A method for characterizing the porosity of shale wettability

Abstract

This application discloses a method for characterizing the wettability pore space of shale, relating to the field of shale porosity analysis. The method includes acquiring a shale sample; sequentially immersing the shale sample in a lipid-soluble fluorescent tracer solution and a water-soluble fluorescent tracer solution; performing laser confocal microscopy analysis on the immersed shale sample to obtain a three-dimensional visualization model of pore spaces with different wettability; determining the volume of the fluorescence scanning region, the volume of oil-wetted pores, and the volume of water-wetted pores using image processing software based on the three-dimensional visualization model; determining the wettability characteristics of the shale sample's pore space based on the fluorescence scanning region volume, the volume of oil-wetted pores, and the volume of water-wetted pores; wherein the wettability characteristics of the shale sample's pore space are water-wettable or oil-wettable. This application can simultaneously achieve visualization and quantitative characterization of pore spaces with different wettability in shale.

Description

Technical Field

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

[0002] The wettability of shale pore spaces influences the occurrence, flowability, 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, exhibiting typical reservoir tightness characteristics. Compared to conventional reservoirs, shale, rich in organic matter, exhibits mixed wettability characteristics in its pore spaces. Current understanding suggests that fluid transport within shale nano-scale pore spaces is difficult, with oil and gas migration primarily relying on micron-scale interconnected pore spaces. Based on the oleophilic and hydrophilic characteristics of pore surfaces, pore spaces can be categorized as oleophilic or hydrophilic. These two types of pore spaces present different resistances to fluid transport; oleophilic pore spaces are more conducive to oil enrichment and transport, while hydrophilic pore spaces are the opposite. Therefore, quantitatively characterizing the distribution characteristics of these two types of pore spaces is an important component of shale reservoir pore structure evaluation, oil-water migration channel distribution characterization, and shale oil enrichment and flow mechanism analysis. However, existing methods cannot simultaneously achieve visualization and quantitative characterization of shale pore spaces with different wettability. Summary of the Invention

[0003] The purpose of this application is to provide a method for characterizing the wettability pore space of shale, which can simultaneously achieve visualization and quantitative characterization of the pore space of shale with different wettability.

[0004] To achieve the above objectives, this application provides the following solution:

[0005] This application provides a method for characterizing the porosity of shale wettability, including:

[0006] Obtain shale samples;

[0007] The shale sample was sequentially immersed in a fat-soluble fluorescent tracer solution and a water-soluble fluorescent tracer solution;

[0008] Laser confocal microscopy analysis was performed on the submerged shale samples to obtain a three-dimensional visualization model of the pore space with different wettability.

[0009] Based on the three-dimensional visualization model, image processing software was used to determine the volume of the fluorescence scanning region, the volume of the oil-wetting pores, and the volume of the water-wetting pores.

[0010] The wettability characteristics of the pore space of the shale sample are determined based on the volume of the fluorescence scanning region, the volume of oil-wetted pores, and the volume of water-wetted pores; the wettability characteristics of the pore space of the shale sample are either water-wettable or oil-wettable.

[0011] In one embodiment, obtaining a shale sample specifically includes:

[0012] Oil was washed from oil-bearing shale oil reservoir samples using Soxhlet extraction;

[0013] Thin sections were prepared from the washed shale oil reservoir samples, vacuumed, and dried to obtain shale samples.

[0014] In one embodiment, the shale sample is sequentially immersed in a fat-soluble fluorescent tracer solution and a water-soluble fluorescent tracer solution, specifically including:

[0015] Shale samples were immersed in a lipid-soluble fluorescent tracer solution for 48 hours to achieve spontaneous osmosis saturation.

[0016] Shale samples that had been immersed in a fat-soluble fluorescent tracer solution were then immersed in a water-soluble fluorescent tracer solution for 48 hours to achieve spontaneous osmosis saturation.

[0017] In one embodiment, the difference in fluorescence wavelength between the lipid-soluble fluorescent tracer solution and the water-soluble fluorescent tracer solution is greater than a set threshold.

