Method for analyzing nmr signals of water in a miscible fluid

Abstract

The application discloses an analysis method for separating the nuclear magnetic signal of water in a mixed phase fluid, and relates to the technical field of gas reservoir development. The method comprises the following steps: adopting a time domain analysis method and a difference spectrum method to separate the nuclear magnetic signal of ethanol in a mixed solution of ethanol and water, and comparing and analyzing the nuclear magnetic signal of ethanol in the separated mixed solution of ethanol and water with the nuclear magnetic signal of the same mass of ethanol and the nuclear magnetic signal of a mixed solution of the same mass ratio of ethanol and heavy water, so as to verify the feasibility of the time domain analysis method and the difference spectrum method for separating the nuclear magnetic signal of water in the mixed solution; then, the time domain analysis method and the difference spectrum method are adopted to separate the nuclear magnetic signal of water in the mixed solution of ethanol and water, and the optimal separation method for separating the nuclear magnetic signal of water in the mixed solution of ethanol and water is determined. The application can quantitatively analyze the T2 relaxation time distribution and content of different fluids in a mixed phase solution, and provides a feasible verification basis for quantitatively analyzing the content and distribution of water in a porous medium in the process of ethanol displacement of a water-containing core.

Description

Technical Field

[0001] This invention relates to the field of gas reservoir development technology for the exploration and development of low-permeability oil and gas reservoirs, and more specifically to a method for analyzing nuclear magnetic resonance signals of separated water in miscible fluids. Background Technology

[0002] During gas reservoir development, the small throat radius, presence of native water, and microfractures make the reservoir prone to capillary self-absorption. Simultaneously, various water-based working fluids, such as drilling fluid, completion fluid, well-washing fluid, workover fluid, and fracturing fluid, come into contact with and infiltrate the formation, creating liquid retention. This results in a large number of pore throats being occupied by liquid, reducing the effective diameter of gas flow channels in the reservoir and drastically increasing flow resistance. This exhibits a significant water-locking effect, severely limiting the economical and efficient development of the gas reservoir.

[0003] To address water-lock damage in gas reservoirs, some experts have proposed injecting a drying agent that reacts rapidly with formation water in the reservoir near the wellbore, thereby reducing drag and consuming the formation water. Ethanol serves as the carrier for this drying agent, and during the chemical reaction, the ethanol and water become miscible. Because there is no interface or capillary force between the two fluids during miscibility, all fluid molecules can move freely, resulting in a single-phase fluid. Therefore, it is impossible to determine the distribution and content of water within the miscible fluid.

[0004] Nuclear magnetic resonance (NMR) technology has been widely used in reservoir engineering and reservoir geology due to its simplicity, speed, and accuracy. To quantitatively study the distribution and content of water in miscible fluids within porous media using NMR, it is necessary to determine the feasibility of separating the NMR signal of water in miscible solutions. Current technology lacks research in this area. Summary of the Invention

[0005] To overcome the defects and shortcomings of the existing technology, this invention provides a method for analyzing the NMR signal of water separation in miscible fluids. The purpose of this invention is to provide a method for analyzing the NMR signal of water separation in miscible fluids, to study the feasibility of using NMR technology to separate the NMR signal of water in miscible solutions, and to meet the need for NMR signal separation in miscible fluids. This invention provides a method for analyzing the NMR signal of water separation in miscible fluids, which rapidly separates the NMR signal of miscible fluids using NMR technology, verifies the feasibility of using NMR technology to separate the NMR signal of water in miscible solutions, and provides a basis for feasibility verification for quantitative analysis of the water content and distribution in a mixed solution of ethanol and water in a porous medium during displacement processes.

[0006] To address the problems existing in the prior art, the present invention is achieved through the following technical solution:

[0007] This invention provides a method for analyzing nuclear magnetic resonance signals of water separation in a miscible fluid, the method comprising the following steps:

[0008] S1. Set up the comparative analysis groups and set the NMR test parameters. The comparative analysis groups include the ethanol group, the water group, the mixed solution group of ethanol and water, the mixed solution group of ethanol and heavy water, and the mixed solution group of heavy water and water.

[0009] S2. The NMR signals of ethanol in the mixed solutions of ethanol and water in multiple experimental groups were separated using time-domain analysis and difference spectroscopy, respectively, and compared with the NMR signals of the same mass of ethanol and the mixed solutions of ethanol and heavy water with the same mass ratio; to verify the feasibility of separating the NMR signals of ethanol in the mixed solutions of ethanol and water using time-domain analysis and difference spectroscopy.

[0010] After the verification of steps S3 and S2 is successful, the NMR signals of water in the mixed solutions of ethanol and water in multiple experimental groups are separated by time-domain analysis and difference spectroscopy, respectively.

[0011] S4. By comparing and analyzing the NMR signal of water in the mixed solution of ethanol and water obtained by time-domain analysis with the NMR signal of water of the same mass and the NMR signal of water and water mixed solution of the same mass specific gravity, the critical mass ratio C when the NMR signal of water in the mixed solution of ethanol and water is most accurate when using time-domain analysis is used.

[0012] S5. By comparing and analyzing the NMR signal of water in a mixed solution of ethanol and water obtained by differential spectroscopy with the NMR signal of water of the same mass and the NMR signal of a mixed solution of water and water of the same mass specific gravity, the critical mass ratio D when the NMR signal of water in a mixed solution of ethanol and water is most accurate is determined.

[0013] S6. Compare the critical mass ratios C and D, and select the method corresponding to the smaller critical mass ratio to separate the NMR signal of water in the mixed solution of ethanol and water.

[0014] In a further preferred embodiment, in step S2, the NMR signals of ethanol in the mixed solutions of ethanol and water in multiple experimental groups are separated using time-domain analysis and difference spectroscopy, respectively. The NMR signals of ethanol separated by time-domain analysis and by difference spectroscopy are obtained for each experimental group. The accuracy of the NMR signals separated by time-domain analysis and by difference spectroscopy is qualitatively analyzed. The analysis reveals a critical mass ratio A. When the mass ratio of ethanol in the mixed solution of ethanol and water is greater than or equal to this critical mass ratio A, the NMR signals of ethanol in the mixed solution of ethanol and water separated by time-domain analysis and difference spectroscopy are the most accurate.

[0015] Further preferably, in step S4, the NMR signal of water in the ethanol-water mixture obtained by time-domain analysis is compared with the NMR signal of the same mass of water and the NMR signal of the same mass of water mixture. When the integral of the absolute value of the difference is zero, the NMR signal of water in the ethanol-water mixture coincides with the NMR signal of the same mass of water or the NMR signal of the same mass of water mixture. At this time, the mass ratio of water to ethanol in the ethanol-water mixture is the critical mass ratio C when the NMR signal of water in the ethanol-water mixture is most accurately separated by time-domain analysis.

