Method for testing liquid production profile of horizontal well by using quantum dot tracer

Abstract

The embodiment of the present application provides a method for testing horizontal well liquid production profile by using quantum dot tracer, and relates to the field of detection and analysis. The method for testing horizontal well liquid production profile by using quantum dot tracer comprises the following steps: S1, selecting different quantum dot tracers according to the composition of fracturing fluid and the number of fracturing sections of the horizontal well; S3, determining the dosage of the quantum dot tracer of each fracturing section according to the requirement of the construction site; S5, mixing the required amount of the quantum dot tracer into the fracturing fluid and pumping to the bottom layer; wherein, different quantum dot tracers are used in each fracturing section; S7, sampling at the flowback port and analyzing to determine the production condition of each section. The method can better realize the test of the horizontal well liquid production profile.

Description

Technical Field

[0001] This invention relates to the field of detection and analysis, and more specifically, to a method for testing the production profile of horizontal wells using quantum dot tracers. Background Technology

[0002] In recent years, with advancements in drilling, completion, and reservoir stimulation technologies, the application of horizontal wells in unconventional oil and gas reservoirs in China has increased significantly, transforming a large amount of untapped reserves into recoverable reserves. Horizontal well production has become one of the main technical means to improve single-well production and transform development methods. However, as production continues, due to the influence of reservoir fracture development and water injection in low-permeability reservoirs, many horizontal wells have experienced a rapid decline in oil production due to rising water cut. Furthermore, after water is produced, the location of the water-producing layer cannot be determined, making it impossible to implement targeted water shut-off measures, resulting in a deterioration in the overall reservoir development effect. To improve the productivity of horizontal wells, production profile testing is typically used to obtain information on the production status of downhole producing layers.

[0003] Horizontal well production profile testing methods mainly include mechanical testing and chemical testing. Mechanical testing involves measuring the production status of each section using downhole equipment. In the early stages of oilfield development, methods using capacitive sensors, conductivity sensors, or turbine flow meters to measure water holdup achieved certain results. However, with the continuous development of the oilfield, it gradually enters a high water-cut development stage, and the overall water cut of the wells continues to increase. The above-mentioned measuring equipment can no longer meet the logging requirements for high or ultra-high water cut wells. Moreover, after tertiary recovery, the viscosity of the produced fluid increases, and the turbine flow meter measurement method can no longer meet the logging requirements under complex conditions. In recent years, horizontal well imaging logging instruments based on array probes have been developed, but these technologies are mainly aimed at high-yield wells and are difficult to apply to low-yield wells in China. Furthermore, they cannot meet the logging requirements for production profiles of horizontal wells in unconventional reservoirs.

[0004] Chemical testing involves injecting tracers into the formation, followed by wellhead sampling and analysis after the test. Currently, there are four main types of traditional tracers in China: chemical tracers, primarily composed of inorganic salts, dyes, halogenated hydrocarbons, and alcohols. These are characterized by formation adsorption, susceptibility to background interference, large usage volumes, and qualitative analysis only. Furthermore, chemical tracers can only trace oil and water phases, not gaseous phases. Isotope tracers include both radioactive and non-radioactive isotopes. Radioactive isotopes include tritium water, tritized alkanes, and tritized alcohols, which have significant environmental impacts and their application is subject to numerous limitations. Radioactive isotopes, mainly composed of non-radioactive isotopes that can be activated, have limited applications, require cumbersome detection methods, and are expensive. Fluorescent particle tracers, mainly composed of micron-sized, submicron-sized, and nano-sized powders, are detected using a spectroscopy system. However, these tracers require large quantities and are susceptible to bacterial contamination, and their thermal stability is poor, so qualitative analysis can only be performed based on fluorescence concentration. Trace element tracers, mainly composed of BK series trace tracers, are rare earth metal chelates. The oil phase consists of solid particles that are prone to decomposition and precipitation, leading to measurement errors.

[0005] The aforementioned mechanical and chemical testing methods have several drawbacks, including short evaluation cycles, long analysis cycles, the inability to perform qualitative analysis and quantitative description, and limitations imposed by wellbore trajectory and wellbore conditions, which pose operational risks. Summary of the Invention

[0006] The present invention includes, for example, providing a method for testing the production profile of a horizontal well using a quantum dot tracer, which can better achieve the testing of the production profile of a horizontal well using a quantum dot tracer.

