—opening up a new world in the field of analytical chemistry. Sensors fabricated using chemiluminescence, bioluminescence, and photosensitive devices combined with fiber optic technology, especially fiber optic sensors and various probe technologies based on fiber optics, possess advantages such as fast response speed, high sensitivity, strong resistance to electromagnetic interference, small size, and applicability to harsh environments where other sensors cannot operate. They have great application potential in process analysis and have experienced rapid development.

[0003] Before and after the interaction between the medium layer and the analyte, changes in the physical or chemical properties will cause changes in the characteristics of the propagating light. Sensors that utilize these changes in light signals to qualitatively or quantitatively analyze chemical substances are called photochemical sensors. Fiber optic chemical sensors transmit light signals via optical fibers. A fixed reagent phase is carried at the end of the fiber. During testing, the sensor is inserted into the solution or gas to be tested. The light beam incident from the light source is sent through the fiber to the modulation region where the sensitive reagent is fixed. The analyte interacts with the reagent phase, causing changes in the optical properties of the light, such as intensity, wavelength (color), frequency, phase, and polarization state. These changes become the modulated signal light, which is then sent through the fiber to a photodetector and signal processing device to obtain information about the analyte.

[0004] With the rapid development of fiber optic manufacturing technology and related materials engineering, optical fibers have evolved from core-clad structures based on quartz glass to composite structures with various materials, including semiconductors, metals, doped quartz glass, oxide glasses, chalcogenide glasses, and functional polymers. This abundance of materials and structures provides a new development path for optical fibers to meet the needs of radiation sensors. More and more sensing materials are being directly drawn into fiber shapes, further improving sensing accuracy and length range. Furthermore, fiber optic sensors, due to their core-clad coating structure, are moisture-proof, corrosion-resistant, and resistant to electromagnetic interference under most environmental conditions. Most optical fibers have a core-clad structure; additionally, a protective polymer layer can be applied to prevent the functional core from contacting water, thus making the fiber waterproof. Glass and coated polymer materials exhibit excellent stability even in highly corrosive environments, enhancing the environmental adaptability of fiber optic sensors. Simultaneously, fiber optic sensors are less susceptible to interference from external electromagnetic fields because commonly used fiber materials are non-conductive, further improving sensing performance.

[0005] In addition, quasi-distributed fiber optic sensors, such as fiber Bragg grating (FBG) sensors, have emerged. However, the measurement points of FBG sensors are limited by the laser bandwidth. Currently, distributed fiber optic sensing technology is maturing. Distributed fiber optic sensors based on backscattering Rayleigh scattering exhibit good accuracy, linearity, and repeatability in measuring the chemical composition of media, and have the potential to replace traditional chemical composition measurement technologies and FBG sensors in many fields. Distributed fiber optic sensors feature extremely high measurement point density, controllable spacing, small mass, corrosion resistance, electrical insulation, high accuracy, and good repeatability. Furthermore, due to their relatively soft and tough properties, they have good adaptability to the shape of structural surfaces.

[0006] Online analysis of the composition of three-phase fluids in underground or well sites has always been a challenge. Existing instruments for sampling downhole fluids and maintaining constant pressure and temperature are very complex and expensive. Each well run can only collect about ten samples of fluid from the formation, which are then sent to a chemical laboratory for analysis and identification under pressure and temperature control. This process is costly, inefficient, and time-consuming, and cannot fully meet the needs for high-density, in-situ, real-time online measurement and analysis of three-phase fluids in underground formations or wells. Summary of the Invention

[0007] The fiber optic chemical sensing-based downhole fluid composition monitoring system proposed in this invention consists of a fiber optic chemical sensing downhole fluid composition measurement and monitoring cable composed of distributed chemical sensing fibers or arrayed chemical sensing grating fibers and high-density array chemical sensing fibers. This cable is then connected to a composite modulation and demodulation instrument inside or outside the oil and gas tubing string in open-hole or cased-hole wells, or inside or outside the casing. This system overcomes the shortcomings of existing traditional downhole three-phase fluid chemical composition measurement technologies and provides an indispensable means, system, and method for long-term real-time measurement and monitoring of the chemical composition and changes of downhole three-phase fluids.

[0008] To achieve the above objectives, the specific technical solution of the present invention is as follows:

[0009] This invention proposes a downhole fluid composition monitoring system based on fiber optic chemical sensing, including a composite modulation and demodulation instrument with distributed fiber optic chemical sensing ports, and a fiber optic chemical sensing downhole fluid composition measurement and monitoring optical cable deployed outside the casing or inside the oil and gas tubing string in open hole or casing well.

