A Method and System for Evaluating the Wettability of Shale Oil CO2 Huff and Puff Reservoirs Based on Two-Dimensional NMR

Abstract

This invention relates to the field of shale oil extraction technology, specifically to a method and system for evaluating the wettability of shale oil CO2 huff and puff reservoirs based on two-dimensional nuclear magnetic resonance (NMR). The method includes: acquiring raw NMR echo train data to obtain an initial two-dimensional spectrum; assessing the noise interference level of the raw data, and if it exceeds a threshold, initiating an inversion correction process to output a corrected two-dimensional spectrum; calculating the T1 / T2 ratio based on the corrected two-dimensional spectrum, segmented according to the T2 relaxation time interval; conducting CO2 huff and puff experiments under different temperature, pressure, and well-drainage time conditions, and repeating the above tests on core samples after huff and puff to obtain the T1 / T2 ratio after huff and puff; finally, comparing the changes in the ratio within the same T2 interval before and after huff and puff, calculating the amount and rate of change, determining the wettability change characteristics, and integrating the results from various conditions to form a complete evaluation conclusion. This invention improves the accuracy of shale oil CO2 huff and puff reservoir wettability evaluation.

Description

Technical Field

[0001] This invention relates to the field of shale oil extraction technology, and in particular to a method and system for evaluating the wettability of shale oil CO2 huff and puff reservoirs based on two-dimensional nuclear magnetic resonance. Background Technology

[0002] Shale oil, as an important unconventional oil and gas resource, is characterized by extremely low reservoir porosity (typically less than 10%), well-developed micro- and nano-scale pores, strong heterogeneity, and abundant organic matter. This results in poor mobility of shale oil, with a primary development recovery rate of only about 5% to 10%. CO2 injection for huff and puff extraction can significantly improve the recovery rate. However, after CO2 injection, it undergoes physicochemical reactions with reservoir crude oil, formation water, and rocks, producing precipitation and dissolution effects. This alters reservoir wettability, thereby affecting the three-phase flow characteristics of oil, gas, and water, and ultimately the recovery effect. Currently, conventional wettability evaluation methods include wetting contact angle measurement, the Amott method, the USBM method, and Micro-CT / microfluidic chip technology. However, these methods have drawbacks, such as only characterizing local surfaces, long testing cycles, high pressure easily damaging cores, and expensive equipment. Summary of the Invention

[0003] This invention provides a method and system for evaluating the wettability of shale oil CO2 huff and puff reservoirs based on two-dimensional nuclear magnetic resonance, which solves the problem that existing methods cannot quickly, comprehensively, and quantitatively evaluate the changes in reservoir wettability during shale oil CO2 huff and puff.

[0004] The objective of this invention can be achieved through the following technical solutions:

[0005] The first aspect of this invention is to provide a method for evaluating the wettability of shale oil CO2 huff and puff reservoirs based on two-dimensional nuclear magnetic resonance, comprising: S1. Using natural shale cores as experimental samples, after pretreatment such as washing and drying, self-water absorption treatment was carried out under normal temperature and pressure conditions to obtain self-water-absorbing cores; nuclear magnetic resonance testing was performed on the self-water-absorbing cores to collect the raw echo train data before throughput; then, based on the raw echo train data before throughput, an initial two-dimensional spectrum was obtained. S2, obtain the noise interference level of the original echo string data, determine whether the noise interference level exceeds the preset interference threshold, if so, start the inversion correction process, correct the initial two-dimensional spectrum, and output the corrected two-dimensional spectrum; S3, based on the corrected two-dimensional spectrum, calculate the T1 / T2 ratio segmented according to the T2 interval; wherein, the T2 interval is the T2 relaxation time interval; S4. Under different temperature, pressure and well-drainage conditions, CO2 huff and puff experiments are carried out on the cores that have completed steps S1-S3 to obtain huff and puffed cores. Steps S1-S3 are repeated on the huff and puffed cores to obtain the corrected two-dimensional spectrum and the T1 / T2 ratio of each T2 interval after huff and puff. S5. Compare the T1 / T2 ratios in the same T2 interval before and after huff and puff, calculate the change in ratio and the rate of change in ratio, and determine the characteristics of reservoir wettability changes under each working condition; integrate the wettability change characteristics under all working conditions to obtain a complete evaluation result of the wettability changes of shale oil CO2 huff and puff reservoirs under different working conditions.

[0006] Furthermore, the degree of noise interference is specifically expressed by the formula:

[0007] In the formula, This represents the energy of the first few echo signals in the original echo train data. This represents the total energy of all echo signals in the original echo train data. This represents the signal-to-noise ratio of the original echo train data; This indicates the level of noise interference in the original echo train data. This represents an exponential function with the natural constant as its base.

[0008] Furthermore, the inversion correction process is initiated to correct the initial two-dimensional map and output the corrected two-dimensional map, including: (1) Preprocess the raw echo train data to remove outliers and baseline drift; (2) Construct a two-dimensional initial kernel matrix, and use truncated singular value decomposition to truncate the two-dimensional initial kernel matrix to filter out high-frequency noise components and obtain the truncated diagonal matrix; reconstruct the kernel matrix A by using the truncated diagonal matrix to obtain an adjusted kernel matrix A; (3) Based on the adjusted kernel matrix A and the initial two-dimensional spectrum, the corrected two-dimensional spectrum is obtained by using non-negative least squares iteration.

[0009] Furthermore, the preprocessing of the original echo train data to remove outliers and eliminate baseline drift includes: The LOF anomaly detection algorithm is used to detect anomalies, and then the anomalies are removed. The positions of the anomalies are then supplemented by interpolation using the average interpolation method. The average value of several points at the end of the original echo string data is used as the baseline offset. The baseline drift is then removed by subtracting the baseline offset from the baseline data of the original echo string data.

