Device and method for evaluating damage of fracturing fluid components to hydrate reservoir

Abstract

The invention relates to the technical field of fracturing fluid, in particular to a device and method for evaluating damage of fracturing fluid components to a hydrate reservoir stratum.The device comprises a core holder used for filling a hydrate core; the injection mechanism is connected with the core holder and is used for injecting one or more of fracturing fluid, water and gas into the core holder; the fracturing fluid infrared imaging mechanism comprises an infrared spectrometer and is used for collecting infrared spectrum signals of initial fracturing fluid and fracturing fluid flowback fluid from the core holder; and the data acquisition and analysis control system is electrically connected with the infrared spectrometer and is used for comparing and analyzing the infrared spectrum signals of the initial fracturing fluid and the fracturing fluid flowback fluid from the infrared spectrometer to obtain the components harmful to the hydrate reservoir in the fracturing fluid. When the device is applied to practical application, the components, harmful to the hydrate reservoir, in the fracturing fluid can be rapidly and accurately evaluated, and the components are used for guiding optimization of the fracturing fluid.

Description

Technical Field

[0001] The present invention relates to the technical field of fracturing fluids, and particularly relates to a device and method for evaluating the damage of fracturing fluid components to hydrate reservoirs. Background Art

[0002] Hydrates are ice-like solid compounds in which water molecules form a crystal lattice through hydrogen bonds, and methane gas molecules are trapped in the crystal structure. In nature, hydrates usually exist in deep-water sedimentary structures and polar regions. Currently, the primary target for trial production and development is deep-water hydrate reservoirs. Hydrate reservoirs are buried deep, have poor reservoir cementation, and strong compaction causes deformation of rock cuttings, blocking pore spaces and significantly reducing intergranular pores. These characteristics together result in a high proportion of low-permeability hydrate reservoirs. As a clean new energy source, hydrates have always been a research hotspot in the industrial and academic fields. The effective development of low-permeability hydrate reservoirs is a key problem that urgently needs to be solved.

[0003] For low-permeability hydrate reservoirs, it is necessary to improve the gas drainage area through fracturing transformation. During the process of fracturing transformation of the reservoir, only by achieving rapid and effective flowback of the fracturing fluid can the fracturing design effect be achieved, thereby improving the recovery rate. During hydraulic fracturing, the fracturing fluid fractures the formation under high pressure, and at the same time, the liquid filtrates into the hydrate porous medium. After soaking for a period of time, the hydrate decomposes and displaces the fracturing fluid to flow back into the wellbore. However, during the fracturing transformation process, the adsorption and retention of the fracturing fluid in the hydrate reservoir will affect the basic physical properties of the reservoir, causing reservoir damage such as skeleton deformation and particle migration, affecting the migration ability of hydrates, and thus affecting the effect of fracturing transformation. Therefore, it is necessary to systematically study the flow behavior and damage degree of fracturing fluids with different components and properties. However, at present, the research on the development of low-permeability hydrates is still in its infancy, with few research devices and imperfect experimental simulation methods.

[0004] Therefore, there is an urgent need for a device and method for evaluating the damage of fracturing fluid components to hydrate reservoirs to guide the optimization of fracturing fluids, thereby improving the sampling rate of hydrates. Summary of the Invention

[0005] The purpose of the present invention is to solve the problem in the prior art that it is impossible to evaluate whether a fracturing fluid damages a hydrate reservoir, and to provide a device and method for evaluating the damage of fracturing fluid components to hydrate reservoirs.

[0006] To achieve the above purpose, in the first aspect of the present invention, a device for evaluating the damage of fracturing fluid components to hydrate reservoirs is provided. The device for evaluating the damage of fracturing fluid components to hydrate reservoirs includes:

[0007] A core holder for loading hydrate cores;

[0008] An injection mechanism, connected to the core holder, for injecting one or more of fracturing fluid, water, and gas into the core holder;

[0009] A fracturing fluid infrared imaging mechanism, including an infrared spectrometer, for collecting infrared spectral signals of the initial fracturing fluid and the fracturing fluid flowback fluid from the core holder;

[0010] A data acquisition, analysis, and control system, electrically connected to the infrared spectrometer, for comparing and analyzing the infrared spectral signals of the initial fracturing fluid and the fracturing fluid flowback fluid from the infrared spectrometer to obtain the components in the fracturing fluid that are harmful to the hydrate reservoir.

[0011] Preferably, the comparing and analyzing the infrared spectral signals of the initial fracturing fluid and the fracturing fluid flowback fluid from the infrared spectrometer to obtain the components in the fracturing fluid that are harmful to the hydrate reservoir specifically includes:

[0012] Based on the infrared spectral signals of the initial fracturing fluid and the fracturing fluid flowback fluid, infrared spectrograms are respectively generated, and the two generated infrared spectrograms are compared with a standard infrared spectral library to determine the functional groups corresponding to the absorption peaks in the two generated infrared spectrograms, and the respective components of the fracturing fluid corresponding to each functional group. According to the change rate of the absorption peaks in the two infrared spectrograms, the components in the fracturing fluid that are harmful to the hydrate reservoir are obtained.

[0013] Preferably, it further includes a low-field nuclear magnetic resonance on-line monitoring instrument, electrically connected to the data acquisition, analysis, and control system, for accommodating the core holder and sending the nuclear magnetic resonance signals of the core holder collected in real time to the data acquisition, analysis, and control system.

[0014] Preferably, the injection mechanism includes:

[0015] A gas source mechanism, a gas booster pump, a first multi-way valve, and a second multi-way valve connected in sequence. The first multi-way valve is also connected to the outlet end of the core holder through a third multi-way valve, and the second multi-way valve is also respectively connected to the inlet end of the holder and the infrared spectrometer;

[0016] And a gas container and a plurality of liquid containers connected in parallel for containing fracturing fluid and water. One ends of the gas container and the liquid containers are both connected to the first multi-way valve, and the other ends are both connected to the injection pump. The injection pump is connected to a first liquid storage container.

[0017] Preferably, a water bath circulation jacket is arranged outside the liquid container. The inner cavity of the water bath circulation jacket is connected in a closed loop through a pipeline to a first temperature control unit and a first circulation pump for controlling the temperature of the liquid in the liquid container.