[0016] More preferably, in step S5, the NMR signal of water in the ethanol-water mixture obtained by differential spectroscopy is compared with the NMR signal of the same mass of water and the NMR signal of the same mass of water and water mixture. When the integral of the absolute value of the difference is zero, the NMR signal of water in the ethanol-water mixture coincides with the NMR signal of the same mass of water or the NMR signal of the same mass of water mixture. At this time, the mass ratio of water to ethanol in the ethanol-water mixture is the critical mass ratio D when the NMR signal of water in the ethanol-water mixture is most accurate when using differential spectroscopy to separate the NMR signal of water in the ethanol-water mixture.

[0017] More preferably, in step S6, the critical mass ratio C for most accurate separation of the NMR signal of water in a mixed solution of ethanol and water using time-domain analysis is less than the critical mass ratio D for most accurate separation of the NMR signal of water in a mixed solution of ethanol and water using difference spectroscopy. In other words, when the NMR signal of water in a mixed solution of ethanol and water is most accurately separated using time-domain analysis, the applicable range of the water to ethanol mass ratio is wider than that of difference spectroscopy, and time-domain analysis is more suitable for separating the NMR signal of water in a mixed solution of ethanol and water.

[0018] More preferably, in step S4, the critical mass ratio C for most accurate separation of the NMR signal of water in the mixed solution of ethanol and water using time-domain analysis is 5.25; and in step S5, the critical mass ratio D for most accurate separation of the NMR signal of water in the mixed solution of ethanol and water using difference spectroscopy is 8.01.

[0019] More preferably, in step S2, the method of separating the NMR signal of ethanol in the mixed solution of ethanol and water using time-domain analysis is as follows:

[0020] According to the set NMR test parameters, the NMR signal of the mixed solution of ethanol and water was measured and recorded as E2; the NMR signal of water with the same mass as water in E2 was recorded as E1; and the NMR signal of the mixed solution of ethanol and heavy water with the same mass ratio as E2 was recorded as E3.

[0021] The attenuation signal of E1 is subtracted from the attenuation signal of E2, and then the T2 relaxation time E2′ of ethanol in the mixed solution of ethanol and water is obtained by inversion using time domain analysis. The difference between E2′ and the relaxation time E3 of the mixed solution of ethanol and heavy water with the same mass ratio, and the relaxation time E2′ of the ethanol solution with the same mass is compared.

[0022] Further preferably, in step S2, the method of separating the NMR signal of ethanol in the mixed solution using differential spectroscopy is as follows:

[0023] According to the set NMR test parameters, the NMR signal of the mixed solution of ethanol and water was measured and recorded as E2; the NMR signal of water with the same mass as water in E2 was recorded as E1; and the NMR signal of the mixed solution of ethanol and heavy water with the same mass ratio as E2 was recorded as E3.

[0024] E1, E2, and E3 are inverted to obtain the T2 relaxation time distribution. Then, the relaxation time of E1 is subtracted from the relaxation time of E2 using the difference spectrum method to obtain the T2 relaxation time E2′ of ethanol in the mixed solution of ethanol and water. The difference between E2′ and the relaxation time E3 of the mixed solution of ethanol and heavy water with the same mass ratio, and the relaxation time E2′ of the ethanol solution with the same mass are compared.

[0025] In a further preferred embodiment, in step S2, by performing qualitative analysis on the NMR signal of ethanol in the ethanol-water mixture, it is determined that as the mass ratio of ethanol in the ethanol-water mixture increases, the T2 relaxation time distribution and NMR signal intensity of the ethanol separated from the ethanol-water mixture gradually approach those of the same mass of ethanol solution and the same mass ratio of ethanol and heavy water mixture.

[0026] Further preferably, in step S4, the critical mass ratio C for determining the most accurate NMR signal for separating water in a mixed solution of ethanol and water using time-domain analysis is specifically as follows:

[0027] The NMR signal W2′ of water in a mixed solution of ethanol and water, the NMR signal W1 of water with the same mass as water in the mixed solution of ethanol and water, and the NMR signal W3 of a mixed solution of heavy water and water with the same mass ratio of water to ethanol as in the mixed solution of ethanol and water were obtained by time-domain analysis.

[0028] The distribution of NMR signals among W1, W2′, and W3 is quantitatively evaluated by integrating the absolute values ​​of the differences among them.

[0029] When the integral of the absolute value of the difference between W2′ and W1 and W3 is 0, the NMR signal of water in the ethanol-water mixture separated by time-domain analysis is the most accurate. At this time, the mass ratio of water to ethanol in the ethanol-water mixture is the critical value C.

[0030] Furthermore, in step S5, the critical mass ratio D for determining the most accurate NMR signal for separating water in a mixed solution of ethanol and water using differential spectroscopy is specifically as follows:

[0031] The NMR signal W2" of water in a mixed solution of ethanol and water, the NMR signal W1 of water with the same mass as water in the mixed solution of ethanol and water, and the NMR signal W3 of a mixed solution of heavy water and water with the same mass ratio of water to ethanol in the mixed solution of ethanol and water were obtained by differential spectroscopy.

[0032] The distribution of NMR signals among W1, W2" and W3 is quantitatively evaluated by integrating the absolute values ​​of the differences among them.

[0033] When the integral of the absolute value of the difference between W2" and W1 and W3 is 0, the NMR signal of water in the ethanol-water mixture separated by the difference spectrum is the most accurate. At this time, the mass ratio of water to ethanol in the ethanol-water mixture is the critical value D.

[0034] More preferably, the NMR test parameters are specifically set as follows: the NMR test waiting time TW is set to 20000ms, and the number of echoes NECH is set to a maximum of 18000.

[0035] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0036] Based on the principle of nuclear magnetic resonance, this invention establishes a method for separating the nuclear magnetic resonance signals of ethanol and water in a mixed solution. This method can quantitatively analyze the T2 relaxation time and distribution of different fluids in a mixed solution, and also provides a basis for feasibility verification for quantitative analysis of the distribution and content of water in a mixed solution of ethanol and water in a porous medium during the displacement process. Attached Figure Description

[0037] Figure 1 A comparison of the relaxation time of ethanol in a 5:1 mixture of ethanol and water separated by time-domain analysis with that of ethanol and heavy water solution (5:1) and ethanol (5).