[0010] Further, the construction of the two-dimensional initial kernel matrix involves truncating the initial kernel matrix using truncated singular value decomposition to filter out high-frequency noise components, obtaining a truncated diagonal matrix. The truncated diagonal matrix is ​​then reconstructed to obtain an adjusted kernel matrix A, including: Singular value decomposition is performed on the initial kernel matrix to obtain column orthogonal matrices, diagonal matrices, and row orthogonal matrices; the diagonal matrix contains singular values ​​on its diagonal. Starting from the first element in the top-left corner of the diagonal matrix, calculate the energy percentage of the first k singular values ​​among all singular values; the energy percentage is specifically expressed by the formula:

[0011] In the formula, Indicates the first A singular value, This represents the number of the first k singular values. This represents the number of all singular values. Indicates the percentage of energy; If the energy percentage of the current k singular values ​​among all singular values ​​is greater than or equal to the preset energy retention ratio, then the first k singular values ​​are retained, and the energy percentages from the (k+1)th to the th singular values ​​are removed. By setting the singular values ​​between each pair to zero, a truncated diagonal matrix is ​​obtained. By reconstructing the truncated diagonal matrix, an adjusted kernel matrix A is obtained; The elements in the initial kernel matrix are determined by a discretized multi-exponential decay model.

[0012] Further, the step of obtaining the corrected two-dimensional map by using non-negative least squares iterative solution based on the adjusted kernel matrix A and the initial two-dimensional map includes: Based on the adjusted kernel matrix A, a non-negative least squares iterative solution is used to force all T1 or T2 distribution values ​​to be non-negative; where, during the iteration process, up to the two adjacent iterations, ... When the iteration stops, the iteration continues; where, These are preset parameters; In the formula, For the first x in the next iteration For the first x in the next iteration for and The L2 norm between; In the iteration process, L1 norm regularization is used for inversion, and the objective function in the inversion process is: Where A is the kernel matrix, b is the preprocessed raw echo train data, and x is the T1 or T2 distribution. To be the optimal regularization parameter, It is the L2 norm. It is an L1 norm. This represents a function that takes the minimum value. During iteration, the initial x is the initial two-dimensional graph; Determine the preset range of values ​​for the regularization parameter, and calculate the optimal target x for each value within the preset range of values ​​for the regularization parameter. and Then with As the x-axis, with The vertical axis represents the optimal target x value for each value within the preset range of all regularization parameters. and Construct an L-curve curve, and then select the regularization parameter corresponding to the inflection point as the optimal regularization parameter. .

[0013] Furthermore, each T2 interval includes: the micropore region with T2 < 0.1 ms; the capillary bound water region with 0.1 ms ≤ T2 ≤ 1 ms; and the free water region with T2 > 1 ms.

[0014] A second aspect of the present invention is to provide a shale oil CO2 huff and puff reservoir wettability evaluation system based on two-dimensional nuclear magnetic resonance, comprising: The reference NMR data acquisition module is used to obtain a self-water-absorbing core by washing and drying natural shale cores as experimental samples under normal temperature and pressure conditions; to perform NMR testing on the self-water-absorbing cores and acquire the raw echo train data before throughput; and then to obtain the initial two-dimensional spectrum based on the raw echo train data before throughput. Inversion correction module: used to obtain the noise interference level of the original echo train data, determine whether the noise interference level exceeds the preset interference threshold, and if so, start the inversion correction process to correct the initial two-dimensional spectrum and output the corrected two-dimensional spectrum. Ratio quantization module: used to calculate the T1 / T2 ratio based on the corrected two-dimensional spectrum, segmented by the T2 interval; wherein, the T2 interval is the T2 relaxation time interval; CO2 Huff and Puff Experiment and Post-Huff and Puff NMR Testing Module: Used to conduct CO2 huff and puff experiments on core samples after steps S1-S3 under different temperature, pressure and well-drainage conditions to obtain post-huff and puff core samples; repeat steps S1-S3 on the post-huff and puff core samples to obtain the corrected two-dimensional spectrum and the T1 / T2 ratio of each T2 interval after huff and puff. The wettability change analysis and comprehensive evaluation module is used to compare the T1 / T2 ratio in the same T2 interval before and after huff and puff, calculate the change in ratio and the rate of change in ratio, and determine the wettability change characteristics of the reservoir under each working condition; it integrates the wettability change characteristics under all working conditions to obtain a complete evaluation result of the wettability change of shale oil CO2 huff and puff reservoir under different working conditions.

[0015] A third aspect of the present invention is to provide an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the method for evaluating the wettability of shale oil CO2 huff and puff reservoirs based on two-dimensional nuclear magnetic resonance.

[0016] A fourth aspect of the present invention is to provide a computer-readable storage medium storing a computer program that, when executed by a processor, implements the method for evaluating the wettability of shale oil CO2 huff and puff reservoirs based on two-dimensional nuclear magnetic resonance.

[0017] Compared with existing technologies, the beneficial effects of this invention are as follows: Using natural shale cores as experimental samples, after pretreatment including oil washing and drying, self-absorbing water treatment is performed under ambient temperature and pressure to obtain self-absorbing cores; nuclear magnetic resonance (NMR) testing is conducted on the self-absorbing cores to acquire raw echo train data before throughput; then, based on the raw echo train data before throughput, an initial two-dimensional spectrum is obtained; through oil washing, drying, and pressurized saturated water treatment, residual fluid interference is eliminated and a repeatable reference NMR signal is established, providing standardized initial data for subsequent wettability evaluation; the noise in the acquired raw echo train data is reduced. The interference level is determined, and it is judged whether the noise interference level exceeds a preset interference threshold. If so, the inversion correction process is initiated to correct the initial two-dimensional spectrum and output the corrected two-dimensional spectrum. By introducing a low signal-to-noise ratio inversion correction process, noise interference is effectively filtered out, and the short relaxation signals that are easily lost in low-porosity shale are restored, improving the accuracy of the spectrum. Based on the corrected two-dimensional spectrum, the T1 / T2 ratio is calculated segmented according to the T2 interval; wherein, the T2 interval is the T2 relaxation time interval. By calculating the T1 / T2 ratio segmented according to the T2 interval, the relaxation information is quantified into a wettability criterion. It can sensitively reflect the water- or oil-wet characteristics of different pore sizes; under different temperature, pressure, and well-drainage conditions, CO2 huff and puff experiments are conducted on core samples after steps S1-S3 to obtain huff and puffed core samples; steps S1-S3 are repeated on the huff and puffed core samples to obtain corrected two-dimensional spectra and T1 / T2 ratios for each T2 interval after huff and puff; by performing the same saturated water and NMR testing procedures on core samples before and after huff and puff, the high comparability of the data is ensured, laying a quantitative foundation for accurately evaluating changes in wettability; by comparing the T1 / T2 ratios for the same T2 interval before and after huff and puff, the ratio is calculated. The changes in T1 / T2 ratio and the rate of change of T1 / T2 ratio were used to determine the characteristics of reservoir wettability changes under each operating condition. By integrating the wettability change characteristics under all operating conditions, a complete evaluation result of reservoir wettability changes under different operating conditions was obtained. By calculating and comparing the changes in T1 / T2 ratio before and after huff and puff, and combining multi-condition integrated analysis, the influence of temperature, pressure, and well-clogging time on shale wettability was systematically revealed, providing direct experimental basis for CO2 huff and puff process optimization. This solved the problem that existing methods cannot quickly, comprehensively, and quantitatively evaluate reservoir wettability changes during shale oil CO2 huff and puff. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A schematic flowchart of the steps for evaluating the wettability of shale oil CO2 huff and puff reservoirs based on two-dimensional nuclear magnetic resonance is provided for this invention. Figure 2 A schematic diagram of the module flow of the shale oil CO2 huff and puff reservoir wettability evaluation system based on two-dimensional nuclear magnetic resonance is provided for this invention. Figure 3 A schematic diagram illustrating the fluid occurrence types and regional analysis in shale cores; Figure 4 Two-dimensional maps of self-absorbed core samples before and after CO2 ingestion under different experimental conditions; Figure 5 A schematic diagram showing the change in the T1 / T2 ratio of the capillary bound water region before and after CO2 ingestion and expulsion under different experimental conditions; Figure 6 This is a schematic diagram showing the changes in the macroscopic wetting contact angle of the shale surface after CO2 huff and puff of shale oil under different experimental conditions. Detailed Implementation

