Method and system for characterizing pore size of different wetting types based on spontaneous imbibition-nmr experiment

Abstract

The present application relates to a method and system for characterizing pore sizes of different wetting types based on spontaneous imbibition-nuclear magnetic resonance experiments, belonging to the field of unconventional oil and gas exploration and development, comprising: 1) preparation and preliminary treatment of shale samples; 2) shale wettability characterization based on spontaneous imbibition of oil / water experiments and nuclear magnetic resonance oil / water quantitative monitoring technology; 3) oil / water nuclear magnetic pore size conversion parameters are calibrated based on nitrogen adsorption experiments and large-view field stitching scanning electron microscope pore size analysis results; 4) based on the decoupling analysis of two-dimensional nuclear magnetic resonance at different imbibition equilibrium stages, the nuclear magnetic resonance response of different wetting type pores is obtained, and the pore size distribution curve of different wetting type pores is determined by combining the oil / water nuclear magnetic pore size conversion parameters. The present application can effectively distinguish the distribution characteristics of fluids in different wetting type pores in shale, and further clarify the content and pore size distribution characteristics of different wetting type pores in shale by means of nuclear magnetic pore size analysis method.

Description

TECHNICAL FIELD

[0001] The present application relates to a method and system for characterizing different wetting type pore sizes based on spontaneous imbibition-nuclear magnetic resonance experiments, and belongs to the field of unconventional oil and gas exploration and development. BACKGROUND

[0002] As an important reservoir of unconventional oil and gas resources, the internal pore structure of shale, especially the size distribution and content of different wetting type pores, has an important influence on the occurrence state, percolation capacity and ultimate recovery of oil and gas. In-depth understanding of the pore size characteristics of different wetting type pores in shale is of great theoretical and practical significance for optimizing fracturing schemes, improving recovery efficiency and guiding efficient development of shale oil and gas.

[0003] Currently, shale pore size characterization techniques mainly include mercury injection method, gas adsorption method, small-angle X-ray scattering, scanning electron microscopy and nuclear magnetic resonance, etc. However, these methods have many limitations in characterizing the pore sizes of different wetting type pores in shale: ① The mercury injection method is widely used for pore size distribution characterization, but shale is mainly composed of micro-nano pores, and the high-pressure injection process can easily cause irreversible damage to the shale sample, changing the pore structure. In addition, the mercury injection method has limited ability to characterize nano-scale pores; ② The gas adsorption method is mainly used for characterization of nano-scale pores less than 300 nm, and it is difficult to fully characterize the pore size distribution of shale; ③ The small-angle X-ray scattering method is suitable for characterizing pores of 1-100 nm, and it is also difficult to fully reveal the pore size distribution characteristics of shale; ④ The scanning electron microscopy method can only observe the pore morphology and pore size characteristics, but the ordinary scanning electron microscopy has limited observation scale and is difficult to characterize the overall pore size distribution of shale; ⑤ The nuclear magnetic resonance method can reflect the pore size and fluid occurrence state through relaxation time, and has the advantages of non-destructive and rapid, but it needs to use nitrogen adsorption and other pore size characterization techniques to calibrate the conversion relationship between relaxation time and pore size. In addition, the comprehensive pore size contribution of all types of pores reflected by the above methods is difficult to distinguish the pore size distribution characteristics of different wetting type pores in shale. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application proposes a method for characterizing different wetting type pore sizes based on spontaneous imbibition-nuclear magnetic resonance experiments.

[0005] Based on the spontaneous imbibition experiment, the present application dynamically monitors the distribution characteristics of the fluid in the imbibition process by introducing the nuclear magnetic resonance technology, and combines the decoupling analysis of nuclear magnetic resonance at different imbibition stages of the sample, which can effectively distinguish the distribution characteristics of the fluid in different wetting type pores inside the shale. With the help of nuclear magnetic pore size analysis method, the content and pore size distribution characteristics of different wetting type pores in shale can be further determined, which has important significance for revealing the wetting characteristics and pore size distribution of the micro-pores in shale reservoirs.

[0006] The application also provides a pore size characterization system for different wetting type pores based on spontaneous imbibition-nuclear magnetic resonance experiments.

[0007] The technical scheme of the application is:

[0008] The pore size characterization method for different wetting type pores based on spontaneous imbibition-nuclear magnetic resonance experiments comprises the following steps:

[0009] 1) shale sample preparation and preliminary treatment;

[0010] 2) shale wettability characterization based on shale spontaneous oil / water imbibition experiments and nuclear magnetic resonance oil / water quantitative monitoring technology; including: shale spontaneous imbibition experiments, oil / water spontaneously enters the pores of the corresponding wetting phase under the action of capillary force, combined with nuclear magnetic resonance technology to quantitatively monitor the distribution characteristics of oil / water in shale pores during the imbibition process, and the content of different wetting type pores is divided by comparing the oil / water distribution in different imbibition equilibrium stages, and then the shale wettability is characterized;

[0011] 3) oil / water nuclear magnetic pore diameter conversion parameter calibration based on nitrogen adsorption experiments and large-view field stitching scanning electron microscope pore diameter analysis results; including: using the results of nitrogen adsorption experiments to calibrate the nuclear magnetic pore diameter conversion parameters of water, and using the results of large-view field stitching scanning electron microscope pore diameter analysis to calibrate the nuclear magnetic pore diameter conversion parameters of oil;

[0012] 4) decoupling analysis based on two-dimensional nuclear magnetic resonance at different imbibition equilibrium stages to obtain the nuclear magnetic resonance response of different wetting type pores, and the pore diameter distribution curve of different wetting type pores is determined by combining the oil / water nuclear magnetic pore diameter conversion parameters.

[0013] According to the preferred embodiment of the application, the shale sample preparation and preliminary treatment comprises the following steps:

[0014] The shale sample is selected to drill a standard plunger sample with a diameter not greater than 2.5 cm along the parallel bedding direction by wire cutting, and then the sample is evenly divided into two parts along the vertical bedding direction to obtain parallel samples A and B;

[0015] The parallel samples A and B are dried at 100-110 DEG C for not less than 12 hours to remove residual fluids in the pores;

[0016] Then, the mass mA and mB of the dried parallel samples A and B are weighed using a high-precision balance;

[0017] The side surface of the sample is coated with epoxy resin.

[0018] Further preferably, the parallel samples A and B are dried at 110 DEG C for 12 hours.

[0019] According to the present application, shale wettability characterization based on shale spontaneous oil / water imbibition experiment and nuclear magnetic resonance oil / water quantitative monitoring technology; including:

[0020] Select n-dodecane or n-octane as the oil phase imbibition liquid, and select KCl aqueous solution as the water phase imbibition liquid;

[0021] Different volumes of oil phase imbibition liquid are measured in a sealed glass tube without hydrogen signal, and the corresponding nuclear magnetic signal amount of different volumes of oil phase imbibition liquid is detected using a nuclear magnetic resonance instrument. Repeat at least 3 points of data, and carry out linear fitting according to the imbibition liquid volume and the detected nuclear magnetic signal amount of different experimental points. A=K 油 *V, wherein A is the measured signal amount, V is the corresponding imbibition liquid volume, and K 油 is the oil phase imbibition liquid nuclear magnetic signal amount vs. volume conversion coefficient, that is, the oil phase imbibition liquid nuclear magnetic signal amount vs. volume conversion coefficient K 油 ;

[0022] Similarly, different volumes of water phase imbibition liquid are measured in a sealed glass tube without hydrogen signal, and the corresponding nuclear magnetic signal amount of different volumes of oil phase imbibition liquid is detected using a nuclear magnetic resonance instrument. Repeat at least 3 points of data, and carry out linear fitting according to the imbibition liquid volume and the detected nuclear magnetic signal amount of different experimental points. A=K 水 ;

[0023] a. First, place the parallel sample A in the oil phase imbibition liquid and carry out spontaneous imbibition experiment. After a period of time, take out the parallel sample A, wipe off the surface fluid, and place it in a glass tube without hydrogen signal for sealing. Then use a nuclear magnetic resonance instrument to detect the nuclear magnetic resonance signal of the sample. Repeat the above operation every certain period of time to take out the sample, wipe off the surface fluid, place it in a glass tube without hydrogen signal for sealing, and use a nuclear magnetic resonance instrument to detect the nuclear magnetic resonance signal of the sample to realize dynamic monitoring of the hydrogen-containing fluid signal, i.e. the nuclear magnetic resonance signal, during the imbibition process of the sample;

