A method for monitoring the fluid production profile of multi-stage fracturing in horizontal wells

Abstract

The present invention relates to a method for monitoring the production profile of multi-stage fracturing of horizontal wells, and belongs to the technical field of special monitoring of horizontal wells. Based on carbon dot fluorescent markers, the present invention includes five steps S1-S5, which realize the combination of proppant with carbon dot fluorescent marker coating with segment plug sanding and injection of displacement fluid, so that the carbon dot fluorescent marker is stably retained in the main fracture near the wellbore position without being discharged back, and the oil phase, water phase and gas phase of each fracturing section of the horizontal well of the oil and gas field are quantitatively detected for a long time through wellhead sampling, and the production profile information of each section of the corresponding horizontal well is obtained, so as to realize accurate monitoring of the production profile of the horizontal well, and the operation is safe and convenient, the monitoring is accurate and fast, the stability is strong, the sensitivity is high, the usage is small, and the long-term tracking monitoring has no radioactive pollution, which effectively reduces the monitoring cost. The problems of poor stability, low sensitivity, low test accuracy, large usage, high cost and radioactive pollution existing in the existing chemical monitoring method are solved.

Description

Technical Field

[0001] The invention relates to a method for monitoring a multi-stage fracturing fluid production profile of a horizontal well, belonging to the technical field of special monitoring of horizontal wells. Background Art

[0002] Testing the production profile of horizontal wells to determine the contribution of each section of the horizontal well has very important practical value for providing technical support for subsequent drilling and repeated fracturing and improving the recovery rate of oil and gas resources. At present, the chemical testing methods widely used for testing the production profile of horizontal wells mostly use tracers, which often have the defects of poor stability, low sensitivity, low test accuracy, large usage, high cost and radioactive contamination. It is difficult to undertake the task of accurately monitoring the production profile of horizontal wells, which is not conducive to reducing monitoring costs, optimizing horizontal well density and optimal economic layout of horizontal wells, and realizing efficient exploitation of oil and gas resources. Therefore, it is urgent to develop a method for monitoring the production profile of multi-stage fracturing of horizontal wells that is safe and convenient to use, accurate and fast to monitor, strong in stability, high in sensitivity, small in usage, effectively reduces costs and completely avoids radioactive contamination. Summary of the invention

[0003] The purpose of the present invention is to provide a method for monitoring the production profile of multi-stage fracturing in horizontal wells based on carbon dot fluorescent markers, which is safe and convenient to operate, accurate and fast to monitor, strong in stability, high in sensitivity, small in usage, low in cost and free of radioactive pollution, in order to solve the problems of poor stability, low sensitivity, low test accuracy, large in usage, high in cost and radioactive pollution in the existing chemical monitoring methods.

[0004] The present invention achieves the above-mentioned purpose through the following technical solutions:

[0005] A method for monitoring the fluid production profile of multi-stage fracturing in a horizontal well, based on carbon dot fluorescent markers, is characterized in that it is achieved by comprising the following steps:

[0006] S1: dividing the horizontal well reservoir into fracturing sections, and selecting different carbon dot fluorescent markers according to the number of fracturing sections; the carbon dot fluorescent marker is a fluorescent polymer microsphere loaded with carbon dots, the diameter of the polymer microsphere is 100nm-1μm, the polymer microsphere is one or more combinations of oil, gas and water, and emits fluorescence under ultraviolet-visible light; under the condition of applying an electric field or light pressure, carbon dot fluorescent markers of different sizes emit light of different frequencies;

[0007] S2: Determine the fracturing construction parameters, select the optimal proppant according to the fracturing fluid and the formation closure pressure, and adhere the carbon dot fluorescent marker corresponding to each fracturing layer section to the proppant through an adhesive polymer to form a proppant with a carbon dot fluorescent marker coating;

[0008] S3: Adding sand to the fracturing layer in a plug-like manner, and retaining the proppant with the carbon dot fluorescent marker coating at a certain distance from the main fracture to the wellbore by alternately injecting the sand-carrying fluid and the pre-fluid;

[0009] S4: After the sand addition is completed, an appropriate amount of displacement fluid is injected into the target fracturing layer according to the reservoir properties of the horizontal well to force the sand-carrying fluid in the wellbore into the fracture to prevent the proppant with the carbon dot fluorescent marker coating from being discharged;

[0010] S5: By sampling at the wellhead, the carbon dot fluorescent markers in each fracturing layer are detected to determine the output of each fracturing layer.