[0018] Preferably, a confining pressure mechanism is provided outside the core holder. The confining pressure mechanism includes a second liquid storage container, which includes an inner cavity for storing confining pressure liquid. The confining pressure liquid in the inner cavity is transported to the confining pressure cavity of the core holder through a pipeline and a confining pressure pump, and the inside of the confining pressure cavity is connected in a closed loop with a third circulation pump through a pipeline.

[0019] Preferably, an outer cavity is integrally provided on the outer surface of the inner cavity. The inside of the outer cavity is connected in a closed loop with a second temperature control unit and a second circulation pump through a pipeline, for controlling the temperature of the confining pressure liquid in the inner cavity.

[0020] Preferably, temperature measuring devices and pressure measuring devices are provided at both the inlet end and the outlet end of the core holder, and both the temperature measuring devices and the pressure measuring devices are electrically connected to the data acquisition and analysis control system.

[0021] Preferably, the fracturing fluid infrared imaging mechanism further includes a vacuum drying oven, which is used to perform vacuum drying treatment on the initial fracturing fluid and the fracturing fluid flowback fluid before obtaining the infrared spectral signal.

[0022] In a second aspect of the present invention, a method for evaluating the damage of fracturing fluid components to hydrate reservoirs is provided, which is applied to the above-mentioned device. The method for evaluating the damage of fracturing fluid components to hydrate reservoirs includes the following steps:

[0023] S1. Detect the airtightness of the device, select a core with the mineral composition and pore structure of a hydrate reservoir, evacuate the dry core, and place the water-saturated core into the core holder after saturation.

[0024] S2. Inject a target gas into both ends of the core holder through the injection mechanism. The hydrate starts to form, and a low-field nuclear magnetic resonance on-line monitoring instrument is used to scan the core to monitor the formation process of the hydrate in real time. When the nuclear magnetic resonance signal of the core no longer decreases and reaches an equilibrium state, it is considered that the formation of the hydrate is completed, and a hydrate core containing the target gas is obtained.

[0025] S3. Select a fracturing fluid suitable for a hydrate reservoir, determine the composition components and weight percentages of the fracturing fluid, and then send the initial fracturing fluid into the fracturing fluid infrared imaging mechanism to collect the infrared spectral signal of the initial fracturing fluid. The data acquisition and analysis control system generates an infrared spectrogram based on the collected infrared spectral signal of the initial fracturing fluid and compares it with a standard infrared spectral library to determine the functional groups corresponding to the absorption peaks in the generated infrared spectrogram, and the composition components of the fracturing fluid corresponding to each functional group.

[0026] S4. Inject fracturing fluid into the core holder through the injection mechanism. Then, successively simulate the filtration process, shut-in process, and flowback process of the fracturing fluid in the hydrate core, and collect the infrared spectral signals of the fracturing fluid flowback fluid at set time intervals during the flowback process. After the infrared spectral signals of the fracturing fluid flowback fluid are stable, generate an infrared spectrogram based on the stable infrared spectral signals of the fracturing fluid flowback fluid collected by the data acquisition and analysis control system, and compare it with the standard infrared spectral library to determine the functional groups corresponding to the absorption peaks in the generated infrared spectrogram and the components of each composition of the fracturing fluid corresponding to each functional group. Based on the change rate of the absorption peaks in the infrared spectrogram of the initial fracturing fluid, obtain the components in the fracturing fluid that are harmful to the hydrate reservoir.

[0027] Preferably, it further includes: repeating steps S1 and S2, and then in step S4, inject the fracturing fluid containing only the components harmful to the hydrate reservoir obtained into the core holder, successively simulate the filtration process, shut-in process, and flowback process of the fracturing fluid in the hydrate core, collect the fracturing fluid flowback fluid and calculate the core permeability, and verify whether the current fracturing fluid components are harmful to the hydrate reservoir according to the core permeability.

[0028] Preferably, the calculation formula for the core permeability is:

[0029]

[0030] Wherein, K is the core permeability, mD; Q is the volume flow rate of the fluid, cm 3 / s, μ is the fluid viscosity, mPa·s; L is the core length, cm; A is the cross-sectional area of the core through which the fluid flows, cm 2 ; Δp is the pressure difference across the core, MPa.

[0031] According to the above technical solution, based on the device for evaluating the damage of fracturing fluid components to the hydrate reservoir, by setting the injection mechanism to inject one or more of fracturing fluid, water, and gas into the core holder as needed, the generation of the hydrate core can be controlled, and the filtration process, shut-in process, and flowback process of the fracturing fluid in the hydrate core can be simulated. Further, the infrared spectral signals of the initial fracturing fluid and the fracturing fluid flowback fluid from the core holder are collected by the infrared spectrometer of the fracturing fluid infrared imaging mechanism, and the data acquisition and analysis control system performs comparative analysis processing on the infrared spectral signals of the initial fracturing fluid and the fracturing fluid flowback fluid from the infrared spectrometer, and finally the components in the fracturing fluid that are harmful to the hydrate reservoir can be obtained, so as to be used to guide the optimization of the fracturing fluid, and further improve the sampling rate of the hydrate. Description of the Drawings

[0032] Figure 1 is a schematic structural diagram of the device for evaluating the damage of fracturing fluid components to the hydrate reservoir;

[0033] Figure 2 is the T2 spectrum of the hydrate formation process in Example 1;

[0034] Figure 3 is the infrared spectrum comparison diagram of the initial fracturing fluid and the fracturing fluid flowback fluid in Example 1;

[0035] Figure 4 is the variation relationship diagram between the concentration of the harmful component hydroxypropyl guar gum thickener in the fracturing fluid and the core permeability in Example 1.