[0024] When the hydrogen-containing fluid signal of the parallel sample A no longer changes, it indicates that the hydrogen-containing fluid content in the parallel sample A no longer changes, and the imbibition reaches equilibrium;

[0025] b. Place the parallel sample A in the water phase imbibition liquid and carry out spontaneous imbibition experiment. After a period of time, take out the parallel sample A, wipe off the surface fluid, and place it in a glass tube without hydrogen signal for sealing. Then use a nuclear magnetic resonance instrument to detect the nuclear magnetic resonance signal of the sample. Repeat the above operation every certain period of time to realize dynamic monitoring of the hydrogen-containing fluid signal during the imbibition process of the sample;

[0026] When the hydrogen-containing fluid signal of the parallel sample A no longer changes, it indicates that the hydrogen-containing fluid content in the parallel sample A no longer changes, and the imbibition reaches equilibrium;

[0027] Subsequently, the imbibition fluid is replaced again with the oil phase imbibition liquid, and steps a and b are repeated;

[0028] Parallel sample A undergoes four imbibition stages of imbibition of oil phase O, imbibition of water phase W, imbibition of oil phase 2O, and imbibition of water phase 2W, and after the last stage of imbibition is balanced, the alternating imbibition experiment is ended, during which the change in the hydrogen-containing fluid signal of the sample in the imbibition process is dynamically monitored using a nuclear magnetic resonance instrument;

[0029] The oil phase nuclear magnetic signal obtained by nuclear magnetic detection in the imbibition process is converted into the oil phase volume by combining the nuclear magnetic signal amount vs. volume conversion coefficient of the imbibition liquid, and the oil phase imbibition liquid nuclear magnetic signal amount vs. volume conversion coefficient K 油 obtained by linear fitting before is converted into the oil phase volume, and similarly, the water phase nuclear magnetic signal obtained by nuclear magnetic detection in the imbibition process is converted into the water phase volume by combining the nuclear magnetic signal amount vs. volume conversion coefficient of the imbibition liquid, and the water phase imbibition liquid nuclear magnetic signal amount vs. volume conversion coefficient K 水 obtained by linear fitting before is converted into the water phase volume;

[0030] Parallel sample B is subjected to the same experimental operation as parallel sample A, except that parallel sample B is first placed in the water phase imbibition liquid, undergoes four imbibition stages of imbibition of water phase W, imbibition of oil phase O, imbibition of water phase 2W, and imbibition of oil phase 2O, and after the imbibition is ended, the hydrogen-containing fluid nuclear magnetic dynamic monitoring result in the imbibition process is converted into the change in the hydrogen-containing fluid volume in the imbibition process by combining the nuclear magnetic signal amount vs. volume conversion coefficient of the imbibition liquid;

[0031] Based on the results of the dynamic monitoring of the oil and water content changes in the imbibition processes of parallel sample A and parallel sample B by nuclear magnetic resonance, the contents of different wetting type pores are divided; specifically, for the imbibition of oil phase 2O stage, the oil-wet and mixed-wet pores will be filled with the oil phase, and the water-wet pores still maintain the water phase filling, therefore, the water phase signal measured by the nuclear magnetic resonance of the sample reflects the content of the water-wet pores; for the imbibition of water phase 2W stage, the oil phase signal measured by the nuclear magnetic resonance reflects the content of the oil-wet pores.

[0032] Further preferably, 8%, 10%, or 15% mass concentration KCl aqueous solution is selected as the water phase imbibition liquid.

[0033] According to the present application, preferably, the oil / water nuclear magnetic pore size conversion parameters are calibrated based on the nitrogen adsorption experiment and the aperture analysis result of the large-view field stitching scanning electron microscope; including:

[0034] After the imbibition is ended, parallel sample A or parallel sample B is dried, and then is prepared into a block-shaped sample with a vertical bedding plane;

[0035] The nitrogen adsorption experiment is carried out on the block sample with a vertical bedding plane by using the ASAP2460-2HD specific surface area and pore size analyzer produced by American Micromeritics Company, and the pore size distribution characteristics of the pores smaller than 200 nm in the sample are obtained by combining the BJH pore interpretation model;

[0036] The block sample with a vertical bedding plane is subjected to mechanical polishing, argon ion polishing and carbon coating treatment, and then the scanning electron microscope large-view field splicing experiment is carried out, so that a splicing image is obtained, the splicing image penetrates through multiple laminae and reflects the pore development of the whole sample under the scanning electron microscope;

[0037] The splicing image is imported into the ImageJ software, all the pores in the view field are extracted by threshold segmentation, and the pore size , area of each pore are exported , the total area of the view field is calculated , the surface pore rate of each pore is calculated , and the normalized distribution characteristics of the surface pores of the sample under the scanning electron microscope are characterized, so that the pore size distribution result extracted by the scanning electron microscope is obtained;

[0038] The cross-plot of the oil phase nuclear magnetic distribution result and the pore size distribution result extracted by the scanning electron microscope is established, the oil phase nuclear magnetic pore size conversion coefficient is obtained according to the linear corresponding relationship between the transverse relaxation time and the pore size, the oil phase nuclear magnetic transverse relaxation time is converted into the oil phase nuclear magnetic pore size , that is, the value of the oil phase nuclear magnetic pore size conversion coefficient is gradually adjusted according to the morphological characteristics, so that the wave peak and wave trough of the nuclear magnetic pore size distribution correspond to the wave peak and wave trough of the pore size distribution extracted by the scanning electron microscope, and at this time the value of the oil phase nuclear magnetic pore size conversion coefficient is the optimal oil phase nuclear magnetic pore size conversion coefficient.

[0039] Further preferably, the granular sample with a particle size of 60-80 meshes and the block sample with a vertical bedding plane and an area of 1-1.5 cm 2 and a thickness of 0.3-0.5 cm are prepared.

[0040] According to the present application, the nuclear magnetic resonance responses of different wetting type pores are obtained based on the decoupling analysis of two-dimensional nuclear magnetic resonance at different infiltration equilibrium stages, and the pore size distribution curves of different wetting type pores are determined by combining the oil / water nuclear magnetic pore size conversion parameters; including:

[0041] When the parallel sample A is balanced at the second oil phase infiltration stage, the water phase T2 projection spectrum reflecting the water-wet pores is obtained by projecting the water region signal in the two-dimensional nuclear magnetic resonance spectrum to the T2 axis direction, and the obtained water phase nuclear magnetic resonance pore size conversion parameter is combined to convert the abscissa Convert the horizontal coordinate of the oil phase T2 projection spectrum of the oil-wet pore and the mixed-wet pore to the NMR pore size of the oil-wet pore and the mixed-wet pore , Convert the vertical coordinate of the oil phase NMR signal amount to the oil-wet pore volume according to the obtained oil phase imbibition liquid NMR signal amount vs volume conversion coefficient K 水 Convert to oil-wet pore volume Finally, according to the obtained NMR pore size of the oil-wet pore and the mixed-wet pore And the pore volume of the oil-wet pore and the mixed-wet pore Calculate , that is, the pore size distribution curve of the oil-wet pore is obtained;

[0042] When the second imbibition of the oil phase of the parallel sample A is balanced, the oil phase T2 projection spectrum reflecting the oil-wet pore is obtained by projecting the oil region signal in the two-dimensional NMR spectrum to the T2 axis direction, and the obtained oil phase NMR pore size conversion parameter Convert the horizontal coordinate of the oil phase T2 projection spectrum of the oil-wet pore to the NMR pore size of the oil-wet pore Convert to oil-wet pore volume Convert the vertical coordinate of the oil phase NMR signal amount to the oil-wet pore volume according to the obtained oil phase imbibition liquid NMR signal amount vs volume conversion coefficient K 油 Convert to oil-wet pore volume Finally, according to the obtained NMR pore size of the oil-wet pore and the mixed-wet pore And the pore volume of the oil-wet pore and the mixed-wet pore Calculate , that is, the pore size distribution curve of the oil-wet pore is obtained;