[0018] 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 lipid-soluble fluorescent tracer is Nile Red, with an excitation wavelength of 552 nm and an emission wavelength of 636 nm.

[0019] In one embodiment, before performing laser confocal microscopy analysis on the submerged shale sample to obtain a three-dimensional visualization model of the pore space with different wettability, the method further includes:

[0020] The shale samples were frozen with liquid nitrogen and vacuum-preserved after immersion.

[0021] In one embodiment, laser confocal microscopy analysis is performed on the submerged shale sample to obtain a three-dimensional visualization model of the pore space with different wettability, specifically including:

[0022] Laser confocal analysis was performed using an excitation wavelength of 490 nm and a fluorescence collection wavelength of 520 nm to collect a three-dimensional spatial distribution map of the water-wetting pore space.

[0023] Laser confocal testing and analysis were performed using an excitation wavelength of 552 nm and a fluorescence acquisition wavelength of 636 nm to obtain a three-dimensional spatial distribution map of the oil-wetting pore space.

[0024] Using image processing software, a three-dimensional visualization model of pore space with different wettability is constructed based on the three-dimensional spatial distribution map of water-wetting pore space and the three-dimensional spatial distribution map of oil-wetting pore space.

[0025] In one embodiment, the wettability characteristics of the pore space of a shale sample are determined based on the volume of the fluorescence scanning region, the volume of oil-wetting pores, and the volume of water-wetting pores, specifically including:

[0026] The ratio of oil-wetting pores to the total sample volume and the ratio of water-wetting pores to the total sample volume are calculated based on the volume of the fluorescence scanning region, the volume of oil-wetting pores, and the volume of water-wetting pores.

[0027] When the proportion of oil-wetting pores to the total volume of the sample is less than the proportion of water-wetting pores to the total volume of the sample, the pore space wettability of the shale sample is oil-wetting.

[0028] When the proportion of water-wetted pores to the total volume of the sample is less than that of oil-wetted pores, the pore space wettability of the shale sample is water-wettable.

[0029] In one embodiment, the shale wettability pore space characterization method further includes:

[0030] The oil-water wettability pore volume ratio is calculated based on the volume of the fluorescence scanning region, the volume of oil-wetting pores, and the volume of water-wetting pores.

[0031] In one embodiment, the image processing software is Imaje J.

[0032] According to the specific embodiments provided in this application, the following technical effects are disclosed:

[0033] This application provides a method for characterizing the wettability pore space of shale. By performing laser confocal microscopy analysis on submerged shale samples, a three-dimensional visualization model of pore spaces with different wettability is obtained, thereby realizing the visualization of the wettability pore space of shale. By determining the wettability characteristics of the pore space of shale samples based on the volume of the fluorescence scanning area, the volume of oil-wetted pores, and the volume of water-wetted pores, the wettability pore space of shale is achieved, thus realizing the quantitative characterization of the wettability pore space of shale. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a flowchart of a method for characterizing the pore space of shale wettability in one embodiment of this application;

[0036] Figure 2 This is a schematic diagram of a shale wettability pore space characterization method according to an embodiment of this application. Detailed Implementation

[0037] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0038] Current quantitative characterization of shale porosity in laboratories mainly focuses on the overall evaluation of shale wettability, primarily using wetting angle testing, spontaneous adsorption, and mineral flotation. These studies aim at the overall wettability of shale and cannot achieve visual observation of micro / nano-scale pore wettability, fluid transport, and enrichment characteristics. However, thanks to the application of high-precision observation techniques such as scanning electron microscopy (SEM) in shale porosity research, combined with experiments on evaporation and condensation, qualitative observation of the micro / nano-scale pore space wettability of shale can be achieved. However, while SEM can observe fluid storage and transport when evaluating the pore space wettability characteristics of shale, its limited field of view hinders quantitative characterization of the overall pore space wettability, raising questions about the reliability of the results. Furthermore, the experiments are time-consuming and costly. Laser confocal microscopy, on the other hand, can effectively analyze the composition and spatial distribution characteristics of fluorescent substances and is widely used in biological research. In recent years, laser confocal microscopy has been widely used in the analysis of fluids in shale oil reservoirs. Residual oil in shale oil reservoirs exhibits fluorescence, and free shale oil is rich in light hydrocarbon components, emitting mainly short-wavelength blue and green fluorescence, while heavy adsorbed shale oil is rich in heavy hydrocarbon components, emitting mainly long-wavelength red fluorescence. Considering its resolution is mainly at the micrometer level, the application of laser confocal microscopy in shale reservoir research mainly focuses on the visualization and quantitative analysis of micrometer-level residual oil composition characteristics and spatial distribution. It shows its strong ability to study fluid distribution in shale pores and demonstrates its potential in the quantitative characterization of shale pore wettability. However, a truly effective method has not yet been developed.