[0011] A method for monitoring the fluid production profile of multi-stage fracturing in a horizontal well, characterized in that the carbon dot fluorescent marker in step S1 includes one or more combinations of oil phase, water phase and gas phase, and the modification method or size of the oil phase carbon dot fluorescent marker, water phase carbon dot fluorescent marker and gas phase carbon dot fluorescent marker used in each fracturing layer segment are different.

[0012] A method for monitoring the fluid production profile of multi-stage fracturing of a horizontal well, characterized in that the preparation of the proppant with a carbon dot fluorescent marker coating in step S2 comprises the following steps:

[0013] Step 1: Select an adhesive polymer, wherein the adhesive polymer is one or more of an oil-soluble polymer, a water-soluble polymer and a gas-soluble polymer;

[0014] Step 2: Mix the carbon dot fluorescent marker and the adhesive polymer at a mixing mass ratio of 1:100-100:1, and stir for 1h-6h to obtain a polymer mixture;

[0015] Step 3: Mix the proppant with the polymer mixture at a mass ratio of 10:1-1:10, stir for 1h-6h, and dry the solid product at 50°C-100°C for 10h-30h to obtain the proppant with the carbon dot fluorescent marker coating, wherein the coating has a thickness of 10μm-30μm.

[0016] A method for monitoring the fluid production profile of multi-stage fracturing of a horizontal well, characterized in that the proppant in step S2 is preferably one or a combination of ceramsite sand, ceramsite, and quartz sand.

[0017] A method for monitoring the fluid production profile of multi-stage fracturing in a horizontal well, characterized in that the plug-type sand addition in step S3 includes three stages:

[0018] The first stage is the main sand adding stage: add ordinary small-size proppant to the target fracturing layer segment plug, with a sand ratio of 3-8%, and add sand to 60-70% of the designed sand volume; then add ordinary medium-size proppant, with a sand ratio of 8-15%, and add sand to 80-90% of the designed sand volume.

[0019] The second stage is the auxiliary body sand adding stage: adding proppant with carbon dot fluorescent marker coating to the target fracturing layer segment plug, the sand ratio is 8-15%, accounting for 5-10% of the total proppant added; the proppant with carbon dot fluorescent marker coating pumped into each segment is different, but the addition amount and construction method are consistent.

[0020] The third stage is the tail sand addition stage: ordinary large-size proppant is continuously added with a sand ratio of 8-15% until the designed total sand volume is reached.

[0021] A method for monitoring the fluid production profile of multi-stage fracturing in a horizontal well, characterized in that when injecting displacement fluid in the step S4, a sufficient amount of displacement fluid is injected into a dense reservoir to prevent sand from settling at the bottom of the well, and an appropriate amount of displacement fluid is injected into a non-dense formation to prevent a large amount of proppant backflow in the fracture.

[0022] A method for monitoring the fluid production profile of multi-stage fracturing in a horizontal well, characterized in that the wellhead sampling in step S5 is carried out to separate the carbon dot fluorescent marker, and the type and content of the carbon dot fluorescent marker are detected and calculated by a specific instrument to obtain the output of each fracturing layer section of the horizontal well; during the entire monitoring process, no intervention or suspension of production is required, and the sampling cycle is: sampling once a day during the return period, sampling once a week at the beginning of the production period, and sampling once a month after one year of production; the monitoring period is 1-60 months.