[0010] The fiber optic chemical sensing downhole fluid composition measurement and monitoring cable includes chemical sensing fibers connected to distributed fiber optic chemical sensing ports;

[0011] The chemical sensing fiber includes a distributed chemical sensing fiber or an array chemical sensing grating fiber.

[0012] In some optional embodiments, the composite modulation and demodulation instrument also has distributed fiber optic temperature sensing ports, and the fiber optic chemical sensing downhole fluid component measurement and monitoring optical cable includes two multimode fibers for measuring temperature changes along the line. The tail ends of the two multimode fibers are fused into a U-shaped structure, and the two distributed fiber optic temperature sensing ports of the composite modulation and demodulation instrument are connected to the two multimode fibers of the fiber optic chemical sensing downhole fluid component measurement and monitoring optical cable.

[0013] In some alternative embodiments, the fiber optic chemical sensing downhole fluid composition measurement and monitoring cable includes a continuous stainless steel tube for wrapping the chemical sensing fiber, and a sheath or two layers of stainless steel armored wire for wrapping the continuous stainless steel tube.

[0014] In some optional embodiments, the chemical sensing fiber is provided with a plurality of fiber optic chemical sensors for measuring and monitoring the composition of downhole fluids, which are distributed at equal intervals.

[0015] The spacing between the fiber optic chemical sensors ranges from 0.5 meters to 5 meters.

[0016] The fiber optic chemical sensor includes a first fiber optic chemical sensor distributed on a distributed chemical sensing fiber and a second fiber optic chemical sensor distributed on an array of chemical sensing grating fibers.

[0017] In some optional embodiments, the fiber optic chemical sensor is a fiber optic chemical sensor suitable for any one or a combination of absorption spectroscopy, fluorescence spectroscopy, phosphorescence spectroscopy, refraction spectroscopy, chemiluminescence spectroscopy, total internal reflection attenuation or evanescent wave spectroscopy, surface plasmon resonance spectroscopy, and Raman spectroscopy.

[0018] In some optional embodiments, the fiber optic chemical sensing downhole fluid component measurement and monitoring optical cable is a first fiber optic chemical sensing downhole fluid component measurement and monitoring optical cable including distributed chemical sensing optical fibers, wherein the distributed chemical sensing optical fibers are bend-insensitive special chemical sensitive optical fibers with a plurality of the fiber optic chemical sensors distributed at equal intervals.

[0019] The fiber optic chemical sensor includes a special chemical-sensitive membrane wrapped around a first fiber core, and a first cladding layer covering the special chemical-sensitive membrane.

[0020] In some optional embodiments, the shape of the special chemical-sensitive membrane includes any one or a combination of thin film type, microsphere type, and cylindrical type.

[0021] In some optional embodiments, the fiber optic chemical sensing downhole fluid component measurement and monitoring optical cable is a second fiber optic chemical sensing downhole fluid component measurement and monitoring optical cable including an array chemical sensing grating optical fiber, wherein the array chemical sensing grating optical fiber is a special chemically sensitive array grating optical fiber with a plurality of the fiber optic chemical sensors distributed at equal intervals.

[0022] The fiber optic chemical sensor includes a special chemical-sensitive grating etched on a second fiber core, and a second cladding covering the special chemical-sensitive grating.

[0023] In some optional embodiments, the continuous stainless steel tube of the fiber optic chemical sensing downhole fluid composition measurement and monitoring cable is provided with a plurality of sampling windows at equal intervals, all located outside the fiber optic chemical sensor, and the length of the sampling windows ranges from 1 cm to 5 cm.

[0024] Another aspect of the present invention provides a downhole fluid composition monitoring method based on fiber optic chemical sensing, applicable to any of the above-described downhole fluid composition monitoring systems based on fiber optic chemical sensing, characterized by comprising the following steps:

[0025] S1: Lay fiber optic chemical sensing downhole fluid composition measurement and monitoring fiber optic cable outside the casing or inside the oil and gas tubing string in open hole or casing well.

[0026] When laying fiber optic chemical sensing downhole fluid composition measurement and monitoring cables in open hole or cased well oil and gas tubing, a counterweight is connected to the tail end of the fiber optic chemical sensing downhole fluid composition measurement and monitoring cables to lower them to the bottom of the well.