[0038] Figure 2 A comparison of the NMR signal of ethanol in a time-domain analysis separated ethanol and water mixture (5:1) with that of ethanol and heavy water solution (5:1) and ethanol (5);

[0039] Figure 3 A comparison of the relaxation time of ethanol in a time-domain analysis-separated ethanol-water mixture (4:2) with that of ethanol and heavy water solution (4:2) and ethanol (4);

[0040] Figure 4A comparison of the NMR signal of ethanol in a time-domain analysis separated ethanol and water mixture (4:2) with that of ethanol and heavy water solution (4:2) and ethanol (4);

[0041] Figure 5 A comparison of the relaxation time of ethanol in a 3:3 mixture of ethanol and water separated by time-domain analysis with that of ethanol and heavy water solution (3:3) and ethanol (3).

[0042] Figure 6 A comparison of the NMR signal of ethanol in a time-domain analysis separated ethanol and water mixture (3:3) with that of ethanol and heavy water solution (3:3) and ethanol (3);

[0043] Figure 7 A comparison of the relaxation time of ethanol in a 1:5 mixture of ethanol and water separated by time-domain analysis with that of ethanol and heavy water solution (1:5) and ethanol (1).

[0044] Figure 8 A comparison of the NMR signal of ethanol in a time-domain analysis separated ethanol and water mixed solution (1:5) with that of ethanol and heavy water solution (1:5) and ethanol (1);

[0045] Figure 9 A comparison of the relaxation time of ethanol in a 5:1 mixture of ethanol and water by differential spectroscopy with that of ethanol and heavy water solution (5:1) and ethanol (5).

[0046] Figure 10 A comparison of the NMR signal of ethanol in a 5:1 mixture of ethanol and water separated by differential spectroscopy with that of ethanol and heavy water solution (5:1) and ethanol (5);

[0047] Figure 11 A comparison of the relaxation time of ethanol in a 4:2 mixture of ethanol and water by differential spectroscopy with that of ethanol and heavy water solution (4:2) and ethanol (4);

[0048] Figure 12 A comparison of the NMR signal of ethanol in a 4:2 mixture of ethanol and water separated by differential spectroscopy with that of ethanol and heavy water solution (4:2) and ethanol (4);

[0049] Figure 13 A comparison of the relaxation time of ethanol in a 3:3 mixture of ethanol and water by differential spectroscopy with that of ethanol and heavy water solution (3:3) and ethanol (3);

[0050] Figure 14A comparison of the NMR signal of ethanol in a 3:3 mixture of ethanol and water separated by differential spectroscopy with that of ethanol and heavy water solution (3:3) and ethanol (3);

[0051] Figure 15 A comparison of the relaxation time of ethanol in a 1:5 mixture of ethanol and water by differential spectroscopy with that of ethanol and heavy water solution (1:5) and ethanol (1);

[0052] Figure 16 A comparison of the NMR signal of ethanol in a 1:5 mixture of ethanol and water separated by differential spectroscopy with that of ethanol and heavy water solution (1:5) and ethanol (1);

[0053] Figure 17 A comparison of the relaxation time of water in a mixture of ethanol and water (5:1) separated by time-domain analysis with that of water and heavy water (1:5) and water (1);

[0054] Figure 18 A comparison of the NMR signal of water in a mixture of ethanol and water (5:1) separated by time-domain analysis with that of water and heavy water solution (1:5) and water (1).

[0055] Figure 19 A comparison of the relaxation time of water in a ethanol-water mixture (3:3) separated by time-domain analysis with that of water and heavy water (3:3) and water (3);

[0056] Figure 20 A comparison of the NMR signal of water in a mixture of ethanol and water (3:3) separated by time-domain analysis with that of water and heavy water solution (3:3) and water (3);

[0057] Figure 21 A comparison of the relaxation time of water in a mixture of ethanol and water (2:4) separated by time-domain analysis with that of water and heavy water (4:2) and water (4);

[0058] Figure 22 A comparison of the NMR signal of water in a time-domain analysis-separated ethanol and water mixture (2:4) with that of water and heavy water solution (4:2) and water (4);

[0059] Figure 23 A comparison of the relaxation time of water in a 1:5 mixture of ethanol and water separated by time-domain analysis with that of a 5:1 mixture of water and a heavy water mixture, and water (5).

[0060] Figure 24 A comparison of the NMR signal of water in a time-domain analysis separated ethanol and water mixture (1:5) with that of water and heavy water solution (5:1) and water (5);

[0061] Figure 25 The relationship between the absolute value of the NMR signal difference between water and an equal mass of water in a mixed solution of ethanol and water, and the mass ratio of water to ethanol, is presented in time-domain analysis.

[0062] Figure 26 This represents the relationship between the absolute value of the NMR signal difference between water and water of equal mass density in a mixed ethanol and water solution, and the mass ratio of water to ethanol, using time-domain analysis.

[0063] Figure 27 A comparison of the relaxation time of water in a 5:1 mixture of ethanol and water by differential spectroscopy with that of a 1:5 mixture of water and a heavy water solution, and the relaxation time of water (1).

[0064] Figure 28 A comparison of the NMR signal intensity of water in a 5:1 mixture of ethanol and water separated by differential spectroscopy with that of water and a heavy water solution (1:5) and water (1);

[0065] Figure 29 A comparison of the relaxation time of water in a 3:3 mixture of ethanol and water separated by differential spectroscopy with that of water and a 3:3 heavy water solution and water (3);

[0066] Figure 30 A comparison of the NMR signal intensity of water in a ethanol and water mixture (3:3) separated by differential spectroscopy with that of water and heavy water solution (3:3) and water (3);

[0067] Figure 31 A comparison of the relaxation time of water in a 2:4 mixture of ethanol and water separated by differential spectroscopy with that of water and a heavy water solution (4:2) and water (4);

[0068] Figure 32 A comparison of the NMR signal intensity of water in a ethanol and water mixture (2:4) separated by differential spectroscopy with that of water and heavy water solution (4:2) and water (4);

[0069] Figure 33 A comparison of the relaxation time of water in a 1:5 mixture of ethanol and water separated by differential spectroscopy with that of water and a heavy water solution (5:1) and water (5);

[0070] Figure 34 A comparison of the NMR signal intensity of water in a 1:5 mixture of ethanol and water separated by differential spectroscopy with that of water and a heavy water solution (5:1) and water (5);

[0071] Figure 35 The relationship between the absolute value of the NMR signal difference between water and an equal mass of water in a mixed solution of ethanol and water by differential spectroscopy and the mass ratio of water to ethanol.

[0072] Figure 36 The relationship between the absolute value of the NMR signal difference between water and water of the same mass ratio in a mixed solution of ethanol and water by differential spectroscopy and the mass ratio of water to ethanol.