[0039] Currently, there are still few methods for quantitatively evaluating the porosity of shale with different wettability. The main methods rely on wetting angle testing, spontaneous adsorption, mineral sorting, and environmental scanning electron microscopy observation combined with evaporation and condensation. However, these methods all have certain limitations, the most significant being the inability to simultaneously achieve visual observation and quantitative analysis.

[0040] Wetting angle testing is a common method for assessing the wettability of shale. It determines hydrophilicity or oleophilicity by measuring the contact angle of a droplet on the shale surface. It directly reflects wettability through droplet morphology and contact angle values, is relatively simple to operate, provides highly visualized results, and offers specific contact angle values ​​(a contact angle less than 90° for aqueous phases is hydrophilic, and greater than 90° is hydrophobic), facilitating lateral comparisons between different samples. Furthermore, it can test the interaction between different fluids (water, oil) and shale, making it suitable for multiphase wettability studies. However, the experiment is greatly affected by human factors, such as droplet volume, placement, and ambient temperature and humidity, all of which can influence the results, requiring strict standardization. More importantly, the wetting angle method can only characterize the surface wettability of shale samples and cannot reflect the complex wetting behavior of the internal pores of shale (such as the capillary effect of micro- and nano-pores).

[0041] Spontaneous adsorption assesses the wettability of shale by measuring its ability to spontaneously absorb wetting fluids (such as water or oil) under capillary forces, and is one of the important methods for studying the wettability of shale reservoirs. Compared with wetting angle testing, spontaneous adsorption can reflect the overall wettability (including micro and nanopores) of the complex pore network inside shale. However, it can usually only qualitatively determine the hydrophilicity and oil tendency, lacks precise numerical calibration similar to contact angle, and also lacks intuitive visualization.

[0042] Mineral sorting (such as centrifugation, flotation, and heavy liquid separation) is used to analyze shale wettability by separating different mineral components (such as clay, quartz, and organic matter) to study their differences in wettability. It can separate different mineral components in shale (such as hydrophilic clay and oleophilic organic matter), clarifying the contribution of each component to the overall wettability. However, sorting processes (such as grinding and chemical treatment) may alter the surface properties of minerals (such as oxidation and contamination), leading to biases in wettability analysis and failing to characterize the wettability features of the complex pore network within the shale.

[0043] Environmental scanning electron microscopy (SEM) observation of evaporation and condensation offers the advantage of direct visualization. First, shale samples are subjected to steam condensation under specific humidity conditions, allowing water vapor to naturally condense in the pores of varying wettability within the shale. SEM, operating under low vacuum conditions and by controlling temperature and pressure, enables the observation and study of the adsorption characteristics of water vapor on different pore surfaces at the micro- and nanoscale. Therefore, compared to other methods, SEM offers a vivid and intuitive approach. However, its representativeness needs further verification due to limitations in the field of view, and it lacks necessary quantitative parameters for evaluating wettability characteristics.

[0044] To date, there is a lack of effective methods for quantitative characterization of wettability pore space in shale reservoirs, and a lack of visualization and quantitative research tools for pore spaces with different wettability. Therefore, a new method is needed to achieve quantitative characterization of oil content, properties, and reservoir space in shale with different occurrence states.