[0027] When fiber optic chemical sensing downhole fluid composition measurement and monitoring cables are laid outside the casing of a casing well or outside the oil and gas tubing string inside a casing well, ring clamps are used to fix the fiber optic chemical sensing downhole fluid composition measurement and monitoring cables at equal intervals outside the casing or outside the oil and gas tubing string.

[0028] S2: Connect the first end of the chemical sensing fiber of the fiber optic chemical sensing downhole fluid composition measurement and monitoring cable to the distributed fiber optic chemical sensing port of the composite modulator-demodulator, and connect the first ends of the two multimode fibers of the fiber optic chemical sensing downhole fluid composition measurement and monitoring cable to the temperature sensing dual-ended fiber optic signal input end of the composite modulator-demodulator.

[0029] S3: Start the composite modulation and demodulation instrument to continuously and in real time acquire the optical data of each chemical sensor on the chemical sensing fiber, as well as the temperature data along the two multimode fibers.

[0030] S4: The optical signals continuously measured by each chemical sensor are modulated and demodulated in real time, and converted into chemical composition data of the downhole fluid corresponding to the location of each fiber chemical sensor; at the same time, the temperature data along the two multimode optical fibers are modulated and demodulated to convert into real-time high-precision temperature data along the line.

[0031] S5: The chemical composition data of the downhole fluid modulated and demodulated in real time by the composite modulation and demodulation instrument is corrected for temperature drift based on the real-time high-precision temperature data along the line to obtain the real-time downhole fluid chemical composition data after temperature drift correction, and the corrected real-time downhole fluid chemical composition data is plotted on the three-dimensional well trajectory map with different color marks.

[0032] S6: Perform comprehensive analysis on the corrected real-time downhole fluid chemical composition data;

[0033] For open-hole downhole acquisition of gaseous or liquid fluid chemical composition data: used to identify rocks or minerals composed of different mineral components at different burial depths, thereby understanding the burial depth and thickness distribution of underground mineral resources;

[0034] Chemical composition data of gaseous or liquid fluids collected outside the casing of casing wells are used to determine the proportion of oil, gas, and water in underground oil and gas reservoirs, accurately evaluate the potential of oil and gas reservoirs, optimize development plans, and improve single-well oil and gas production and recovery rate; or, based on long-term monitoring of changes in the chemical composition data of gaseous or liquid fluids, to comprehensively evaluate the fluid migration and changes in each oil and gas producing layer, thereby discovering the distribution of residual oil and gas or remaining oil and gas resources.

[0035] Chemical composition data of gaseous or liquid fluids collected outside the oil and gas tubing string in the casing well, located between the casing and the tubing annulus: used to determine whether fluids from the formation outside the casing have entered the casing well, and accordingly to determine whether the downhole casing has suffered damage; or to determine whether oil and gas from the oil and gas production section have entered between the casing and the tubing annulus, and accordingly to determine whether the separator above the oil and gas production section is intact;

[0036] Chemical composition data of gaseous or liquid fluids collected in the oil and gas tubing within the casing well are used to determine the proportion of oil, gas, and water produced by each oil and gas producing layer, optimize the extraction plan, change the production system, take downhole engineering measures to seal high-water-producing layers, expand the production capacity of oil or gas producing layers, increase the oil and gas production of a single well, and improve the recovery rate.

[0037] The beneficial effects of this invention are:

[0038] This invention involves deploying either a first fiber optic chemical sensing downhole fluid component measurement and monitoring cable, composed of distributed chemical sensing fibers or arrayed chemical sensing grating fibers, or a second fiber optic chemical sensing downhole fluid component measurement and monitoring cable, inside or outside the oil and gas tubing string in the open hole or casing well where measurement or monitoring is required. The distributed chemical sensing fibers or arrayed chemical sensing grating fibers, each containing several fiber optic chemical sensors, are then connected to the distributed fiber optic chemical sensing port of a composite modulation and demodulation instrument. This forms a fiber optic chemical sensing-based downhole fluid component monitoring system. This system overcomes the shortcomings of existing traditional downhole three-phase fluid chemical component measurement technologies, providing a low-cost, high-density, high-precision, and high-reliability method and technology for continuous measurement and long-term real-time dynamic monitoring of downhole fluid chemical component distribution changes. It can be effectively applied to the continuous measurement and long-term dynamic monitoring of downhole fluid chemical anomalies. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the structure of the distributed chemical sensing fiber in an embodiment of the present invention;

[0040] Figure 2 This is a schematic diagram of the structure of the first fiber optic chemical sensing downhole fluid composition measurement and monitoring optical cable in an embodiment of the present invention;

[0041] Figure 3This is a schematic diagram of the structure of the array chemical sensing grating fiber in an embodiment of the present invention;

[0042] Figure 4 This is a schematic diagram of the structure of the second fiber optic chemical sensing downhole fluid composition measurement and monitoring optical cable in an embodiment of the present invention;

[0043] Figure 5 This is a schematic diagram of the fiber optic chemical sensing downhole fluid composition measurement and monitoring cable being deployed in an open-hole well, as described in this embodiment of the invention.