[0036] Explanation of the reference numerals

[0037] 1. Injection mechanism; 11. Gas source mechanism; 12. Pressure reducing valve; 13. Gas booster pump; 14. First multi-way valve; 15. Second multi-way valve; 16. Third multi-way valve; 17. First temperature control unit; 18. First circulation pump; 19. First liquid storage container; 110. Injection pump; 111. Water bath circulation jacket; 112. Liquid container; 113. Gas container; 2. Core holder; 21. Second liquid storage container; 22. Confining pressure pump; 23. Third circulation pump; 24. Second temperature control unit; 25. Second circulation pump; 26. Temperature measuring device; 27. Pressure measuring device; 3. Low-field nuclear magnetic resonance on-line monitoring instrument; 4. Fracturing fluid infrared imaging mechanism; 41. Vacuum drying oven; 42. Infrared spectrometer; 5. Data acquisition and analysis control system. Detailed implementation manners

[0038] The following details the specific implementation manners of the embodiments of the present invention. It should be understood that the specific implementation manners described herein are only for explaining and illustrating the embodiments of the present invention, and are not used to limit the embodiments of the present invention.

[0039] In the description of the present application, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating relative importance or implicitly indicating the number of the indicated technical features. Thus, unless otherwise stated, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features; the meaning of "plurality" is two or more. The term "comprising" and any deformation thereof mean non-exclusive inclusion, and may include one or more other features, units, components and / or their combinations.

[0040] In addition, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, or the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific situations.

[0041] In the first aspect of the present invention, a device for evaluating the damage of fracturing fluid components to hydrate reservoirs is provided. As Figures 1-4 shown, the device for evaluating the damage of fracturing fluid components to hydrate reservoirs includes:

[0042] A core holder 2 for loading hydrate cores;

[0043] An injection mechanism 1, connected to the core holder 2, for injecting one or more of fracturing fluid, water, and gas into the core holder 2;

[0044] A fracturing fluid infrared imaging mechanism 4, including an infrared spectrometer 42, for collecting infrared spectral signals of the initial fracturing fluid and the fracturing fluid backflow fluid from the core holder 2;

[0045] A data acquisition, analysis, and control system 5, electrically connected to the infrared spectrometer 42, for comparing and analyzing the infrared spectral signals of the initial fracturing fluid and the fracturing fluid backflow fluid from the infrared spectrometer 42 to obtain the components in the fracturing fluid that are harmful to the hydrate reservoir.

[0046] According to the above technical solution, based on the device for evaluating the damage of fracturing fluid components to hydrate reservoirs, by setting the injection mechanism to inject one or more of fracturing fluid, water, and gas into the core holder as needed, the generation of hydrate cores can be controlled, and the filtration process, shut-in process, and backflow process of the fracturing fluid in the hydrate cores can be simulated. Further, the infrared spectrometer of the fracturing fluid infrared imaging mechanism is used to collect the infrared spectral signals of the initial fracturing fluid and the fracturing fluid backflow fluid from the core holder, and the data acquisition, analysis, and control system compares and analyzes the infrared spectral signals of the initial fracturing fluid and the fracturing fluid backflow fluid from the infrared spectrometer, and finally the components in the fracturing fluid that are harmful to the hydrate reservoir can be obtained, so as to be used to guide the optimization of the fracturing fluid and further improve the sampling rate of hydrates.

[0047] In the device for evaluating the damage of fracturing fluid components to hydrate reservoirs of the present invention, preferably, the comparing and analyzing the infrared spectral signals of the initial fracturing fluid and the fracturing fluid backflow fluid from the infrared spectrometer 42 to obtain the components in the fracturing fluid that are harmful to the hydrate reservoir specifically includes:

[0048] Based on the infrared spectral signals of the initial fracturing fluid and the fracturing fluid flowback fluid, infrared spectrograms are respectively generated, and the two generated infrared spectrograms are compared with a standard infrared spectral library to determine the functional groups corresponding to the absorption peaks in the two generated infrared spectrograms, and the components of the fracturing fluid corresponding to each functional group. According to the change rate of the absorption peaks in the two infrared spectrograms, the components that are harmful to the hydrate reservoir in the fracturing fluid are obtained. By analyzing and comparing the change rates of the absorption peaks corresponding to the same fracturing fluid component in the two infrared spectrograms, in practical applications, it is possible to accurately determine whether the current fracturing fluid component will damage the hydrate reservoir, thereby guiding the optimization and selection of the fracturing fluid, and further improving the sampling rate of the hydrate.

[0049] In the device for evaluating the damage of fracturing fluid components to the hydrate reservoir according to the present invention, during the process of generating a hydrate core based on the core holder 2 and the injection mechanism 1, in order to accurately obtain the generation rate of the hydrate core and the changes in the core pores during the hydrate generation process. In a preferred embodiment, it further includes a low-field nuclear magnetic resonance on-line monitoring instrument 3, which is electrically connected to the data acquisition and analysis control system 5, is used to accommodate the core holder 2, and sends the nuclear magnetic resonance signal of the core holder 2 collected in real time to the data acquisition and analysis control system 5. Specifically, the core is scanned using the low-field nuclear magnetic resonance on-line monitoring instrument 3 to monitor the hydrate generation process in real time. When the nuclear magnetic resonance signal of the core no longer decreases and reaches an equilibrium state, it is considered that the hydrate generation is completed, and a hydrate core containing a target gas such as methane is obtained. The T2 spectrum of the hydrate generation process in the specific initial state is as Figure 2 shown.

[0050] In the device for evaluating the damage of fracturing fluid components to the hydrate reservoir according to the present invention, the injection mechanism 1 can be in various structural forms, as long as it can inject at least one of the fracturing fluid, water, and gas into the core holder 2 according to actual needs, for generating a hydrate core containing a target gas and simulating the filtration process, shut-in process, and flowback process of the fracturing fluid in the hydrate core. In a preferred embodiment, the injection mechanism 1 includes a gas source mechanism 11, a gas booster pump 13, a first multi-way valve 14, and a second multi-way valve 15 connected in sequence. The first multi-way valve 14 is also connected to the outlet end of the core holder 2 through a third multi-way valve 16, and the second multi-way valve 15 is also respectively connected to the inlet end of the core holder 2 and the infrared spectrometer 42; and a gas container 113 and a plurality of liquid containers 112 connected in parallel for containing the fracturing fluid and water. One end of the gas container 113 and the liquid containers 112 is connected to the first multi-way valve 14, and the other end is connected to the injection pump 110. The injection pump 110 is connected to the first liquid storage container 19. By such as Figure 1The injection mechanism 1 with the integrated design as shown can, in actual application, quickly and accurately inject fracturing fluid, water, and gas into the core holder 2 according to the actual formation of hydrate cores and the requirements of simulating the filtration process, shut-in process, and flowback process of fracturing fluid in hydrate cores. A pressure reducing valve 12 is provided on the pipeline connecting the gas source mechanism 11 and the gas booster pump 13.

