Method for measuring waxy content of crude oil by nuclear magnetic resonance and system therefor

Abstract

This invention relates to a method for measuring the wax content of crude oil using nuclear magnetic resonance (NMR), comprising: heating the crude oil sample to be tested to a homogeneous fluid state and then injecting it into a sample tube; cooling the sample tube in a low-temperature environment to allow complete precipitation of paraffin wax in the crude oil; placing the cooled sample tube in an NMR instrument and acquiring NMR signals using a free induction decay sequence; performing a two-component fitting on the acquired NMR signals to obtain the initial signal amplitudes A1 and A2 of the solid and liquid phases, and calculating the ratio x between the initial signal amplitudes of the solid and liquid phases based on A1 and A2; calculating the mass ratio y between the solid and liquid phases using a pre-established calibration model y=k·x; and calculating the wax content c of the crude oil sample to be tested based on the solid-liquid mass ratio y. This invention also relates to a corresponding system. The method and system for measuring the wax content of crude oil using NMR of this invention effectively solve the problems of long testing time and environmental unfriendliness associated with the national standard method.

Description

Technical Field

[0001] This invention relates to the fields of petroleum engineering and oilfield development, and particularly to the field of crude oil wax content measurement, specifically a method and system for measuring crude oil wax content using nuclear magnetic resonance. Background Technology

[0002] Crude oil is an extremely complex mixture of natural hydrocarbons. Paraffin wax, a solid hydrocarbon in crude oil, typically exists in a dissolved colloidal state. When crude oil is extracted from high-temperature, high-pressure formations to the surface, the temperature and pressure drop, reducing the solubility of paraffin wax and causing it to crystallize and precipitate. This leads to wax buildup in wells and pipelines, and can even cause blockages. At lower temperatures, high-wax crude oil easily loses its fluidity, negatively impacting crude oil extraction, storage, and transportation, and increasing production costs. The pour point of crude oil is directly related to its wax content. Therefore, measuring the wax content of crude oil is crucial for accurately understanding its physical properties, mitigating production risks, optimizing processes, and maximizing product value.

[0003] The existing national standard GB / T 26982-2022, "Determination of Wax Content in Crude Oil," specifies two methods (Method A and Method B) for measuring the wax content in crude oil. The greatest advantage of this method lies in the authority and accuracy of its results. However, the complex experimental procedures and large consumption of chemical reagents make this method time-consuming, labor-intensive, costly, and require highly skilled operators, while also posing significant safety risks. Therefore, this method is not suitable for real-time monitoring or large-scale screening scenarios.

[0004] The method for nuclear magnetic resonance FID sequence measurement in the article "Novel Nuclear Magnetic Resonance Techniques To Assess the Wax Precipitation Evolution in Crude Oil Systems" published by GC Savulescu et al. in the journal *Energy & Fuels* in 2023 is most similar to that of this invention. The specific steps are as follows: Preparation of standard samples: Dissolve the wax in toluene or deuterated toluene to prepare wax solutions of different concentrations (5-15%).

[0005] Where m is the total mass of the sample, m1 is the mass of the solid phase (paraffin) in the sample, m2 is the mass of the liquid phase (oil) in the sample, and x is the mass fraction of paraffin.

[0006] Data acquisition: Using the FID sequence, signals were acquired between 13 μs (the first point that can be measured by the NMR instrument) and 268 μs, with a data point interval of 1 μs.

[0007] Data Fitting: FID analysis is based on the difference in proton relaxation rates between crystalline and amorphous phases, using a double Gaussian equation: Among them, L e Compared with the initial signal amplitude of the liquid phase, T l The corrected FID relaxation time of the liquid phase is represented by S, and the initial signal amplitude of the solid phase is represented by T. s The corrected FID relaxation time of the solid phase is represented by t, where t is the acquisition time.

[0008] Substituting L and S into the above formula at t=0, calculate the proportion f of solid-phase NMR signal at time 0: Where f represents the proportion of NMR signal of solid phase component at time 0; S represents the NMR signal of solid phase component at time 0; and L represents the NMR signal of liquid phase component at time 0.

[0009] At t=0, , ,therefore: k1 represents the NMR signal per unit mass of the solid phase component, and k2 represents the NMR signal per unit mass of the liquid phase component.