[0023] The beneficial effects of the present invention compared with the prior art are:

[0024] The method for monitoring the production profile of multi-stage fracturing in horizontal wells is based on carbon dot fluorescent markers. The present invention includes five steps S1-S5, which realize the combination of proppant with carbon dot fluorescent marker coating with segment plug sanding and injection of displacement fluid, so that the carbon dot fluorescent marker is stably retained near the wellbore position of the main fracture and is not discharged back. Through wellhead sampling, the production profile of the horizontal well is accurately monitored, and the operation is safe and convenient, the monitoring is accurate and fast, the stability is strong, the sensitivity is high, the usage is small, and there is no radioactive pollution in long-term tracking monitoring, which effectively reduces the monitoring cost. The problems of poor stability, low sensitivity, low test accuracy, large usage, high cost and radioactive pollution in the existing chemical monitoring method are solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the workflow of the present invention;

[0026] Figure 2 It is a schematic diagram of the physical structure of the proppant with a carbon dot fluorescent marker coating of the present invention;

[0027] Figure 3 It is a schematic diagram of the planar structure of the proppant with a carbon dot fluorescent marker coating of the present invention;

[0028] Figure 4 It is a schematic diagram of the proppant with carbon dot fluorescent marker coating of the present invention being retained in the fracture near the wellbore. DETAILED DESCRIPTION

[0029] The following is a further detailed description of the method for monitoring the production profile of multi-stage fracturing in horizontal wells in conjunction with the accompanying drawings (see Figure 1-4 ):

[0030] A method for monitoring the fluid production profile of multi-stage fracturing in a horizontal well, based on carbon dot fluorescent markers, is characterized in that it is achieved by comprising the following steps:

[0031] S1: dividing the horizontal well reservoir into fracturing sections, and selecting different carbon dot fluorescent markers according to the number of fracturing sections; the carbon dot fluorescent marker is a fluorescent polymer microsphere loaded with carbon dots, the diameter of the polymer microsphere is 100nm-1μm, the polymer microsphere is one or more combinations of oil, gas and water, and emits fluorescence under ultraviolet-visible light; under the condition of applying an electric field or light pressure, carbon dot fluorescent markers of different sizes emit light of different frequencies;

[0032] S2: Determine the fracturing construction parameters, select the optimal proppant according to the fracturing fluid and the formation closure pressure, and adhere the carbon dot fluorescent marker corresponding to each fracturing layer section to the proppant through an adhesive polymer to form a proppant with a carbon dot fluorescent marker coating;

[0033] S3: Adding sand to the fracturing layer in a plug-like manner, and retaining the proppant with the carbon dot fluorescent marker coating at a certain distance from the main fracture to the wellbore by alternately injecting the sand-carrying fluid and the pre-fluid;

[0034] S4: After the sand addition is completed, an appropriate amount of displacement fluid is injected into the target fracturing layer according to the reservoir properties of the horizontal well to force the sand-carrying fluid in the wellbore into the fracture to prevent the proppant with the carbon dot fluorescent marker coating from being discharged;

[0035] S5: By sampling at the wellhead, the carbon dot fluorescent markers in each fracturing layer are detected to determine the output of each fracturing layer.

[0036] A method for monitoring the fluid production profile of multi-stage fracturing in a horizontal well, characterized in that the carbon dot fluorescent marker in step S1 includes one or more combinations of oil phase, water phase and gas phase, and the modification methods or sizes of the oil phase carbon dot fluorescent marker, water phase carbon dot fluorescent marker and gas phase carbon dot fluorescent marker used in each fracturing layer segment are different.

[0037] A method for monitoring the fluid production profile of multi-stage fracturing of a horizontal well, characterized in that the preparation of the proppant with a carbon dot fluorescent marker coating in step S2 comprises the following steps:

[0038] Step 1: Select an adhesive polymer, wherein the adhesive polymer is one or more of an oil-soluble polymer, a water-soluble polymer and a gas-soluble polymer;

[0039] Step 2: Mix the carbon dot fluorescent marker and the adhesive polymer at a mixing mass ratio of 1:100-100:1, and stir for 1h-6h to obtain a polymer mixture;

[0040] Step 3: Mix the proppant with the polymer mixture at a mass ratio of 10:1-1:10, stir for 1h-6h, and dry the solid product at 50°C-100°C for 10h-30h to obtain the proppant with the carbon dot fluorescent marker coating, wherein the coating has a thickness of 10μm-30μm.

[0041] A method for monitoring the fluid production profile of multi-stage fracturing of a horizontal well, characterized in that the proppant in step S2 is preferably one or a combination of ceramsite sand, ceramsite, and quartz sand.