[0051] Further preferably, an external water bath circulation jacket 111 is provided outside the liquid container 112. The inner cavity of the water bath circulation jacket 111 is connected in a closed loop to the first temperature control unit 17 and the first circulation pump 18 through pipelines, for controlling the temperature of the liquid in the liquid container 112, thereby accurately controlling the temperature of the fracturing fluid and formation water injected into the core holder 2.

[0052] In the device for evaluating the damage of fracturing fluid components to hydrate reservoirs according to the present invention, preferably, a confining pressure mechanism is provided outside the core holder 2. The confining pressure mechanism includes a second liquid storage container 21. The second liquid storage container 21 includes an inner cavity for storing confining pressure fluid. The confining pressure fluid in the inner cavity is transported to the confining pressure cavity of the core holder 2 through pipelines and a confining pressure pump 22. The inside of the confining pressure cavity is connected in a closed loop to a third circulation pump 23 through pipelines, thereby accurately controlling the confining pressure in the confining pressure cavity of the core holder 2. Specifically, the confining pressure fluid is a fluorinated fluid. The confining pressure in the confining pressure cavity is usually 1 - 5 MPa higher than the core pore pressure.

[0053] Further preferably, an outer cavity is integrally provided on the outer surface of the inner cavity. The inside of the outer cavity is connected in a closed loop to the second temperature control unit 24 and the second circulation pump 25 through pipelines, for controlling the temperature of the confining pressure fluid in the inner cavity, thereby accurately controlling the temperature of the confining pressure fluid entering the confining pressure cavity.

[0054] In the device for evaluating the damage of fracturing fluid components to hydrate reservoirs according to the present invention, preferably, temperature measuring devices 26 and pressure measuring devices 27 are provided at both the inlet end and the outlet end of the core holder 2. The temperature measuring devices 26 and the pressure measuring devices 27 are both electrically connected to the data acquisition and analysis control system 5. Thus, in actual application, the temperature values and pressure values at both ends of the core holder 2 can be accurately obtained, and further, hydrate cores containing the target gas can be better generated, as well as the filtration process, shut-in process, and flowback process of fracturing fluid in hydrate cores can be simulated.

[0055] In the device for evaluating the damage of fracturing fluid components to hydrate reservoirs according to the present invention, preferably, the fracturing fluid infrared imaging mechanism 4 further includes a vacuum drying oven 41, which is used for vacuum drying the initial fracturing fluid and fracturing fluid flowback fluid before obtaining the infrared spectral signal, thereby improving the accuracy of the collected infrared spectral signal.

[0056] In a second aspect of the present invention, a method for evaluating the damage of fracturing fluid components to hydrate reservoirs is provided, which is applied to the above-mentioned device. The method for evaluating the damage of fracturing fluid components to hydrate reservoirs includes the following steps:

[0057] S1. Detect the airtightness of the device, select a core with the mineral composition and pore structure of the hydrate reservoir, evacuate the dry core, and place the water-saturated core into the core holder 2.

[0058] S2. Inject the target gas into both ends of the core holder 2 through the injection mechanism 1. The hydrate starts to form, and the core is scanned using a low-field nuclear magnetic resonance on-line monitoring instrument 3 to monitor the formation process of the hydrate in real time. When the nuclear magnetic resonance signal of the core no longer decreases and reaches the equilibrium state, it is considered that the formation of the hydrate is completed, and a hydrate core containing the target gas is obtained.

[0059] S3. Select a fracturing fluid suitable for the hydrate reservoir, determine the composition components and weight percentages of the fracturing fluid. Then, send the initial fracturing fluid into the fracturing fluid infrared imaging mechanism 4 to collect the infrared spectral signal of the initial fracturing fluid. The data acquisition and analysis control system 5 generates an infrared spectrogram based on the collected infrared spectral signal of the initial fracturing fluid and compares it with the standard infrared spectral library to determine the functional groups corresponding to the absorption peaks in the generated infrared spectrogram, and the composition components of the fracturing fluid corresponding to each functional group.

[0060] S4. Inject the fracturing fluid into the core holder 2 through the injection mechanism 1. Then, sequentially simulate the filtration process, shut-in process, and flowback process of the fracturing fluid in the hydrate core, and collect the infrared spectral signal of the fracturing fluid flowback fluid at set time intervals during the flowback process. After the infrared spectral signal of the fracturing fluid flowback fluid is stable, the data acquisition and analysis control system 5 generates an infrared spectrogram based on the collected stable infrared spectral signal of the fracturing fluid flowback fluid and compares it with the standard infrared spectral library to determine the functional groups corresponding to the absorption peaks in the generated infrared spectrogram, and the composition components of the fracturing fluid corresponding to each functional group. Based on the change rate of the absorption peaks in the infrared spectrogram of the initial fracturing fluid, the components in the fracturing fluid that are harmful to the hydrate reservoir are obtained.

[0061] According to the above technical solution, based on the method for evaluating the damage of fracturing fluid components to hydrate reservoirs, in practical applications, the components in the fracturing fluid that are harmful to the hydrate reservoir can be accurately obtained, so as to guide the optimization of the fracturing fluid, and further improve the sampling rate of the hydrate.

[0062] In the method for evaluating the damage of fracturing fluid components to hydrate reservoirs described in the present invention, preferably, it further includes:

[0063] Repeat steps S1 and S2, and then in step S4, inject the fracturing fluid containing only the components that are harmful to the hydrate reservoir obtained into the core holder 2, successively simulate the filtration process, shut-in process, and flowback process of the fracturing fluid in the hydrate core, collect the flowback fluid of the fracturing fluid, and calculate the core permeability. Verify whether the current fracturing fluid components are harmful to the hydrate reservoir based on the core permeability, so as to further verify the accuracy of the evaluation results based on the core permeability.