[0010] Calibration: Using the FID sequence, the reference sample was measured as described above to establish a linear relationship between the wax content x and the proportion of solid-phase NMR signal at time 0, f. It is important to note that establishing a linear relationship between x and f requires establishing the following assumptions: k1≈k2 Under this assumption: Sample testing: The sample to be tested was measured using the FID sequence as described above. The f value was obtained by substituting the fitted L and S values, and the wax content was calculated.

[0011] This method has the following problems: 1. The lowest test temperature is 0℃, which cannot guarantee complete paraffin precipitation; 2. The double Gaussian fitting has poor applicability to samples with solid-liquid combinations, and the fitting residual for the liquid phase component is large; 3. In fact, the relationship between f and x is only linear when k1=k2, and is fractional under other conditions. Therefore, there is a system modeling error when performing linear fitting. The larger the difference between k1 and k2, the lower the linear fitting R. 2The smaller the value, the better. 4. This method uses toluene as the liquid phase component of the standard. Since the NMR signal contribution per unit mass of toluene differs from that of actual crude oil, there is a calibration mismatch error when using toluene as the liquid phase standard to calibrate actual crude oil samples, and this error cannot be corrected.

[0012] Therefore, this calibration method only results in relatively small measurement errors when calibrating physical objects. Summary of the Invention

[0013] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method and system for measuring the wax content of crude oil using nuclear magnetic resonance.

[0014] To achieve the above objectives, the method and system for measuring the wax content of crude oil using nuclear magnetic resonance according to the present invention are as follows: The main feature of this method for measuring the wax content of crude oil using nuclear magnetic resonance is that the method includes the following steps: (1) After heating the crude oil sample to be tested to a homogeneous fluid state, inject it into the sample tube; (2) The sample tube is placed in a low-temperature environment to cool it, so that the paraffin in the crude oil is completely precipitated; (3) Place the cooled sample tube in the nuclear magnetic resonance instrument and acquire the nuclear magnetic resonance signal using a free induction decay sequence; (4) Perform two-component fitting on the acquired nuclear magnetic resonance signal to obtain the initial signal amplitudes A1 and A2 of the solid phase and liquid phase, and calculate the ratio x between the initial signal amplitudes of the solid phase and the liquid phase based on the initial signal amplitudes A1 and A2. (5) Calculate the mass ratio y between the solid phase component and the liquid phase component using the pre-established calibration model y = k·x; (6) Calculate the wax content c of the crude oil sample to be tested based on the solid-liquid mass ratio y.

[0015] Preferably, step (4) involves performing a two-component fitting process using the following formula: Where S(t) is the signal intensity at time t, which is dimensionless; A1 is the initial signal amplitude of the solid phase component, which is proportional to the number of hydrogen nuclei in the solid phase component; The initial signal amplitude of the solid phase component is proportional to the number of hydrogen nuclei in the liquid phase component; The characteristic relaxation time of the solid phase component; is the characteristic relaxation time of the liquid phase component.

[0016] Preferably, step (4) further includes calculating the solid-liquid amplitude ratio x in the following manner: Establish the relationship between wax content and nuclear magnetic resonance signal: Where c is the mass percentage of the solid component, i.e., the wax content; The mass of the solid phase component in the sample to be tested; The mass of the liquid phase component in the sample to be tested; Since the intensity of the nuclear magnetic resonance signal is proportional to the number of hydrogen nuclei in the sample being tested, then: in, The nuclear magnetic resonance signal of the solid phase component per unit mass; denoted as NMR signal per unit mass of liquid phase component; x is the ratio of the initial signal amplitude of the solid phase to that of the liquid phase.

[0017] Preferably, the calibration model described in step (5) is established in the following manner: (5.1) Prepare several standard samples with known wax content, using aviation kerosene as solvent and solid paraffin as solute; (5.2) Process the standard samples according to steps (1) to (4) to obtain the initial signal amplitudes A1 and A2 of each standard sample; (5.3) Calculate the solid-liquid amplitude ratio x = A1 / A2 and the solid-liquid mass ratio y = m1 / m2 for each standard sample; (5.4) Perform linear fitting on y and x, set the intercept to 0, and obtain the slope k.