[0020] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0021] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0022] To address the problems existing in the background technology, a method and system for evaluating the wettability of shale oil CO2 huff and puff reservoirs based on two-dimensional nuclear magnetic resonance were designed, which has important practical significance.

[0023] like Figure 1 As shown, the first aspect of this invention is to provide a method for evaluating the wettability of shale oil CO2 huff and puff reservoirs based on two-dimensional nuclear magnetic resonance, comprising the following steps: Step S1: Using natural shale cores as experimental samples, after pretreatment such as washing and drying, self-water absorption is performed under normal temperature and pressure conditions to obtain self-water-absorbing cores; nuclear magnetic resonance testing is performed on the self-water-absorbing cores to collect the raw echo train data before throughput; then, based on the raw echo train data before throughput, an initial two-dimensional spectrum is obtained.

[0024] It should be noted that, in order to establish a benchmark for the nuclear magnetic resonance relaxation signal of shale cores under a fully water-saturated state before CO2 influx and to obtain raw echo train data that can objectively reflect the rock pore structure and initial wettability characteristics, the natural shale cores need to undergo oil washing and drying pretreatment to eliminate the interference of residual fluids on the nuclear magnetic resonance signal. Then, pressurized saturated deionized water is added under a preset pressure to ensure that the water can overcome the high capillary force of the shale micro-nano pores and fully enter all connected hydrophilic pores, so that the core reaches a fully water-saturated state. Finally, two-dimensional spectra of T1-T2 relaxation time (two-dimensional nuclear magnetic resonance T1-T2 correlation spectrum or two-dimensional T1-T2 relaxation correlation spectrum) are collected and used for subsequent analysis.

[0025] It should be further noted that, since two-dimensional spectra can be used to qualitatively analyze the overall wettability of cores, it has been found in the art that when the fluid in the core has strong wettability to the solid surface, the mineral-related micromagnetic gradient may shorten the T2 relaxation time, leading to an increase in the T1 / T2 ratio. Therefore, the overall wettability of the core can be determined by comparing the T1 / T2 ratio of nuclear magnetic resonance when the core pores are saturated with a single fluid. Since capillary bound water is mainly spontaneously stored in the core pores under the action of capillary forces during the core's self-absorption process, reflecting the water permeability of the core pores, the change in overall wettability of the core can be analyzed by analyzing the T1 / T2 ratio of the capillary bound water zone formed by the core's self-absorption before and after CO2 injection. The larger the T1 / T2 ratio, the stronger the overall water permeability of the core; conversely, the weaker the overall water permeability of the core.

[0026] Specifically, natural shale cores were used as experimental samples. After washing and drying pretreatment, they were subjected to self-water absorption treatment under normal temperature and pressure conditions to obtain self-water-absorbing cores. Nuclear magnetic resonance (NMR) tests were performed on the self-water-absorbing cores (i.e., using an NMR core analyzer) to acquire the raw echo train data before throughput. Then, based on the raw echo train data of the NMR before throughput, a two-dimensional spectrum of the T1-T2 relaxation time was obtained, which was recorded as the initial two-dimensional spectrum (this process was obtained through multi-exponential inversion, where multi-exponential inversion usually adopts a numerical algorithm combining non-negative least squares method with inverse Laplace transform).

[0027] Among them, the nonnegative least squares method and the inverse Laplace transform are well-known techniques, and will not be described in detail here.

[0028] In this study, natural shale cores were used as experimental samples. After pretreatment including oil washing and drying, they underwent self-water absorption treatment under ambient temperature and pressure to obtain self-water-absorbing cores. The specific process for obtaining self-water-absorbing cores was as follows: a. Place the natural shale core in a Soxhlet extractor and wash it continuously at 110°C for 72 hours using a toluene / methanol mixed solvent (volume ratio 3:1) to remove residual crude oil from the core; b. Place the washed core in a constant temperature drying oven and dry it at 105℃ for 48 hours until constant weight (the difference between two weighings is less than 0.01g). After cooling to room temperature, weigh and record the dry weight. c. Place the dried core in a container of deionized water at normal temperature and pressure, so that the core is completely submerged and naturally absorbs water under the action of capillary force; d. Every 12 hours, take out the core, wipe off the surface free water with a damp cloth and weigh it until the difference between two consecutive weighings is less than 0.01g, which is considered to be the state of self-absorption saturation. e. Take out the core, wipe off the surface free water with a damp cloth, weigh and record the saturated weight of the self-absorbed water, and obtain the self-absorbed water core.

[0029] At this point, the raw echo train data and initial two-dimensional spectrum before throughput are obtained.

[0030] Step S2: Obtain the noise interference level of the original echo string data, determine whether the noise interference level exceeds the preset interference threshold, and if so, start the inversion correction process to correct the initial two-dimensional spectrum and output the corrected two-dimensional spectrum.