[0064] In a specific embodiment, the calculation formula for the core permeability is as follows:

[0065]

[0066] where K is the core permeability, mD; Q is the volume flow rate of the fluid, cm 3 / s, μ is the fluid viscosity, mPa·s; L is the core length, cm; A is the cross-sectional area of the core through which the fluid flows, cm 2 ; Δp is the pressure difference across the core, MPa.

[0067] The present invention will be described in detail below through embodiments, but the protection scope of the present invention is not limited thereto.

[0068] Example 1

[0069] Adopt the device for evaluating the damage of fracturing fluid components to the hydrate reservoir as shown in Figure 1 . Specifically, the device for evaluating the damage of fracturing fluid components to the hydrate reservoir includes:

[0070] A core holder 2 for loading hydrate cores;

[0071] An injection mechanism 1 connected to the core holder 2 for injecting one or more of fracturing fluid, water, and gas into the core holder 2;

[0072] A fracturing fluid infrared imaging mechanism 4, including an infrared spectrometer 42, for collecting infrared spectral signals of the initial fracturing fluid and the fracturing fluid flowback fluid from the core holder 2;

[0073] The data acquisition, analysis and control system 5 is electrically connected to the infrared spectrometer 42 and is used to perform comparative analysis processing on the infrared spectral signals of the initial fracturing fluid and the fracturing fluid flowback fluid from the infrared spectrometer 42 to obtain the components in the fracturing fluid that are harmful to the hydrate reservoir; the performing comparative analysis processing on the infrared spectral signals of the initial fracturing fluid and the fracturing fluid flowback fluid from the infrared spectrometer 42 to obtain the components in the fracturing fluid that are harmful to the hydrate reservoir specifically includes: generating infrared spectrograms respectively based on the infrared spectral signals of the initial fracturing fluid and the fracturing fluid flowback fluid, comparing both of the generated two infrared spectrograms with a standard infrared spectral library, determining the functional groups corresponding to the absorption peaks in the two generated infrared spectrograms, as well as the respective components of the fracturing fluid corresponding to each functional group, and obtaining the components in the fracturing fluid that are harmful to the hydrate reservoir according to the change rate of the absorption peaks in the two infrared spectrograms;

[0074] Specifically, it further includes a low-field nuclear magnetic resonance on-line monitoring instrument 3, which is electrically connected to the data acquisition and analysis control system 5, is used to accommodate the core holder 2, and sends the nuclear magnetic resonance signals of the core holder 2 collected in real time to the data acquisition and analysis control system 5; the injection mechanism 1 includes: a gas source mechanism 11, a gas booster pump 13, a first multi-way valve 14, and a second multi-way valve 15 connected in sequence. The first multi-way valve 14 is also connected to the outlet end of the core holder 2 through a third multi-way valve 16, and the second multi-way valve 15 is also respectively connected to the inlet end of the core holder 2 and the infrared spectrometer 42; and a gas container 113 and a plurality of liquid containers 112 connected in parallel for containing fracturing fluid and water. One ends of the gas container 113 and the liquid containers 112 are both connected to the first multi-way valve 14, and the other ends are both connected to the injection pump 110. The injection pump 110 is connected to the first liquid storage container 19; a water bath circulation jacket 111 is arranged outside the liquid container 112, and the inner cavity of the water bath circulation jacket 111 is connected in a closed loop with the first temperature control unit 17 and the first circulation pump 18 through pipelines for controlling the liquid temperature in the liquid container 112; a confining pressure mechanism is arranged outside the core holder 2. The confining pressure mechanism includes a second liquid storage container 21. The second liquid storage container 21 includes an inner cavity for storing confining pressure fluid. The confining pressure fluid in the inner cavity is transported to the confining pressure cavity of the core holder 2 through pipelines and a confining pressure pump 22. The inside of the confining pressure cavity is connected in a closed loop with a third circulation pump 23 through pipelines; an outer cavity is integrally arranged on the outer surface of the inner cavity, and the inside of the outer cavity is connected in a closed loop with the second temperature control unit 24 and the second circulation pump 25 through pipelines for controlling the temperature of the confining pressure fluid in the inner cavity; temperature measuring devices 26 and pressure measuring devices 27 are arranged at both the inlet end and the outlet end of the core holder 2. The temperature measuring devices 26 and the pressure measuring devices 27 are both electrically connected to the data acquisition and analysis control system 5; the fracturing fluid infrared imaging mechanism 4 further includes a vacuum drying oven 41 for performing vacuum drying treatment on the initial fracturing fluid and the fracturing fluid flowback fluid before obtaining the infrared spectral signal.

[0075] In actual application, step 100: Connect the experimental device, check the airtightness of the device, select a core with typical mineral components and pore structures of a hydrate reservoir, evacuate the dry core, saturate the core with formation water, place the saturated core into the core holder 2, and place the core holder 2 at the magnet and signal monitoring coil of the low-field nuclear magnetic resonance on-line monitoring instrument 3. Use the second temperature control unit 24 and the confining pressure pump 22 to regulate the temperature and pressure of the fluorinated liquid. Turn on the second circulation pump 25 and the third circulation pump 23, control the temperature of the fluorinated liquid to be 4°C, and keep the confining pressure always 3 MPa higher than the pore pressure of the core.

[0076] Step 200: Open the valve switches of the first multi-way valve 14 connecting the gas booster pump 13, the second multi-way valve 15, the third multi-way valve 16, and the gas container 113 containing methane gas. Open the valve switch of the second multi-way valve 15 connecting the first multi-way valve 14 and the inlet end of the core holder 2. Open the valve switch of the third multi-way valve 16 connecting the outlet end of the core holder 2 and the first multi-way valve 14. The valve switches of the connecting pipelines of other multi-way valves are all in the closed state. Use the injection pump 110 to inject methane gas at both ends of the core in the constant pressure mode, set the pressure of the injection pump to 8 MPa, and hydrate starts to form. Use the low-field nuclear magnetic resonance on-line monitoring instrument 3 to scan the core and monitor the hydrate formation process in real time. When the nuclear magnetic resonance signal of the core no longer decreases and reaches the equilibrium state, it is considered that the hydrate formation is completed, and a core containing methane hydrate is obtained. Obtain the T2 spectrum of hydrate formation in the initial state, as Figure 2 shown, and then close all valve switches after generation;