[0018] Preferably, when the sample to be tested and the calibration sample are... and When the values ​​are the same, the wax content c is calculated using the following formula: The wax content c is expressed as a percentage.

[0019] More preferably, when the sample to be tested and the calibration sample are... and When the values ​​are different, the method further includes a step of obtaining the correction coefficient: (7.1) Weigh a quantitative amount of crude oil to be tested as a calibration sample and process it according to steps (1) to (4) to obtain the initial signal amplitudes A1 and A2; (7.2) Based on the corrected sample mass m and the nuclear magnetic resonance signal of the solid phase component per unit mass Calculate the NMR signal per unit mass of the liquid phase component of the corrected sample based on the initial signal amplitudes A1 and A2. ; (7.3) Calculate the correction factor a = / ,in The NMR signal of the liquid phase component per unit mass of the calibration sample; (7.4) When calculating the solid-liquid mass ratio y in step (6), the corrected solid-liquid mass ratio y_corrected = k·x·a is used, where a is the correction coefficient; (7.5) Calculate the corrected wax content c based on the corrected solid-liquid mass ratio y_corrected. : .

[0020] Preferably, the crude oil sample to be tested must meet the following conditions: The wax content is not less than 5%; Moisture content not exceeding 0.5%; The asphalt content is no higher than 3%.

[0021] Preferably, the low-temperature environment described in step (2) is below -28°C and the cooling time is not less than 30 minutes to ensure that the paraffin is completely precipitated.

[0022] Preferably, the acquisition parameters of the free induction attenuation sequence mentioned in step (3) include: sampling bandwidth 5000kHz, number of sampling points 1024, gain 2, waiting time 3000 ms, number of accumulations 4, and single acquisition time ≤12 seconds.

[0023] The system for measuring the wax content of crude oil using nuclear magnetic resonance for implementing the above-described method is characterized in that the system comprises: A heating device used to heat crude oil samples into a homogeneous fluid; A cryogenic cooling device is used to cool the sample until the paraffin is completely precipitated. Nuclear magnetic resonance (NMR) instruments are used to acquire the free induction decay signal of a sample; The data processing unit is used to perform two-component fitting on the acquired signal and calculate the wax content based on the correction coefficient.

[0024] The method and system for measuring the wax content of crude oil using nuclear magnetic resonance according to the present invention have the following significant advantages: 1. High efficiency and batch testing capability: The cold bath allows for batch cooling of samples, with each sample requiring only about 12 seconds for NMR testing. Excluding sample preparation time, the entire process from cooling to completion of testing for a batch of samples can be controlled within one hour, significantly outperforming the national standard method and other existing methods. 2. Green and environmentally friendly: This method does not add any chemical reagents to the crude oil being tested, and the testing process is pollution-free; 3. More Complete Calculation Model and Correction Mechanism: Compared with common methods that directly establish a linear relationship between wax content and the proportion of solid-phase NMR signal, this invention has the following advantages and innovations in data processing: ① This invention introduces a correction coefficient, which significantly reduces the calibration mismatch error caused by the difference between the calibration sample and the actual test sample; ② This invention selects to establish a linear relationship between m1 / m2 and A1 / A2 during calibration, and then calculates the wax content. This calibration method ensures that the intercept between m1 / m2 and A1 / A2 is always a linear relationship with zero under any circumstances, and there is no systematic modeling error; ③ The calibration model of this invention has only one model parameter, namely the slope k. / It has a clear physical meaning; 4. High accuracy: Without considering the differences in solid paraffin, the method of this invention has a relative error of less than 10% between the NMR wax content test results and the actual wax content. The selection of the two-component fitting model (Gaussian + exponential), the setting of low-temperature cooling conditions, the optimization of the calculation model and the introduction of correction coefficients improve the measurement accuracy through the synergistic effect of multiple links.

[0025] 5. Innovative combination of technical solutions: From data acquisition to result output, this solution achieves full-process optimization through raw data filtering optimization, data fitting formula optimization, construction of a scientific data model with physical meaning and theoretical linearity, and the introduction of correction coefficients, forming a complete and innovative technical solution that improves measurement accuracy. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of establishing a calibrator after obtaining A1 and A2 through fitting in a specific embodiment of the present invention. Detailed Implementation

[0027] To more clearly describe the technical content of the present invention, the following description is provided in conjunction with specific embodiments.

