Shale wettability pore space characterization method

Abstract

The invention discloses a shale wettability pore space characterization method, and relates to the field of shale pore analysis, and the method comprises the following steps: obtaining a shale sample; sequentially immersing the shale sample in a fat-soluble fluorescent tracer solution and a water-soluble fluorescent tracer solution; performing laser confocal test analysis on the immersed shale sample to obtain three-dimensional visual models of pore spaces with different wettability; determining a fluorescence scanning area volume, an oil wetting pore volume and a water wetting pore volume by utilizing image processing software according to the three-dimensional visual model; determining the wettability characteristic of the pore space of the shale sample according to the volume of the fluorescence scanning area, the volume of the oil-wetted pore and the volume of the water-wetted pore; the wettability characteristic of the pore space of the shale sample is water wettability or oil wettability. According to the invention, visualization and quantitative characterization of pore spaces with different wettability of shale can be realized at the same time.

Description

Technical Field

[0001] The present application relates to the field of shale pore analysis, and in particular to a method for characterizing the wettability pore space of shale. Background Art

[0002] The wettability of shale pore spaces influences the occurrence, mobility, and spatial distribution of fluids (oil, water, and gas) within them. Therefore, quantitative characterization of shale pore space wettability is crucial. Shale primarily develops micro- and nano-scale pore spaces, typical of dense reservoirs. Compared to conventional reservoirs, shale, rich in organic matter, exhibits mixed wettability within its pore space. Current understanding suggests that fluid migration in shale's nano-scale pore spaces is difficult, with oil and gas migration primarily dependent on interconnected micron-scale pore spaces. Pore spaces can be categorized as oil-wet or water-wet, depending on the oil-wet and water-wet properties of the pore surface. These two types of pore spaces exhibit different resistances to fluid migration: oil-wet pore spaces are more conducive to oil accumulation and migration, while water-wet pore spaces are less so. Therefore, quantitatively characterizing the distribution of these two types of pore spaces is crucial for evaluating shale reservoir pore structure, characterizing the distribution of oil and water migration pathways, and elucidating the mechanisms of shale oil accumulation and flow. However, existing methods cannot simultaneously visualize and quantitatively characterize pore spaces of varying wettability in shale. Summary of the Invention

[0003] The purpose of this application is to provide a shale wettability pore space characterization method that can simultaneously realize the visualization and quantitative characterization of shale pore spaces with different wettability.

[0004] To achieve the above objectives, this application provides the following solutions: This application provides a shale wettability pore space characterization method, including: Obtain shale samples; Sequentially immersing the shale sample in a fat-soluble fluorescent tracer solution and a water-soluble fluorescent tracer solution; Laser confocal microscopy was performed on the submerged shale samples to obtain a three-dimensional visualization model of pore spaces with different wettability. Determining the fluorescence scanning area volume, oil-wetted pore volume, and water-wetted pore volume using image processing software according to the three-dimensional visualization model; The wettability characteristics of the pore space of the shale sample are determined according to the volume of the fluorescence scanning area, the oil-wet pore volume and the water-wet pore volume; the wettability characteristics of the pore space of the shale sample are water-wetness or oil-wetness.

[0005] In one embodiment, obtaining a shale sample specifically includes: The oil-bearing shale oil reservoir samples were washed with Soxhlet extraction; The shale oil reservoir samples after oil washing are subjected to thin section preparation, vacuuming and drying to obtain shale samples.

[0006] In one embodiment, immersing the shale sample in a fat-soluble fluorescent tracer solution and a water-soluble fluorescent tracer solution in sequence specifically includes: The shale samples were immersed in a fat-soluble fluorescent tracer solution and spontaneously imbibed for 48 h; The shale sample immersed in the fat-soluble fluorescent tracer solution was immersed in the water-soluble fluorescent tracer solution and spontaneously imbibed to saturate for 48 hours.

[0007] In one embodiment, the difference in fluorescence wavelength between the fat-soluble fluorescent tracer solution and the water-soluble fluorescent tracer solution is greater than a set threshold.