[0073] Figure 37 This is a flowchart of NMR signal separation for water in a mixed fluid of ethanol and water. Detailed Implementation

[0074] The following are exemplary embodiments of the invention as defined by the claims and their equivalents, taken in conjunction with the accompanying drawings, to aid in a comprehensive understanding. The specific details described herein are to be considered exemplary only and not to limit the scope of the invention. Therefore, those skilled in the art can make various changes and modifications to the embodiments without departing from the scope and spirit of the invention.

[0075] Example 1

[0076] As a preferred embodiment of the present invention, this embodiment provides a more detailed explanation and description of the technical solution of the present invention through specific examples for ease of understanding.

[0077] This invention provides a method for analyzing the NMR signals of water separation in miscible fluids, particularly a method for analyzing the NMR signals of ethanol and water in a mixed solution of ethanol and water. It verifies the feasibility of using NMR technology to separate the NMR signals of water in miscible solutions. This not only adds a new method for separating NMR signals of miscible flows using NMR technology, but also provides a basis for verifying the feasibility of quantitatively analyzing the content and distribution of water in a mixed solution of ethanol and water within porous media during displacement processes.

[0078] Based on nuclear magnetic resonance (NMR), a hydrogen atom can be considered as a nucleus with a spin and a current loop rotating around its core. This nucleus generates a magnetic moment called the nuclear magnetic moment (μ), also known as a magnetic dipole. While a single hydrogen nucleus possesses a nuclear magnetic moment, a group of hydrogen nuclei does not exhibit a magnetic moment. However, when an external static magnetic field Bo is applied, the entire group of nuclei is magnetized and exhibits a macroscopic magnetization vector. This macroscopic magnetization vector is parallel to the applied magnetic field Bo. According to Curie's law, the macroscopic magnetization vector M of the nuclei in the Bo magnetic field is:

[0079]

[0080] In the formula, k represents the Boltzmann constant; This represents the gyromagnetic ratio; the gyromagnetic ratio of the hydrogen nucleus is 26.7519 × 10⁻⁶. 7 (rad T - 1 S -1T represents absolute temperature, K; h represents Planck's constant; I represents the spin quantum number of the atomic nucleus, I = 0, 1 / 2, 1, 3 / 2...

[0081] As can be seen from the above formula, the macroscopic magnetization vector M is the direct measurement object of nuclear magnetic resonance. When the atomic nucleus is selected, its value is determined by the number of spins per unit volume N, the applied magnetic field strength BO, and the temperature T.

[0082] Due to the nature of nuclear magnetic resonance (NMR) technology, the identification of different fluids using NMR can currently be divided into two main categories:

[0083] ① Fluid identification methods based on pulse scanning sequences and time parameters mainly distinguish the NMR signals of different fluids by selecting appropriate scanning pulse sequences and test parameters. This is because different fluids have different diffusion capabilities under an applied gradient field, resulting in different relaxation times. This difference can be highlighted by changing the echo interval, etc. Then, the NMR signals are inverted and processed using the difference spectrum method (DSM) and time domain analysis (TDA) to obtain the relaxation time distribution of different fluids. The difference spectrum method refers to determining the proton polarization waiting time during NMR testing using the CPMG pulse sequence; that is, the time between the end of one CPMG pulse test and the start of a new CPMG pulse sequence. The waiting time needs to be large enough to ensure complete proton polarization. If the TW is too small, some spin nuclei may not have fully recovered to thermal equilibrium before being subjected to a 90-degree pulse and starting NMR, thus weakening the detected NMR signal. When the TW value decreases to a certain extent, the NMR signal of these incompletely polarized spin nuclei may be completely undetectable. By measuring the T2 relaxation time of a mixed oil, gas, and water mixture using different TW values, and subtracting the relaxation times, the NMR signal of a particular fluid can be preserved. This involves inverting the attenuation curves of two NMR signals with different waiting times to obtain the corresponding T2 spectrum. Then, subtracting the T2 spectrum of the shorter waiting time from the T2 spectrum of the longer waiting time yields the difference spectrum, which represents the T2 spectrum distribution of the remaining fluid. The time-domain analysis method involves subtracting the echo train signal of the shorter waiting time (TWS) from the echo train signal of the longer waiting time (TWL) to obtain the echo train difference of the other fluid. Multi-exponential inversion is then used to invert this echo train difference to obtain the T2 signal distribution of this fluid. Both the time-domain analysis method and the difference spectrum method belong to the dual-TW method, with the time-domain analysis method being an extension and improvement of the difference spectrum method. It performs subtraction operations in the time domain and inverts the echo train difference. This method is more accurate and has less noise than the difference spectrum method.

[0084] ② Fluid identification methods based on added reagents are primarily based on the fact that the signal intensity of nuclear magnetic resonance (NMR) is related to the fluid and temperature, and is generally a constant. Different fluids exhibit differences in their T1 and T2 values, and these values ​​can be altered by changing the magnetic field around the protons. Therefore, the difference in T1 and T2 values ​​is used to distinguish different fluids. Common methods mainly involve adding two main types of reagents: paramagnetic reagents and ferromagnetic reagents, which shorten the T1 and T2 times respectively, highlighting the signals of other liquids and thus distinguishing the fluids.

[0085] In addition, fluids that do not show detectable NMR signals can be directly distinguished and identified. A commonly used reagent is heavy water, whose chemical and physical properties are very similar to ordinary water, and it can largely replace ordinary water.

[0086] Based on the principles of nuclear magnetic resonance (NMR), the NMR signal is only related to the number of hydrogen nuclei, the gyromagnetic ratio, the applied magnetic field, and the temperature. Therefore, the NMR signal of an ethanol-water mixture can be considered as the sum of the NMR signals of equal volumes of ethanol and water. Based on the aforementioned NMR identification methods for oil, gas, and water, and the principles of NMR, it can be seen that the NMR signal of an ethanol-water mixture can be considered as the sum of the NMR signals of individual masses of water and ethanol. Therefore, the NMR signal of an equal mass of ethanol can be subtracted from a portion of the mixture to separate the NMR signal of water in the ethanol-water mixture. This is why time-domain analysis and difference spectroscopy are used for NMR signal separation.

[0087] Reference manual attached Figure 7 As shown, the technical solution of the present invention will be described in detail below.

[0088] The first step is to set up multiple mixed solutions of ethanol, water and heavy water with different mass ratios, and set the NMR test parameters.

[0089] Based on the above principle, several mixed solutions of ethanol, water, and heavy water with different mass ratios were designed (as shown in Table 1). The waiting time TW for NMR testing was set to 20,000 ms, and the number of echoes NECH was set to a maximum of 18,000 to ensure that the hydrogen nuclei in the fluid could fully relax.