[0043] When the second imbibition of the oil phase of the parallel sample A is balanced, the oil-wet pore and the mixed-wet pore in the parallel sample A are all filled with oil, and the oil phase T2 projection spectrum reflecting the oil-wet pore and the mixed-wet pore is obtained by projecting the oil region signal in the two-dimensional NMR spectrum to the T2 axis direction, and the obtained oil phase NMR pore size conversion parameter Convert the horizontal coordinate of the oil phase T2 projection spectrum of the oil-wet pore and the mixed-wet pore to the NMR pore size of the oil-wet pore and the mixed-wet pore Convert to oil-wet pore volume Convert the vertical coordinate of the oil phase NMR signal amount to the oil-wet pore volume according to the obtained oil phase imbibition liquid NMR signal amount vs volume conversion coefficient K 油 Convert to oil-wet pore volume ;

[0044] Finally, according to the obtained NMR pore size of the oil-wet pore and the mixed-wet pore And the pore volume of the oil-wet pore and the mixed-wet pore Calculate The pore size distribution curve of the oil-wet pores and the mixed-wet pores is obtained, and the pore size distribution curve of the mixed-wet pores is obtained by subtracting the pore size distribution curve of the oil-wet pores from the pore size distribution curve of the oil-wet pores and the mixed-wet pores.

[0045] The pore size characterization system based on spontaneous imbibition-nuclear magnetic resonance experiment of different wetting type pores comprises:

[0046] The preparation module is configured to prepare and pretreat the shale sample.

[0047] The shale wettability characterization module is configured to characterize the shale wettability based on shale spontaneous imbibition oil / water experiment and nuclear magnetic resonance oil / water quantitative monitoring technology, and comprises the following steps: through the alternating spontaneous imbibition experiment, the oil / water spontaneously enters the pores of the corresponding wetting phase under the action of capillary force, the distribution characteristics of the oil / water in the shale pores in the imbibition process are quantitatively monitored by combining the nuclear magnetic resonance technology, the contents of different wetting type pores are divided by comparing the oil / water distribution in the shale at different imbibition equilibrium stages, and then the shale wettability is characterized.

[0048] The oil / water nuclear magnetic pore size conversion parameter calibration module is configured to calibrate the oil / water nuclear magnetic pore size conversion parameters based on the nitrogen adsorption experiment and the large-view-field splicing scanning electron microscope pore size analysis result, and comprises the following steps: the nuclear magnetic pore size conversion parameters of water are calibrated by using the nitrogen adsorption experiment result, and the nuclear magnetic pore size conversion parameters of oil are calibrated by using the large-view-field splicing scanning electron microscope pore size analysis result.

[0049] The pore size characterization module is configured to obtain the nuclear magnetic resonance response of different wetting type pores based on the decoupling analysis of the two-dimensional nuclear magnetic resonance at different imbibition equilibrium stages, and determine the pore size distribution curve of the different wetting type pores by combining the oil / water nuclear magnetic pore size conversion parameters.

[0050] Compared with the prior art, the shale wettability characterization system has the following beneficial effects:

[0051] 1. Based on the alternating spontaneous imbibition oil and water experiment, the imbibition characteristics of the sample pores under the coexistence of oil and water are dynamically revealed, and the prior art only considers the imbibition characteristics of the sample pores under a single fluid.

[0052] 2. The oil and water in the sample pores under the coexistence of oil and water are divided and quantified by the two-dimensional nuclear magnetic resonance technology, and the quantitative monitoring of the content change of the oil and water in the sample pores in the imbibition process is realized, the contents of the oil-wet pores, the water-wet pores and the mixed-wet pores in the sample are accurately quantified by combining the division method of the different wetting type pores.

[0053] 3. The sample pore size distribution curve obtained by nitrogen adsorption experiment and large field stitching scanning electron microscope experiment is used for marking the nuclear magnetic resonance pore size conversion coefficient of water and oil two phases, and provides a basis for nuclear magnetic pore size analysis of oil and water two phases;

[0054] 4. Based on the two-dimensional nuclear magnetic resonance decoupling method, the oil-wet pore, water-wet pore and mixed-wet pore T2 projection spectrum are separated for the first time, and the nuclear magnetic pore size distribution curves of the three types of wetting pores are obtained by combining the oil and water nuclear magnetic resonance pore size conversion coefficients, which provides a new idea for the characterization of oil-wet pores, water-wet pores and mixed pores in shale.

[0055] 5. The experimental idea of the present application is clear, the experimental process is rigorous, the operability is strong, and the reproducibility is high, which has practical significance for revealing the pore size wettability characteristics of shale. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 It is a flowchart of the pore size characterization method of different wetting type pores based on spontaneous imbibition-nuclear magnetic resonance experiment;

[0057] Figure 2 It is a schematic diagram of the signal amount-volume calibration relationship of imbibition fluid;

[0058] Figure 3 It is a schematic diagram of the one-dimensional nuclear magnetic dynamic monitoring result of the first imbibition stage of sample A;

[0059] Figure 4 It is a schematic diagram of the two-dimensional nuclear magnetic oil-water signal dynamic monitoring result of the first imbibition stage of sample A;

[0060] Figure 5 It is a schematic diagram of the two-dimensional nuclear magnetic oil-water signal dynamic monitoring result of the imbibition process of sample A;

[0061] Figure 6 It is a schematic diagram of the pore hydrogen-containing fluid volume dynamic monitoring result of the imbibition process of sample A;

[0062] Figure 7 It is a schematic diagram of the pore hydrogen-containing fluid volume dynamic monitoring result of the imbibition process of sample A;

[0063] Figure 8 It is a schematic diagram of the nitrogen adsorption pore size distribution;

[0064] Figure 9 It is a schematic diagram of the water phase nuclear magnetic pore size conversion coefficient calibration;

[0065] Figure 10 It is a schematic diagram of the oil phase nuclear magnetic pore size conversion coefficient calibration;

[0066] Figure 11 It is a schematic diagram of the two-dimensional nuclear magnetic signal decoupling analysis of different wetting pores;

[0067] Figure 12 Schematic diagram of different wetting pore size distribution;

[0068] Figure 13 Schematic diagram of shale sample preparation and pre-treatment process. DETAILED DESCRIPTION

[0069] The present application will be described in detail below with reference to the drawings and specific embodiments, wherein the specific embodiments and descriptions are only used to explain the present application, but not as a limitation to the present application.

[0070] Terminology:

[0071] 1. Spontaneous imbibition experiment, in which the sample performs unidirectional spontaneous imbibition in the parallel bedding direction, and after one-stage imbibition equilibrium, the imbibition fluid type is changed for alternating imbibition, and the alternating imbibition is two cycles;

[0072] 2. Nuclear magnetic resonance experiment, the instrument is a MicroMr20-025V instrument produced by Suzhou Nu Mai Company, the resonance frequency is 20 MHz, the magnet strength is 0.5 T, the coil diameter is 25 mm, the one-dimensional nuclear magnetic resonance adopts CPMG sequence, the two-dimensional nuclear magnetic resonance adopts IR-CPMG sequence, and the inversion software is Nu Mai nuclear magnetic resonance data analysis software V1.1.

[0073] Example 1

[0074] The different wetting type pore size characterization method based on spontaneous imbibition-nuclear magnetic resonance experiment, as shown in Figure 1 By introducing the nuclear magnetic resonance technology to dynamically monitor the distribution characteristics of the fluid in the imbibition process, and combining the decoupling analysis of the nuclear magnetic resonance at different imbibition stages of the sample, the distribution characteristics of the fluid in the different wetting type pores inside the shale can be effectively distinguished, and by means of the nuclear magnetic pore size analysis method, the content and pore size distribution characteristics of the different wetting type pores in the shale can be further clarified. Including:

[0075] 1) Preparation and pre-treatment of shale sample;

[0076] 2) Shale wettability characterization based on shale spontaneous imbibition oil / water experiment and nuclear magnetic resonance oil / water quantitative monitoring technology; including: shale through alternating spontaneous imbibition experiment, oil / water spontaneously enters the corresponding wetting pore under the action of capillary force, combined with nuclear magnetic resonance technology to quantitatively monitor the distribution characteristics of oil / water in shale pores during imbibition, by comparing the distribution of oil / water in shale at different imbibition equilibrium stages, the content of different wetting type pores is divided, and then the wettability of shale is characterized;

[0077] 3) Calibration of oil / water NMR pore size conversion parameters based on nitrogen adsorption experiment and large field of view stitching scanning electron microscope aperture analysis results; including: using nitrogen adsorption experiment results to calibrate the NMR pore size conversion parameters of water, using large field of view stitching scanning electron microscope aperture analysis results to calibrate the NMR pore size conversion parameters of oil;

[0078] 4) Based on the decoupling analysis of two-dimensional nuclear magnetic resonance at different imbibition equilibrium stages, the nuclear magnetic resonance response of different wetting type pores is obtained, and the pore size distribution curve of different wetting type pores is determined combined with the oil / water nuclear magnetic pore size conversion parameters.