[0008] In one embodiment, the water-soluble fluorescent tracer is fluorescein, with an excitation wavelength of 490 nm and an emission wavelength of 520 nm; the fat-soluble fluorescent tracer is Nile red, with an excitation wavelength of 552 nm and an emission wavelength of 636 nm.

[0009] In one embodiment, before performing laser confocal laser testing and analysis on the submerged shale sample to obtain a three-dimensional visualization model of pore spaces with different wettability, the method further includes: The submerged shale samples were frozen in liquid nitrogen and stored in a vacuum.

[0010] In one embodiment, laser confocal microscopy is performed on the submerged shale sample to obtain a three-dimensional visualization model of pore spaces with different wettability, specifically including: Laser confocal testing and analysis were performed using an excitation wavelength of 490 nm and a fluorescence wavelength of 520 nm to collect a three-dimensional spatial distribution map of the water-wetted pore space; Laser confocal testing and analysis were performed using an excitation wavelength of 552 nm and a fluorescence wavelength of 636 nm to collect a three-dimensional spatial distribution map of the oil-wetted pore space; Image processing software was used to construct three-dimensional visualization models of pore spaces with different wettability based on the three-dimensional spatial distribution maps of water-wet pore space and oil-wet pore space.

[0011] In one embodiment, determining the wettability characteristics of the pore space of a shale sample based on the fluorescence scanning area volume, the oil-wet pore volume, and the water-wet pore volume specifically includes: The ratio of oil-wet pores to the total volume of the sample and the ratio of water-wet pores to the total volume of the sample were calculated based on the volume of the fluorescence scanning area, the volume of oil-wet pores and the volume of water-wet pores; When the ratio of oil-wet pores to the total volume of the sample is smaller than the ratio of water-wet pores to the total volume of the sample, the wettability of the pore space of the shale sample is oil-wet; When the ratio of water-wet pores to the total volume of the sample is smaller than the ratio of oil-wet pores to the total volume of the sample, the wettability of the pore space of the shale sample is water-wet.

[0012] In one embodiment, the shale wettability pore space characterization method further includes: The oil-water wettability pore volume ratio was calculated based on the fluorescence scanning area volume, oil-wetted pore volume, and water-wetted pore volume.

[0013] In one embodiment, the image processing software is Imaje J.

[0014] According to the specific embodiments provided in this application, this application discloses the following technical effects: The present application provides a method for characterizing the wettability pore space of shale. By performing laser confocal testing and analysis on the immersed shale sample, a three-dimensional visualization model of the pore space with different wettabilities is obtained, thereby realizing visualization of the wettability pore space of shale. The wettability characteristics of the pore space of the shale sample are determined based on the volume of the fluorescence scanning area, the oil-wetted pore volume, and the water-wetted pore volume, thereby realizing quantitative characterization of the wettability pore space of shale. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0016] Figure 1 This is a flow chart of a method for characterizing pore space of shale wettability in one embodiment of the present application; Figure 2 Schematic diagram of a method for characterizing pore space of shale wettability in one embodiment of the present application. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0018] Existing laboratory quantitative characterization of shale pore wettability primarily focuses on overall assessment of shale wettability, primarily through wetting angle measurements, spontaneous imbibition methods, and mineral flotation. These methods, however, are limited in their ability to visualize micro- and nano-scale pore wettability and fluid migration and enrichment characteristics. The application of high-precision observation techniques such as scanning electron microscopy in shale pore research, combined with evaporation-condensation experiments, has enabled qualitative observation of micro- and nano-scale pore wettability in shale. However, while SEM methods can observe fluid occurrence and migration, they are limited by their small field of view, resulting in insufficient quantitative characterization of overall pore space wettability. The reliability of the results remains uncertain, and the experimental time and cost are high. Laser confocal microscopy (LSCM) allows for effective analysis of the composition and spatial distribution of fluorescent substances and is widely used in biological research. In recent years, laser confocal microscopy (LCMS) technology has been widely used in shale oil reservoir fluid analysis research. The residual oil in shale oil reservoirs has the characteristic of fluorescence, and the free shale oil is rich in light hydrocarbon components, mainly emitting short-wavelength blue, green and other fluorescence. The heavy adsorbed shale oil is rich in heavy hydrocarbon components, mainly emitting long-wavelength red fluorescence. Combined with its resolution mainly at the micron level, the application of laser confocal microscopy in shale reservoir research mainly focuses on the visualization and quantitative analysis of the residual oil component characteristics and spatial distribution at the micron level, showing its strong ability in studying fluid distribution in shale pores and its potential in the quantitative characterization of shale pore wettability. However, a practical and effective method has not yet been formed.