[0045] Based on this, this application constructs a shale wettability pore space characterization method based on spontaneous percolation and cryo-laser confocalization. First, it realizes the visualization characterization of the three-dimensional distribution of different wettability pore spaces in shale reservoirs. Second, it realizes the evaluation of micron-level pore wettability in shale reservoirs and determines the proportion of oil-water differential wettability pore spaces.

[0046] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0047] In one exemplary embodiment, such as Figure 1 As shown, a method for characterizing the pore space of shale wettability is provided. This method is executed by computer equipment, specifically by a computer device such as a terminal or server alone, or by a terminal and server together, and includes the following steps.

[0048] Step 101: Obtain shale samples.

[0049] Step 102: Immerse the shale sample sequentially in a fat-soluble fluorescent tracer solution and a water-soluble fluorescent tracer solution.

[0050] Step 103: Perform laser confocal microscopy analysis on the submerged shale samples to obtain a three-dimensional visualization model of the pore space with different wettability.

[0051] Step 104: Based on the three-dimensional visualization model, use image processing software to determine the volume of the fluorescence scanning area, the volume of the oil-wetting pores, and the volume of the water-wetting pores.

[0052] Step 105: Determine the wettability characteristics of the pore space of the shale sample based on the volume of the fluorescence scanning area, the volume of the oil-wetted pores, and the volume of the water-wetted pores; the wettability characteristics of the pore space of the shale sample are water-wetness or oil-wetness.

[0053] By performing laser confocal microscopy analysis on submerged shale samples, a three-dimensional visualization model of pore spaces with different wettability was obtained, thereby realizing the visualization of shale wettability pore space. The wettability characteristics of shale sample pore space were determined based on the volume of fluorescence scanning area, oil wettability pore volume, and water wettability pore volume, thus achieving quantitative characterization of shale wettability pore space.

[0054] In one exemplary embodiment, obtaining shale samples specifically includes: washing oil from oil-bearing shale oil reservoir samples using Soxhlet extraction; and preparing thin sections, vacuuming, and drying the washed shale oil reservoir samples to obtain shale samples.

[0055] In an exemplary embodiment, the shale sample is sequentially immersed in a lipid-soluble fluorescent tracer solution and a water-soluble fluorescent tracer solution, specifically including: immersing the shale sample in the lipid-soluble fluorescent tracer solution for spontaneous osmosis saturation for 48 hours; and immersing the shale sample after immersion in the lipid-soluble fluorescent tracer solution in the water-soluble fluorescent tracer solution for spontaneous osmosis saturation for 48 hours.

[0056] In one exemplary embodiment, the difference in fluorescence wavelength between the lipid-soluble fluorescent tracer solution and the water-soluble fluorescent tracer solution is greater than a set threshold.

[0057] In one exemplary embodiment, the water-soluble fluorescent tracer is fluorescein, with an excitation wavelength of 490 nm and an emission wavelength of 520 nm; the lipid-soluble fluorescent tracer is Nile Red, with an excitation wavelength of 552 nm and an emission wavelength of 636 nm.

[0058] In one exemplary embodiment, before performing laser confocal microscopy analysis on the submerged shale sample to obtain a three-dimensional visualization model of the pore space with different wettability, the method further includes: freezing the submerged shale sample with liquid nitrogen and vacuuming it for preservation.

[0059] In one exemplary embodiment, laser confocal microscopy analysis was performed on the submerged shale sample to obtain a three-dimensional visualization model of pore spaces with different wettability. Specifically, this included: using an excitation wavelength of 490 nm and a fluorescence acquisition wavelength of 520 nm for laser confocal microscopy analysis to acquire a three-dimensional spatial distribution map of water-wetted pore spaces; using an excitation wavelength of 552 nm and a fluorescence acquisition wavelength of 636 nm for laser confocal microscopy analysis to acquire a three-dimensional spatial distribution map of oil-wetted pore spaces; and using image processing software to construct a three-dimensional visualization model of pore spaces with different wettability based on the three-dimensional spatial distribution maps of water-wetted pore spaces and oil-wetted pore spaces.