[0028] Before describing the embodiments of the present invention in detail, it should be noted that, in the following, the terms “comprising,” “including,” or any other variations are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0029] The implementation of this technical solution will be described in detail below. The core principle of the nuclear magnetic resonance method for measuring the wax content of crude oil according to this invention is as follows: 1. Paraffin wax in crude oil will gradually precipitate as the temperature decreases. Maintaining a sufficiently low temperature for a period of time can ensure that the paraffin wax is completely precipitated.

[0030] 2. Rapidly measure the crude oil from which paraffin has completely separated using the FID sequence (Free Induction Decay Sequence). Since the T2 decay rate of solid paraffin (solid phase) is extremely fast, while that of liquid oil is slower, a Gaussian function plus an exponential function two-component fitting can be performed on the original decay curve to obtain the NMR (Nuclear Magnetic Resonance) signal quantities contributed by the solid and liquid phases at time t. In the formula, S(t) is the signal strength at time t, which is dimensionless; The initial signal amplitude of the solid phase component is proportional to the number of hydrogen nuclei in the solid phase component; The initial signal amplitude of the solid phase component is proportional to the number of hydrogen nuclei in the liquid phase component; The characteristic relaxation time of the solid phase component; is the characteristic relaxation time of the liquid phase component.

[0031] 3. Establish the relationship between wax content and NMR signal: In the formula, c is the mass percentage of the solid component, i.e., the wax content (%). The mass of the solid phase component (paraffin) in the sample to be tested; This represents the mass of the liquid phase component (oil) in the sample to be tested.

[0032] Since the intensity of an NMR signal is proportional to the number of hydrogen nuclei in the sample being tested: The NMR signal is for the solid phase component per unit mass. is the NMR signal per unit mass of the liquid phase component; x is the ratio of the initial signal amplitude of the solid phase to that of the liquid phase. Let y be the ratio of the mass of the solid phase to the mass of the liquid phase, i.e., y = m1 / m2. From the definition of x, we can obtain: , y is the ratio of the mass of the solid phase to the mass of the liquid phase; k is the slope, which can be calculated to be equal to the ratio of k2 to k1. When the values ​​of k1 and k2 of the sample to be tested are the same as those of the calibration sample, the wax content can be calculated by the following formula: c represents the wax content (%). 4. Coefficient Correction Theoretically, without considering NMR noise and fitting errors of the two-component data, the relative error of the test is 0 when the k2 / k1 of the standard sample is equal to that of the crude oil sample to be tested; when the k2 / k1 of the standard sample is not equal to that of the crude oil sample to be tested, the error mainly comes from the difference in k2 / k1. Therefore, when measuring unknown crude oil samples, it is necessary to reduce systematic errors through coefficient correction.

[0033] Based on the differences between different types of crude oil and theoretical estimates, the relative difference in k2 between different oil components exceeds 30%, while the relative difference in k1 between different solid paraffins is less than 5%. Without correction, if the difference between the sample to be tested and the calibration sample is large, the relative error in the measured wax content can exceed 20%. In contrast, the overall difference in NMR signal contribution from solid paraffins is relatively small, and due to the short relaxation time of solids, it is difficult to directly measure the k1 value of waxy crude oil.

[0034] Therefore, the k2 value can be calibrated to reduce relative error. After calibration, a quantitative sample of the crude oil to be tested needs to be taken, its NMR signal measured, and its k2 calculated to correct the data for the actual test sample.

[0035] Given the crude oil mass m, and assuming that crude oil k1 is equal to standard sample k1, the contribution of hydrogen atoms to the NMR signal per unit mass of the liquid phase component of the crude oil to be tested, k2, can be obtained based on the crude oil NMR fitting parameters A1 and A2. .