[0019] Currently, there are relatively few methods for quantitatively evaluating pores in shales with varying wettability. These methods primarily rely on wetting angle measurements, spontaneous imbibition, mineral sorting, and environmental scanning electron microscopy combined with evaporation and condensation. However, these methods all have limitations, the most significant being the inability to simultaneously achieve visual observation and quantitative analysis.

[0020] The wetting angle test is a commonly used method for assessing shale wettability. It measures the contact angle of a liquid droplet on the shale surface to determine its hydrophilicity or oleophilicity. Directly reflecting wettability through droplet morphology and contact angle values ​​is relatively simple to perform, offers highly visual results, and provides specific contact angle values ​​(a water contact angle less than 90° indicates hydrophilicity, while a contact angle greater than 90° indicates hydrophobicity). This facilitates lateral comparisons between different samples and allows for testing the interaction between different fluids (water, oil) and shale, making it suitable for multiphase wettability studies. However, experimental factors such as droplet volume, placement, and ambient temperature and humidity can affect the results, necessitating strict standardization. More importantly, the wetting angle method only characterizes the surface wettability of shale samples and fails to capture the complex wetting behavior within the pores of the shale, such as the capillary effect of micro- and nano-pores.

[0021] Spontaneous imbibition, a key method for studying shale reservoir wettability, assesses wettability by measuring the ability of shale to spontaneously absorb wetting phase fluids (such as water or oil) under capillary forces. Compared to wetting angle measurements, spontaneous imbibition can reflect the overall wettability of complex pore networks within shale (including micro- and nanopores). However, it typically only provides a qualitative assessment of water-wetting and oil-wetting properties, lacking precise numerical calibration similar to contact angles, and lacks intuitive visualization.

[0022] When analyzing shale wettability, mineral sorting (e.g., centrifugation, flotation, and heavy liquid separation) primarily separates different mineral components (e.g., clay, quartz, and organic matter) to investigate their wettability differences. This allows for the separation of different mineral components within shale (e.g., hydrophilic clay and lipophilic organic matter) and the clarification of their contributions to overall wettability. However, sorting processes (e.g., grinding and chemical treatment) can alter mineral surface properties (e.g., oxidation and contamination), leading to biased wettability analysis and inability to characterize the wettability characteristics of the complex pore network within the shale.

[0023] The environmental scanning electron microscopy (ESEM) method, combined with evaporation-condensation observation, offers the advantage of direct visualization. First, shale samples are subjected to steam condensation under certain humidity conditions, allowing water vapor to naturally condense in pore spaces with varying wettability. Under low vacuum conditions, the ESEM, by controlling the observation temperature and pressure, allows for micro- and nanoscale observation of water vapor adsorption characteristics on various pore surfaces. Therefore, compared to other methods, ESEM offers a more vivid and intuitive approach. However, due to limitations in the observation field, the representativeness of the results remains to be verified, and the method lacks the necessary quantitative parameters for evaluating wettability.

[0024] To date, there has been a lack of effective methods for quantitatively characterizing the wettability of pore space in shale reservoirs, including a lack of visualization and quantitative research methods for studying pore spaces with different wettabilities. Therefore, a new method is needed to quantitatively characterize the content, properties, and reservoir space of shale oil in different occurrence states.

[0025] Based on this, this application constructs a shale wettability pore space characterization method based on spontaneous imbibition and cryo-laser confocal microscopy. The first is to realize the visual characterization of the three-dimensional distribution of pore spaces with different wettabilities in shale reservoirs, and the second is to realize the evaluation of the micron-level pore wettability of shale reservoirs and determine the proportion of pore spaces with differential wetting between oil and water.