[0044] Figure 6 This is a schematic diagram of the fiber optic chemical sensing downhole fluid composition measurement and monitoring optical cable being laid outside the casing in an embodiment of the present invention.

[0045] Figure 7 This is a schematic diagram of the fiber optic chemical sensing downhole fluid composition measurement and monitoring optical cable being laid outside the oil and gas tubing string in an embodiment of the present invention.

[0046] Figure 8 This is a schematic diagram of the fiber optic chemical sensing downhole fluid composition measurement and monitoring optical cable being laid in the oil and gas tubing string in an embodiment of the present invention;

[0047] Figure label:

[0048] 1-First fiber optic chemical sensing downhole fluid component measurement and monitoring cable; 2-Second fiber optic chemical sensing downhole fluid component measurement and monitoring cable; 3-Composite modulation and demodulation instrument; 41-Distributed chemical sensing fiber; 42-Multimode fiber; 43-U-shaped structure; 44-Stainless steel tube; 45-Sheath; 46-First cladding; 47-First fiber core; 48-Special chemical sensing membrane; 51-Array chemical sensing grating fiber; 52-Second cladding; 53-Second fiber core; 54-Special chemical sensing grating; 6-Counterweight rod; 7-Ring clip. Detailed Implementation

[0049] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0050] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "longitudinal," "lateral," "horizontal," "inner," "outer," "front," "rear," "top," and "bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0051] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set up," "have," "install," "connect," and "connect" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0052] The present invention will now be described in detail with reference to the accompanying drawings and embodiments:

[0053] Example 1:

[0054] like Figures 1 to 8 As shown, this embodiment provides a downhole fluid composition monitoring system based on fiber optic chemical sensing, including a composite modulation and demodulation instrument 3 with distributed fiber optic chemical sensing ports, and a fiber optic chemical sensing downhole fluid composition measurement and monitoring optical cable deployed outside the casing or inside the casing of an open hole or a cased well.

[0055] The fiber optic chemical sensing downhole fluid composition measurement and monitoring cable includes chemical sensing fibers connected to distributed fiber optic chemical sensing ports;

[0056] Chemical sensing optical fibers include distributed chemical sensing optical fibers 41 or arrayed chemical sensing grating optical fibers 51.

[0057] This embodiment involves deploying either a first fiber optic chemical sensing downhole fluid component measurement and monitoring cable 1 (composed of distributed chemical sensing fiber 41 or array chemical sensing grating fiber 51) or a second fiber optic chemical sensing downhole fluid component measurement and monitoring cable 2 to the oil and gas tubing string inside or outside the casing of the open hole or casing well where measurement or monitoring is required. The distributed chemical sensing fiber 41 or array chemical sensing grating fiber 51, which contains several fiber optic chemical sensors, is connected to the distributed fiber optic chemical sensing port of the composite modulation and demodulation instrument 3. This forms a downhole fluid component monitoring system based on fiber optic chemical sensing. This system overcomes the shortcomings of existing traditional downhole three-phase fluid chemical component measurement technologies, providing a low-cost, high-density, high-precision, and high-reliability method and technology for continuous measurement and long-term real-time dynamic monitoring of downhole fluid chemical component distribution changes. It can be effectively applied to the continuous measurement and long-term dynamic monitoring of downhole fluid chemical anomalies.

[0058] In some optional embodiments, the composite modulation and demodulation instrument 3 also has distributed optical fiber temperature sensing ports. The optical fiber chemical sensing downhole fluid component measurement and monitoring cable includes two multimode optical fibers 42 for measuring temperature changes along the line. The tail ends of the two multimode optical fibers 42 are fused into a U-shaped structure 43. The two distributed optical fiber temperature sensing ports of the composite modulation and demodulation instrument 3 are connected to the two multimode optical fibers 42 of the optical fiber chemical sensing downhole fluid component measurement and monitoring cable.