[0079] Example 2

[0080] The shale sample preparation and pretreatment according to the shale pore size characterization method based on spontaneous imbibition-nuclear magnetic resonance experiment of example 1, the difference lies in:

[0081] The shale sample preparation and pretreatment according to the shale pore size characterization method based on spontaneous imbibition-nuclear magnetic resonance experiment of example 1, the difference lies in: Figure 13 As shown in the figure, including:

[0082] The shale sample preparation and pretreatment according to the shale pore size characterization method based on spontaneous imbibition-nuclear magnetic resonance experiment of example 1, the difference lies in:

[0083] The shale sample preparation and pretreatment according to the shale pore size characterization method based on spontaneous imbibition-nuclear magnetic resonance experiment of example 1, the difference lies in:

[0084] Then the high-precision balance is used to weigh the parallel sample A with a mass mA of 14.8350g and the parallel sample B with a mass mB of 13.4031g, respectively.

[0085] The sample side is coated with epoxy resin to reduce the influence of the evaporation of imbibition fluid from the sample side on the subsequent imbibition process.

[0086] The shale sample preparation and pretreatment according to the shale pore size characterization method based on spontaneous imbibition-nuclear magnetic resonance experiment of example 1, the difference lies in:

[0087] The shale sample preparation and pretreatment according to the shale pore size characterization method based on spontaneous imbibition-nuclear magnetic resonance experiment of example 1, the difference lies in:

[0088] The shale sample preparation and pretreatment according to the shale pore size characterization method based on spontaneous imbibition-nuclear magnetic resonance experiment of example 1, the difference lies in:

[0089] Salt water can inhibit the swelling of clay minerals due to water absorption, avoiding the influence on the experimental water absorption results, and 10% KCl solution has obvious inhibitory effect (reference: doi: 10.1016 / j.enggeo.2017.12.002), and the rest such as 8%, 15% concentration of KCl solution can also be used for water phase imbibition liquid simulation.

[0090] Different volumes of oil phase imbibition liquid were measured in a sealed glass tube without hydrogen signal, and the corresponding nuclear magnetic signal amount of different volumes of oil phase imbibition liquid was detected by using a MicroMr20-025V type nuclear magnetic resonance instrument of Suzhou Nuomei Company, at least 3 points of data were repeatedly obtained, and linear fitting was carried out according to the imbibition liquid volume (V1, V2, V3…) and the detected nuclear magnetic signal amount (A1, A2, A3…) of different experimental points, A=K 油 *V, wherein A is the measured signal amount, V is the corresponding imbibition liquid volume, and K 油 is the imbibition liquid nuclear magnetic signal amount vs. volume conversion coefficient, and the oil phase imbibition liquid nuclear magnetic signal amount vs. volume conversion coefficient is obtained.

[0091] Similarly, different volumes of water phase imbibition liquid were measured in a sealed glass tube without hydrogen signal, and the corresponding nuclear magnetic signal amount of different volumes of oil phase imbibition liquid was detected by using a MicroMr20-025V type nuclear magnetic resonance instrument of Suzhou Nuomei Company, at least 3 points of data were repeatedly obtained, and linear fitting was carried out according to the imbibition liquid volume and the detected nuclear magnetic signal amount. 水 Similarly, different volumes of water phase imbibition liquid were measured in a sealed glass tube without hydrogen signal, and the corresponding nuclear magnetic signal amount of different volumes of oil phase imbibition liquid was detected by using a MicroMr20-025V type nuclear magnetic resonance instrument of Suzhou Nuomei Company, at least 3 points of data were repeatedly obtained, and linear fitting was carried out according to the imbibition liquid volume and the detected nuclear magnetic signal amount.

[0092] The fitting results are shown in Figure 2 , wherein Figure 2 (a) is the dodecane nuclear magnetic signal amount vs. volume conversion coefficient calibration graph, Figure 2 (b) is the 10% KCl solution nuclear magnetic signal amount vs. volume conversion coefficient calibration graph; the conversion coefficient of dodecane is 5288.4, is 1, and the fitting result is reliable, that is ; the conversion coefficient of 10% KCl solution is 4386.4, is 1, and the fitting result is reliable, that is .

[0093] a、firstly, the parallel sample A is placed in the oil phase infiltration liquid to carry out spontaneous infiltration experiment (the sample only contacts the infiltration liquid on one side, and the infiltration liquid spontaneously infiltrates into the pores of the sample under the action of capillary force), after a period of time, the parallel sample A is taken out, the surface fluid is wiped off, the parallel sample A is sealed in a glass tube without hydrogen signal, and a nuclear magnetic resonance instrument of MicroMr20-025V type of Suzhou Nuomai Company is used to detect the nuclear magnetic resonance signal of the sample, and the above operation is repeated every certain period of time to take out the sample, wipe off the surface fluid, seal it in a glass tube without hydrogen signal, and use a nuclear magnetic resonance instrument of MicroMr20-025V type of Suzhou Nuomai Company to detect the nuclear magnetic resonance signal of the sample to realize dynamic monitoring of the hydrogen-containing fluid signal, i.e. the nuclear magnetic resonance signal, in the sample infiltration process; for the one-dimensional nuclear magnetic monitoring result, the one-dimensional nuclear magnetic result measured in the initial state is used as the base signal for base removal inversion, and the dynamic change monitoring result of the fluid distribution in the pores in the infiltration process is obtained as shown in Figure 3 For the two-dimensional nuclear magnetic monitoring result, the shale two-dimensional nuclear magnetic resonance hydrogen-containing fluid identification chart proposed by Li Jinbu et al. is used for fluid identification, and the change result of the oil / water signal amount in the sample pores in the infiltration process is obtained as shown in Figure 4 , wherein Figure 4 , wherein (a) is the change graph of the water region signal amount extracted from the two-dimensional nuclear magnetic resonance of the parallel sample A in the oil infiltration stage, Figure 4 , wherein (b) is the change graph of the oil region signal amount extracted from the two-dimensional nuclear magnetic resonance of the parallel sample A in the oil infiltration stage;

[0094] When the hydrogen-containing fluid signal of the parallel sample A no longer changes (i.e. the fluid distribution result monitored by the one-dimensional nuclear magnetic resonance no longer changes and the fluid signal amount monitored by the two-dimensional nuclear magnetic resonance is nearly unchanged), it indicates that the hydrogen-containing fluid content in the parallel sample A no longer changes, and the infiltration reaches equilibrium; the monitoring result of the first oil infiltration stage of the parallel sample shows that the sample reaches infiltration equilibrium after 202 hours of continuous infiltration;

[0095] b, the parallel sample A is placed in the water phase infiltration liquid to carry out spontaneous infiltration experiment, after a period of time, the parallel sample A is taken out, the surface fluid is wiped off, the parallel sample A is sealed in a glass tube without hydrogen signal, and a nuclear magnetic resonance instrument of MicroMr20-025V type of Suzhou Nuomai Company is used to detect the nuclear magnetic resonance signal of the sample, and the above operation is repeated every certain period of time to realize dynamic monitoring of the hydrogen-containing fluid signal in the sample infiltration process;

[0096] When the hydrogen-containing fluid signal of the parallel sample A no longer changes, it indicates that the hydrogen-containing fluid content in the parallel sample A no longer changes, and the infiltration reaches equilibrium;

[0097] Subsequently, the infiltration fluid is replaced again to the oil phase infiltration liquid, and the steps a and b are repeated;