[0031] It should be noted that, in order to ensure that the distortion of the inversion results caused by the weak NMR signal and low signal-to-noise ratio of low-porosity shale can be effectively corrected, and to avoid misjudgment of pore structure and wettability characteristics due to the loss of short T2 relaxation signal or noise interference, it is necessary to determine whether the noise interference level of the original echo train data exceeds the preset threshold. If so, a low signal-to-noise ratio inversion correction process including truncated singular value decomposition, L1 norm regularization, and non-negative least squares iteration is initiated to correct the initial two-dimensional map, thereby outputting a corrected two-dimensional map that can truly reflect the fluid occurrence state in micro and nano pores.

[0032] Specifically, it is determined whether the noise interference level of the original echo train data exceeds a preset interference threshold. If so, the inversion correction process is initiated to correct the initial two-dimensional spectrum and output the corrected two-dimensional spectrum. The original echo train data typically consists of multiple echo signals (hundreds to thousands). If not, meaning the noise interference level of the original echo train data does not exceed the preset interference threshold, no adjustment is made, and the initial two-dimensional spectrum is directly used for subsequent ratio analysis.

[0033] The noise interference level of the original echo train data is obtained based on the signal-to-noise ratio of the original echo train data and the proportion of the energy of the first few echo signals in the total energy. The noise interference level of the original echo train data is specifically expressed by the following formula:

[0034] In the formula, This represents the energy of the first few echo signals of the original echo train data (i.e., the sum of the energies of the first few echo signals). This represents the total energy of all echo signals in the original echo train data. This represents the signal-to-noise ratio of the original echo train data; This indicates the level of noise interference in the original echo train data. This represents an exponential function with the natural constant as its base. Here, it is expressed through... Perform a negative correlation mapping on the data, mapping the data to the range of 0 to 1.

[0035] In this embodiment, the first few echo signals are eight. The number of the first eight echo signals is not specifically limited in this embodiment; the implementer can determine it according to specific circumstances. The first few echo signals mentioned here refer to eight echo signals taken sequentially in chronological order.

[0036] in, This indicates the proportion of the energy of the first 8 echo signals in the total energy of the entire echo train. The smaller this proportion, the more severe the signal attenuation or submersion in noise in the early stages of acquisition, making it impossible to effectively identify, i.e., the stronger the noise interference. Conversely, the larger this proportion, the weaker the noise interference, i.e., the smaller the noise interference. This represents the signal-to-noise ratio (SNR) of the original echo train data. A lower SNR indicates stronger noise interference, while a higher SNR indicates weaker noise interference. The process of obtaining the SNR is well-known and will not be described in detail here.

[0037] This gives us the noise level of the original echo train data.

[0038] In this embodiment, the preset interference threshold is 0.7. However, the preset interference threshold is not specifically limited in this embodiment, and the implementer can determine it according to the specific circumstances.

[0039] The process involves initiating the inversion correction procedure, correcting the initial two-dimensional map, and outputting the corrected two-dimensional map. The specific correction procedure is as follows: (1) Preprocessing the original echo train data to remove outliers and baseline drift includes: using the LOF (Local Outlier Factor) anomaly detection algorithm to detect outliers, then removing them, and interpolating the outlier locations using the average interpolation method; using the average of several points at the end of the original echo train data (in this embodiment, the average of the last 200 points) as the baseline offset; and then subtracting the baseline offset from the baseline data of the original echo train data to remove baseline drift. The number of 200 data points is not specifically limited and can be determined by the implementer based on specific circumstances.

[0040] The LOF anomaly detection algorithm and the average interpolation method are both well-known techniques, and will not be elaborated on here.

[0041] (2) Construct a two-dimensional initial kernel matrix, and truncate the two-dimensional initial kernel matrix using truncated singular value decomposition to filter out high-frequency noise components, obtaining a truncated diagonal matrix; reconstruct the kernel matrix using the truncated diagonal matrix to obtain an adjusted kernel matrix A; including: Constructing a two-dimensional initial kernel matrix The elements of the two-dimensional initial kernel matrix are determined by the Kronecker product of a multi-exponential decay model in two dimensions (e.g., T1 and T2); specifically, the two-dimensional initial kernel matrix... ;in, and These are single-parameter kernel matrices of dimensions T1 and T2, respectively. This represents the Kronecker product. The discretization of the multi-exponential decay model is a well-known technique, and the process of determining the kernel matrix elements is also a well-known technique, so it will not be elaborated upon here.

[0042] For the two-dimensional initial kernel matrix Singular value decomposition (SVD) is performed to obtain column orthogonal matrices, diagonal matrices, and row orthogonal matrices. The diagonal matrix contains singular values ​​along its diagonal lines. SVD is a well-known technique and will not be elaborated upon here. Starting from the top-left element of the diagonal matrix, the energy percentage of the first k singular values ​​among all singular values ​​is calculated. The energy percentage is expressed by the formula:

[0043] In the formula, Indicates the first A singular value, This represents the number of the first k singular values. This represents the number of all singular values. This indicates the percentage of energy used.

[0044] If the energy percentage of the current k singular values ​​among all singular values ​​is greater than or equal to the preset energy retention ratio, then the first k singular values ​​are retained, and the energy percentages from the (k+1)th to the th singular values ​​are removed. The singular values ​​between the elements are set to zero to obtain the truncated diagonal matrix. In this embodiment, the preset energy retention ratio is 0.95. However, this preset energy retention ratio is not specifically limited in this embodiment, and the implementer can determine it according to the specific circumstances.

[0045] It's important to note that the magnitude of the singular values ​​in the kernel matrix A directly reflects the contribution weight and stability of the corresponding eigendirection in the inversion. Large singular values ​​correspond to the main energy in the signal space, resulting in computational stability and minimal noise interference during inversion. Conversely, the eigendirection corresponding to extremely small singular values ​​primarily amplifies high-frequency noise, introducing oscillations during inversion. When the original echo train data has a low signal-to-noise ratio, retaining all singular values ​​for inversion would cause the extremely small singular values ​​to drastically amplify minute noise in the acquired data, leading to numerous spurious oscillation peaks or even negative values ​​in the solved T2 distribution, completely losing its physical meaning. Therefore, by setting a threshold and directly zeroing out extremely small singular values ​​smaller than this threshold from the kernel matrix, although this sacrifices the ability to distinguish extremely fine structures at T2 time (loss of some resolution), it effectively filters out interference from noise channels, significantly reducing the ill-conditioned nature of the inversion problem and ensuring a stable output of a slightly coarse but true porosity distribution map even under low signal-to-noise ratio conditions. This is a necessary trade-off between controllable resolution loss and solution stability.