[0059] In some optional embodiments, the fiber optic chemical sensing downhole fluid composition measurement and monitoring cable includes a continuous stainless steel tube 44 for wrapping the chemical sensing fiber, and a sheath 45 or two layers of stainless steel armored wire for wrapping the continuous stainless steel tube 44. In this embodiment, the sheath 45 is made of a high-strength, wear-resistant composite material.

[0060] In some optional embodiments, the chemical sensing fiber is provided with a plurality of fiber optic chemical sensors for measuring and monitoring the composition of downhole fluids, which are distributed at equal intervals.

[0061] The spacing between the fiber optic chemical sensors ranges from 0.5 meters to 5 meters.

[0062] The fiber optic chemical sensor includes a first fiber optic chemical sensor distributed on a distributed chemical sensing fiber 41 and a second fiber optic chemical sensor distributed on an array chemical sensing grating fiber 51.

[0063] In some optional embodiments, the fiber optic chemical sensor is a fiber optic chemical sensor suitable for any one or a combination of absorption spectroscopy, fluorescence spectroscopy, phosphorescence spectroscopy, refraction spectroscopy, chemiluminescence spectroscopy, total internal reflection attenuation or evanescent wave spectroscopy, surface plasmon resonance spectroscopy, and Raman spectroscopy.

[0064] In some optional embodiments, the fiber optic chemical sensing downhole fluid component measurement and monitoring optical cable is a first fiber optic chemical sensing downhole fluid component measurement and monitoring optical cable 1 including a distributed chemical sensing optical fiber 41, wherein the distributed chemical sensing optical fiber 41 is a bend-insensitive special chemical sensitive optical fiber with a plurality of the fiber optic chemical sensors distributed at equal intervals.

[0065] The fiber optic chemical sensor includes a special chemical-sensitive membrane 48 wrapped around a first fiber core 47, and a first cladding 46 covering the special chemical-sensitive membrane 48. In this embodiment, the fiber optic chemical sensor on the distributed chemical sensing fiber 41 is the first fiber optic chemical sensor.

[0066] In fabricating the distributed chemical sensing fiber 41, windows of 1 to 5 centimeters in length need to be stripped from the cladding of the first fiber core 47 at equal intervals, and a special chemical-sensitive film 48 is wrapped around the window. Then, the first cladding 46 is covered over the special chemical-sensitive film 48. In this embodiment, the thickness of the first cladding 46 is the same as the thickness of the special chemical-sensitive film 48 and the cladding thickness of the fiber core; that is, the first fiber optic chemical sensor in this embodiment consists of the special chemical-sensitive film 48 and the first cladding 46.

[0067] In some optional embodiments, the shape of the special chemical sensing membrane 48 includes any one or a combination of thin film type, microsphere type, and cylindrical type. In this embodiment, the special chemical sensing membrane 48 is thin film type, and the thin film type special chemical sensing membrane 48 in this embodiment can be a thin film made of styrene-butadiene-benzene copolymer adsorbing bromothymol blue indicator.

[0068] In some optional embodiments, the fiber optic chemical sensing downhole fluid component measurement and monitoring optical cable is a second fiber optic chemical sensing downhole fluid component measurement and monitoring optical cable 2 including an array chemical sensing grating optical fiber 51, and the array chemical sensing grating optical fiber 51 is a special chemically sensitive array grating optical fiber with a plurality of the fiber optic chemical sensors distributed at equal intervals.

[0069] The fiber optic chemical sensor includes a special chemical-sensitive grating 54 etched on the second fiber core 53, and a second cladding 52 covering the special chemical-sensitive grating 54. In this embodiment, the fiber optic chemical sensor of the array chemical sensing grating fiber 51 is a second fiber optic chemical sensor.

[0070] When fabricating the array chemical sensing grating fiber 51, windows of 1 to 5 centimeters in length need to be stripped from the cladding of its second fiber core 53 at equal intervals, and a special chemical sensing grating 54 is inscribed at the window. Then, the second cladding 52 is covered on the special chemical sensing grating 54. In this embodiment, the second fiber chemical sensor consists of the special chemical sensing grating 54 and the second cladding 52.

[0071] In some optional embodiments, the continuous stainless steel capillary tube 44 of the fiber optic chemical sensing downhole fluid component measurement and monitoring cable has several sampling windows at equal intervals, all located outside the fiber optic chemical sensor. The length of the sampling windows ranges from 1 cm to 5 cm. By setting the sampling windows, the influence of the stainless steel capillary tube 44 on the monitoring and measurement of the fiber optic chemical sensor can be avoided.