[0098] After the above operation, parallel sample A undergoes four imbibition stages of imbibition oil phase (O)→imbibition water phase (W)→imbibition oil phase (2O)→imbibition water phase (2W), and after the last stage of imbibition equilibrium, the alternating imbibition experiment ends. During the experiment, the change of hydrogen-containing fluid signal in the sample during the imbibition process is dynamically monitored by using a nuclear magnetic resonance instrument, as shown in FIG. 2. Figure 5 Wherein, Figure 5 FIG. 2(a) is a diagram of the change of the water region signal amount extracted from the two-dimensional nuclear magnetic resonance of parallel sample A in the four imbibition stages, Figure 5 FIG. 2(b) is a diagram of the change of the oil region signal amount extracted from the two-dimensional nuclear magnetic resonance of parallel sample A in the four stages;

[0099] Combined with the nuclear magnetic signal amount vs volume conversion coefficient of the imbibition liquid, the oil phase nuclear magnetic signal detected by the nuclear magnetic resonance during the imbibition process is converted into the oil phase volume (oil phase volume = oil phase nuclear magnetic signal / K 油 ) according to the oil phase imbibition liquid nuclear magnetic signal amount vs volume conversion coefficient K 油 obtained by linear fitting before, and similarly, the water phase nuclear magnetic signal detected by the nuclear magnetic resonance during the imbibition process is converted into the water phase volume (water phase volume = water phase nuclear magnetic signal / K 水 ) according to the water phase imbibition liquid nuclear magnetic signal amount vs volume conversion coefficient K 水 obtained by linear fitting before; the nuclear magnetic dynamic monitoring result of the hydrogen-containing fluid during the imbibition process is converted into the change result of the volume of the hydrogen-containing fluid during the imbibition process, as shown in FIG. 3. Figure 6 Wherein, Figure 6 FIG. 3(a) is a diagram of the change of the water-containing volume in the sample of parallel sample A in the four imbibition stages, Figure 6 FIG. 3(b) is a diagram of the change of the oil-containing volume in the sample of parallel sample A in the four stages;

[0100] Parallel sample B carries out the same experimental operation as parallel sample A, except that parallel sample B is first placed in the water phase imbibition liquid and undergoes four imbibition stages of imbibition water phase W→imbibition oil phase O→imbibition water phase 2W→imbibition oil phase 2O. After the imbibition ends, combined with the nuclear magnetic signal amount vs volume conversion coefficient of the imbibition liquid, the nuclear magnetic dynamic monitoring result of the hydrogen-containing fluid during the imbibition process is converted into the change result of the volume of the hydrogen-containing fluid during the imbibition process, as shown in FIG. 4. Figure 7 Wherein, Figure 7 FIG. 4(a) is a diagram of the change of the water-containing volume in the sample of parallel sample B in the four imbibition stages, Figure 7 FIG. 4(b) is a diagram of the change of the oil-containing volume in the sample of parallel sample B in the four stages;

[0101] Combined with the results of the dynamic monitoring of the oil and water content changes in the imbibition process of parallel sample A and parallel sample B by nuclear magnetic resonance, the content of different wetting type pores is divided; specifically, the specific division can be combined with examples Figure 6 and Figure 7For the oil phase 2O stage, the oil-wet and mixed-wet pores will be filled with oil phase, while the water-wet pores will still be filled with water phase. Therefore, the water signal measured by NMR reflects the water-wet pore content. For the water phase 2W stage, the oil signal measured by NMR reflects the oil-wet pore content. In the 2O and 2W stages, the fluid in the mixed-wet pores is replaced due to the change of the imbibition liquid. Therefore, the portion of the oil-wet pores / water-wet pores that is replaced is determined as the mixed-wet pore content.

[0102] The oil / water NMR pore size conversion parameters are calibrated based on the nitrogen adsorption experiment and the aperture analysis results of the large-view field stitching scanning electron microscope; including:

[0103] After the imbibition is completed, the parallel sample A or the parallel sample B is dried, and then 1.5 g of a granular sample with a mesh size of 60-80 is prepared. The nitrogen adsorption experiment is carried out by using the ASAP2460-2HD specific surface area and pore size analyzer produced by the American Micromeritics Company, and the pore size distribution characteristics of the pores smaller than 200 nm in the sample are obtained by combining the BJH pore interpretation model, as shown in Figure 8 .

[0104] The BJH pore interpretation model is a commonly used interpretation model for nitrogen adsorption experiments, which is built-in the data analysis software of the ASAP2460-2HD specific surface area and pore size analyzer.

[0105] Considering that water in shale mainly exists in small pores, the pore size distribution results of the <200 nm pores obtained by using nitrogen adsorption are calibrated, and the imbibition liquid of the water phase in the first imbibition stage of the parallel sample B is imbibed. Therefore, the water phase NMR pore size conversion parameters are calibrated by using the sample NMR signal at the equilibrium time of this stage. The calibration process only needs to consider the contribution of the pores with low relaxation time representing the small pore distribution. The linear model is used for calibration, that is, , wherein is the water phase NMR conversion pore size, is the water phase NMR pore size conversion coefficient, is the one-dimensional NMR transverse relaxation time of the water phase in this stage, and when the water phase NMR pore size distribution results of the <200 nm part after conversion are similar to the nitrogen adsorption pore size distribution results, the corresponding to the water phase NMR pore size conversion coefficient is the final water phase NMR pore size conversion coefficient.

[0106] For parallel sample B, during the first permeation stage, the aqueous phase permeates. At permeation equilibrium, the aqueous phase fills both the water-wetted pores and the mixed-wetting pores. The NMR results measured during this stage represent the NMR distribution of the aqueous phase within the pores. Considering that the water-wetted pores are predominantly small pores, the low relaxation time portion of the NMR results during this stage represents the NMR contribution of the water-wetted pores. The NMR pore size conversion factor of the water-wetted pores is calibrated using the pore size distribution of <200 nm pores characterized by nitrogen adsorption. A cross-plot of the NMR distribution results of the aqueous phase and the pore size distribution results of nitrogen adsorption was established. Based on the linear correlation between transverse relaxation time and pore size, the aqueous phase NMR pore size conversion coefficient was used to determine the pore size distribution. The transverse relaxation time of aqueous NMR Converted to aqueous NMR aperture (Right now The conversion coefficient of the aqueous phase NMR aperture is gradually adjusted based on morphological characteristics. The value of is chosen such that the peak of the NMR pore size distribution representing water-wet pores corresponds to the peak of the pore size distribution of nitrogen adsorption. The value of is the optimal NMR aperture conversion factor for aqueous phase. The calibration results are as follows: Figure 9 As shown, The value is 230.

[0107] Block samples with vertical bedding planes were prepared into small blocks of about 1 cm2. After mechanical polishing, argon ion polishing and carbon plating, a large field-of-view stitching experiment of scanning electron microscopy was carried out to obtain a 200 μm × 1000 μm stitched image. This stitched image runs through multiple layers and reflects the overall porosity development of the sample under the scanning electron microscope.

[0108] Mechanical polishing, argon ion polishing, and carbon plating are existing techniques for sample pretreatment in scanning electron microscopy (SEM). Large field-of-view stitching experiments in SEM are existing techniques that automatically capture and stitch images based on SEM experiments and using the Zeiss Atlas 5 software that is compatible with the SEM.

[0109] Import the stitched image into ImageJ software, extract all pores within the field of view using threshold segmentation, and export the pore size of each pore. ,area The total area of ​​the field of view was calculated. Calculate the porosity of each pore. Through calculation Characterizing the normalized distribution features of facial faces under scanning electron microscopy (e.g.) Figure 10) to obtain the pore size distribution results extracted by scanning electron microscopy; due to the resolution limit of scanning electron microscopy, this method only counts the pore size distribution characteristics of pores >10 nm; considering that the oil phase accounts for a high proportion in shale and most pores are oil phase occurrence spaces, the pore size distribution results extracted by the above scanning electron microscopy are used for calibration, and the oil phase is imbibed in the first stage of imbibition of parallel sample A, and most pores are filled with oil phase at the imbibition equilibrium stage, so the nuclear magnetic resonance signal of the sample at this stage represents the oil phase nuclear magnetic resonance distribution.