[0036] m grams of crude oil solid phase mass: m1 = A1 / k1 m grams of crude oil liquid phase mass: m2 = m - m1 Hydrogen atom NMR signal contribution per unit mass of liquid phase component of the crude oil under test: k2 =A2 / m2 Correction coefficient: a=k2 / k2 Corrected solid-liquid mass ratio: a is the correction coefficient; y is the corrected solid-liquid mass ratio; k2 k1 represents the NMR signal contribution of hydrogen atoms per unit mass of the liquid phase component of the sample to be tested, and k2 represents the NMR signal contribution of H protons per unit mass of the liquid phase component of the calibration sample.

[0037] Since different solid paraffins may have different k1 values, although there is still a systematic error between the wax content after correction by this method and the actual wax content, it has greatly reduced the large systematic error caused by the difference in liquid phase components.

[0038] As a preferred embodiment of the present invention, the key steps involved in the present invention are as follows: (1) Sample preparation: Heat the crude oil and pour it into a test tube; (2) Cooling: Place the test tube in a low-temperature cold bath to cool until the paraffin is completely precipitated; (3) Calibration: Place the test tube into the NMR instrument and use the FID sequence to measure the NMR signal of samples with known different wax contents (e.g., 5%, 10%, 15%, 20%, 30%). Perform two-component fitting on the original data to obtain the fitting equation for each sample, thereby obtaining A1 and A2; then establish the linear relationship between y and x.

[0039] (4) Obtaining the correction coefficient: Weigh the crude oil to be tested quantitatively, cool it at low temperature until the paraffin is completely precipitated, measure the NMR signal, perform data fitting, and calculate its correction coefficient a; (3) Actual sample testing: Place the test tube into the NMR instrument and use FID sequence to measure the NMR signal of the sample. Perform two-component fitting on the original data to obtain the fitting equation for each sample, thus obtaining A1 and A2; substitute the calculated x value into the NMR instrument. Then the wax content c is obtained.

[0040] In one specific embodiment of the present invention, the instrument used for NMR signal measurement is a PQ001-SFC model device manufactured by Numatrices Analytical Instruments Co., Ltd. With a sampling bandwidth of 5000 kHz, this instrument can detect NMR signals as early as 11 μs using the FID sequence. In the following steps, the NMR signal measurement uses the FID sequence with uniform parameters: sampling bandwidth 5000 kHz, number of sampling points 1024, gain 2, waiting time 3000 ms, and accumulation count 4. The single signal acquisition time is approximately 12 s.

[0041] This invention requires the crude oil to be tested to meet the following conditions: ① Wax content above 5%. For samples with a wax content below 5%, the two-component fitting R... 2 The value may be less than 0.9, indicating a poor fit. ②Water content ≤ 0.5%. Water in crude oil contributes to the NMR signal, affecting the wax content test results; ③ Asphaltene content ≤ 3%. Asphaltene in crude oil is relatively stable and contributes to short relaxation signals, thus making the wax content test results appear higher.