[0072] Example 2:

[0073] This embodiment provides a downhole fluid composition monitoring method based on fiber optic chemical sensing, applicable to any of the downhole fluid composition monitoring systems based on fiber optic chemical sensing described above. The method is characterized by the following steps:

[0074] S1: Lay fiber optic chemical sensing downhole fluid composition measurement and monitoring fiber optic cable outside the casing or inside the oil and gas tubing string in open hole or casing well.

[0075] When the fiber optic chemical sensing downhole fluid composition measurement and monitoring cable is laid in the oil and gas tubing string in the open hole or casing well, a counterweight 6 is connected to the tail end of the fiber optic chemical sensing downhole fluid composition measurement and monitoring cable to lower it to the bottom of the well.

[0076] When the fiber optic chemical sensing downhole fluid composition measurement and monitoring cable is laid outside the casing of a casing well or outside the oil and gas tubing string inside the casing well, the fiber optic chemical sensing downhole fluid composition measurement and monitoring cable is fixed at equal intervals outside the casing or outside the oil and gas tubing string using ring clamps 7.

[0077] In this embodiment, the ring clip 7 is a metal ring clip 7 or a ring clip 7 made of high-strength wear-resistant composite material.

[0078] S2: Connect the first end of the chemical sensing fiber of the fiber optic chemical sensing downhole fluid composition measurement and monitoring cable to the distributed fiber optic chemical sensing port of the composite modulation and demodulation instrument 3, and connect the first ends of the two multimode fibers 42 of the fiber optic chemical sensing downhole fluid composition measurement and monitoring cable to the temperature sensing dual-ended fiber optic signal input end of the composite modulation and demodulation instrument 3.

[0079] S3: Start the composite modulation and demodulation instrument 3 to continuously and in real time acquire the optical data of each chemical sensor on the chemical sensing fiber, as well as the temperature data along the two multimode fibers 42.

[0080] S4: The optical signals continuously measured by each chemical sensor are modulated and demodulated in real time, and converted into chemical composition data of the downhole fluid corresponding to the location of each fiber chemical sensor; at the same time, the temperature data along the line of the two multimode optical fibers 42 are modulated and demodulated to convert into real-time high-precision temperature data along the line.

[0081] S5: The chemical composition data of the downhole fluid modulated and demodulated in real time by the composite modulation and demodulation instrument 3 is corrected for temperature drift based on the real-time high-precision temperature data along the line, so as to obtain the real-time downhole fluid chemical composition data after temperature drift correction, and the corrected real-time downhole fluid chemical composition data is plotted on the three-dimensional well trajectory map with different color marks.

[0082] S6: Perform comprehensive analysis on the corrected real-time downhole fluid chemical composition data;

[0083] For open-hole downhole acquisition of gaseous or liquid fluid chemical composition data: used to identify rocks or minerals composed of different mineral components at different burial depths, thereby understanding the burial depth and thickness distribution of underground mineral resources;

[0084] Chemical composition data of gaseous or liquid fluids collected outside the casing of casing wells are used to determine the proportion of oil, gas, and water in underground oil and gas reservoirs, accurately evaluate the potential of oil and gas reservoirs, optimize development plans, and improve single-well oil and gas production and recovery rate; or, based on long-term monitoring of changes in the chemical composition data of gaseous or liquid fluids, to comprehensively evaluate the fluid migration and changes in each oil and gas producing layer, thereby discovering the distribution of residual oil and gas or remaining oil and gas resources.

[0085] Chemical composition data of gaseous or liquid fluids collected outside the oil and gas tubing string in the casing well, located between the casing and the tubing annulus: used to determine whether fluids from the formation outside the casing have entered the casing well, and accordingly to determine whether the downhole casing has suffered damage; or to determine whether oil and gas from the oil and gas production section have entered between the casing and the tubing annulus, and accordingly to determine whether the separator above the oil and gas production section is intact;

[0086] Chemical composition data of gaseous or liquid fluids collected in the oil and gas tubing within the casing well are used to determine the proportion of oil, gas, and water produced by each oil and gas producing layer, optimize the extraction plan, change the production system, take downhole engineering measures to seal high-water-producing layers, expand the production capacity of oil or gas producing layers, increase the oil and gas production of a single well, and improve the recovery rate.