[0077] Step 300: Experimentally prepare the fracturing fluid, clarify the composition components and weight percentages of the fracturing fluid. After treatment, with the help of the infrared spectrometer 42, use the data acquisition and analysis control system 5 to collect infrared spectral signals in real time, obtain all spectral information of each composition component and the initial fracturing fluid sample at infrared wavelengths. Take the transmittance as the ordinate and the wave number as the abscissa to draw the infrared spectra of each sample until the infrared spectrum is stable and the test ends. Then, by comparing with the standard infrared spectral library, analyze the surface chemical structure composition of each composition component of the fracturing fluid and the initial fracturing fluid, clarify the functional groups corresponding to each absorption peak in the infrared spectrum of the initial fracturing fluid, and the composition components of the fracturing fluid corresponding to each functional group;

[0078] Specifically, as Figure 3 shown, the hydroxypropyl guar gum thickener shows absorption peaks around the wave numbers 2850 - 2930 cm -1 nearby, and the corresponding functional group is the -CH2- bond; it shows an absorption peak around the wave number 1086 cm -1 nearby, and the corresponding functional group is the C-O-C bond; the organic boron crosslinking agent shows an absorption peak around the wave number 1370 cm -1 nearby, and the corresponding functional group is the B-O bond; the ammonium persulfate breaker shows an absorption peak around the wave number 1010 cm -1 nearby, and the corresponding functional group is the S-O bond, and it shows an absorption peak around the wave number 794 cm -1 nearby, and the corresponding functional group is the O-O bond; potassium chloride clay stabilizer is an inorganic salt clay stabilizer. Since potassium chloride is an ionic compound composed of potassium ions and chloride ions and there is no typical covalent bond functional group, it has no obvious specific functional group absorption peak in the infrared spectrum; the pentanediol bactericide shows an absorption peak around 1460 cm -1 nearby, and the corresponding functional group is the -CH2- bond; it shows an absorption peak around the wave number 1258 cm-1 An absorption peak appears nearby, and the corresponding functional group is the C-O bond;

[0079] Step 400: Inject the fracturing fluid into the hydrate core in a constant flow mode with the aid of the injection pump 110. Open the first multi-way valve 14 to connect the liquid container 112 containing the fracturing fluid and the valve switch connecting the second multi-way valve 15. Open the valve switch of the second multi-way valve 15 connecting the inlet end of the core holder 2 and the first multi-way valve 14. The valve switches of the multi-way valves connecting other pipelines are all in the closed state. Control the temperature of the liquid in the water bath circulation jacket 111 of the liquid container 112 through the first temperature control unit 17, and then control the temperature of the fracturing fluid in the liquid container 112. In this embodiment, normal temperature fracturing fluid is injected into the hydrate core to simulate the fracturing fluid filtration process. Then, after the injection of the fracturing fluid is completed, close all valve switches and shut in the well for a period of time to ensure that the fracturing fluid fully penetrates into the hydrate core, simulating the fracturing fluid shut-in process, and real-time monitor the nuclear magnetic resonance signal of the fracturing fluid flowing in the core, the pressure changes at the inlet and outlet ends of the core, and the stable pressure value during the shut-in process. Then open the valve switches of the first multi-way valve 14 connecting the gas booster pump 13, the gas container 113 containing methane gas, and the third multi-way valve 16. Open the valve switches of the second multi-way valve 15 connecting the inlet end of the core holder 2 and the vacuum drying oven 41. Open the valve switches of the third multi-way valve 16 connecting the outlet end of the core holder 2 and the first multi-way valve 14. The valve switches of the multi-way valves connecting other pipelines are all in the closed state. Inject methane gas into the core in a constant pressure mode with the aid of the injection pump 110 to simulate the fracturing fluid backflow process, and use the low-field nuclear magnetic resonance on-line monitoring instrument 3 to real-time monitor the nuclear magnetic resonance signal of the fracturing fluid flowing in the core during the backflow process;

[0080] Step 500: Collect the fracturing fluid backflow fluid once every 1 minute. After processing, use the infrared spectrometer 42 until the infrared spectrum of the fracturing fluid backflow fluid is stable, and then stop collecting. The infrared spectrogram of the fracturing fluid backflow fluid is shown in Figure 3 as shown; By comparing the infrared spectrogram of the fracturing fluid backflow fluid with the infrared spectrogram of the initial fracturing fluid, identify the functional groups that damage the hydrate reservoir core, so as to optimize the composition and proportion of the fracturing fluid;

[0081] Specifically, there is a certain absorption peak corresponding to the C-O-C bond of hydroxypropyl guar gum in the initial fracturing fluid. The transmittance of this absorption peak increases significantly in the fracturing fluid flowback fluid, indicating that after the gel breaker of hydroxypropyl guar gum breaks, the molecular chain breaks and the crosslinking degree decreases significantly. However, there is still some unbroken guar gum during the fracturing process, and the residual hydroxypropyl guar gum adsorbs on the core surface, blocking the core pore channels, thereby reducing the core permeability; the porosity also decreases because the pore space is occupied by hydroxymethyl guar gum, restricting the flow channels of gas and water after the hydrate decomposes, and affecting the production efficiency; although the ammonium persulfate gel breaker has good gel breaking performance, its dosage may still not be sufficient to completely degrade hydroxypropyl guar gum. Therefore, the dosage of ammonium persulfate gel breaker can be appropriately increased to improve the gel breaking efficiency, promote the degradation of hydroxypropyl guar gum, and reduce the formation residue; there is an absorption peak corresponding to the C-O bond of the pentanediol bactericide in the initial fracturing fluid. The transmittance of this absorption peak increases significantly in the fracturing fluid flowback fluid, indicating that the bactericide reacts with the microorganisms in the fracturing fluid flowback fluid, effectively killing or inhibiting the growth and reproduction of microorganisms in the formation, thus avoiding the blockage of the formation caused by the metabolites of microorganisms. Therefore, pentanediol can be selected as the bactericide; there is an absorption peak corresponding to the B-O bond of the organic boron crosslinking agent in the initial fracturing fluid. The transmittance of this absorption peak decreases in the fracturing fluid flowback fluid, indicating that the crosslinking effect of the organic boron crosslinking agent during the fracturing process is excellent, crosslinking polymers such as hydroxypropyl guar gum. During the crosslinking process, the boron atom forms a coordination bond with the -OH bond of hydroxypropyl guar gum, resulting in a change in the vibration mode of the B-O bond, increasing the dipole moment of the B-O bond, and enhancing the infrared absorption intensity, thereby leading to a decrease in the passing rate of the B-O bond in the fracturing fluid flowback fluid. Therefore, organic boron can be selected as the gel breaker; there are absorption peaks corresponding to the S-O and O-O bonds of the ammonium persulfate gel breaker in the initial fracturing fluid. The transmittances of both absorption peaks increase significantly in the fracturing fluid flowback fluid; indicating that the ammonium persulfate has excellent gel breaking performance, triggering the degradation reaction of hydroxypropyl guar gum in the fracturing fluid to achieve gel breaking, thereby reducing the viscosity of the fracturing fluid, improving the fracturing fluid flowback efficiency, reducing the residue of the fracturing fluid in the core, and reducing the damage to the formation core permeability. Therefore, ammonium persulfate can be selected as the gel breaker;