[0042] A method for monitoring the fluid production profile of multi-stage fracturing in a horizontal well, characterized in that the plug-type sand addition in step S3 includes three stages:

[0043] The first stage is the main sand adding stage: add ordinary small-size proppant to the target fracturing layer segment plug, with a sand ratio of 3-8%, and add sand to 60-70% of the designed sand volume; then add ordinary medium-size proppant, with a sand ratio of 8-15%, and add sand to 80-90% of the designed sand volume.

[0044] The second stage is the auxiliary body sand adding stage: adding proppant with carbon dot fluorescent marker coating to the target fracturing layer segment plug, the sand ratio is 8-15%, accounting for 5-10% of the total proppant added; the proppant with carbon dot fluorescent marker coating pumped into each segment is different, but the addition amount and construction method are consistent.

[0045] The third stage is the tail sand addition stage: ordinary large-size proppant is continuously added with a sand ratio of 8-15% until the designed total sand volume is reached.

[0046] A method for monitoring the fluid production profile of multi-stage fracturing in a horizontal well, characterized in that when injecting displacement fluid in the step S4, a sufficient amount of displacement fluid is injected into a dense reservoir to prevent sand from settling at the bottom of the well, and an appropriate amount of displacement fluid is injected into a non-dense formation to prevent a large amount of proppant backflow in the fracture.

[0047] A method for monitoring the fluid production profile of multi-stage fracturing in a horizontal well, characterized in that the wellhead sampling in step S5 is carried out to separate the carbon dot fluorescent marker, and the type and content of the carbon dot fluorescent marker are detected and calculated by a specific instrument to obtain the output of each fracturing layer section of the horizontal well; during the entire monitoring process, no intervention or suspension of production is required, and the sampling cycle is: sampling once a day during the return period, sampling once a week at the beginning of the production period, and sampling once a month after one year of production; the monitoring period is 1-60 months.

[0048] Embodiment 1

[0049] In the first embodiment, the method for monitoring the production profile of multi-stage fracturing of a horizontal well is described by taking the staged fracturing of a tight oil horizontal well as an example. Figure 1 As shown, the following steps are included:

[0050] S1: Divide the reservoir into fracturing sections and select different carbon dot fluorescent markers according to the number of fracturing sections of the horizontal well;

[0051] In the present embodiment 1, the number of fracturing transformation sections is 8, and the carbon dot fluorescent markers selected are a combination of oil phase carbon dot fluorescent markers and water phase carbon dot fluorescent markers, wherein there are 8 oil phase carbon dot fluorescent markers and 8 water phase carbon dot fluorescent markers, and each test section selects one oil phase carbon dot fluorescent marker and one water phase carbon dot fluorescent marker, and the oil phase carbon dot fluorescent markers selected for each test section are different from each other, and the water phase carbon dot fluorescent markers are different from each other.

[0052] S2: Determine the fracturing construction parameters, select the optimal proppant according to the fracturing fluid and the formation closure pressure, and adhere the carbon dot fluorescent marker corresponding to each section to the proppant through an adhesive polymer to form a proppant with a carbon dot fluorescent marker coating;

[0053] In the first embodiment of the present invention, low viscosity fracturing fluid (1-3 mPa·S) is used for fracturing, and the minimum horizontal principal stress of fracturing is about 20MPa. 70 / 100 mesh quartz sand + 40 / 70 quartz sand are selected as proppants. 70 / 100 mesh quartz sand is used to support microcracks, and 40 / 70 mesh quartz sand is used to support main cracks. 40 / 70 mesh quartz sand is used as a carrier. Each oil-phase carbon dot fluorescent marker is mixed with an oil-soluble polymer at a ratio of 1:50 for 3 hours to form a mixed solution. Each water-phase carbon dot fluorescent marker is mixed with a water-soluble polymer at a ratio of 1:50 for 3 hours to form a mixed solution. The proppant used in each fracturing layer section is mixed with the above mixed solution at a ratio of 1:1 for 3 hours, and then the solid particles are filtered to obtain a solid product. The obtained solid product is dried at 50°C for 20 hours to obtain a proppant with a carbon dot fluorescent marker coating (see Figure 2 and Figure 3 ).