[0026] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0027] In an exemplary embodiment, Figure 1As shown, a method for characterizing pore space of shale wettability is provided. The method is executed by a computer device, and specifically can be executed by a computer device such as a terminal or a server alone, or can be executed by a terminal and a server together, and includes the following steps.

[0028] Step 101: Obtain a shale sample.

[0029] Step 102: Sequentially immersing the shale sample in a fat-soluble fluorescent tracer solution and a water-soluble fluorescent tracer solution.

[0030] Step 103: Perform laser confocal microscopy testing and analysis on the submerged shale sample to obtain a three-dimensional visualization model of pore spaces with different wettabilities.

[0031] Step 104: Determine the volume of the fluorescence scanning area, the volume of the oil-wet pores, and the volume of the water-wet pores according to the three-dimensional visualization model using image processing software.

[0032] Step 105: Determine the wettability of the pore space of the shale sample according to the volume of the fluorescence scanning area, the oil-wet pore volume, and the water-wet pore volume; the wettability of the pore space of the shale sample is water-wetness or oil-wetness.

[0033] By performing laser confocal testing and analysis on the submerged shale samples, a three-dimensional visualization model of pore spaces with different wettabilities is obtained, thereby realizing the visualization of the shale wettability pore space. The wettability characteristics of the shale sample pore space are determined based on the fluorescence scanning area volume, oil-wet pore volume and water-wet pore volume, thereby realizing the quantitative characterization of the shale wettability pore space.

[0034] In an exemplary embodiment, obtaining a shale sample specifically includes: washing the oil-containing shale oil reservoir sample using Soxhlet extraction; and making thin sections, vacuuming, and drying the washed shale oil reservoir sample to obtain a shale sample.

[0035] In an exemplary embodiment, the shale sample is immersed in a fat-soluble fluorescent tracer solution and a water-soluble fluorescent tracer solution in sequence, specifically comprising: immersing the shale sample in the fat-soluble fluorescent tracer solution for spontaneous imbibition saturation for 48 hours; immersing the shale sample immersed in the fat-soluble fluorescent tracer solution in the water-soluble fluorescent tracer solution for spontaneous imbibition saturation for 48 hours.

[0036] In an exemplary embodiment, the difference in fluorescence wavelength between the fat-soluble fluorescent tracer solution and the water-soluble fluorescent tracer solution is greater than a set threshold.

[0037] In an exemplary embodiment, the water-soluble fluorescent tracer is fluorescein, with an excitation wavelength of 490 nm and an emission wavelength of 520 nm; the fat-soluble fluorescent tracer is Nile red, with an excitation wavelength of 552 nm and an emission wavelength of 636 nm.

[0038] In an exemplary embodiment, before performing laser confocal testing and analysis on the submerged shale sample to obtain a three-dimensional visualization model of pore spaces with different wettability, the method further includes: freezing the submerged shale sample with liquid nitrogen and preserving it under vacuum.

[0039] In an exemplary embodiment, laser confocal testing and analysis are performed on the submerged shale sample to obtain a three-dimensional visualization model of pore spaces with different wettabilities, specifically including: using an excitation wavelength of 490 nm and collecting a fluorescence wavelength of 520 nm for laser confocal testing and analysis, and collecting a three-dimensional spatial distribution map of the water-wet pore space; using an excitation wavelength of 552 nm and collecting a fluorescence wavelength of 636 nm for laser confocal testing and analysis, and collecting a three-dimensional spatial distribution map of the oil-wet pore space; using image processing software to construct a three-dimensional visualization model of pore spaces with different wettabilities based on the three-dimensional spatial distribution map of the water-wet pore space and the three-dimensional spatial distribution map of the oil-wet pore space.