[0046] (3) Based on the adjusted kernel matrix A and the initial two-dimensional spectrum, the corrected two-dimensional spectrum is obtained by solving iteratively using non-negative least squares; the specific process includes: Based on the adjusted kernel matrix A, a non-negative least squares iterative solution is used to force all T1 or T2 distribution values ​​to be non-negative; where, during the iteration process, up to the two adjacent iterations, ... When the iteration stops, the iteration continues; where, These are preset parameters; in this embodiment... Among them, No specific limitations are set; the implementer can determine the implementation based on the specific circumstances. In the formula, For the first x in the next iteration For the first x in the next iteration for and The L2 norm between.

[0047] Among them, all are forced during the iteration process. (Negative components are frozen to 0). During iteration, the initial x is the initial two-dimensional graph.

[0048] In the iteration process, L1 norm regularization is used for inversion, and the objective function in the inversion process is: Where A is the kernel matrix, b is the preprocessed raw echo train data, and x is the T1 or T2 distribution. To be the optimal regularization parameter, It is the L2 norm. It is an L1 norm. This represents the function that takes the minimum value.

[0049] The preset range of values ​​for the regularization parameter is determined as follows: to Calculate the optimal target x for each value within the preset range of regularization parameters. and Then with The x-axis represents the "sparseness" or "simplicity" of the solution, with... The vertical axis represents the degree to which the solution fits the original data. The optimal target x corresponds to each value within the preset range of all regularization parameters. and Construct an L-curve curve, and then select the regularization parameter corresponding to the inflection point (the point of maximum curvature) as the optimal regularization parameter. That is, the optimal regularization parameter that strikes a balance between "simple solution" and "good fit". .

[0050] It should be noted that because the original nuclear magnetic resonance echo train data of low-porosity shale has an extremely low signal-to-noise ratio, direct inversion would result in a relaxation spectrum that is violently oscillating, contains negative values, and is physically absurd, making it unusable for subsequent wettability evaluation. Therefore, in order to gradually approximate the optimal relaxation distribution that minimizes the fitting error and is the simplest solution while ensuring the physical authenticity of the solution, a non-negative least squares iterative algorithm is used for solving the problem. By adjusting the solution in each iteration to reduce the target value, forcing all signal amplitudes to be non-negative, and stopping when the solution no longer changes significantly, a physically reasonable and stable corrected two-dimensional spectrum is output.

[0051] It's important to further clarify that in iterative algorithms for solving L1 norm regularization problems using non-negative least squares, the objective function may exist in a relatively flat region. Within this region, although the components of x change very little (i.e., the iteration stopping condition is met), the corresponding objective function value may still be much higher than the global optimum. This is because the objective function of this problem is non-convex, and the non-differentiability of the L1 norm leads to insufficient gradient information, making it difficult for the algorithm to continue effectively decreasing in the flat region; it can only slowly wander or get stuck in a local plateau. Therefore, the iteration stopping condition of "solution stability" alone cannot guarantee that x at this point is the optimal solution that minimizes the objective function; it only satisfies the engineering requirement of numerical convergence.

[0052] Finally, the x corresponding to the optimal λ is directly used as the corrected two-dimensional spectrum.

[0053] Step S3: Based on the corrected two-dimensional spectrum, calculate the T1 / T2 ratio segmented by the T2 interval; wherein the T2 interval is the T2 relaxation time interval.

[0054] It should be noted that in order to convert the relaxation information contained in the corrected two-dimensional spectrum into a single index that can be directly quantified to evaluate the wettability of the core, and to eliminate the interference of non-wetting factors such as core size and porosity on the NMR signal, it is necessary to calculate the T1 / T2 ratio segmented according to the T2 relaxation time interval, and use this ratio as the quantitative criterion for the initial wettability of the core.

[0055] Specifically, based on the corrected two-dimensional map, the T1 / T2 ratio is calculated segment by segment according to the T2 relaxation time interval, and the ratio is used as a quantitative criterion for the initial wettability of the core. CO2 huff and puff experiments are carried out under different temperature, pressure and well-drainage conditions to obtain cores after huff and puff. The correction of the two-dimensional map is repeated on the cores after huff and puff to obtain the corrected two-dimensional map after huff and puff and the T1 / T2 ratio of each T2 interval after huff and puff.

[0056] The T2 relaxation time interval is divided into three parts: micropore region: T2 < 0.1 ms; capillary bound water region: 0.1 ms ≤ T2 ≤ 1 ms; free water region: T2 > 1 ms; the unit ms is milliseconds.

[0057] The process of determining the three T2 relaxation time intervals is explained below: By comparing the changes in the corrected two-dimensional spectra of dry cores, self-absorbed cores, and pressurized saturated water cores, the fluid occurrence types and regions in the cores are analyzed.

[0058] In the dry core state, in the corrected two-dimensional NMR spectrum, the signal amplitude in the micropore region with T2 less than 0.1 ms is significantly higher than in other regions, mainly due to the organic matter and hydrogen in the mineral structure water present in the micropores. Meanwhile, related studies have shown that the T1 / T2 ratio of organic matter in the two-dimensional NMR spectrum is much larger than that of mineral structure water. Therefore, the signal in the region with T2 less than 0.1 ms can be divided into two parts: organic matter and mineral structure water. Figure 3 -a); After the core absorbs water, the water enters the hydrophilic pores under the action of capillary force, causing an increase in the amplitude of the nuclear magnetic resonance signal in the two-dimensional nuclear magnetic resonance spectrum, such as... Figure 3 As shown in -b, after self-absorption of water, the main increase in signal amplitude is in the pore region with T2 between 0.1 and 1 ms. This part can be classified as capillary-bound water ( Figure 3 -b); After pressurizing and saturating the core with water, the NMR signal amplitude in all effectively connected pores increased significantly. The signal amplitude increase was particularly pronounced in the medium and large pore regions with T2 greater than 1 ms; this portion can be classified as free water (…). Figure 3 -c).

[0059] Initial wettability is determined based on the T1 / T2 ratio: when the T1 / T2 ratio is less than 2, it is considered strong oil wettability; 2~5 is weak oil wettability / neutral wettability; 5~10 is weak water wettability; and greater than or equal to 10 is strong water wettability.