[0082] Step 600: To further verify the damage degree of hydroxypropyl guar gum to the hydrate core, repeat the process of injecting liquid into the hydrate core in the above-mentioned embodiment. With the help of the injection pump 110, inject the additive hydroxypropyl guar gum thickener in the fracturing fluid into the hydrate core in the constant flow mode, collect the fracturing fluid flowback fluid and use the formula Calculate the core permeability at the corresponding time, and it is found that with the injection of hydroxypropyl guar gum, the concentration of the flowback fluid starts to rise rapidly from 0 mg / L, slows down after about 360 - 480 s, and finally stabilizes. At the initial stage of the injection of hydroxypropyl guar gum, the core permeability also drops rapidly, from 15.3 mD to about 3.1 mD quickly. It is analyzed that hydroxypropyl guar gum causes great damage to the core. At the initial stage of injection, due to the relatively large internal space of the core, the macromolecules of the injected hydroxypropyl guar gum attach and accumulate in the core pores, resulting in some macromolecules of hydroxypropyl guar gum blocking some pore channels, increasing the resistance of the fluid passing through the core, and thus leading to a rapid decrease in permeability. With the continuous injection, the pores are further filled, and the rate of permeability decline slows down. When the pore structure is basically shaped under the influence of hydroxypropyl guar gum, the permeability tends to be stable, as specifically shown in Figure 4 shown, so the thickening agent of the fracturing fluid needs to be further optimized.

[0083] After testing, when the device for evaluating the damage of fracturing fluid components to hydrate reservoirs described in the present invention is actually applied, the components in the fracturing fluid that are harmful to the hydrate reservoir can be accurately obtained, so as to be used to guide the optimization of the preparation of the fracturing fluid, and further improve the sampling rate of hydrates.

[0084] The device and method for evaluating the damage of fracturing fluid components to hydrate reservoirs provided by the present invention can control the generation of hydrate cores and simulate the filtration process, shut-in process, and flowback process of the fracturing fluid in the hydrate cores by setting an injection mechanism to inject one or more of fracturing fluid, water, and gas into the core holder as needed. Further, the infrared spectrometer of the fracturing fluid infrared imaging mechanism collects the infrared spectral signals of the initial fracturing fluid and the fracturing fluid flowback fluid from the core holder, and the data acquisition and analysis control system conducts comparative analysis and processing on the infrared spectral signals of the initial fracturing fluid and the fracturing fluid flowback fluid from the infrared spectrometer, and finally the components in the fracturing fluid that are harmful to the hydrate reservoir can be obtained, which can be used to guide the optimization of the fracturing fluid, and further improve the sampling rate of hydrates.

[0085] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention. To avoid unnecessary repetition, the present invention will not separately describe various possible combinations. But these simple modifications and combinations should also be regarded as the content disclosed by the present invention and all fall within the protection scope of the present invention.

Claims

1. A device for evaluating the damage of fracturing fluid components to hydrate reservoirs, characterized in that: The device for evaluating the damage of fracturing fluid components to hydrate reservoirs includes: A core holder (2) for loading hydrate cores; An injection mechanism (1) connected to the core holder (2) and used to inject one or more of fracturing fluid, water and gas into the core holder (2); A fracturing fluid infrared imaging mechanism (4), comprising an infrared spectrometer (42), for collecting infrared spectrum signals of the initial fracturing fluid and the fracturing fluid flowback fluid from the core holder (2); The data acquisition and analysis control system (5) is electrically connected to the infrared spectrometer (42) and is used to compare and analyze the infrared spectrum signals of the initial fracturing fluid and the fracturing fluid return fluid from the infrared spectrometer (42) to obtain the components in the fracturing fluid that are harmful to the hydrate reservoir.

2. The device for evaluating the damage of fracturing fluid components to hydrate reservoirs according to claim 1, characterized in that: The infrared spectral signals of the initial fracturing fluid and the fracturing fluid flowback fluid from the infrared spectrometer (42) are compared and analyzed to obtain the components in the fracturing fluid that are harmful to the hydrate reservoir, specifically including: Based on the infrared spectral signals of the initial fracturing fluid and the fracturing fluid flowback fluid, infrared spectra are generated respectively, and the two generated infrared spectra are compared with the standard infrared spectrum library to determine the functional groups corresponding to the absorption peaks in the two generated infrared spectra and the components of the fracturing fluid corresponding to each functional group. According to the change rate of the absorption peaks in the two infrared spectra, the components in the fracturing fluid that are harmful to the hydrate reservoir are obtained.

3. The device for evaluating the damage of fracturing fluid components to hydrate reservoirs according to claim 1 or 2, characterized in that: It also includes a low-field nuclear magnetic resonance online monitoring instrument (3), which is electrically connected to the data acquisition, analysis and control system (5), and is used to accommodate the core holder (2) and send the nuclear magnetic resonance signal of the core holder (2) collected in real time to the data acquisition, analysis and control system (5).