[0087] It is understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A downhole fluid composition monitoring system based on fiber optic chemical sensing, characterized in that, Includes a composite modulation and demodulation instrument (3) with a distributed fiber optic chemical sensing port, and a fiber optic chemical sensing downhole fluid composition measurement and monitoring cable deployed outside the casing or inside the casing of an open hole or a cased well. The fiber optic chemical sensing downhole fluid composition measurement and monitoring cable includes chemical sensing fibers connected to distributed fiber optic chemical sensing ports; The chemical sensing fiber includes a distributed chemical sensing fiber (41) or an array chemical sensing grating fiber (51). The composite modulation and demodulation instrument (3) also has a distributed optical fiber temperature sensing port. The optical fiber chemical sensing downhole fluid component measurement and monitoring cable includes two multimode optical fibers (42) for measuring temperature changes along the line. The tail ends of the two multimode optical fibers (42) are fused into a U-shaped structure (43). The two distributed optical fiber temperature sensing ports of the composite modulation and demodulation instrument (3) are connected to the two multimode optical fibers (42) of the optical fiber chemical sensing downhole fluid component measurement and monitoring cable. The fiber optic chemical sensing downhole fluid composition measurement and monitoring cable includes a continuous stainless steel tube (44) for wrapping the chemical sensing fiber, and a sheath (45) or two layers of stainless steel armored wire for wrapping the continuous stainless steel tube (44). The chemical sensing fiber is equipped with several fiber optic chemical sensors that are evenly spaced on it for measuring and monitoring the composition of downhole fluids. The spacing range of the fiber optic chemical sensors is: 0.5 meters to 5 meters; The fiber optic chemical sensing downhole fluid composition measurement and monitoring optical cable is a first fiber optic chemical sensing downhole fluid composition measurement and monitoring optical cable (1) including a distributed chemical sensing fiber (41). The distributed chemical sensing fiber (41) is a bend-insensitive special chemical sensitive fiber with several fiber optic chemical sensors distributed at equal intervals. The fiber optic chemical sensor includes a special chemical-sensitive membrane (48) wrapped around a first fiber core (47) and a first cladding (46) covering the special chemical-sensitive membrane (48).

2. The downhole fluid composition monitoring system based on fiber optic chemical sensing according to claim 1, characterized in that, The fiber optic chemical sensor is applicable to any one or a combination of absorption spectroscopy, fluorescence spectroscopy, phosphorescence spectroscopy, refraction spectroscopy, chemiluminescence spectroscopy, total internal reflection attenuation or evanescent wave spectroscopy, surface plasmon resonance spectroscopy, and Raman spectroscopy.

3. The downhole fluid composition monitoring system based on fiber optic chemical sensing according to claim 1, characterized in that, The shape of the special chemical sensitive membrane (48) includes any one or a combination of thin film type, microsphere type, and cylindrical type.

4. The downhole fluid composition monitoring system based on fiber optic chemical sensing according to claim 1, characterized in that, The continuous stainless steel tube (44) of the fiber optic chemical sensing downhole fluid composition measurement and monitoring optical cable has several sampling windows at equal intervals, all located outside the fiber optic chemical sensor. The length of the sampling windows ranges from 1 cm to 5 cm.

5. A downhole fluid composition monitoring system based on fiber optic chemical sensing, characterized in that, Includes a composite modulation and demodulation instrument (3) with a distributed fiber optic chemical sensing port, and a fiber optic chemical sensing downhole fluid composition measurement and monitoring cable deployed outside the casing or inside the casing of an open hole or a cased well. The fiber optic chemical sensing downhole fluid composition measurement and monitoring cable includes chemical sensing fibers connected to distributed fiber optic chemical sensing ports; The chemical sensing fiber includes a distributed chemical sensing fiber (41) or an array chemical sensing grating fiber (51). The composite modulation and demodulation instrument (3) also has a distributed optical fiber temperature sensing port. The optical fiber chemical sensing downhole fluid component measurement and monitoring cable includes two multimode optical fibers (42) for measuring temperature changes along the line. The tail ends of the two multimode optical fibers (42) are fused into a U-shaped structure (43). The two distributed optical fiber temperature sensing ports of the composite modulation and demodulation instrument (3) are connected to the two multimode optical fibers (42) of the optical fiber chemical sensing downhole fluid component measurement and monitoring cable. The fiber optic chemical sensing downhole fluid composition measurement and monitoring cable includes a continuous stainless steel tube (44) for wrapping the chemical sensing fiber, and a sheath (45) or two layers of stainless steel armored wire for wrapping the continuous stainless steel tube (44). The chemical sensing fiber is equipped with several fiber optic chemical sensors that are evenly spaced on it for measuring and monitoring the composition of downhole fluids. The spacing range of the fiber optic chemical sensors is: 0.5 meters to 5 meters; The fiber optic chemical sensing downhole fluid component measurement and monitoring optical cable is a second fiber optic chemical sensing downhole fluid component measurement and monitoring optical cable (2) including an array chemical sensing grating optical fiber (51). The array chemical sensing grating optical fiber (51) is a special chemically sensitive array grating optical fiber with several fiber optic chemical sensors distributed at equal intervals. The fiber optic chemical sensor includes a special chemical-sensitive grating (54) etched on a second fiber core (53) and a second cladding (52) covering the special chemical-sensitive grating (54).