[0060] Step S4: Under different temperature, pressure, and well-drainage conditions, CO2 huff and puff experiments are carried out on the cores that have completed steps S1-S3 to obtain huff and puffed cores; Step S1-S3 is repeated on the huff and puffed cores to obtain the corrected two-dimensional spectrum and the T1 / T2 ratio of each T2 interval after huff and puff.

[0061] It should be noted that, in order to simulate the actual changes in reservoir wettability under different CO2 huff and puff process parameters (temperature, pressure, and well-drainage time) in shale oil reservoirs, and to obtain the nuclear magnetic resonance relaxation signal of the core after huff and puff for subsequent comparative analysis, it is necessary to conduct CO2 huff and puff experiments on the cores that have completed the initial test under different operating conditions to obtain the cores after huff and puff. The cores after huff and puff are then subjected to repeated saturation water, nuclear magnetic resonance testing, inversion correction, and T1 / T2 ratio calculation to obtain the corrected two-dimensional spectrum after huff and puff and the T1 / T2 ratio for each T2 interval.

[0062] The system allows for the setting of different operating parameters: temperature (5 gradients: 40℃, 50℃, 60℃, 70℃, 80℃); pressure (4 gradients: 10MPa, 15MPa, 20MPa, 25MPa); and well shut-in time (4 gradients: 2 days, 5 days, 10 days, 15 days).

[0063] Two-dimensional nuclear magnetic resonance (NMR) tests were performed on dried core samples after CO2 huff and puff, yielding corrected two-dimensional NMR spectra of the self-absorbed core samples. Subsequently, self-absorbed core samples after CO2 huff and puff were tested under different experimental conditions, including ambient temperature and pressure and 25 MPa pressure, obtaining corrected two-dimensional NMR spectra of the self-absorbed core samples before and after CO2 huff and puff under different conditions, as detailed below. Figure 4 As shown.

[0064] By comparing the changes in the T1 / T2 ratio of the capillary bound water zone formed by self-absorption of water in shale cores before and after shale oil CO2 huff and puff experiments, the wettability characteristics of shale oil CO2 huff and puff reservoirs are analyzed (specifically, as shown in...). Figure 5 (As shown). It can be observed that after CO2 huff and puff, with the increase of huff and puff pressure, temperature, and well-clogging time, the T1 / T2 ratio of the capillary bound water zone formed by the core's self-absorption gradually decreases, indicating that the overall wettability of the core gradually weakens. This is consistent with the core wettability change law obtained from the change of macroscopic water wetting contact angle on the core surface, demonstrating the accuracy of using the T1 / T2 ratio of the capillary bound water zone in the two-dimensional nuclear magnetic resonance spectrum after core self-absorption to judge the change in the overall wettability of the core.

[0065] It should be noted that the wetting contact angle is the angle formed by a droplet on a solid surface (usually measured by the droplet profile), used to quantify the wettability (hydrophilic, neutral, or oleophilic) of a solid surface. In petroleum engineering, it is a commonly used indicator for evaluating the affinity of rocks for water or oil, and is a routine indicator for assessing reservoir wettability. In this invention, it serves as a means of verifying macroscopic wettability, used to corroborate the accuracy of microscopic wettability assessment results based on nuclear magnetic resonance (NMR). This is corroborated by comparing the consistency of the changing trends. Specifically: after CO2 huff and puff, if the macroscopic wetting contact angle increases (indicating reduced water wettability on the core surface), and simultaneously the T1 / T2 ratio of the capillary bound water zone measured by NMR also decreases (indicating reduced overall water wettability of the core), and the changes in both are consistent, then the accuracy of the NMR assessment results is corroborated. Conversely, if the trends contradict each other, it suggests possible experimental error. That is, when the changes in both are inconsistent, the original echo train data is reacquired and the two-dimensional spectrum is corrected to obtain an accurate T1 / T2 ratio.

[0066] In the shale oil CO2 huff and puff experiment, core samples were washed and dried. According to the industry standard SY / T5153-2017 "Methods for Determining the Wettability of Reservoir Rocks", the wetting contact angle of the dried core samples was measured to obtain the wetting contact angle of the dried core samples after CO2 huff and puff. The changes in the wetting contact angle of the core samples before and after CO2 huff and puff were analyzed (specifically as follows). Figure 6As shown in the figure, it can be observed that with the increase of injection pressure, temperature and simmering time, the wetting contact angle of the core surface after CO2 injection gradually increases, indicating that the wettability of the core gradually weakens.

[0067] Step S5: Compare the T1 / T2 ratios in the same T2 interval before and after huff and puff, calculate the change in ratio and the rate of change in ratio, and determine the characteristics of reservoir wettability changes under each working condition; integrate the wettability change characteristics under all working conditions to obtain a complete evaluation result of the wettability changes of shale oil CO2 huff and puff reservoirs under different working conditions.

[0068] It should be noted that, in order to determine the specific impact and trend of different CO2 huff and puff conditions on the wettability of shale reservoirs, and to form a systematic evaluation conclusion that can be used as a reference for field process optimization, it is necessary to compare the T1 / T2 ratios in the same T2 interval before and after huff and puff, calculate the change in ratio and the rate of change to determine whether the wettability is enhanced, weakened, or basically unchanged under the condition. Then, the variation characteristics under all temperature, pressure, and well simmering time conditions are integrated to obtain a complete evaluation result of the changes in wettability of shale oil CO2 huff and puff reservoirs under different conditions.

[0069] Specifically, calculate the change and rate of change for each operating condition within the same T2 interval; where the change is the difference between the T1 / T2 ratio of each T2 interval after throughput and the T1 / T2 ratio of each T2 interval before throughput; and the rate of change is the percentage of the change in the T1 / T2 ratio of each T2 interval before throughput.

[0070] Determine the direction of change in wettability based on the amount of change: If the change is greater than 0, the wettability increases; if the change is less than 0, the wettability decreases and the oil wettability increases; if the change is equal to 0, the wettability shows no significant change.

[0071] Determine the degree of change based on the absolute value of the rate of change: When the absolute value of the rate of change is less than 5%, the change is not obvious; when the absolute value of the rate of change is greater than or equal to 5% and less than 20%, the change is obvious; when the absolute value of the rate of change is greater than or equal to 20%, the change is significant.