[0054] S3: Add sand to the fractured layer in a plug-like manner, and retain the proppant with carbon dot fluorescent marker coating at a certain distance from the main fracture close to the wellbore by alternately injecting sand-carrying fluid and pre-fluid (see Figure 4 );

[0055] In the first embodiment, in the main sand adding stage of a certain layer section, the sand-carrying fluid and the pre-fluid are alternately injected into the target fracturing layer section for several times. During the single injection of the sand-carrying fluid, the sand ratio of the sand-carrying fluid remains unchanged, and the proppant of the injected sand-carrying fluid includes 70 / 100 mesh quartz sand, reaching 60% of the designed sand volume; 40 / 70 mesh quartz sand, reaching 85% of the designed sand volume. In the auxiliary sand adding stage, the proppant with a carbon dot fluorescent marker coating is added to the target fracturing layer section, accounting for 5% of the total amount of proppant added; in the tail additional sand adding stage, 10% of 20 / 40 mesh quartz sand is continuously added.

[0056] S4: After the sand addition is completed, an appropriate amount of displacement fluid is injected into the target fracturing layer according to the reservoir physical properties to force the sand-carrying fluid in the wellbore into the fracture, so that the proppant with the carbon dot fluorescent marker coating is not discharged back;

[0057] In this embodiment, the displacement fluid volume is 30m 3 , accounting for 2.0% of the total fracturing fluid.

[0058] S5: The production of each section is determined by sampling at the wellhead and detecting the carbon dot fluorescent markers therein.

[0059] In the first embodiment, the output fluid is collected at the wellhead of the horizontal well, with the sampling volume of not less than 500 ml each time. The type and quantity of each carbon dot fluorescent marker in the output fluid are measured by a specific instrument to determine the output of each section of the horizontal well.

[0060] Embodiment 2

[0061] In the second embodiment, taking the staged fracturing of a shale oil horizontal well as an example, a method for monitoring the production profile of multi-stage fracturing of a horizontal well based on carbon dot fluorescent markers is described, including the following steps:

[0062] Step 1. In this embodiment, the number of fracturing transformation sections is 12, and the carbon dot fluorescent markers selected are a combination of oil phase carbon dot fluorescent markers and water phase carbon dot fluorescent markers, wherein there are 12 oil phase carbon dot fluorescent markers and 12 water phase carbon dot fluorescent markers, and each test section selects one oil phase carbon dot fluorescent marker and one water phase carbon dot fluorescent marker, and the oil phase carbon dot fluorescent markers selected for each test section are different from each other, and the water phase carbon dot fluorescent markers are different from each other.

[0063] Step 2, in the second embodiment, medium viscosity fracturing fluid (5-9mPa·S) is used as the main material, and a small amount of low viscosity fracturing fluid (1-3mPa·S) is used for fracturing. The minimum horizontal principal stress is about 47MPa. 70 / 100 mesh ceramsite + 40 / 70 ceramsite is selected as a proppant, 70 / 140 mesh ceramsite is used to support microcracks, 40 / 70 ceramsite is used to support main cracks, and 40 / 70 mesh ceramsite is used as a carrier. Each oil-phase carbon dot fluorescent marker is mixed and stirred with an oil-soluble polymer at a ratio of 1:30 for 4 hours to form a mixed solution, and each water-phase carbon dot fluorescent marker is mixed and stirred with a water-soluble polymer at a ratio of 1:30 for 4 hours to form a mixed solution. The proppant used in each fracturing stage is mixed and stirred with the above-mentioned mixed solution at a ratio of 1:1 for 4 hours, and then the solid particles are filtered, and then the solid product is obtained by filtering. The obtained solid product is dried at 50°C for 30 hours to obtain a proppant with a carbon dot fluorescent marker coating.