[0042] In practical applications, the complete implementation steps are as follows: (1) Preparation of standard samples ① Using aviation kerosene (excluding wax and water) as solvent and solid paraffin as solute, prepare several standard samples with a wax content of 5% to 30%: weigh the corresponding mass of solid paraffin and aviation kerosene and add them to a beaker, seal the mouth of the beaker, heat in an oven at 70℃, and stir moderately during the heating process to make the sample evenly mixed; ② Take sufficient amounts of standard samples with different wax contents and pour them into different beakers. Seal the mouths of the beakers to prevent excessive volatilization and loss of crude oil during heating. ③ Place the sample in the beaker into a 70℃ oven and heat. Stir several times with a glass rod during heating. Once the sample becomes a homogeneous fluid, remove the beaker from the oven, quickly pour the crude oil into a test tube, and plug the tube opening. The height of the sample should exceed 4cm. ④ Place the test tube in an oven at 70℃ and heat for 10 minutes to allow the liquid adhering to the walls to flow down as much as possible; (2) Preparation of crude oil samples to be tested ① Pour a sufficient amount of crude oil into a beaker, seal the mouth of the beaker, and prevent the crude oil from evaporating excessively during heating; ② Place the crude oil in the beaker into a 70℃ oven and heat it. Stir several times with a glass rod during heating. After the sample becomes a homogeneous fluid, remove the beaker from the oven, quickly pour the crude oil into a test tube, and plug the tube opening. The height of the sample should be more than 4cm. ③ Place the test tube in an oven at 70℃ and heat for 10 minutes to allow the liquid adhering to the walls to flow down as much as possible; (3) Sample preparation for correction coefficient: Weigh a quantitative amount of crude oil to be tested and pour it into a small chromatographic bottle (not exceeding the uniform area of ​​the probe). (4) Sample cooling: Place all test tubes containing samples into a -28℃ cold bath and cool for more than 30 minutes; (Preliminary experimental verification showed that the proportion of NMR signal of solid components was the same when cooled at -28℃ for 20 minutes and at -28℃ for 24 hours. Therefore, it is believed that cooling at -28℃ for 30 minutes can completely precipitate paraffin in crude oil and that there is an overflow in the cooling time). (5) Calibration ① Remove the test tube from the cold bath, quickly wipe the surface of the test tube dry (there should be no liquid droplets on the surface and bottom of the test tube), and place it in the instrument to test the NMR signal; ② Perform two-component fitting based on the measured NMR signal. The fitting formula is as follows: Fitting constraints are ≤ , ≤0.04ms. Because the solid phase decay rate is faster than the liquid phase decay rate, therefore ≤ Furthermore, experiments have verified that solid paraffin... Much less than 0.04ms; ③ After completing steps ① and ② for all standard samples, the fitted A1, Substitute x = A1 / Substituting the corresponding wax content into y = m1 / m2, a linear fit was performed, with the intercept set to 0, to obtain the linear relationship between y and x. ; (6) Obtaining the correction coefficient ① Remove the calibration coefficient sample from the cold bath, quickly wipe the surface of the chromatographic vial dry (there should be no liquid droplets on the surface and bottom of the test tube), and place it in the instrument to test the NMR signal; ② Perform two-component fitting based on the measured NMR signal. The fitting formula is the same as that used for calibration. ③Based on the sample mass m of the correction coefficient, the contribution of the NMR signal of hydrogen atoms of the liquid phase component per unit mass of the solid phase k1, and A1 and A2, the correction coefficient a of the crude oil to be tested is obtained; (7) Wax content test of the sample ① Remove the test tube from the cold bath, quickly wipe the surface of the test tube dry (there should be no liquid droplets on the surface and bottom of the test tube), and place it in the instrument to test the NMR signal; ② Perform two-component fitting based on the measured NMR signal. The fitting formula is the same as that used for calibration. ③ The fitted A1, Substitute x = A1 / After obtaining x, substitute x into Then, the corrected wax content c is calculated.

[0043] In one specific embodiment of the present invention, a wax content standard sample prepared by using aviation kerosene (without wax and water) as solvent and solid paraffin as solute is used to measure the wax content of simulated crude oil samples with known wax content prepared by using unwaxed light crude oil and diesel oil as solvent and solid paraffin as solute, respectively.

[0044] (1) Using aviation kerosene (excluding wax and water) as solvent and solid paraffin as solute, standard samples with wax contents of 5%, 10%, 20%, and 30% were prepared. After cooling at -28℃ for 30 min, the NMR signals of each standard sample were measured, and the A1 value was obtained by fitting. Then establish the markings, such as Figure 1 As shown, the scaling equation is y = 0.8356x, R0 2 =0.9988.

[0045] (2) Weigh 0.5g of each of the two types of crude oil to be tested, cool them at -28℃ for 30min, measure the NMR signal, and calculate their respective correction coefficients, as shown in Table 2: (2) Using SQ crude oil and diesel as solvents, solid paraffin was added quantitatively to prepare simulated waxy crude oil. After heating, the mixture was poured into test tubes, cooled at -28℃ for 30 min, and the NMR signal was measured. The wax content was calculated. The measurement data and results are shown in Table 3. As can be seen from Table 3, the accuracy of wax content testing is significantly improved after the test data of the present invention is corrected by the correction coefficient.

[0046] In comparison, we processed the NMR data measured from the sample in this example using a conventional method, namely, establishing a linear relationship between wax content and the proportion of solid-phase NMR signal. The calibration and data comparison results are as follows: As can be seen from Table 4, the data processing method of the present invention yields wax content test results that are far superior to conventional methods for establishing a linear relationship between wax content and the proportion of solid-phase NMR signal.