[0007] The embodiments of the present invention can be implemented as follows:

[0008] In a first aspect, the present invention provides a method for testing the production profile of a horizontal well using a quantum dot tracer, the method comprising:

[0009] S1. Select different quantum dot tracers based on the composition of the fracturing fluid and the number of fracturing stages in the horizontal well;

[0010] S3. Determine the amount of quantum dot tracer used in each fracturing section based on the needs of the construction site;

[0011] S5. The required amount of the quantum dot tracer is mixed into the fracturing fluid and pumped to the bottom layer; wherein, a different quantum dot tracer is used for each fracturing section;

[0012] S7. Take samples at the return outlet and analyze them to determine the output of each section.

[0013] In an optional implementation, step S1 includes the following sub-steps:

[0014] S11. Different quantum dot tracers were diluted with water to obtain control groups, and the light intensity of each quantum dot tracer in the control groups was measured.

[0015] S13. Based on the type of fracturing fluid determined during construction, different quantum dot tracers are mixed with the fracturing fluid to obtain test groups, and the light intensity of the quantum dot tracers in the test groups is detected.

[0016] S13. Based on the comparison between the light intensity of the control group and the light intensity of the test group, quantum dot tracers whose light intensity is not affected by the fracturing fluid are screened out.

[0017] In an optional implementation, step S3 includes the following sub-steps:

[0018] S31. Determine the minimum detection concentration of each quantum dot tracer in the corresponding fracturing fluid through experiments;

[0019] S33. Determine the amount of quantum tracer based on the amount of fracturing fluid used in each fracturing section and the minimum detection limit of the corresponding quantum tracer.

[0020] In an optional implementation, step S5 includes the following sub-steps:

[0021] S51. Dissolve the required amount of quantum dot tracer in water;

[0022] S53. Use a sand mixing truck to begin injecting fracturing fluid into the fracturing section;

[0023] S55. After the displacement of the sand mixing truck stabilizes, the water-soluble quantum dot tracer is pumped into the sand mixing truck according to the preset displacement to mix evenly with the fracturing fluid, so that the quantum dot tracer is injected into the formation along with the fracturing pressure.

[0024] In an optional implementation, step S7 includes the following sub-steps:

[0025] S71. At the initial stage of the return process, take a test sample once at the first preset time interval, and take multiple groups each time;

[0026] S73. After the backflow stabilizes, take a test sample once at the second preset time interval until the sampling and discharge are completed, and take multiple groups each time.

[0027] S75. The collected test samples are processed and analyzed in groups to determine the output of each segment; wherein the second preset time is greater than the first preset time.

[0028] In an optional implementation, the first preset time is two hours and the second preset time is five hours.

[0029] In an optional implementation, step S75 includes the following sub-steps:

[0030] S751. Centrifuge each set of test samples collected in each batch to obtain a test sample solution;

[0031] S753. The solution of the obtained test sample is purified to obtain a purified test solution;

[0032] S755. The purified detection solution was tested using a fluorescence spectrophotometer, and the test data was analyzed to obtain the type, concentration, and proportion of quantum dot tracer for each detection solution.

[0033] S755. Calculate the contribution rate of liquid production in each fracturing stage based on the type, concentration, and proportion of quantum dot tracers.

[0034] In an optional implementation, step S31 includes the following sub-steps:

[0035] S311. Establish curves of light intensity versus concentration for each fracturing fluid and its corresponding quantum dot tracer;

[0036] S313. Determine the minimum detection concentration based on the established curve of light intensity versus concentration of the quantum dot tracer.

[0037] In an optional implementation, step S13 includes the following sub-steps:

[0038] S131. Based on the type of fracturing fluid determined during construction, different quantum dot tracers are mixed with the fracturing fluid one by one;

[0039] S133. The mixtures of different quantum dot tracers and fracturing fluids are placed in a preset environment, and the light intensity of the quantum dot tracers in each test group is tested one by one.

[0040] In an optional implementation, the preset environment is ambient temperature and atmospheric pressure; and / or, formation temperature and atmospheric pressure; and / or, formation temperature and formation pressure.

[0041] The beneficial effects of the method for testing the production profile of horizontal wells using quantum dot tracers provided in this invention include, for example:

[0042] Because fracturing fluids contain drag reducers, flow aids, clay stabilizers, and breaker agents, each chemical reagent, due to its structure and functional group composition, can affect the intensity of quantum dots to varying degrees. For example, breaker agents, being persulfates, can damage the benzene rings of the quantum dot luminescent material, thus directly quenching the quantum dots. This application avoids the problem of test failure caused by the fracturing fluid's influence on the quantum dot intensity by selecting different quantum dot tracers based on the fracturing fluid composition and the number of fracturing stages in the horizontal well before testing. Secondly, the amount of quantum dot tracer can be calculated from the amount of fracturing fluid used, enabling quantitative measurement. Furthermore, the quantum dot tracer can be uniformly mixed into the fracturing fluid, allowing for precise marking of each stage and ensuring collection during flowback. Attached Figure Description

[0043] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a schematic flowchart of a method for testing the production profile of a horizontal well using quantum dot tracers, provided in an embodiment of the present invention. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0046] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0047] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0048] It should be noted that, where there is no conflict, the features in the embodiments of the present invention can be combined with each other.