[0064] Step 3, in the second embodiment, in the main sand adding stage of a certain section of the sand adding process, the sand carrying fluid and the pre-fluid are alternately injected into the target fracturing layer several times. During the single injection of the sand carrying fluid, the sand ratio of the sand carrying fluid remains unchanged, and the proppant of the injected sand carrying fluid includes 70 / 100 mesh ceramsite, reaching 60% of the designed sand volume; 40 / 70 mesh ceramsite, reaching 85% of the designed sand volume. In the auxiliary sand adding stage, the proppant with a carbon dot fluorescent marker coating is added to the target fracturing layer segment in a plug-like manner, accounting for 5% of the total amount of proppant added. In the tail additional sand adding stage, 10% of 20 / 40 mesh ceramsite is continuously added.

[0065] Step 4: In the second embodiment, the displacement fluid volume is 80m 3 , accounting for 3.5% of the total fracturing fluid.

[0066] Step 5, in the second embodiment, the output fluid is collected at the wellhead of the horizontal well, and the sampling volume each time is not less than 500 ml. The type and quantity of each carbon dot fluorescent marker in the output fluid are determined by specific instrument detection to determine the output of each section of the horizontal well.

[0067] Embodiment 3

[0068] In the third embodiment, taking the staged fracturing of a shale gas horizontal well as an example, a method for monitoring the production profile of multi-stage fracturing of a horizontal well based on carbon dot fluorescent markers is described, including the following steps:

[0069] Step 1. In the present third embodiment, the number of fracturing transformation sections is 23, and the carbon dot fluorescent markers selected are a combination of water-phase carbon dot fluorescent markers and gas-phase carbon dot fluorescent markers, wherein there are 23 water-phase carbon dot fluorescent markers and 23 gas-phase carbon dot fluorescent markers. Each test section selects one water-phase carbon dot fluorescent marker and one gas-phase carbon dot fluorescent marker. The water-phase carbon dot fluorescent markers selected for each test section are different from each other, and the gas-phase carbon dot fluorescent markers are different from each other.

[0070] Step 2, in this embodiment 3, low viscosity fracturing fluid (1-3 mPa·S) is used as the main material, and a small amount of medium viscosity fracturing fluid (5-9 mPa·S) is used for fracturing. The minimum horizontal principal stress is about 50 MPa. 70 / 140 mesh quartz sand + 40 / 70 ceramsite is selected as a proppant, 70 / 140 mesh quartz sand is used to support microcracks, 40 / 70 ceramsite is used to support main cracks, and 40 / 70 mesh ceramsite is used as a carrier. Each water-phase carbon dot fluorescent marker is mixed and stirred with a water-soluble polymer at a ratio of 1:30 for 4 hours to form a mixed solution, and each gas-phase carbon dot fluorescent marker is mixed and stirred with a gas-soluble polymer at a ratio of 1:30 for 4 hours to form a mixed solution. The proppant used in each fracturing stage is mixed and stirred with the above-mentioned mixed solution at a ratio of 1:1 for 4 hours, and then the solid particles are filtered, and then the solid product is filtered to obtain a solid product, and the obtained solid product is dried at 50°C for 30 hours to obtain a proppant with a carbon dot fluorescent marker coating.

[0071] Step 3, in the third embodiment, during the sand adding process of a certain section, in the main sand adding stage, the sand carrying fluid and the pre-fluid are alternately injected into the target fracturing layer section for several times. During the single injection of the sand carrying fluid, the sand ratio of the sand carrying fluid remains unchanged, and the proppant of the injected sand carrying fluid includes 70 / 140 mesh quartz sand, reaching 60% of the designed sand volume, and 40 / 70 mesh ceramsite, reaching 85% of the designed sand volume. In the auxiliary sand adding stage, the proppant with a carbon dot fluorescent marker coating is added to the target fracturing layer section, accounting for 5% of the total amount of proppant added. In the tail additional sand adding stage, 10% of 20 / 40 mesh ceramsite is continuously added.

[0072] Step 4: In the third embodiment, the displacement fluid volume is 60m3 , accounting for 3.0% of the total fracturing fluid.

[0073] Step 5. In the third embodiment, the produced fluid is collected at the wellhead of the horizontal well, and the sampling volume each time is not less than 500 ml. The gas sampling is carried out through the gas filter installed at the wellhead. The type and quantity of each carbon dot fluorescent marker in the produced fluid and gas sample are determined by specific instrument detection to determine the output situation of each section of the horizontal well.