[0040] In an exemplary embodiment, the wettability characteristics of the pore space of a shale sample are determined based on the volume of the fluorescence scanning area, the volume of oil-wet pores, and the volume of water-wet pores, specifically including: calculating the ratio of oil-wet pores to the total volume of the sample and the ratio of water-wet pores to the total volume of the sample based on the volume of the fluorescence scanning area, the volume of oil-wet pores, and the volume of water-wet pores; when the ratio of oil-wet pores to the total volume of the sample is less than the ratio of water-wet pores to the total volume of the sample, the wettability characteristics of the pore space of the shale sample are oil-wet; when the ratio of water-wet pores to the total volume of the sample is less than the ratio of oil-wet pores to the total volume of the sample, the wettability characteristics of the pore space of the shale sample are water-wet.

[0041] In an exemplary embodiment, the shale wettability pore space characterization method further includes: calculating the oil-water wettability pore volume ratio based on the fluorescence scanning area volume, the oil-wet pore volume, and the water-wet pore volume.

[0042] In an exemplary embodiment, the image processing software is Imaje J.

[0043] Based on laser confocal microscopy, the wettability characteristics of shale pore space are determined by comparing the differences in oil and water spatial distribution in pores after spontaneous oil and water absorption in shale pore space, and the visualization and quantitative evaluation of shale pore spaces with different wettability are achieved, which provides data support for the evaluation of wettability characteristics of shale reservoir pore space and the selection of shale oil development methods. Figure 2As shown, this application also provides a method for characterizing pore space of shale wettability. The specific steps in practical application include: sample pretreatment, spontaneous imbibition of oil-water phase fluid tracer, vacuum freezing treatment and laser confocal three-dimensional visualization observation, as well as quantitative analysis and evaluation of the proportion of pores with different wettabilities. Among them: S1: Sample pretreatment. For oil-bearing shale oil reservoir samples, Soxhlet extraction is first used to wash the oil to remove residual soluble organic matter in the sample and prevent residual oil fluorescence interference.

[0044] S2: Thin slice sample preparation. Use wire cutting to prepare the oil-washed sample, about 1.0 cm thick and no less than 1 cm in area. 2 Thin sections of rock core were mechanically polished and smoothed, following the smoothing procedures outlined in the "Technical Specifications for Rock and Mineral Identification, Part 2: Rock Thin Section Preparation." The final thickness was controlled to approximately 0.5 cm to ensure the required three-dimensional pore reconstruction for laser confocal microscopy analysis. After thin sections were prepared, they were vacuum-dried at 80°C for 48 hours to remove residual organic solvents and water from the oil wash.

[0045] S3: Prepare spontaneous oil and aqueous fluid tracers. Prepare deionized water and n-decane as fluorescent tracer fluids, respectively. Select water-soluble and fat-soluble fluorescent tracers as solvents, respectively. The fluorescence wavelengths of the two should be sufficiently different to effectively distinguish them. For example, for a water-soluble fluorescent tracer, choose fluorescein with excitation / emission wavelengths of 490 nm / 520 nm (green fluorescence). For a fat-soluble fluorescent tracer, choose Nile Red with excitation / emission wavelengths of 552 nm / 636 nm (yellow to red fluorescence).

[0046] S4: Sequentially spontaneously imbibe oil and water tracers to mark oil- and water-wet pores. Considering the mixed wetting and relatively oil-wet characteristics of shale oil reservoir samples, the pretreated thin section sample was first vacuumed and spontaneously imbibed with a saturated fat-soluble tracer solution for 48 hours. The sample was then removed and immersed in a water-soluble tracer solution for 48 hours to spontaneously imbibe saturation. This yielded samples of water- and oil-wet pore spaces filled with different fluorescent tracer fluids.

[0047] S5: Freeze to prevent fluid diffusion. After the oil-water phase tracer is absorbed, the sample is immediately frozen in liquid nitrogen and then removed and stored under vacuum to prevent fluid diffusion from affecting the test results.

[0048] S6: Laser confocal scanning of the sample is carried out to achieve three-dimensional imaging of the pore space distribution and determine the three-dimensional distribution characteristics of the oil-water wettability pore space. The vacuum-freezing treated sample is taken out, and under low-temperature conditions, laser confocal testing and analysis are performed on the core sample. First, the excitation wavelength is set at 490 nm, the fluorescence wavelength is collected at 520 nm, and the three-dimensional spatial distribution of the water-wet pore space is collected; the excitation wavelength is set at 552 nm, and the fluorescence wavelength spectrum at 636 nm is collected for the three-dimensional spatial distribution of the oil-wet pore space. Using image processing software such as Image J, three-dimensional visualization models of different wettability pore spaces are established respectively to stereoscopically display the distribution characteristics of different wettability pore spaces.