[0047] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of the preferred embodiments of the invention includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as will be understood by those skilled in the art to which embodiments of the invention pertain.

[0048] It should be understood that various parts of the present invention can be implemented using hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented using software or firmware stored in memory and executed by a suitable instruction execution device.

[0049] Those skilled in the art will understand that all or part of the steps of the methods in the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, the program includes one or a combination of the steps of the method embodiments.

[0050] The storage media mentioned above can be read-only memory, disk, or optical disk, etc.

[0051] In the description of this specification, references to terms such as "an embodiment," "some embodiments," "example," "specific example," or "embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0052] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

[0053] The cutting path optimization method and system based on the dynamic calculation starting point of the contour, as described in this invention, have the following significant advantages compared with the prior art: 1. High efficiency and batch testing capability: The cold bath allows for batch cooling of samples, with each sample requiring only about 12 seconds for NMR testing. Excluding sample preparation time, the entire process from cooling to completion of testing for a batch of samples can be controlled within one hour, significantly outperforming the national standard method and other existing methods. 2. Green and environmentally friendly: This method does not add any chemical reagents to the crude oil being tested, and the testing process is pollution-free; 3. More Complete Calculation Model and Correction Mechanism: Compared with common methods that directly establish a linear relationship between wax content and the proportion of solid-phase NMR signal, this invention has the following advantages and innovations in data processing: ① This invention introduces a correction coefficient, which significantly reduces the calibration mismatch error caused by the difference between the calibration sample and the actual test sample; ② This invention selects to establish a linear relationship between m1 / m2 and A1 / A2 during calibration, and then calculates the wax content. This calibration method ensures that the intercept between m1 / m2 and A1 / A2 is always a linear relationship with zero under any circumstances, and there is no systematic modeling error; ③ The calibration model of this invention has only one model parameter, namely the slope k. / It has a clear physical meaning; 4. High accuracy: Without considering the differences in solid paraffin, the method of this invention has a relative error of less than 10% between the NMR wax content test results and the actual wax content. The selection of the two-component fitting model (Gaussian + exponential), the setting of low-temperature cooling conditions, the optimization of the calculation model and the introduction of correction coefficients improve the measurement accuracy through the synergistic effect of multiple links.

[0054] 5. Innovative combination of technical solutions: From data acquisition to result output, this solution achieves full-process optimization through raw data filtering optimization, data fitting formula optimization, construction of a scientific data model with physical meaning and theoretical linearity, and the introduction of correction coefficients, forming a complete and innovative technical solution that improves measurement accuracy.

[0055] In this specification, the invention has been described with reference to specific embodiments thereof. However, it will be apparent that various modifications and variations can be made without departing from the spirit and scope of the invention. Therefore, the specification and drawings should be considered illustrative rather than restrictive.

Claims

1. A method for measuring the wax content of crude oil using nuclear magnetic resonance, characterized in that, The method includes the following steps: (1) After heating the crude oil sample to be tested to a homogeneous fluid state, inject it into the sample tube; (2) The sample tube is placed in a low-temperature environment to cool it, so that the paraffin in the crude oil is completely precipitated; (3) Place the cooled sample tube in the nuclear magnetic resonance instrument and acquire the nuclear magnetic resonance signal using a free induction decay sequence; (4) Perform two-component fitting on the acquired nuclear magnetic resonance signal to obtain the initial signal amplitudes A1 and A2 of the solid phase and liquid phase, and calculate the ratio x between the initial signal amplitudes of the solid phase and the liquid phase based on the initial signal amplitudes A1 and A2. (5) Calculate the mass ratio y between the solid phase component and the liquid phase component using the pre-established calibration model y = k·x; (6) Calculate the wax content c of the crude oil sample to be tested based on the solid-liquid mass ratio y.

2. The method for measuring the wax content of crude oil using nuclear magnetic resonance according to claim 1, characterized in that, The step (4) described above uses the following formula for two-component fitting: Where S(t) is the signal intensity at time t, which is dimensionless; A1 is the initial signal amplitude of the solid phase component, which is proportional to the number of hydrogen nuclei in the solid phase component; The initial signal amplitude of the solid phase component is proportional to the number of hydrogen nuclei in the liquid phase component; The characteristic relaxation time of the solid phase component; is the characteristic relaxation time of the liquid phase component.