[0049] Example

[0050] Please refer to Figure 1 This invention provides a method for testing the production profile of a horizontal well using quantum dot tracers, the method comprising:

[0051] S1. Select different quantum dot tracers based on the composition of the fracturing fluid and the number of fracturing stages in the horizontal well;

[0052] S3. Determine the amount of quantum dot tracer used in each fracturing section based on the needs of the construction site;

[0053] S5. The required amount of the quantum dot tracer is mixed into the fracturing fluid and pumped to the bottom layer; wherein, a different quantum dot tracer is used for each fracturing section;

[0054] S7. Take samples at the return outlet and analyze them to determine the output of each section.

[0055] Because fracturing fluids contain drag reducers, flow aids, clay stabilizers, and breaker agents, each chemical reagent, due to its structure and group composition, can affect the quantum dot light intensity to varying degrees. For example, the breaker agent, being a persulfate, can damage the benzene ring of the quantum dot luminescent element, thus directly quenching the quantum dots. This application avoids the problem of test failure caused by the fracturing fluid's influence on the quantum dot light intensity by selecting different quantum dot tracers based on the fracturing fluid composition and the number of fracturing stages in the horizontal well before testing. Secondly, by determining the amount of quantum dot tracer used in each fracturing stage according to the needs of the construction site, quantitative measurement of the fracturing fluid dosage can be achieved. Furthermore, the quantum dot tracer can be uniformly mixed into the fracturing fluid, allowing the quantum dots to accurately mark each stage and ensuring their collection during flowback.

[0056] Please refer to Figure 1 In this embodiment, step S1 includes the following sub-steps:

[0057] S11. Different quantum dot tracers were diluted with water to obtain control groups, and the light intensity of each quantum dot tracer in the control groups was measured.

[0058] S13. Based on the type of fracturing fluid determined during construction, different quantum dot tracers are mixed with the fracturing fluid to obtain test groups, and the light intensity of the quantum dot tracers in the test groups is detected.

[0059] S13. Based on the comparison between the light intensity of the control group and the light intensity of the test group, quantum dot tracers whose light intensity is not affected by the fracturing fluid are screened out.

[0060] By using water as a control group, quantum dot tracers that are not affected by fracturing fluid can be easily and quickly screened out.

[0061] In this embodiment, step S13 includes the following sub-steps:

[0062] S131. Based on the type of fracturing fluid determined during construction, different quantum dot tracers are mixed with the fracturing fluid one by one;

[0063] S133. The mixtures of different quantum dot tracers and fracturing fluids are placed in a preset environment, and the light intensity of the quantum dot tracers in each test group is tested one by one.

[0064] In this embodiment, the preset environment is ambient temperature and atmospheric pressure; and / or, formation temperature and atmospheric pressure; and / or, formation temperature and formation pressure.

[0065] It should be noted that, according to the design, the fracturing fluid formulation is determined on-site. The quantum dot tracer is mixed with the fracturing fluid and tested under different conditions, such as ambient temperature and pressure, formation temperature and pressure, and formation temperature and pressure. Formation temperature is generally between 70 and 140°C. The effects of different fracturing fluid components (drag reducers, flow aids, clay stabilizers, breaker agents, etc.) on the quantum dot light intensity are tested. The blank sample is simply the quantum dot solution mixed with water.

[0066] Please refer to Figure 1 In this embodiment, in an optional implementation, step S3 includes the following sub-steps:

[0067] S31. Determine the minimum detection concentration of each quantum dot tracer in the corresponding fracturing fluid through experiments;

[0068] S33. Determine the amount of quantum tracer based on the amount of fracturing fluid used in each fracturing section and the minimum detection limit of the corresponding quantum tracer.

[0069] Determining the minimum detection concentration facilitates quantitative testing.