[0049] S7: Based on the laser confocal scanning results, the wettability of shale pores is quantitatively evaluated. Based on the three-dimensional model of the laser confocal scanning results, first, the volume V1 of the fluorescence scanning area is determined. Using image processing software such as Image J, the voxel with a fluorescence wavelength of 636 nm is quantitatively analyzed as the oil-wet pore volume V2; the voxel with a fluorescence wavelength of 520 nm is quantitatively analyzed as the water-wet pore volume V3. Accordingly, the ratio of the oil-wet pores to the total sample volume V2 / V1 and the ratio of the water-wet pores to the total sample volume V3 / V1 can be quantitatively obtained.

[0050] When V2 / V1 < V3 / V1, the pore space of the sample is mainly oil-wet. Shale oil is easily adsorbed on the oil-wet pore walls, and its occurrence state mostly shows the characteristics of the adsorbed state. The migration of shale oil in the pores is affected by capillary resistance. Therefore, it is recommended to develop this shale reservoir by means of surfactant solution, carbon dioxide huff and puff, and injection of light hydrocarbons to increase the gas-oil ratio. When V3 / V1 < V2 / V1, the pore space is mainly water-wet. Shale oil is not adsorbed on the water-wet surface and mostly exists in a free state in the pores, and is less affected by capillary resistance. Therefore, it is recommended to develop this shale reservoir by means of water injection and pressurization.

[0051] This application can visualize the three-dimensional distribution of different wettability spaces and quantitatively characterize the wettability of the pore space, and also provides the following specific application scenarios.

[0052] Example 1: After obtaining the ratio of the oil-wet pores to the total sample volume V2 / V1 and the ratio of the water-wet pores to the total sample volume V3 / V1, it is necessary to further use them to judge how to optimize the segmented fracturing plan.

[0053] 1) In the area with a high proportion of oil-wet pores (V2 / V1 > 0.6), high-viscosity fracturing fluid is used to form a more effective fracture network.

[0054] 2) In the area with a high proportion of water-wet pores (V3 / V1 > 0.6), low-viscosity fracturing fluid is used to improve the fluid penetration ability.

[0055] Example 2: Simulating fluid flow and oil-gas release: Using the three-dimensional pore structure data obtained by laser confocal scanning, combined with the volume ratio of oil-wet pores to the total sample volume V2 / V1 and the volume ratio of water-wet pores to the total sample volume V3 / V1, a seepage model of shale pores was established to simulate fluid flow and oil and gas release.

[0056] From the above principle design and specific implementation methods, it can be seen that this application uses the principle of spontaneous imbibition to mark the pore spaces with different wettability in shale. Combined with laser confocal technology, it is possible to realize the three-dimensional visualization distribution and quantitative evaluation of the pore spaces with different wettability in shale, which has the following advantages: Compared with the overall wettability of shale oil, the present application can visualize the spatial distribution characteristics of micron-level pore wettability and simultaneously achieve quantitative analysis of the volume percentage of pores wetted by oil and water.

[0057] By using the spontaneous imbibition of water and oil-phase tracers by shale to mark the differentially wettable pore space, combined with laser confocal scanning technology, this application can realize the visualization and quantitative evaluation of the differentially wettable pore space in shale oil reservoirs.