3. The method for measuring the wax content of crude oil using nuclear magnetic resonance according to claim 2, characterized in that, Step (4) further includes calculating the solid-liquid amplitude ratio x in the following manner: Establish the relationship between wax content and nuclear magnetic resonance signal: Where c is the mass percentage of the solid component, i.e., the wax content; The mass of the solid phase component in the sample to be tested; The mass of the liquid phase component in the sample to be tested; Since the intensity of the nuclear magnetic resonance signal is proportional to the number of hydrogen nuclei in the sample being tested, then: in, The nuclear magnetic resonance signal of the solid phase component per unit mass; denoted as NMR signal per unit mass of liquid phase component; x is the ratio of the initial signal amplitude of the solid phase to that of the liquid phase.

4. The method for measuring the wax content of crude oil using nuclear magnetic resonance according to claim 3, characterized in that, The calibration model described in step (5) is established in the following way: (5.1) Prepare several standard samples with known wax content, using aviation kerosene as solvent and solid paraffin as solute; (5.2) Process the standard samples according to steps (1) to (4) to obtain the initial signal amplitudes A1 and A2 of each standard sample; (5.3) Calculate the solid-liquid amplitude ratio x = A1 / A2 and the solid-liquid mass ratio y = m1 / m2 for each standard sample; (5.4) Perform linear fitting on y and x, set the intercept to 0, and obtain the slope k.

5. The method for measuring the wax content of crude oil using nuclear magnetic resonance according to claim 3, characterized in that, When the sample to be tested and the calibration sample are and When the values ​​are the same, the wax content c is calculated using the following formula: The wax content c is expressed as a percentage.

6. The method for measuring the wax content of crude oil using nuclear magnetic resonance according to claim 5, characterized in that, When the sample to be tested and the calibration sample are and When the values ​​are different, the method further includes a step of obtaining the correction coefficient: (7.1) Weigh a quantitative amount of crude oil to be tested as a calibration sample and process it according to steps (1) to (4) to obtain the initial signal amplitudes A1 and A2; (7.2) Based on the corrected sample mass m and the nuclear magnetic resonance signal of the solid phase component per unit mass Calculate the NMR signal per unit mass of the liquid phase component of the corrected sample based on the initial signal amplitudes A1 and A2. ; (7.3) Calculate the correction factor a = / ,in The NMR signal of the liquid phase component per unit mass of the calibration sample; (7.4) When calculating the solid-liquid mass ratio y in step (6), the corrected solid-liquid mass ratio y_corrected = k·x·a is used, where a is the correction coefficient; (7.5) Calculate the corrected wax content c based on the corrected solid-liquid mass ratio y_corrected. : 。 7. The method for measuring the wax content of crude oil using nuclear magnetic resonance according to claim 1, characterized in that, The crude oil sample to be tested must meet the following conditions: The wax content is not less than 5%; Moisture content not exceeding 0.5%; The asphalt content is no higher than 3%.

8. The method for measuring the wax content of crude oil using nuclear magnetic resonance according to claim 1, characterized in that, The low-temperature environment mentioned in step (2) is below -28°C, and the cooling time is not less than 30 minutes, to ensure that the paraffin is completely extracted.

9. The method for measuring the wax content of crude oil using nuclear magnetic resonance according to claim 1, characterized in that, The acquisition parameters of the free induction attenuation sequence mentioned in step (3) include: sampling bandwidth 5000 kHz, number of sampling points 1024, gain 2, waiting time 3000 ms, number of accumulations 4, and single acquisition time ≤12 seconds.

10. A system for measuring the wax content of crude oil using nuclear magnetic resonance for implementing the method of any one of claims 1 to 9, characterized in that, The system includes: A heating device used to heat crude oil samples into a homogeneous fluid; A cryogenic cooling device is used to cool the sample until the paraffin is completely precipitated. Nuclear magnetic resonance (NMR) instruments are used to acquire the free induction decay signal of a sample; The data processing unit is used to perform two-component fitting on the acquired signal and calculate the wax content based on the correction coefficient.

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