[0060] 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 region, the volume of oil-wetted pores, and the volume of water-wetted pores. Specifically, this includes: calculating the ratio of oil-wetted pores to the total sample volume and the ratio of water-wetted pores to the total sample volume based on the volume of the fluorescence scanning region, the volume of oil-wetted pores, and the volume of water-wetted pores; when the ratio of oil-wetted pores to the total sample volume is less than the ratio of water-wetted pores to the total sample volume, the wettability characteristics of the pore space of the shale sample are oil-wetted; when the ratio of water-wetted pores to the total sample volume is less than the ratio of oil-wetted pores to the total sample volume, the wettability characteristics of the pore space of the shale sample are water-wetted.

[0061] 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 region volume, oil wettability pore volume, and water wettability pore volume.

[0062] In one exemplary embodiment, the image processing software is Imaje J.

[0063] Based on laser confocal microscopy, this study determines the wettability characteristics of shale pore spaces by comparing the differences in oil-water spatial distribution after spontaneous oil and water absorption. This enables visualization and quantitative evaluation of shale pore spaces with different wettability, providing data support for evaluating the wettability characteristics of shale reservoir pore spaces and for selecting shale oil development methods. Figure 2 As shown, this application also provides a method for characterizing the porosity of shale wettability, with specific steps in practical applications: sample pretreatment, spontaneous absorption of oil-water phase fluid tracers, vacuum freezing treatment, laser confocal three-dimensional visualization observation, and quantitative analysis and evaluation of the proportion of porosity with different wettability. Among these steps:

[0064] 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 and prevent interference from residual oil fluorescence.

[0065] S2: Thin-section sample preparation. Samples after oil washing are prepared using wire cutting, approximately 1.0 cm thick, with an area of ​​not less than 1 cm². 2 Core thin section samples were mechanically polished and ground, following the grinding procedure outlined in "Technical Specifications for Rock and Mineral Identification Part 2: Rock Thin Section Sample Preparation." The final thickness was controlled to approximately 0.5 cm to ensure compliance with the requirements for three-dimensional pore reconstruction in laser confocal microscopy analysis. After preparation, the thin sections were vacuum-dried at 80°C for 48 hours to remove residual organic solvents and water from the washing process.

[0066] S3: Prepare self-absorbing oil and aqueous phase fluid tracers. Prepare deionized water and n-decane fluorescent tracer fluids separately, using water-soluble and lipid-soluble fluorescent tracers as solvents, respectively. The fluorescence wavelengths of the two should have a significant difference to achieve effective differentiation. For example, the water-soluble fluorescent tracer can be fluorescein, with excitation / emission wavelengths of 490 nm / 520 nm (green fluorescence), and the lipid-soluble fluorescent tracer can be Nile Red, with excitation / emission wavelengths of 552 nm / 636 nm (yellow to red fluorescence).

[0067] S4: Sequential spontaneous adsorption of oil and water tracers to mark oil-water wetted pores. Considering the mixed wetting and relatively oleophilic characteristics of shale oil reservoir samples, the pretreated thin-section samples were first vacuum-absorbed to spontaneously adsorb saturated lipid-soluble tracer solutions for 48 hours. Then, the samples were removed and immersed in water-soluble tracer solutions for spontaneous adsorption saturation for 48 hours, resulting in water-oil wetted pore spaces filled with different fluorescent tracer fluids.

[0068] S5: Place the fluid for diffusion through freeze treatment. After the imbibition oil-water phase fluid tracer is finished, to avoid affecting the observation results, the sample is immediately put into liquid nitrogen for freezing, and then taken out for vacuum preservation under freezing conditions to prevent the fluid diffusion from affecting the test results.