[0070] It should be noted that the amount of quantum dot tracer used needs to be determined based on the volume of fracturing fluid used. For example, if a section of fracturing requires 2000 cubic meters of fracturing fluid and the minimum detectable concentration of quantum dot tracer is 1 mg / L, then the entire section requires 2 kg of quantum dot tracer. The amount of quantum tracer used = the volume of fracturing fluid used * the minimum detectable concentration of quantum dot tracer in the fracturing fluid. Different quantum dots are used to label each section, allowing for precise measurement of production data for each section.

[0071] Specifically, step S31 includes the following sub-steps:

[0072] S311. Establish curves of light intensity versus concentration for each fracturing fluid and its corresponding quantum dot tracer;

[0073] S313. Determine the minimum detection concentration based on the established curve of light intensity versus concentration of the quantum dot tracer.

[0074] Since the concentration of the sample solution is normally proportional to the light intensity, when the concentration and light intensity are not proportional, the threshold point is determined as the lowest detectable concentration.

[0075] It should be noted that the standard curve for quantum dot tracers, which measures the change in light intensity as a function of concentration, is established by plotting the concentration of each quantum dot in the designed formulation on the horizontal axis and the light intensity on the vertical axis. This is to confirm the minimum detectable concentration of each quantum dot tracer in the corresponding fracturing fluid system. Generally, testing requires the tracer to be placed under formation temperature conditions for a period of time, typically ranging from 5 to 20 days.

[0076] In this embodiment, step S5 includes the following sub-steps:

[0077] S51. Dissolve the required amount of quantum dot tracer in water;

[0078] S53. Use a sand mixing truck to begin injecting fracturing fluid into the fracturing section;

[0079] S55. After the displacement of the sand mixing truck stabilizes, the water-soluble quantum dot tracer is pumped into the sand mixing truck according to the preset displacement to mix evenly with the fracturing fluid, so that the quantum dot tracer is injected into the formation along with the fracturing pressure.

[0080] This ensures that the quantum tracer is injected uniformly and stably into the fracturing section, facilitating detection and quantitative analysis.

[0081] It should be noted that the quantum dot tracer is dissolved in water and mixed evenly. During construction, a separate pump is used. Once the pumping rate stabilizes (within 5 minutes), the aqueous solution of the quantum dot tracer is pumped at a constant rate onto the fracturing fluid mixing truck. The solution is then mixed evenly with the fracturing fluid in the mixing truck and pumped into the formation along with the fracturing fluid. This ensures that the quantum dot solution is uniformly mixed with the fracturing fluid throughout the entire process.

[0082] Please refer to Figure 1 In this embodiment, step S7 includes the following sub-steps:

[0083] S71. At the initial stage of the return process, take a test sample once at the first preset time interval, and take multiple groups each time;

[0084] S73. After the backflow stabilizes, take a test sample once at the second preset time interval until the sampling and discharge are completed, and take multiple groups each time.

[0085] S75. The collected test samples are processed and analyzed in groups to determine the output of each segment; wherein the second preset time is greater than the first preset time.

[0086] In this embodiment, the first preset time is two hours, and the second preset time is five hours.

[0087] This ensures that the collected samples are easy to process.

[0088] It should be noted that during the backflow sampling phase, due to the large backflow volume in the initial stage and the lack of a clear pattern in the backflow liquid volume, sampling was conducted every 2 hours, with three parallel samples taken each time. Once the backflow stabilized, the sampling interval became 5 hours, with three parallel samples taken each time, until the backflow was completed.

[0089] In an optional implementation, step S75 includes the following sub-steps:

[0090] S751. Centrifuge each set of test samples collected in each batch to obtain a test sample solution;

[0091] S753. The solution of the obtained test sample is purified to obtain a purified test solution;

[0092] S755. The purified detection solution was tested using a fluorescence spectrophotometer, and the test data was analyzed to obtain the type, concentration, and proportion of quantum dot tracer for each detection solution.

[0093] S755. Calculate the contribution rate of liquid production in each fracturing stage based on the type, concentration, and proportion of quantum dot tracers.

[0094] It should be noted that after the test samples are collected, since the samples contain not only quantum dots but also sediment, formation ions, etc., they generally need to be centrifuged twice to remove insoluble ions from the solution, then purified, and finally tested using a fluorescence spectrophotometer. Because the test parameters for each quantum dot are different, the light intensity between different quantum dots is unaffected. This is because the test parameters for each quantum dot in the mixed sample can be used to identify different quantum dots. By comparing the light intensity curve of the quantum dot tracer with concentration, the concentration and proportion of a certain quantum dot in the mixed sample can be determined by the light intensity, thereby deriving the amount of backflow of the segment labeled by that quantum dot.