[0090] Table 1. Solution ratios for different mass ratios

[0091]

[0092] The second step involves using time-domain analysis to separate the NMR signals of ethanol in multiple mixed solutions of ethanol and water with different mass ratios from step S1, obtaining the NMR signals of ethanol separated by time-domain analysis.

[0093] First, the NMR signal of ethanol in the mixed solution of ethanol and water was separated using time-domain analysis. According to the set test parameters, the NMR signal E2 of the mixed solution of ethanol, water, and heavy water with a mass ratio of 1:5:0 (group 5), the NMR signal E1 of the mixed solution of ethanol, water, and heavy water with a mass ratio of 0:5:0 (group 3), and the NMR signal E3 of the mixed solution of ethanol, water, and heavy water with a mass ratio of 1:0:5 (group 2) were measured. The attenuation signal of E1 was subtracted from the attenuation signal of E2. Then, the NMR signal of the mixed solution of ethanol, water, and heavy water with a mass ratio of 1:5:0 was obtained using time-domain analysis. The T2 relaxation time E2′ of ethanol in the aqueous mixture (Group 5) was measured and compared with the relaxation time E2′ of the aqueous mixture (Group 2) containing ethanol, water, and heavy water at a mass ratio of 1:0:5 (Group 2), and the relaxation time E2′ of the aqueous mixture (Group 1) containing ethanol, water, and heavy water at a mass ratio of 1:0:0 (Group 1). A similar method can be used to compare the NMR signals E2′ of ethanol separated from aqueous mixtures with different mass ratios with the NMR signals E3 of aqueous mixtures containing the same mass ratio of ethanol and heavy water, and E2′ of aqueous mixtures containing the same mass of ethanol. Figures 1-8 As shown.

[0094] The third step involves using the difference spectrum method to separate the NMR signals of ethanol in multiple mixed solutions of ethanol, water and heavy water with different mass ratios from step S1, according to the set NMR test parameters, and obtaining the NMR signal of ethanol separated by the difference spectrum method.

[0095] The NMR signals of ethanol in the mixed solution were separated using the difference spectrum method. According to the set test parameters, the NMR signals E2 of the ethanol, water, and heavy water mixed solution with a mass ratio of 1:5:0 (group 5), E1 of the ethanol, water, and heavy water mixed solution with a mass ratio of 0:5:0 (group 3), and E3 of the ethanol, water, and heavy water mixed solution with a mass ratio of 1:0:5 (group 2) were measured. The T2 relaxation time distributions of E1, E2, and E3 were inverted. Then, the relaxation time of E1 was subtracted from the relaxation time of E2 using the difference spectrum method to obtain the NMR signal of the ethanol, water, and heavy water mixed solution with a mass ratio of 1:5:0. The T2 relaxation time E2′ of ethanol in the water mixture solution (Group 5) was measured and compared with the relaxation time E3 of the ethanol, water, and heavy water mixture solution (Group 2) with a mass ratio of 1:0:5, and the relaxation time E2″ of the ethanol, water, and heavy water mixture solution (Group 1) with a mass ratio of 1:0:0. The differences among the three were also analyzed. Similarly, the NMR signals E2′ of ethanol separated from ethanol and water mixture solutions with different mass ratios were obtained using the difference spectroscopy method and compared with the NMR signals E3 of the ethanol, water, and heavy water mixture solution with the same mass ratio, and E2″ of the ethanol mixture solution with the same mass ratio. Figures 9-16 As shown.

[0096] Fourthly, as the proportion of ethanol in the ethanol-water mixture increases, the T2 relaxation time distribution and NMR signal intensity of the ethanol separated from the ethanol-water mixture (Group 5) gradually converge with those of the same mass ethanol solution (Group 3) and the same mass ratio of ethanol and heavy water solution (Group 2). When the mass ratio of ethanol to water in the ethanol-water mixture exceeds a certain critical value, the T2 relaxation time of the ethanol separated from the ethanol-water mixture coincides with the T2 relaxation time distributions of the same mass ratio of ethanol and heavy water solution and the same mass ethanol solution. This indicates that the NMR signal separation of ethanol in the ethanol-water mixture is most accurate. In other words, there is a critical mass ratio of ethanol to water in the ethanol-water mixture. When the mass ratio of ethanol to water in the mixture is greater than or equal to this critical value, the time-domain analysis method and difference spectroscopy method are most accurate for separating the NMR signal of ethanol in the ethanol-water mixture.

[0097] Fifth, following the same method described above, find the critical mass ratio of water to ethanol in a mixed solution of ethanol and water when the NMR signal of water separation using time-domain analysis is most accurate; and find the critical mass ratio of water to ethanol in a mixed solution of ethanol and water when the NMR signal of water separation using difference spectroscopy is most accurate.

[0098] By verifying the separation of the T2 relaxation time of ethanol from a mixed solution of ethanol and water, it was found that the NMR signal of ethanol is most accurately separated when the mass ratio of ethanol to water in the mixed solution is greater than or equal to a certain value. Therefore, the same method can be used to separate the T2 relaxation time of water in a mixed solution of ethanol and water to find the critical mass ratio of water to ethanol in the mixed solution that provides the most accurate NMR signal separation. First, following the above steps, the relaxation time of water in mixed solutions of ethanol and water with different mass ratios in Table 1 was separated using time-domain analysis and difference spectroscopy. Figures 17 to 24 , Figures 27 to 34 As shown. Then, the NMR signals W2′ of water in the ethanol and water mixture, W1 of the same mass of water, and W3 of the same mass ratio of heavy water and water mixture were obtained by time-domain analysis and difference spectroscopy. When the integral of the absolute value of the difference between W2′ and W1, and between W2′ and W3 is 0 (e.g. Figure 25 and Figure 26 , Figure 35 and Figure 36 As shown in Table 2), the NMR signals of the two solutions overlap, indicating that the NMR signal of water in the ethanol-water mixture separated by different methods is the most accurate. At this point, the mass ratio of water to ethanol in the ethanol-water mixture is the critical mass ratio, as shown in Table 2. The specific experimental analysis procedure is as follows: Figure 37 As shown.

[0099] Table 2. Critical mass ratios of water and ethanol when the NMR signals of water in mixed solutions obtained by different methods coincide with the NMR signals of the same mass of water and the NMR signals of mixed solutions of heavy water and water with the same mass ratio.

[0100]

[0101] Example 2

[0102] As another preferred embodiment of the present invention, please refer to the appendix to the specification. Figure 37 As shown in the figure, this embodiment discloses a method for analyzing the nuclear magnetic resonance signal of water separation in a miscible fluid. The method includes the following steps:

[0103] S1. Set up the comparative analysis groups and set the NMR test parameters. The comparative analysis groups include the ethanol group, the water group, the mixed solution group of ethanol and water, the mixed solution group of ethanol and heavy water, and the mixed solution group of water and heavy water.