[0074] The above description is only a preferred embodiment of the present invention. The above examples do not impose any form of limitation on the essential content of the present invention. After reading this specification, ordinary technicians in the technical field may make any simple modifications or deformations to the above specific implementation methods based on the technical essence of the present invention, as well as any equivalent embodiments that may be changed or modified into equivalent changes using the technical content disclosed above, without departing from the essence and scope of the present invention, which still fall within the scope of the technical solution of the present invention.

Claims

1. A method for monitoring the fluid production profile of multi-stage fracturing in horizontal wells, based on carbon dot fluorescent markers, characterized in that: It is achieved by including the following steps: S1: dividing the horizontal well reservoir into fracturing sections, and selecting different carbon dot fluorescent markers according to the number of fracturing sections; the carbon dot fluorescent marker is a fluorescent polymer microsphere loaded with carbon dots, the diameter of the polymer microsphere is 100nm-1μm, the polymer microsphere is one or more combinations of oil, gas and water, and emits fluorescence under ultraviolet-visible light; under the condition of applying an electric field or light pressure, carbon dot fluorescent markers of different sizes emit light of different frequencies; S2: Determine the fracturing construction parameters, select the optimal proppant according to the fracturing fluid and the formation closure pressure, and adhere the carbon dot fluorescent marker corresponding to each fracturing layer section to the proppant through an adhesive polymer to form a proppant with a carbon dot fluorescent marker coating; S3: Adding sand to the fracturing layer in a plug-like manner, and retaining the proppant with the carbon dot fluorescent marker coating at a certain distance from the main fracture to the wellbore by alternately injecting the sand-carrying fluid and the pre-fluid; S4: After the sand addition is completed, an appropriate amount of displacement fluid is injected into the target fracturing layer according to the reservoir properties of the horizontal well to force the sand-carrying fluid in the wellbore into the fracture to prevent the proppant with the carbon dot fluorescent marker coating from being discharged; S5: sampling at the wellhead to detect the carbon dot fluorescent markers in each fractured layer section to determine the output of each fractured layer section; The carbon dot fluorescent markers in step S1 include one or more combinations of oil phase, water phase and gas phase, and the modification methods or sizes of the oil phase carbon dot fluorescent markers, water phase carbon dot fluorescent markers and gas phase carbon dot fluorescent markers used in each fracturing layer section are different; The slug-type sand adding in step S3 includes three stages: The first stage is the main sand adding stage: add ordinary small-size proppant to the target fracturing layer segment plug, with a sand ratio of 3-8%, and add sand to 60-70% of the designed sand volume; then add ordinary medium-size proppant, with a sand ratio of 8-15%, and add sand to 80-90% of the designed sand volume; The second stage is the secondary body sanding stage: adding proppant with carbon dot fluorescent marker coating to the target fracturing layer segment plug, with a sand ratio of 8-15%, accounting for 5-10% of the total proppant added; the proppant with carbon dot fluorescent marker coating pumped into each segment is different, but the addition amount and construction method are consistent; The third stage is the tail sand addition stage: ordinary large-size proppant is continuously added with a sand ratio of 8-15% until the designed total sand volume is reached.

2. A method for monitoring the fluid production profile of multi-stage fracturing in a horizontal well according to claim 1, characterized in that: The preparation of the proppant with the carbon dot fluorescent marker coating in step S2 comprises the following steps: Step 1: Select an adhesive polymer, wherein the adhesive polymer is one or more of an oil-soluble polymer, a water-soluble polymer and a gas-soluble polymer; Step 2: Mix the carbon dot fluorescent marker and the adhesive polymer at a mixing mass ratio of 1:100-100:1, and stir for 1h-6h to obtain a polymer mixture; Step 3: Mix the proppant with the polymer mixture at a mass ratio of 10:1-1:10, stir for 1h-6h, and dry the solid product at 50°C-100°C for 10h-30h to obtain the proppant with the carbon dot fluorescent marker coating, wherein the coating has a thickness of 10μm-30μm.

3. The method for monitoring the fluid production profile of multi-stage fracturing in a horizontal well according to claim 1, characterized in that: The proppant in step S2 is preferably one or a combination of ceramsite sand, ceramsite and quartz sand.

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