[0072] The direction and degree of change are used as characteristics of wettability changes; Record the wettability change characteristics (direction + degree) of each T2 interval under all operating conditions and store them in the operating condition database. Based on the wettability change characteristics (direction + degree) of each operating condition in the database, and considering the change trends of the three intervals, select the operating condition that causes the reservoir wettability to change in the direction most favorable to crude oil recovery (such as moderately increasing water wettability or avoiding excessive oil wetting) as the optimal operating condition, which will be used to guide the design of CO2 huff and puff process parameters for shale oil in the field.

[0073] It's important to note that on the pore surface of hydrophilic rocks, the hydrogen nuclei of water undergo strong physicochemical interactions with the solid surface. This surface interaction simultaneously shortens both the T1 relaxation time (longitudinal relaxation) and the T2 relaxation time (lateral relaxation). However, in addition to being affected by the same surface relaxation mechanism as T1, T2 is also significantly affected by the internal magnetic field gradient within the pores. The paramagnetic minerals (such as pyrite and siderite) commonly found in shale reservoirs, as well as the interface between organic matter and water, generate extremely strong internal magnetic field inhomogeneities within the micro- and nano-pores. When water molecules diffuse through this inhomogeneous magnetic field within the pores, they accelerate the dispersion of the lateral magnetization vector, leading to additional attenuation of T2. Therefore, although both T1 and T2 shorten with increasing hydrophilicity, the shortening of T2 is much greater than that of T1. The direct result is a widening of the numerical difference between T1 and T2, i.e., a significantly increased T1 / T2 ratio. This explains why a larger T1 / T2 ratio indicates a more intense interaction between water molecules and the pore walls, and a stronger water permeability of the core.

[0074] This concludes the embodiment.

[0075] like Figure 2 As shown, a second aspect of the present invention is to provide a shale oil CO2 huff and puff reservoir wettability evaluation system based on two-dimensional nuclear magnetic resonance, comprising: The reference nuclear magnetic resonance data acquisition module 101 is used to obtain a self-water-absorbing core by washing and drying a natural shale core as an experimental sample, and then performing self-water-absorbing treatment under normal temperature and pressure conditions; to perform nuclear magnetic resonance testing on the self-water-absorbing core and acquire the raw echo train data before throughput; and then to obtain an initial two-dimensional spectrum based on the raw echo train data before throughput. Inversion correction module 102: used to obtain the noise interference level of the original echo string data, determine whether the noise interference level exceeds the preset interference threshold, and if so, start the inversion correction process to correct the initial two-dimensional spectrum and output the corrected two-dimensional spectrum. Ratio quantization module 103: used to calculate the T1 / T2 ratio based on the corrected two-dimensional spectrum, segmented by the T2 interval; wherein, the T2 interval is the T2 relaxation time interval; CO2 huff and puff experiment and post-huff and puff NMR test module 104: used to conduct CO2 huff and puff experiments on cores that have completed steps S1-S3 under different temperature, pressure and well-drainage conditions to obtain post-huff and puff cores; repeat steps S1-S3 on the post-huff and puff cores to obtain the corrected two-dimensional spectrum and the T1 / T2 ratio of each T2 interval after huff and puff. Module 105: Wettability Change Analysis and Comprehensive Evaluation: Used to compare the T1 / T2 ratio in the same T2 interval before and after huff and puff, calculate the change in ratio and the rate of change in ratio, determine the wettability change characteristics of the reservoir under each working condition; integrate the wettability change characteristics under all working conditions to obtain a complete evaluation result of the wettability change of shale oil CO2 huff and puff reservoir under different working conditions.

[0076] A third aspect of the present invention is to provide an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement a method for evaluating the wettability of shale oil CO2 huff and puff reservoirs based on two-dimensional nuclear magnetic resonance.

[0077] A fourth aspect of the present invention is to provide a computer-readable storage medium storing a computer program that, when executed by a processor, implements a method for evaluating the wettability of shale oil CO2 huff and puff reservoirs based on two-dimensional nuclear magnetic resonance.

[0078] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, optical storage, etc.) containing computer-usable program code.

[0079] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, systems, and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0080] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0081] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for evaluating the wettability of shale oil CO2 huff and puff reservoirs based on two-dimensional nuclear magnetic resonance, characterized in that, Includes the following steps: S1. Using natural shale cores as experimental samples, after pretreatment such as washing and drying, self-water absorption treatment was carried out under normal temperature and pressure conditions to obtain self-water-absorbing cores; nuclear magnetic resonance testing was performed on the self-water-absorbing cores to collect the raw echo train data before throughput; then, based on the raw echo train data before throughput, an initial two-dimensional spectrum was obtained. S2, obtain the noise interference level of the original echo string data, determine whether the noise interference level exceeds the preset interference threshold, if so, start the inversion correction process, correct the initial two-dimensional spectrum, and output the corrected two-dimensional spectrum; S3, based on the corrected two-dimensional spectrum, calculate the T1 / T2 ratio segmented according to the T2 interval; wherein, the T2 interval is the T2 relaxation time interval; S4. Under different temperature, pressure and well-drainage conditions, CO2 huff and puff experiments are carried out on the cores that have completed steps S1-S3 to obtain huff and puffed cores. Steps S1-S3 are repeated on the huff and puffed cores to obtain the corrected two-dimensional spectrum and the T1 / T2 ratio of each T2 interval after huff and puff. S5. Compare the T1 / T2 ratios in the same T2 interval before and after huff and puff, calculate the change in ratio and the rate of change in ratio, and determine the characteristics of reservoir wettability changes under each working condition; integrate the wettability change characteristics under all working conditions to obtain a complete evaluation result of the wettability changes of shale oil CO2 huff and puff reservoirs under different working conditions.

2. The method for evaluating the wettability of shale oil CO2 huff and puff reservoirs based on two-dimensional nuclear magnetic resonance according to claim 1, characterized in that, The degree of noise interference is specifically expressed by the formula: In the formula, This represents the energy of the first few echo signals in the original echo train data. This represents the total energy of all echo signals in the original echo train data. This represents the signal-to-noise ratio of the original echo train data; This indicates the level of noise interference in the original echo train data. This represents an exponential function with the natural constant as its base.