[0104] S2. The NMR signals of ethanol in the mixed solutions of ethanol and water in multiple experimental groups were separated using time-domain analysis and difference spectroscopy, respectively, and compared with the NMR signals of the same mass of ethanol and the mixed solutions of ethanol and heavy water of the same mass ratio; to verify the feasibility of separating the NMR signals of ethanol in the mixed solutions using time-domain analysis and difference spectroscopy.

[0105] The NMR signals of ethanol in mixed solutions of ethanol and water in multiple experimental groups were separated using time-domain analysis and difference spectroscopy, respectively. The NMR signals of ethanol separated by time-domain analysis and difference spectroscopy were obtained for each experimental group. The accuracy of the NMR signals separated by time-domain analysis and difference spectroscopy was qualitatively analyzed. The analysis revealed a critical mass ratio A. When the mass ratio of ethanol in the mixed solution of ethanol and water is greater than or equal to this critical mass ratio A, the NMR signals of ethanol in the mixed solution of ethanol and water separated by time-domain analysis and difference spectroscopy are the most accurate.

[0106] After the verification of steps S3 and S2 is successful, the NMR signals of water in the mixed solutions of ethanol and water in multiple experimental groups are separated by time-domain analysis and difference spectroscopy, respectively.

[0107] S4. By comparing and analyzing the NMR signal of water in the mixed solution of ethanol and water obtained by time-domain analysis with the NMR signal of water of the same mass and the NMR signal of water and water mixed solution of the same mass specific gravity, the critical mass ratio C when the NMR signal of water in the mixed solution of ethanol and water is most accurate when using time-domain analysis is used.

[0108] In step S4, the NMR signal of water in the ethanol-water mixture obtained by time-domain analysis is compared with the NMR signal of the same mass of water and the NMR signal of the same mass of water and water mixture. When the integral of the absolute value of the difference is zero, the NMR signal of water in the ethanol-water mixture coincides with the NMR signal of the same mass of water or the NMR signal of the same mass of water mixture. At this time, the mass ratio of water to ethanol in the ethanol-water mixture is the critical mass ratio C when the NMR signal of water in the ethanol-water mixture is most accurately separated by time-domain analysis.

[0109] S5. By comparing and analyzing the NMR signal of water in a mixed solution of ethanol and water obtained by differential spectroscopy with the NMR signal of water of the same mass and the NMR signal of a mixed solution of water and water of the same mass specific gravity, the critical mass ratio D when the NMR signal of water in a mixed solution of ethanol and water is most accurate is determined.

[0110] In step S5, the NMR signal of water in the ethanol-water mixture obtained by differential spectroscopy is compared with the NMR signal of the same mass of water and the NMR signal of the same mass of water and water mixture. When the integral of the absolute value of the difference is zero, the NMR signal of water in the ethanol-water mixture coincides with the NMR signal of the same mass of water or the NMR signal of the same mass of water mixture. At this time, the mass ratio of water to ethanol in the ethanol-water mixture is the critical mass ratio D when the NMR signal of water in the ethanol-water mixture is most accurate when using differential spectroscopy to separate the NMR signal of water in the ethanol-water mixture.

[0111] S6. Compare the critical mass ratio C and critical mass ratio D, and select the method corresponding to the smaller critical mass ratio to separate the NMR signal of water in the mixed solution of ethanol and water.

[0112] The critical mass ratio C for most accurate separation of the NMR signal of water in a mixed solution of ethanol and water using time-domain analysis is less than the critical mass ratio D for most accurate separation using difference spectroscopy. Therefore, time-domain analysis has a wider applicable range for the water-to-ethanol mass ratio when separating the NMR signal of water in a mixed solution of ethanol and water than difference spectroscopy. Specifically, time-domain analysis is more suitable for separating the NMR signal of water in a mixed solution of ethanol and water.

[0113] In step S6, since the critical mass ratios of water and ethanol obtained by the difference spectrum method and the time-domain analysis method are different when separating the NMR signal of water in a mixed solution of ethanol and water most accurately, the critical mass ratio of water to ethanol obtained by the two methods is greater than that of the time-domain analysis method. This means that when separating the NMR signal of water in a mixed solution of ethanol and water, the time-domain analysis method has a smaller critical mass ratio and a wider range of applications than the difference spectrum method. Therefore, compared with the difference spectrum method, the time-domain analysis method is more suitable for separating the NMR signal of water in a mixed solution of ethanol and water.

[0114] As one implementation method of this embodiment, in step S2, the method of separating the NMR signal of ethanol in the mixed solution using time-domain analysis is specifically as follows:

[0115] According to the set NMR test parameters, the NMR signal of the mixed solution of ethanol and water was measured and recorded as E2; the NMR signal of water with the same mass as water in E2 was recorded as E1; and the NMR signal of the mixed solution of ethanol and heavy water with the same mass ratio as E2 was recorded as E3.

[0116] The attenuation signal of E1 is subtracted from the attenuation signal of E2, and then the T2 relaxation time E2′ of ethanol in the mixed solution of ethanol and water is obtained by inversion using time domain analysis. The difference between E2′ and the relaxation time E3 of the mixed solution of ethanol and heavy water with the same mass ratio, and the relaxation time E2′ of the ethanol solution with the same mass is compared.

[0117] In step S2, the NMR signal of ethanol in the mixed solution is separated using the difference spectrum method, specifically as follows:

[0118] According to the set NMR test parameters, the NMR signal of the mixed solution of ethanol and water was measured and recorded as E2; the NMR signal of water with the same mass as water in E2 was recorded as E1; and the NMR signal of the mixed solution of ethanol and heavy water with the same mass ratio as E2 was recorded as E3.

[0119] E1, E2, and E3 are inverted to obtain the T2 relaxation time distribution. Then, the relaxation time of E1 is subtracted from the relaxation time of E2 using the difference spectrum method to obtain the T2 relaxation time E2′ of ethanol in the mixed solution of ethanol and water. The difference between E2′ and the relaxation time E3 of the mixed solution of ethanol and heavy water with the same mass ratio, and the relaxation time E2′ of the ethanol solution with the same mass are compared.

[0120] In step S2, by qualitatively analyzing the NMR signal of ethanol in the ethanol-water mixture, it was determined that as the mass ratio of ethanol in the ethanol-water mixture increases, the T2 relaxation time distribution and NMR signal of the ethanol separated from the ethanol-water mixture gradually approach those of the same mass of ethanol solution and the same mass ratio of ethanol and heavy water mixture.