[0110] The cross plot of the oil phase nuclear magnetic distribution results and the pore size distribution results extracted by scanning electron microscopy is established, and the oil phase nuclear magnetic pore size conversion coefficient is determined according to the linear correspondence between the transverse relaxation time and the pore size. The oil phase nuclear magnetic transverse relaxation time is converted into the oil phase nuclear magnetic pore size , and the value of the oil phase nuclear magnetic pore size conversion coefficient is gradually adjusted according to the morphological characteristics so that the peaks and troughs of the nuclear magnetic pore size distribution and the pore size distribution extracted by scanning electron microscopy correspond, and the value of the oil phase nuclear magnetic pore size conversion coefficient at this time is the optimal oil phase nuclear magnetic pore size conversion coefficient.

[0111] At the equilibrium stage of the first stage of imbibition of oil phase in parallel sample A, the oil-wet pores and the mixed-wet pores in the sample are filled with oil phase, and these two parts of pores account for a high proportion (the oil-wet and mixed-wet proportion of parallel sample A is about 75.5%, and the oil-wet and mixed-wet proportion of parallel sample B is about 81.1%), and the water-wet pores are mainly small pores, so the contribution of the one-dimensional spectrum of nuclear magnetic resonance at this stage reflects the contribution of almost all pores, and therefore the normalized pore size distribution results extracted by the above large-view field splicing scanning electron microscopy can be used for nuclear magnetic pore size conversion calibration, and the calibration results are shown in Figure 10 , and the value of C is 100, which is the nuclear magnetic pore size conversion coefficient of the oil phase.

[0112] Based on the decoupling analysis of two-dimensional nuclear magnetic resonance at different imbibition equilibrium stages, the nuclear magnetic resonance response of pores of different wetting types is obtained, and the pore size distribution curve of pores of different wetting types is determined in combination with the oil / water nuclear magnetic pore size conversion parameters; including:

[0113] At the equilibrium stage of the second stage of imbibition of oil phase (20) in parallel sample A, the oil-wet pores and the mixed-wet pores in parallel sample A are filled with oil, and water is only present in water-wet pores, so at this moment the nuclear magnetic response of water in the nuclear magnetic resonance spectrum of the sample is from the contribution of water in water-wet pores, and the water phase T2 projection spectrum reflecting water-wet pores is obtained by projecting the water region signal in the two-dimensional nuclear magnetic resonance spectrum to the T2 axis direction (i.e. adding the water region signals corresponding to the same T2 value), and in combination with the obtained water phase nuclear magnetic resonance pore size conversion parameter , the abscissa of the water phase T2 projection spectrum of water-wet pores Convert the NMR pore size of water-wet pore , , the ordinate water phase NMR signal amount according to the obtained water phase imbibition liquid NMR signal amount vs volume conversion coefficient K 水 Convert to water-wet pore volume , finally according to the obtained water-wet pore NMR pore size And water-wet pore volume Calculate , that is, the pore size distribution curve of water-wet pore is obtained, as shown in Figure 11 ; wherein, Figure 11 (a) in the T2 projection spectrum contributed by oil-wet pore and mixed-wet pore, Figure 11 (b) in the T2 projection spectrum of mixed-wet pore, Figure 11 (c) in the T2 projection spectrum of water-wet pore, Figure 11 (d) in the T2 projection spectrum of oil-wet pore, Figure 11 (e) in the two-dimensional NMR spectrum of parallel sample A in the second imbibition oil phase equilibrium stage, Figure 11 (f) in the two-dimensional NMR spectrum of parallel sample A in the second imbibition water phase equilibrium stage. Figure 11 In the formula, A is the cheese root signal, B is the bound oil signal, C is the free oil signal, D is the structural water signal, and E is the free water signal.

[0114] In the second imbibition water phase (2w) stage of parallel sample A, water-wet pore and mixed-wet pore in parallel sample A all contain water, and oil only exists in oil-wet pore, so at this moment the NMR response of oil in the sample NMR spectrum comes from the contribution of oil in oil-wet pore. The oil phase T2 projection spectrum reflecting oil-wet pore is obtained by projecting the oil area signal in the two-dimensional NMR spectrum to the T2 axis direction (i.e. adding the oil area signal corresponding to the same T2 value), combined with the obtained oil phase NMR pore size conversion parameter Convert the abscissa of oil-wet pore oil phase T2 projection spectrum To the NMR pore size of oil-wet pore , the ordinate oil phase NMR signal amount according to the obtained oil phase imbibition liquid NMR signal amount vs volume conversion coefficient K 油 Convert to oil-wet pore volume , finally according to the obtained oil-wet pore NMR pore size And oil-wet pore volume Calculate , that is, the pore size distribution curve of oil-wet pore is obtained; as shown in Figure 11 ;

[0115] During the second oil phase equilibrium stage of parallel sample A, oil was present in both oil-wetted pores and mixed-wetted pores. By decoupling the oil region signal in the two-dimensional nuclear magnetic resonance spectrum by projecting it onto the T2 axis (i.e., accumulating the oil region signals corresponding to the same T2 value), the T2 projection spectrum of the oil phase reflecting the joint contribution of oil-wetted pores and mixed-wetted pores was obtained. Similarly, the oil phase nuclear magnetic resonance pore size conversion parameters were combined with this. The abscissa of the T2 projection spectrum of the oil phase, which is contributed by both oil-wetted porosity and mixed-wetted porosity. Converted to NMR pore size contributed by both oil-wetted pores and mixed-wetted pores The ordinate is the oil phase NMR signal quantity, which is obtained by comparing the oil phase permeate NMR signal quantity with the volume conversion factor K. 油 The volume is converted to a combination of oil-wetted pores and mixed-wetted pores. Finally, the NMR pore size was determined based on the combined contribution of oil-wetted porosity and mixed-wetting porosity. and the pore volume contributed by both calculate This yields the pore size distribution curve jointly contributed by oil-wetted pores and mixed-wetting pores. Subtracting the previously obtained pore size distribution curve of oil-wetted pores from the pore size distribution curve jointly contributed by oil-wetted and mixed-wetting pores gives the pore size distribution curve of mixed-wetting pores. Figure 12 As shown.

[0116] Example 3

[0117] A pore size characterization system based on spontaneous adsorption-NMR experiments for different wetting types includes:

[0118] The preparation module is configured for: preparation and pretreatment of shale samples;

[0119] The shale wettability characterization module is configured as follows: Shale wettability characterization based on spontaneous oil / water adsorption experiments and nuclear magnetic resonance (NMR) quantitative oil-water monitoring technology; including: through alternating spontaneous adsorption experiments, oil / water spontaneously enters the pores of the corresponding wetting phase under the action of capillary force; combined with NMR technology, the distribution characteristics of oil / water in shale pores during the adsorption process are quantitatively monitored; by comparing the distribution of oil and water in shale at different adsorption equilibrium stages, the content of pores of different wetting types is identified, thereby characterizing shale wettability;

[0120] The oil / water NMR pore size conversion parameter calibration module is configured to calibrate the oil / water NMR pore size conversion parameters based on nitrogen adsorption experiments and large field-of-view stitched scanning electron microscopy pore size analysis results; including: calibrating the NMR pore size conversion parameters of water using nitrogen adsorption experiment results, and calibrating the NMR pore size conversion parameters of oil using large field-of-view stitched scanning electron microscopy pore size analysis results;

[0121] The pore size characterization module is configured to obtain nuclear magnetic resonance responses of different wetting type pores based on decoupling analysis of two-dimensional nuclear magnetic resonance at different infiltration equilibrium stages, and determine pore size distribution curves of the different wetting type pores in combination with oil / water nuclear magnetic pore size conversion parameters.