3. The method for evaluating the wettability of shale oil CO2 huff and puff reservoirs based on two-dimensional nuclear magnetic resonance according to claim 1, characterized in that, The process then initiates the inversion correction procedure to correct the initial two-dimensional map and outputs the corrected two-dimensional map, including: (1) Preprocess the raw echo train data to remove outliers and baseline drift; (2) Construct a two-dimensional initial kernel matrix, and use truncated singular value decomposition to truncate the two-dimensional initial kernel matrix to filter out high-frequency noise components and obtain the truncated diagonal matrix; reconstruct the kernel matrix A by using the truncated diagonal matrix to obtain an adjusted kernel matrix A; (3) Based on the adjusted kernel matrix A and the initial two-dimensional spectrum, the corrected two-dimensional spectrum is obtained by using non-negative least squares iteration.

4. The method for evaluating the wettability of shale oil CO2 huff and puff reservoirs based on two-dimensional nuclear magnetic resonance according to claim 3, characterized in that, The preprocessing of the raw echo train data, including outlier removal and baseline drift removal, includes: The LOF anomaly detection algorithm is used to detect anomalies, and then the anomalies are removed. The positions of the anomalies are then supplemented by interpolation using the average interpolation method. The average value of several points at the end of the original echo string data is used as the baseline offset. The baseline drift is then removed by subtracting the baseline offset from the baseline data of the original echo string data.

5. The method for evaluating the wettability of shale oil CO2 huff and puff reservoirs based on two-dimensional nuclear magnetic resonance according to claim 3, characterized in that, The construction of the two-dimensional initial kernel matrix involves truncating the initial kernel matrix using truncated singular value decomposition to filter out high-frequency noise components, resulting in a truncated diagonal matrix. The truncated diagonal matrix is ​​then reconstructed to obtain an adjusted kernel matrix A, comprising: Singular value decomposition is performed on the initial kernel matrix to obtain column orthogonal matrices, diagonal matrices, and row orthogonal matrices; the diagonal matrix contains singular values ​​on its diagonal. Starting from the first element in the top-left corner of the diagonal matrix, calculate the energy percentage of the first k singular values ​​among all singular values; the energy percentage is specifically expressed by the formula: In the formula, Indicates the first A singular value, This represents the number of the first k singular values. This represents the number of all singular values. Indicates the percentage of energy; If the energy percentage of the current k singular values ​​among all singular values ​​is greater than or equal to the preset energy retention ratio, then the first k singular values ​​are retained, and the energy percentages from the (k+1)th to the th singular values ​​are removed. By setting the singular values ​​between each pair to zero, a truncated diagonal matrix is ​​obtained. By reconstructing the truncated diagonal matrix, an adjusted kernel matrix A is obtained; The elements in the initial kernel matrix are determined by a discretized multi-exponential decay model.

6. The method for evaluating the wettability of shale oil CO2 huff and puff reservoirs based on two-dimensional nuclear magnetic resonance according to claim 4, characterized in that, The process of obtaining the corrected two-dimensional map by using non-negative least squares iterative solution based on the adjusted kernel matrix A and the initial two-dimensional map includes: Based on the adjusted kernel matrix A, a non-negative least squares iterative solution is used to force all T1 or T2 distribution values ​​to be non-negative; where, during the iteration process, up to the two adjacent iterations, ... When the iteration stops, the iteration continues; where, These are preset parameters; In the formula, For the first x in the next iteration For the first x in the next iteration for and The L2 norm between; In the iteration process, L1 norm regularization is used for inversion, and the objective function in the inversion process is: Where A is the kernel matrix, b is the preprocessed raw echo train data, and x is the T1 or T2 distribution. To be the optimal regularization parameter, It is the L2 norm. It is an L1 norm. This represents a function that takes the minimum value. During iteration, the initial x is the initial two-dimensional graph; Determine the preset range of values ​​for the regularization parameter, and calculate the optimal target x corresponding to each value within the preset range of values ​​for the regularization parameter. and Then with As the x-axis, with The vertical axis represents the optimal target x value for each value within the preset range of all regularization parameters. and Construct an L-curve curve, and then select the regularization parameter corresponding to the inflection point as the optimal regularization parameter. .

7. The method for evaluating the wettability of shale oil CO2 huff and puff reservoirs based on two-dimensional nuclear magnetic resonance according to claim 1, characterized in that, The T2 intervals include: the micropore region is T2 < 0.1 ms; the capillary bound water region is 0.1 ms ≤ T2 ≤ 1 ms; and the free water region is T2 > 1 ms.

8. A shale oil CO2 huff-and-puff reservoir wettability evaluation system based on two-dimensional nuclear magnetic resonance (NMR), used to implement the shale oil CO2 huff-and-puff reservoir wettability evaluation method based on two-dimensional NMR as described in any one of claims 1-7, characterized in that, include: The reference NMR data acquisition module is used to obtain a self-water-absorbing core by washing and drying natural shale cores as experimental samples under normal temperature and pressure conditions; to perform NMR testing on the self-water-absorbing cores and acquire the raw echo train data before throughput; and then to obtain the initial two-dimensional spectrum based on the raw echo train data before throughput. Inversion correction module: used to obtain the noise interference level of the original echo train data, determine whether the noise interference level exceeds the preset interference threshold, and if so, start the inversion correction process to correct the initial two-dimensional spectrum and output the corrected two-dimensional spectrum. Ratio quantization module: used to calculate the T1 / T2 ratio based on the corrected two-dimensional spectrum, segmented by the T2 interval; wherein, the T2 interval is the T2 relaxation time interval; CO2 Huff and Puff Experiment and Post-Huff and Puff NMR Testing Module: Used to conduct CO2 huff and puff experiments on core samples after steps S1-S3 under different temperature, pressure and well-drainage conditions to obtain post-huff and puff core samples; repeat steps S1-S3 on the post-huff and puff core samples to obtain the corrected two-dimensional spectrum and the T1 / T2 ratio of each T2 interval after huff and puff. The wettability change analysis and comprehensive evaluation module is used to compare the T1 / T2 ratio in the same T2 interval before and after huff and puff, calculate the change in ratio and the rate of change in ratio, and determine the wettability change characteristics of the reservoir under each working condition; it integrates the wettability change characteristics under all working conditions to obtain a complete evaluation result of the wettability change of shale oil CO2 huff and puff reservoir under different working conditions.

9. An electronic device, characterized in that, The system includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the method for evaluating the wettability of shale oil CO2 huff and puff reservoirs based on two-dimensional nuclear magnetic resonance as described in any one of claims 1-7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the method for evaluating the wettability of shale oil CO2 huff and puff reservoirs based on two-dimensional nuclear magnetic resonance as described in any one of claims 1-7.

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