[0058] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0059] This document uses specific examples to illustrate the principles and implementation methods of this application. The description of the above examples is only intended to help understand the method and core concept of this application. At the same time, for those skilled in the art, based on the concept of this application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A method for characterizing pore space wettability of shale, characterized in that: The shale wettability pore space characterization method includes: Obtaining shale samples specifically includes: washing oil from the oil-bearing shale oil reservoir sample by Soxhlet extraction; preparing thin sections, vacuuming, and drying the washed shale oil reservoir sample to obtain a shale sample; The shale sample is sequentially immersed in a fat-soluble fluorescent tracer solution and a water-soluble fluorescent tracer solution; the fat-soluble fluorescent tracer solution is Nile red; the water-soluble fluorescent tracer solution is fluorescein; Laser confocal microscopy was performed on the submerged shale samples to obtain a three-dimensional visualization model of pore spaces with different wettability. Determining the fluorescence scanning area volume, oil-wetted pore volume, and water-wetted pore volume using image processing software according to the three-dimensional visualization model; The wettability characteristics of the pore space of the shale sample are determined according to the volume of the fluorescence scanning area, the oil-wet pore volume and the water-wet pore volume; the wettability characteristics of the pore space of the shale sample are water-wetness or oil-wetness.

2. The shale wettability pore space characterization method according to claim 1, characterized in that: The shale sample is sequentially immersed in a fat-soluble fluorescent tracer solution and a water-soluble fluorescent tracer solution, specifically comprising: The shale samples were immersed in a fat-soluble fluorescent tracer solution and spontaneously imbibed for 48 h; The shale sample immersed in the fat-soluble fluorescent tracer solution was immersed in the water-soluble fluorescent tracer solution and spontaneously imbibed to saturate for 48 hours.

3. The shale wettability pore space characterization method according to claim 1, characterized in that: The difference in fluorescence wavelength between the fat-soluble fluorescent tracer solution and the water-soluble fluorescent tracer solution is greater than a set threshold.

4. The shale wettability pore space characterization method according to claim 1, characterized in that: The water-soluble fluorescent tracer is fluorescein, with an excitation wavelength of 490 nm and an emission wavelength of 520 nm; the fat-soluble fluorescent tracer is Nile red, with an excitation wavelength of 552 nm and an emission wavelength of 636 nm.

5. The shale wettability pore space characterization method according to claim 1, characterized in that: Before performing laser confocal laser testing and analysis on the submerged shale samples to obtain a three-dimensional visualization model of pore spaces with different wettability, the following steps are also included: The submerged shale samples were frozen in liquid nitrogen and stored in a vacuum.

6. The shale wettability pore space characterization method according to claim 1, characterized in that: Laser confocal microscopy was performed on the submerged shale samples to obtain a three-dimensional visualization model of pore spaces with different wettability, including: Laser confocal testing and analysis were performed using an excitation wavelength of 490 nm and a fluorescence wavelength of 520 nm to collect a three-dimensional spatial distribution map of the water-wetted pore space; Laser confocal testing and analysis were performed using an excitation wavelength of 552 nm and a fluorescence wavelength of 636 nm to collect a three-dimensional spatial distribution map of the oil-wetted pore space; Image processing software was used to construct three-dimensional visualization models of pore spaces with different wettability based on the three-dimensional spatial distribution maps of water-wet pore space and oil-wet pore space.

7. The shale wettability pore space characterization method according to claim 1, characterized in that: The wettability characteristics of the pore space of the shale sample are determined based on the fluorescence scanning area volume, oil-wet pore volume, and water-wet pore volume, specifically including: The ratio of oil-wet pores to the total volume of the sample and the ratio of water-wet pores to the total volume of the sample were calculated based on the volume of the fluorescence scanning area, the volume of oil-wet pores and the volume of water-wet pores; When the ratio of oil-wet pores to the total volume of the sample is smaller than the ratio of water-wet pores to the total volume of the sample, the wettability of the pore space of the shale sample is oil-wet; When the ratio of water-wet pores to the total volume of the sample is smaller than the ratio of oil-wet pores to the total volume of the sample, the wettability of the pore space of the shale sample is water-wet.

8. The shale wettability pore space characterization method according to claim 7, characterized in that: The shale wettability pore space characterization method further includes: The oil-water wettability pore volume ratio was calculated based on the fluorescence scanning area volume, oil-wetted pore volume, and water-wetted pore volume.

9. The shale wettability pore space characterization method according to claim 1, characterized in that: The image processing software is Imaje J.

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