Claims

1. A method for characterizing pore size of different wetting types based on spontaneous adsorption-nuclear magnetic resonance experiments, characterized in that, include: 1) Preparation and pretreatment of shale samples; 2) Shale wettability characterization based on spontaneous oil / water adsorption experiments and nuclear magnetic resonance (NMR) quantitative oil-water monitoring technology; including: through alternating spontaneous adsorption experiments, oil / water spontaneously enters the pores of the corresponding wetting phase under the action of capillary force in shale; combined with NMR technology, the distribution characteristics of oil / water in shale pores during the adsorption process are quantitatively monitored; by comparing the distribution of oil and water in shale at different adsorption equilibrium stages, the content of pores of different wetting types is classified, thereby characterizing shale wettability; 3) Calibrate the NMR pore size conversion parameters of oil / water based on nitrogen adsorption experiments and large field-of-view mosaic scanning electron microscopy pore size analysis results; including: calibrating the NMR pore size conversion parameters of water using nitrogen adsorption experiment results, and calibrating the NMR pore size conversion parameters of oil using large field-of-view mosaic scanning electron microscopy pore size analysis results; 4) Based on the decoupling analysis of two-dimensional nuclear magnetic resonance at different permeation equilibrium stages, the nuclear magnetic resonance responses of pores with different wetting types were obtained. The pore size distribution curves of pores with different wetting types were determined by combining oil / water nuclear magnetic pore size conversion parameters; including: When parallel sample A reached equilibrium during the second oil phase permeation stage, the T2 projection spectrum of the aqueous phase, reflecting the water-wetted porosity, was obtained by projecting the water region signal in the two-dimensional nuclear magnetic resonance spectrum onto the T2 axis. This spectrum was then combined with the obtained aqueous phase nuclear magnetic resonance pore size conversion parameters. The abscissa of the T2 projection spectrum of the aqueous phase in the water-wetted pores NMR pore size converted to water-wet pores , The vertical axis represents the aqueous phase NMR signal quantity, which is determined by the NMR signal quantity of the aqueous phase permeate versus the volume conversion coefficient K. 水 Converted to water-wet pore volume Finally, based on the obtained NMR pore size of the water-wet pores... and water-wet pore volume calculate This yields the pore size distribution curve of the water-wetted pores; During the second aqueous phase equilibrium of parallel sample A, the T2 projection spectrum of the oil phase, reflecting the oil wet porosity, was obtained by decoupling the oil region signal in the two-dimensional nuclear magnetic resonance spectrum by projecting it onto the T2 axis. This was then combined with the obtained oil phase nuclear magnetic resonance pore size conversion parameters. The abscissa of the T2 projection spectrum of the oil phase in the oil-wet pores. NMR pore size converted to oil-wet pores The ordinate is the oil phase NMR signal quantity, which is obtained by comparing the oil phase permeate NMR signal quantity with the volume conversion factor K. 油 Converted to oil-wet pore volume Finally, based on the obtained NMR pore size of the oil-wet pores... and oil-wet pore volume calculate This yields the pore size distribution curve of the oil-wet pores; During the second oil phase equilibrium stage of parallel sample A, oil was present in both oil-wetted pores and mixed-wetted pores. By decoupling the oil region signal in the two-dimensional nuclear magnetic resonance spectrum by projecting it onto the T2 axis, the T2 projection spectrum of the oil phase reflecting the combined contribution of oil-wetted pores and mixed-wetted pores was obtained. Similarly, the oil phase nuclear magnetic resonance pore size conversion parameters were combined with this. The abscissa of the T2 projection spectrum of the oil phase, which is contributed by both oil-wetted porosity and mixed-wetted porosity. Converted to NMR pore size contributed by both oil-wetted pores and mixed-wetted pores The ordinate is the oil phase NMR signal quantity, which is obtained by comparing the oil phase permeate NMR signal quantity with the volume conversion factor K. 油 The volume is converted to a combination of oil-wetted pores and mixed-wetted pores. ; Finally, based on the NMR pore size jointly contributed by the obtained oil-wetted pores and mixed-wetting pores... and the pore volume contributed by both calculate That is, the pore size distribution curve jointly contributed by oil-wet pores and mixed-wet pores is obtained. Subtracting the previously obtained pore size distribution curve of oil-wet pores from the pore size distribution curve jointly contributed by oil-wet pores and mixed-wet pores gives the pore size distribution curve of mixed-wet pores.

2. The method for characterizing pore size of different wetting types based on spontaneous percolation-nuclear magnetic resonance experiments according to claim 1, characterized in that, Shale sample preparation and pretreatment; including: Shale samples were selected and standard plunger samples with a diameter of no more than 2.5 cm were drilled along the direction parallel to the bedding using wire cutting. The samples were then evenly divided into two parts along the direction perpendicular to the bedding to obtain parallel samples A and B. Parallel samples A and B were dried at 100-110℃ for no less than 12 hours to remove residual fluid from the pores. Subsequently, the masses mA and mB of parallel samples A and B after drying were measured using a high-precision balance. Apply epoxy resin to the sides of the sample.

3. The method for characterizing pore size of different wetting types based on spontaneous percolation-nuclear magnetic resonance experiments according to claim 2, characterized in that, Parallel samples A and B were dried at 110℃ for 12 hours.

4. The method for characterizing pore size of different wetting types based on spontaneous percolation-nuclear magnetic resonance experiments according to claim 1, characterized in that, Shale wettability characterization based on spontaneous oil / water absorption experiments and quantitative nuclear magnetic resonance oil-water monitoring technology; including: n-Dodecane or n-octane was selected as the oil phase percolation liquid, and KCl aqueous solution was selected as the aqueous phase percolation liquid. Different volumes of oil-phase permeate were measured in sealed glass tubes without hydrogen signal. The NMR signal corresponding to different volumes of oil-phase permeate was detected using a nuclear magnetic resonance (NMR) spectrometer. Data were obtained at least three times. A linear fit was performed between the permeate volume at different experimental points and the detected NMR signal, with A=K. 油 *V, where A is the measured signal quantity, V is the corresponding osmotic volume, and K is the osmotic volume. 油 The NMR signal versus volume conversion coefficient for the oil phase permeate is given by K, which is the NMR signal versus volume conversion coefficient for the oil phase permeate. 油 ; Similarly, different volumes of aqueous permeate were measured in sealed glass tubes without hydrogen signal, and the NMR signal corresponding to different volumes of oil permeate was detected using an NMR spectrometer. This process was repeated at least three times. Linear fitting was then performed between the permeate volume at different experimental points and the detected NMR signal to obtain the NMR signal-to-volume conversion coefficient K for the aqueous permeate. 水 ; a. First, place parallel sample A in the oil phase permeation liquid and conduct a spontaneous permeation experiment. After a period of time, take out parallel sample A, wipe off the surface fluid, place parallel sample A in a glass tube without hydrogen signal and seal it, and use a nuclear magnetic resonance spectrometer to detect the nuclear magnetic resonance signal of the sample. Repeat the above operation every period of time, take out the sample, wipe off the surface fluid, place it in a glass tube without hydrogen signal and seal it, and use a nuclear magnetic resonance spectrometer to detect the nuclear magnetic resonance signal of the sample to achieve dynamic monitoring of the hydrogen-containing fluid signal, i.e., the nuclear magnetic resonance signal, during the sample permeation process. Once the hydrogen-containing fluid signal in parallel sample A no longer changes, it indicates that the hydrogen-containing fluid content in parallel sample A no longer changes, and the percolation has reached equilibrium. b. Place parallel sample A in an aqueous permeation solution and conduct a spontaneous permeation experiment. After a period of time, remove parallel sample A, wipe off the surface fluid, place parallel sample A in a glass tube without hydrogen signal and seal it. Use a nuclear magnetic resonance spectrometer to detect the nuclear magnetic resonance signal of the sample. Repeat the above operation at regular intervals to achieve dynamic monitoring of the hydrogen-containing fluid signal during the sample permeation process. Once the hydrogen-containing fluid signal in parallel sample A no longer changes, it indicates that the hydrogen-containing fluid content in parallel sample A no longer changes, and the percolation has reached equilibrium. Subsequently, the percolating fluid was changed to an oil phase percolating liquid, and steps a and b were repeated. Parallel sample A underwent four percolation stages: oil phase O → water phase W → oil phase 2O → water phase 2W. The alternating percolation experiment ended after the last stage reached percolation equilibrium. During the process, nuclear magnetic resonance was used to dynamically monitor the changes in the hydrogen-containing fluid signal of the sample. Combining the NMR signal quantity vs. volume conversion coefficient of the permeate, the NMR signal of the oil phase obtained by NMR detection during the permeation process is used to calculate the NMR signal quantity vs. volume conversion coefficient K of the oil phase permeate obtained by previous linear fitting. 油 To convert to oil phase volume, similarly, the NMR signal of the aqueous phase obtained by NMR detection during the percolation process is converted to the volume conversion coefficient K based on the NMR signal quantity of the aqueous percolation liquid obtained by the previous linear fitting. 水 Converted to aqueous phase volume; Parallel sample B was subjected to the same experimental procedures as parallel sample A. The difference was that parallel sample B was first placed in an aqueous permeation solution and went through four permeation stages: permeation of aqueous phase W, permeation of oil phase O, permeation of aqueous phase 2W, and permeation of oil phase 2O. After the permeation was completed, the NMR signal quantity vs. volume conversion coefficient of the permeation solution was also combined to convert the NMR dynamic monitoring results of the hydrogen-containing fluid during the permeation process into the results of the change in the volume of the hydrogen-containing fluid during the permeation process. Based on the results of dynamic monitoring of oil and water content changes during the permeation process of parallel samples A and B using nuclear magnetic resonance (NMR), the content of pores with different wetting types was classified. Specifically, for the oil phase 2O stage of permeation, both oil-wetted and mixed-wetted pores will be filled by the oil phase, while water-wetted pores will remain filled by the water phase. Therefore, the pore content reflected by the water phase signal measured by NMR is the water-wetted pore content. For the water phase 2W stage of permeation, the pore content reflected by the oil phase signal measured by NMR is the oil-wetted pore content.