[0121] In another implementation of this embodiment, in step S4, the critical mass ratio C for determining the most accurate NMR signal separation of water in a mixed solution of ethanol and water using time-domain analysis is specifically as follows:

[0122] The NMR signal W2′ of water in a mixed solution of ethanol and water, the NMR signal W1 of water with the same mass as water in the mixed solution of ethanol and water, and the NMR signal W3 of a mixed solution of heavy water and water with the same mass ratio of water to ethanol as in the mixed solution of ethanol and water were obtained by time-domain analysis.

[0123] The distribution of NMR signals among W1, W2′, and W3 is quantitatively evaluated by integrating the absolute values ​​of the differences among them.

[0124] When the integral of the absolute value of the difference between W2′ and W1 and W3 is 0, the NMR signal of water in the ethanol-water mixture separated by time-domain analysis is the most accurate. At this time, the mass ratio of water to ethanol in the ethanol-water mixture is the critical value C.

[0125] In another implementation of this embodiment, in step S5, the critical mass ratio D for determining the most accurate NMR signal separation of water in a mixed solution of ethanol and water using differential spectroscopy is specifically as follows:

[0126] The NMR signal W2" of water in a mixed solution of ethanol and water, the NMR signal W1 of water with the same mass as water in the mixed solution of ethanol and water, and the NMR signal W3 of a mixed solution of heavy water and water with the same mass ratio of water to ethanol in the mixed solution of ethanol and water were obtained by differential spectroscopy.

[0127] The distribution of NMR signals among W1, W2" and W3 is quantitatively evaluated by integrating the absolute values ​​of the differences among them.

[0128] When the integral of the absolute value of the difference between W2" and W1 and W3 is 0, the NMR signal of water in the ethanol-water mixture separated by the difference spectrum is the most accurate. At this time, the mass ratio of water to ethanol in the ethanol-water mixture is the critical value D.

[0129] As an example, the NMR test parameters are specifically set as follows: the NMR test waiting time TW is set to 20000ms, and the number of echoes NECH is set to a maximum of 18000.

[0130] Example 3

[0131] As another preferred embodiment of the present invention, this embodiment proposes an analysis method for NMR signals of water separation in miscible fluids. This method can not only meet the NMR signal separation requirements of components in similar miscible flows, but also provide a basis for feasibility verification for quantitative analysis of the water content and distribution in a mixed solution of ethanol and water in a porous medium during displacement.

[0132] Five different mass ratios of ethanol, water and heavy water were designed (as shown in Table 1). In step S1, the test parameters of the nuclear magnetic resonance test fluid were first set to ensure that the fluid was fully relaxed and to avoid signal acquisition loss.

[0133] Then, through step S2, time-domain analysis is used ( Figure 1 ) and difference spectrum method ( Figures 7 to 16 The NMR signal of water in the ethanol-water mixture was obtained and qualitatively compared with the NMR signals of ethanol and heavy water with the same mass ratio. It can be seen that when the mass ratio of ethanol to water in the ethanol-water mixture is greater than a certain critical value (critical value A / critical value B), the T2 relaxation time of ethanol separated from the ethanol-water mixture coincides with the T2 relaxation time distribution of the ethanol-water mixture with the same mass ratio of ethanol and heavy water and the ethanol solution with the same mass ratio. That is, the NMR signal of ethanol in the ethanol-water mixture is most accurately separated.

[0134] Based on the above analysis, to accurately separate the NMR signal of water in an ethanol-water mixture, it is necessary to know the critical mass ratio of water to ethanol for the most accurate separation. Step S4 shows that the most accurate NMR separation of water in the ethanol-water mixture using time-domain analysis, i.e., when the NMR signal of water obtained by time-domain analysis coincides with the NMR signal of water in the same mass ratio, is 5.23. When the NMR signal of water in the ethanol-water mixture obtained by time-domain analysis coincides with the NMR signals of heavy water and water in the same mass ratio, the critical mass ratio of water to ethanol is 5.27, with an average value of 5.25.

[0135] When the NMR signal of water in the ethanol-water mixture obtained by the differential spectroscopy method is most accurate in step S5, that is, when the NMR signal of water in the ethanol-water mixture obtained by the differential spectroscopy method coincides with the NMR signal of water in the same mass ratio, the critical mass ratio of water to ethanol in the ethanol-water mixture is 7.94; when the NMR signal of water in the ethanol-water mixture obtained by the differential spectroscopy method coincides with the NMR signal of heavy water and water in the same mass ratio, the critical mass ratio of water to ethanol in the ethanol-water mixture is 8.07, and the average value is 8.01.

Claims

1. A method for analyzing the nuclear magnetic resonance signal of water separation in a miscible fluid, characterized in that: The method includes the following steps: S1. Set up the comparative analysis groups and set the NMR test parameters. The comparative analysis groups include the ethanol group, the water group, the mixed solution group of ethanol and water, the mixed solution group of ethanol and heavy water, and the mixed solution group of water and heavy water. S2. The NMR signals of ethanol in the mixed solutions of ethanol and water in multiple experimental groups were separated using time-domain analysis and difference spectroscopy, respectively. The NMR signals of ethanol separated by time-domain analysis and by difference spectroscopy were obtained for each experimental group. The accuracy of the NMR signals separated by time-domain analysis and by difference spectroscopy was qualitatively analyzed. The analysis revealed a critical mass ratio A; when the mass ratio of ethanol in the mixed solution of ethanol and water is greater than this critical mass ratio A, the NMR signal of ethanol separated by time-domain analysis is accurate. Similarly, a critical mass ratio B exists; when the mass ratio of ethanol in the mixed solution of ethanol and water is greater than this critical mass ratio B, the NMR signal of ethanol separated by difference spectroscopy is accurate. After the verification of steps S3 and S2 is successful, the NMR signals of water in the mixed solutions of ethanol and water in multiple experimental groups are separated by time-domain analysis and difference spectroscopy, respectively. S4. Compare and analyze the NMR signals of water in a mixed solution of ethanol and water obtained by time-domain analysis with those of water of the same mass and a mixed solution of water and water of the same specific gravity to determine the critical mass ratio C at which the time-domain analysis method is most accurate in separating the NMR signal of water in a mixed solution of ethanol and water; specifically, The analysis compares the absolute values ​​of the differences between the NMR signals of water in a mixed solution of ethanol and water obtained by time-domain analysis and those of water in a mixed solution of water with the same mass and specific gravity. When the integral of this absolute value is zero, the NMR signal of water in the mixed solution of ethanol and water coincides with the NMR signal of water with the same mass or the NMR signal of water in a mixed solution of water with the same specific gravity. At this point, the mass ratio of water to ethanol in the mixed solution of ethanol and water is the critical mass ratio C at which the NMR signal of water in the mixed solution is most accurately separated by time-domain analysis. S5. Compare and analyze the NMR signals of water in a mixed solution of ethanol and water obtained by differential spectroscopy with those of water of the same mass and a mixed solution of water and water of the same specific gravity to determine the critical mass ratio D at which the differential spectroscopy method is most accurate in separating the NMR signal of water in a mixed solution of ethanol and water; specifically, The analysis compares the integral of the absolute value of the difference between the NMR signal of water in a mixed solution of ethanol and water obtained by differential spectroscopy and the NMR signal of water in a mixed solution of water and water with the same mass and specific gravity. When the integral of the absolute value of this difference is zero, the NMR signal of water in the mixed solution of ethanol and water coincides with the NMR signal of water with the same mass or the NMR signal of water in a mixed solution of water and water with the same specific gravity. At this point, the mass ratio of water to ethanol in the mixed solution of ethanol and water is the critical mass ratio D at which the NMR signal of water in the mixed solution is most accurately separated by differential spectroscopy. S6. Compare the critical mass ratios C and D, and select the method corresponding to the smaller critical mass ratio to separate the NMR signal of water in the mixed solution of ethanol and water.