4. The device for evaluating the damage of fracturing fluid components to hydrate reservoirs according to claim 1, characterized in that: The injection mechanism (1) comprises: A gas source mechanism (11), a gas booster pump (13), a first multi-way valve (14) and a second multi-way valve (15) connected in sequence, wherein the first multi-way valve (14) is further connected to the outlet end of the core holder (2) via a third multi-way valve (16), and the second multi-way valve (15) is further connected to the inlet end of the core holder (2) and the infrared spectrometer (42), respectively; and a gas container (113) and a plurality of liquid containers (112) connected in parallel for containing fracturing fluid and water, wherein one end of the gas container (113) and the liquid container (112) are connected to the first multi-way valve (14), and the other end of the gas container (113) and the liquid container (112) are connected to an injection pump (110), and the injection pump (110) is connected to a first liquid storage container (19).

5. The device for evaluating the damage of fracturing fluid components to hydrate reservoirs according to claim 4, characterized in that: A water bath circulation jacket (111) is arranged outside the liquid container (112), and the inner cavity of the water bath circulation jacket (111) is connected in a closed loop with a first temperature control unit (17) and a first circulation pump (18) via a pipeline, so as to control the temperature of the liquid in the liquid container (112).

6. The device for evaluating the damage of fracturing fluid components to hydrate reservoirs according to claim 1, characterized in that: A confining pressure mechanism is arranged outside the core holder (2), and the confining pressure mechanism comprises a second liquid storage container (21). The second liquid storage container (21) comprises an inner cavity for storing confining pressure liquid. The confining pressure liquid in the inner cavity is transported to the confining pressure cavity of the core holder (2) through a pipeline and a confining pressure pump (22). The interior of the confining pressure cavity is connected to a third circulation pump (23) in a closed loop through a pipeline.

7. The device for evaluating the damage of fracturing fluid components to hydrate reservoirs according to claim 6, characterized in that: An outer cavity is integrally provided on the outer surface of the inner cavity, and the interior of the outer cavity is connected to a second temperature control unit (24) and a second circulation pump (25) in a closed loop via a pipeline, so as to control the temperature of the confining pressure liquid in the inner cavity.

8. The device for evaluating the damage of fracturing fluid components to hydrate reservoirs according to claim 1, characterized in that: The inlet and outlet ends of the core holder (2) are both provided with a temperature measuring device (26) and a pressure measuring device (27), and the temperature measuring device (26) and the pressure measuring device (27) are both electrically connected to the data acquisition, analysis and control system (5).

9. The device for evaluating the damage of fracturing fluid components to hydrate reservoirs according to claim 1, characterized in that: The fracturing fluid infrared imaging mechanism (4) further comprises a vacuum drying box (41) for performing vacuum drying treatment on the initial fracturing fluid and the fracturing fluid flowback fluid before acquiring the infrared spectrum signal.

10. A method for evaluating the damage of fracturing fluid components to hydrate reservoirs, characterized in that: The device for evaluating the damage of fracturing fluid components to hydrate reservoirs as described in any one of claims 1 to 9, the device comprising a low-field nuclear magnetic resonance online monitoring instrument (3), and the method for evaluating the damage of fracturing fluid components to hydrate reservoirs comprises the following steps: S1. Testing the air tightness of the device, selecting a core having the mineral composition and pore structure of a hydrate reservoir, evacuating the dry core, saturating the core with water and placing it in a core holder (2); S2. Injecting the target gas into both ends of the core holder (2) through the injection mechanism (1), hydrates begin to form, and using a low-field nuclear magnetic resonance online monitoring instrument (3) to scan the core to monitor the hydrate formation process in real time. When the core nuclear magnetic resonance signal no longer decreases, an equilibrium state is reached, and it is considered that hydrate formation has been completed, and a hydrate core containing the target gas is obtained; S3, selecting a fracturing fluid suitable for the hydrate reservoir, and determining the components and weight percentages of the fracturing fluid, then sending the initial fracturing fluid into the fracturing fluid infrared imaging mechanism (4) to collect infrared spectrum signals of the initial fracturing fluid, and the data acquisition and analysis control system (5) generating an infrared spectrum according to the collected infrared spectrum signals of the initial fracturing fluid and comparing it with a standard infrared spectrum library, determining the functional groups corresponding to the absorption peaks in the generated infrared spectrum, and the components of the fracturing fluid corresponding to the functional groups; S4, injecting fracturing fluid into the core holder (2) through the injection mechanism (1), then simulating the filtration process, the soaking process and the backflow process of the fracturing fluid in the hydrate core in turn, and collecting the infrared spectrum signal of the fracturing fluid backflow at set intervals during the backflow process. After the infrared spectrum signal of the fracturing fluid backflow is stable, the data acquisition and analysis control system (5) generates an infrared spectrum according to the collected stable infrared spectrum signal of the fracturing fluid backflow, and compares it with a standard infrared spectrum library to determine the functional groups corresponding to the absorption peaks in the generated infrared spectrum, as well as the components of the fracturing fluid corresponding to the functional groups. Based on the change rate of the absorption peaks in the infrared spectrum of the initial fracturing fluid, the components in the fracturing fluid that are harmful to the hydrate reservoir are obtained.

11. The method for evaluating the damage of fracturing fluid components to hydrate reservoirs according to claim 10, characterized in that: Also includes: Repeat steps S1 and S2, and then in step S4, inject the fracturing fluid containing only the obtained components harmful to the hydrate reservoir into the core holder (2), simulate the filtration process, soaking process and flowback process of the fracturing fluid in the hydrate core in sequence, collect the fracturing fluid flowback fluid and calculate the core permeability, and verify whether the current fracturing fluid components are harmful to the hydrate reservoir based on the core permeability.

12. The method for evaluating the damage of fracturing fluid components to hydrate reservoirs according to claim 11, characterized in that: The calculation formula of the core permeability is: Where K is the core permeability, mD; Q is the volume flow rate of the fluid, cm 3 / s, μ is the fluid viscosity, mPa·s; L is the core length, cm; A is the cross-sectional area of ​​the core through which the fluid flows, cm 2 ; Δp is the pressure difference between the two ends of the core, MPa.

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