5. The method for characterizing pore size of different wetting types based on spontaneous percolation-nuclear magnetic resonance experiments according to claim 4, characterized in that, KCl aqueous solutions with a mass concentration of 8%, 10%, or 15% were selected as the aqueous phase percolation solution.

6. The method for characterizing pore size of different wetting types based on spontaneous percolation-nuclear magnetic resonance experiments according to claim 1, characterized in that, Oil / water NMR pore size conversion parameters were calibrated based on nitrogen adsorption experiments and large-field-of-view mosaicked scanning electron microscopy pore size analysis results; including: After the infiltration was completed, parallel sample A or parallel sample B was dried and then prepared into block samples perpendicular to the stratification plane. Nitrogen adsorption experiments were conducted on block samples with vertical stratification planes using a specific surface area and pore size analyzer. The pore size distribution characteristics of pores smaller than 200 nm in the samples were obtained by combining the BJH pore interpretation model. After mechanical polishing, argon ion polishing and carbon plating, block samples with vertical bedding planes were subjected to a large field-of-view stitching experiment under a scanning electron microscope to obtain stitched images. These stitched images penetrate multiple layers and reflect the overall porosity development of the sample under the scanning electron microscope. Import the stitched image into ImageJ software, extract all pores within the field of view using threshold segmentation, and export the pore size of each pore. ,area The total area of ​​the field of view was calculated. Calculate the porosity of each pore. Through calculation The normalized distribution characteristics of the faces under a scanning electron microscope (SEM) of the sample are used to obtain the pore size distribution results extracted by the SEM. A cross-plot of the NMR distribution results and the pore size distribution results extracted by scanning electron microscopy was established. Based on the linear correspondence between transverse relaxation time and pore size, the pore size conversion factor of the NMR in the oil phase was used to determine the pore size distribution. The transverse relaxation time of the oil phase NMR Converted to oil phase NMR aperture ,Right now The conversion coefficient of NMR aperture in the oil phase was gradually adjusted based on morphological characteristics. The value of is chosen such that the peaks and troughs of the NMR aperture distribution correspond to those of the aperture distribution extracted by the scanning electron microscope. The value of is the optimal NMR aperture conversion factor for the oil phase.

7. The method for characterizing pore size of different wetting types based on spontaneous percolation-nuclear magnetic resonance experiments according to claim 6, characterized in that, Prepare granular samples of 60-80 mesh size with an area of ​​1-1.5 cm². 2 Block samples with a thickness of 0.3-0.5cm perpendicular to the bedding plane.

8. A pore size characterization system for different wetting types based on spontaneous adsorption-nuclear magnetic resonance experiments, characterized in that, include: The preparation module is configured for: preparation and pretreatment of shale samples; The shale wettability characterization module is configured as follows: Shale wettability characterization based on spontaneous oil / water adsorption experiments and nuclear magnetic resonance (NMR) quantitative oil-water monitoring technology; including: through alternating spontaneous adsorption experiments, oil / water spontaneously enters the pores of the corresponding wetting phase under the action of capillary force; combined with NMR technology, the distribution characteristics of oil / water in shale pores during the adsorption process are quantitatively monitored; by comparing the distribution of oil and water in shale at different adsorption equilibrium stages, the content of pores of different wetting types is identified, thereby characterizing shale wettability; The oil / water NMR pore size conversion parameter calibration module is configured to calibrate the oil / water NMR pore size conversion parameters based on nitrogen adsorption experiments and large field-of-view stitched scanning electron microscopy pore size analysis results; including: calibrating the NMR pore size conversion parameters of water using nitrogen adsorption experiment results, and calibrating the NMR pore size conversion parameters of oil using large field-of-view stitched scanning electron microscopy pore size analysis results; The pore size characterization module is configured to: obtain the NMR response of pores with different wetting types based on decoupled analysis of two-dimensional NMR at different permeation equilibrium stages; and determine the pore size distribution curves of pores with different wetting types by combining oil / water NMR pore size conversion parameters; including: When parallel sample A reached equilibrium during the second oil phase permeation stage, the T2 projection spectrum of the aqueous phase, reflecting the water-wetted porosity, was obtained by projecting the water region signal in the two-dimensional nuclear magnetic resonance spectrum onto the T2 axis. This spectrum was then combined with the obtained aqueous phase nuclear magnetic resonance pore size conversion parameters. The abscissa of the T2 projection spectrum of the aqueous phase in the water-wetted pores NMR pore size converted to water-wet pores , The vertical axis represents the aqueous phase NMR signal quantity, which is determined by the NMR signal quantity of the aqueous phase permeate versus the volume conversion coefficient K. 水 Converted to water-wet pore volume Finally, based on the obtained NMR pore size of the water-wet pores... and water-wet pore volume calculate This yields the pore size distribution curve of the water-wetted pores; During the second aqueous phase equilibrium of parallel sample A, the T2 projection spectrum of the oil phase, reflecting the oil wet porosity, was obtained by decoupling the oil region signal in the two-dimensional nuclear magnetic resonance spectrum by projecting it onto the T2 axis. This was then combined with the obtained oil phase nuclear magnetic resonance pore size conversion parameters. The abscissa of the T2 projection spectrum of the oil phase in the oil-wet pores. NMR pore size converted to oil-wet pores The ordinate is the oil phase NMR signal quantity, which is obtained by comparing the oil phase permeate NMR signal quantity with the volume conversion factor K. 油 Converted to oil-wet pore volume Finally, based on the obtained NMR pore size of the oil-wet pores... and oil-wet pore volume calculate This yields the pore size distribution curve of the oil-wet pores; During the second oil phase equilibrium stage of parallel sample A, oil was present in both oil-wetted pores and mixed-wetted pores. By decoupling the oil region signal in the two-dimensional nuclear magnetic resonance spectrum by projecting it onto the T2 axis, the T2 projection spectrum of the oil phase reflecting the combined contribution of oil-wetted pores and mixed-wetted pores was obtained. Similarly, the oil phase nuclear magnetic resonance pore size conversion parameters were combined with this. The abscissa of the T2 projection spectrum of the oil phase, which is contributed by both oil-wetted porosity and mixed-wetted porosity. Converted to NMR pore size contributed by both oil-wetted pores and mixed-wetted pores The ordinate is the oil phase NMR signal quantity, which is obtained by comparing the oil phase permeate NMR signal quantity with the volume conversion factor K. 油 The volume is converted to a combination of oil-wetted pores and mixed-wetted pores. ; Finally, based on the NMR pore size jointly contributed by the obtained oil-wetted pores and mixed-wetting pores... and the pore volume contributed by both calculate That is, the pore size distribution curve jointly contributed by oil-wet pores and mixed-wet pores is obtained. Subtracting the previously obtained pore size distribution curve of oil-wet pores from the pore size distribution curve jointly contributed by oil-wet pores and mixed-wet pores gives the pore size distribution curve of mixed-wet pores.

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