2. The method for analyzing the NMR signal of water separation in a miscible fluid as described in claim 1, characterized in that: In step S6, the critical mass ratio C for the most accurate separation of the NMR signal of water in a mixed solution of ethanol and water using time-domain analysis is less than the critical mass ratio D for the most accurate separation of the NMR signal of water in a mixed solution of ethanol and water using difference spectroscopy. This means that time-domain analysis has a wider range of applications than difference spectroscopy, and it is suitable for separating the NMR signal of water in a mixed solution of ethanol and water.

3. The method for analyzing the NMR signal of water separation in a miscible fluid as described in claim 2, characterized in that: In step S4, the critical mass ratio C for the most accurate separation of water in the mixed solution of ethanol and water using time-domain analysis is 5.25; in step S5, the critical mass ratio D for the most accurate separation of water in the mixed solution of ethanol and water using difference spectroscopy is 8.

01.

4. The method for analyzing the NMR signal of water separation in a miscible fluid as described in claim 1, characterized in that: In step S2, the NMR signal of ethanol in the mixed solution is separated using time-domain analysis, specifically as follows: According to the set NMR test parameters, the NMR signal of the mixed solution of ethanol and water was measured and recorded as E2; the NMR signal of water with the same mass as water in E2 was recorded as E1; and the NMR signal of the mixed solution of ethanol and heavy water with the same mass ratio as E2 was recorded as E3. The attenuation signal of E1 is subtracted from the attenuation signal of E2, and then the T2 relaxation time E2′ of ethanol in the mixed solution of ethanol and water is obtained by inversion using time domain analysis. The difference between E2′ and the relaxation time E3 of the mixed solution of ethanol and heavy water with the same mass ratio, and the relaxation time E2′ of the ethanol solution with the same mass is compared.

5. The method for analyzing the NMR signal of water separation in a miscible fluid as described in any one of claims 1-4, characterized in that: In step S2, the NMR signal of ethanol in the mixed solution is separated using the difference spectrum method, specifically as follows: According to the set NMR test parameters, the NMR signal of the mixed solution of ethanol and water was measured and recorded as E2; the NMR signal of water with the same mass as water in E2 was recorded as E1; and the NMR signal of the mixed solution of ethanol and heavy water with the same mass ratio as E2 was recorded as E3. E1, E2, and E3 are inverted to obtain the T2 relaxation time distribution. Then, the relaxation time of E1 is subtracted from the relaxation time of E2 using the difference spectrum method to obtain the T2 relaxation time E2′ of ethanol in the mixed solution of ethanol and water. The difference between E2′ and the relaxation time E3 of the mixed solution of ethanol and heavy water with the same mass ratio, and the relaxation time E2′ of the ethanol solution with the same mass are compared.

6. The method for analyzing the NMR signal of water separation in a miscible fluid as described in any one of claims 1-4, characterized in that: In step S2, by qualitatively analyzing the NMR signal of ethanol in the ethanol-water mixture, it was determined that as the mass ratio of ethanol in the ethanol-water mixture increases, the T2 relaxation time distribution and NMR signal of the ethanol separated from the ethanol-water mixture gradually approach those of the same mass of ethanol solution and the same mass ratio of ethanol and heavy water mixture.

7. The method for analyzing the NMR signal of water separation in a miscible fluid as described in any one of claims 1-4, characterized in that: In step S4, the critical mass ratio C for determining the most accurate NMR signal for separating water in a mixed solution of ethanol and water using time-domain analysis is specifically: The NMR signal W2′ of water in a mixed solution of ethanol and water, the NMR signal W1 of water with the same mass as water in the mixed solution of ethanol and water, and the NMR signal W3 of a mixed solution of heavy water and water with the same mass ratio of water to ethanol as in the mixed solution of ethanol and water were obtained by time-domain analysis. The distribution of NMR signals among W1, W2′, and W3 is quantitatively evaluated by integrating the absolute values ​​of the differences among them. When the integral of the absolute value of the difference between W2′ and W1 and W2 is 0, the NMR signal of water in the ethanol-water mixture separated by time-domain analysis is the most accurate. At this time, the mass ratio of water to ethanol in the ethanol-water mixture is the critical value C.

8. The method for analyzing the NMR signal of water separation in a miscible fluid as described in any one of claims 1-4, characterized in that: In step S5, the critical mass ratio D for determining the most accurate NMR signal separation of water in a mixed solution of ethanol and water using differential spectroscopy is specifically: The NMR signal W2" of water in a mixed solution of ethanol and water, the NMR signal W1 of water with the same mass as water in the mixed solution of ethanol and water, and the NMR signal W3 of a mixed solution of heavy water and water with the same mass ratio of water to ethanol in the mixed solution of ethanol and water were obtained by differential spectroscopy. The distribution of NMR signals among W1, W2" and W3 is quantitatively evaluated by integrating the absolute values ​​of the differences among them. When the absolute value of the difference between W2" and W1 and W2 is integrated to 0, the NMR signal of water in the ethanol-water mixture separated by the difference spectrum is the most accurate. At this time, the mass ratio of water to ethanol in the ethanol-water mixture is the critical value D.

9. The method for analyzing the nuclear magnetic resonance signal of water separation in a miscible fluid as described in any one of claims 1-4, characterized in that: The specific NMR test parameters are set as follows: the NMR test waiting time TW is set to 20000ms, and the number of echoes NECH is set to a maximum of 18000.

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