6. A downhole fluid component monitoring method based on fiber optic chemical sensing, applicable to the downhole fluid component monitoring system based on fiber optic chemical sensing as described in any one of claims 1-5, characterized in that, Specifically, the following steps are included: S1: Lay fiber optic chemical sensing downhole fluid composition measurement and monitoring fiber optic cable outside the casing or inside the oil and gas tubing string in open hole or casing well. When the fiber optic chemical sensing downhole fluid composition measurement and monitoring cable is laid in the oil and gas tubing string in the open hole or casing well, a counterweight bar (6) is connected to the tail end of the fiber optic chemical sensing downhole fluid composition measurement and monitoring cable and lowered to the bottom of the well. When the fiber optic chemical sensing downhole fluid composition measurement and monitoring cable is laid outside the casing of a casing well or outside the oil and gas tubing string inside the casing well, the fiber optic chemical sensing downhole fluid composition measurement and monitoring cable is fixed at equal intervals outside the casing or outside the oil and gas tubing string using ring clamps (7). S2: Connect the first end of the chemical sensing fiber of the fiber optic chemical sensing downhole fluid composition measurement and monitoring cable to the distributed fiber optic chemical sensing port of the composite modulation and demodulation instrument (3), and connect the first ends of the two multimode fibers (42) of the fiber optic chemical sensing downhole fluid composition measurement and monitoring cable to the temperature sensing dual-end fiber optic signal input end of the composite modulation and demodulation instrument (3). S3: Start the composite modulation and demodulation instrument (3) to continuously and in real time collect the optical data of each chemical sensor on the chemical sensing fiber, as well as the temperature data along the two multimode fibers (42). S4: The optical signals continuously measured by each chemical sensor are modulated and demodulated in real time and converted into chemical composition data of the downhole fluid corresponding to the location of each fiber chemical sensor; at the same time, the temperature data along the line of the two multimode optical fibers (42) are modulated and demodulated to convert into real-time high-precision temperature data along the line. S5: The chemical composition data of the downhole fluid modulated and demodulated in real time by the composite modulation and demodulation instrument (3) is corrected for temperature drift based on the real-time high-precision temperature data along the line, and the real-time downhole fluid chemical composition data after temperature drift correction is obtained. The corrected real-time downhole fluid chemical composition data is then plotted on the three-dimensional well trajectory map using different color marks. S6: Perform comprehensive analysis on the corrected real-time downhole fluid chemical composition data; For open-hole downhole acquisition of gaseous or liquid fluid chemical composition data: used to identify rocks or minerals composed of different mineral components at different burial depths, thereby understanding the burial depth and thickness distribution of underground mineral resources; Chemical composition data of gaseous or liquid fluids collected outside the casing of casing wells are used to determine the proportion of oil, gas, and water in underground oil and gas reservoirs, accurately evaluate the potential of oil and gas reservoirs, optimize development plans, and improve single-well oil and gas production and recovery rate; or, based on long-term monitoring of changes in the chemical composition data of gaseous or liquid fluids, to comprehensively evaluate the fluid migration and changes in each oil and gas producing layer, thereby discovering the distribution of residual oil and gas or remaining oil and gas resources. Chemical composition data of gaseous or liquid fluids collected outside the oil and gas tubing string in the casing well, located between the casing and the tubing annulus: used to determine whether fluids from the formation outside the casing have entered the casing well, and accordingly to determine whether the downhole casing has suffered damage; or to determine whether oil and gas from the oil and gas production section have entered between the casing and the tubing annulus, and accordingly to determine whether the separator above the oil and gas production section is intact; Chemical composition data of gaseous or liquid fluids collected in the oil and gas tubing within the casing well are used to determine the proportion of oil, gas, and water produced by each oil and gas producing layer; and to optimize the production scheme and improve the recovery rate by reducing or blocking the flow of fluid from the water-producing layer into the oil and gas tubing.

Images