[0095] The beneficial effects of the method for testing the production profile of horizontal wells using quantum dot tracers provided in this invention include, for example:

[0096] Because fracturing fluids contain drag reducers, flow aids, clay stabilizers, and breaker agents, each chemical reagent, due to its structure and functional group composition, can affect the intensity of quantum dots to varying degrees. For example, breaker agents, being persulfates, can damage the benzene rings of the quantum dot luminescent material, thus directly quenching the quantum dots. This application avoids the problem of fracturing fluid affecting the intensity of quantum dots and causing test failure by selecting different quantum dot tracers based on the composition of the fracturing fluid and the number of fracturing stages in the horizontal well before testing. Secondly, the amount of quantum dot tracer can be calculated from the fracturing fluid dosage, enabling quantitative measurement. Furthermore, the quantum dot tracer can be uniformly mixed into the fracturing fluid, allowing for precise marking of each stage and ensuring collection during flowback.

[0097] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for testing the production profile of a horizontal well using quantum dot tracers, characterized in that, The method includes: S1. Select different quantum dot tracers based on the composition of the fracturing fluid and the number of fracturing stages in the horizontal well, including the following sub-steps: S11. Different quantum dot tracers were diluted with water to obtain control groups, and the light intensity of each quantum dot tracer in the control groups was measured. S12. Based on the type of fracturing fluid determined during construction, different quantum dot tracers are mixed with the fracturing fluid to obtain test groups, and the light intensity of the quantum dot tracers in the test groups is detected. S13. Based on the comparison between the light intensity of the control group and the light intensity of the experimental group, quantum dot tracers whose light intensity is not affected by the fracturing fluid are screened out. S2. Determine the dosage of the quantum dot tracer for each fracturing section based on the needs of the construction site, including the following sub-steps: S21. Determine the minimum detection concentration of each quantum dot tracer in the corresponding fracturing fluid through experiments; S22. Determine the amount of quantum dot tracer based on the amount of fracturing fluid used in each fracturing section and the minimum detection limit of the corresponding quantum dot tracer. S3. Mix the required amount of the quantum dot tracer into the fracturing fluid and pump it into the formation; wherein, each fracturing stage uses a different quantum dot tracer, including the following sub-steps: S31. Dissolve the required amount of quantum dot tracer in water; S32. Use a sand mixing truck to begin injecting fracturing fluid into the fracturing section; S33. After the displacement of the sand mixing truck stabilizes, the water-soluble quantum dot tracer is pumped into the sand mixing truck according to the preset displacement to mix evenly with the fracturing fluid, so that the quantum dot tracer is injected into the formation with the fracturing fluid. S4. Take samples at the return outlet and analyze them to determine the output of each section, including the following sub-steps: S41. At the initial stage of the return process, take a test sample once at the first preset time interval, and take multiple groups each time; S42. After the back-out is stable, take a test sample once at the second preset time interval until the back-out is completed, and take multiple groups each time; S43. The collected test samples are processed and analyzed in groups to determine the output of each segment; wherein the second preset time is longer than the first preset time, specifically: S431. Centrifuge each set of test samples collected in each batch to obtain a test sample solution; S432. The solution of the obtained test sample is purified to obtain a purified test solution; S433. The purified detection solution was tested using a fluorescence spectrophotometer, and the test data was analyzed to obtain the type, concentration, and proportion of quantum dot tracer for each detection solution. S434. Calculate the contribution rate of liquid production in each fracturing stage based on the type, concentration, and proportion of quantum dot tracers.

2. The method for testing the production profile of a horizontal well using quantum dot tracers according to claim 1, characterized in that, The first preset time is two hours, and the second preset time is five hours.

3. The method for testing the production profile of a horizontal well using quantum dot tracers according to claim 1, characterized in that, Step S21 includes the following sub-steps: S211. Establish curves of light intensity versus concentration for each fracturing fluid and its corresponding quantum dot tracer; S212. Determine the minimum detection concentration based on the established curve of light intensity versus concentration of the quantum dot tracer.

4. The method for testing the production profile of a horizontal well using quantum dot tracers according to claim 1, characterized in that, Step S12 includes the following sub-steps: S121. Place the mixtures of different quantum dot tracers and fracturing fluids in a preset environment, and test the light intensity of the quantum dot tracers in each test group.

5. The method for testing the production profile of a horizontal well using quantum dot tracers according to claim 4, characterized in that, The preset environment is normal temperature and pressure; or formation temperature and normal pressure; or formation temperature and formation pressure.

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