[0069] 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. Take out the sample after vacuum freezing treatment and perform laser confocal test analysis on the core sample under low temperature conditions. First, set the excitation wavelength at 490 nm, collect the fluorescence wavelength at 520 nm, and collect the three-dimensional spatial distribution of the water-wet pore space; set the excitation wavelength at 552 nm, and collect the spectral map of the fluorescence wavelength at 636 nm for the three-dimensional spatial distribution of the oil-wet pore space. Using image processing software such as Imaje J, establish three-dimensional visualization models of different wettability pore spaces respectively, and stereoscopically display the distribution characteristics of different wettability pore spaces.

[0070] S7: Based on the laser confocal scanning results, quantitatively evaluate the wettability of shale pores. Based on the three-dimensional model of the laser confocal scanning results, first determine the volume V1 of the fluorescence scanning area. Using image processing software such as Imaje J, quantitatively analyze the voxel of the fluorescence wavelength at 636 nm as the oil-wet pore volume V2; quantitatively analyze the voxel of the fluorescence wavelength at 520 nm 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.

[0071] 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 injecting 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 the 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.

[0072] 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.

[0073] 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.

[0074] 1) In the area with a high proportion of oil-wet pores (V2 / V1 > 0.6), use high-viscosity fracturing fluid to form a more effective fracture network.

[0075] 2) In areas with a high proportion of water-wetted pores (V3 / V1 > 0.6), low-viscosity fracturing fluid is used to improve fluid permeability.

[0076] Example 2: Simulating fluid flow and oil / gas release:

[0077] Using three-dimensional pore structure data obtained by laser confocal scanning, and combining the ratio of oil-wetted pores to the total sample volume V2 / V1 and the ratio of water-wetted pores to the total sample volume V3 / V1, a seepage model of shale pores is established to simulate fluid flow and oil and gas release.

[0078] As can be seen from the above principle design and specific implementation methods, this application utilizes the principle of spontaneous permeation to mark the pore spaces of shale with different wettability, and then combines it with laser confocal microscopy technology to make it 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:

[0079] Compared to the overall wettability of shale oil, this application can visualize and characterize the spatial distribution characteristics of micron-level pore wettability, and can also achieve quantitative analysis of the pore volume percentage of oil and water wettability.

[0080] By using spontaneous water absorption from shale and oil phase tracers to label differentially wettable pore spaces, and combining this with laser confocal scanning technology, this application enables the visualization and quantitative evaluation of differentially wettable pore spaces in shale oil reservoirs.

[0081] The technical features of the above embodiments can be combined in any way. For the sake of brevity, 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.

[0082] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for characterizing the pore space of shale wettability, characterized in that, The method for characterizing the porosity of shale wettability includes: Obtaining shale samples specifically includes: washing oil from oil-bearing shale oil reservoir samples using Soxhlet extraction; and preparing thin sections, vacuuming, and drying the washed shale oil reservoir samples to obtain shale samples. The shale sample was sequentially immersed in a lipid-soluble fluorescent tracer solution and a water-soluble fluorescent tracer solution; the lipid-soluble fluorescent tracer solution was Nile Red; the water-soluble fluorescent tracer solution was fluorescein. Laser confocal microscopy analysis was performed on the submerged shale samples to obtain a three-dimensional visualization model of the pore space with different wettability. Based on the three-dimensional visualization model, image processing software was used to determine the volume of the fluorescence scanning region, the volume of the oil-wetting pores, and the volume of the water-wetting pores. The wettability characteristics of the pore space of the shale sample are determined based on the volume of the fluorescence scanning region, the volume of oil-wetted pores, and the volume of water-wetted pores; the wettability characteristics of the pore space of the shale sample are either water-wettable or oil-wettable.

2. The method for characterizing the pore space of shale wettability according to claim 1, characterized in that, The shale sample was sequentially immersed in a fat-soluble fluorescent tracer solution and a water-soluble fluorescent tracer solution, specifically including: Shale samples were immersed in a lipid-soluble fluorescent tracer solution for 48 hours to achieve spontaneous osmosis saturation. Shale samples that had been immersed in a fat-soluble fluorescent tracer solution were then immersed in a water-soluble fluorescent tracer solution for 48 hours to achieve spontaneous osmosis saturation.

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

4. The method for characterizing the pore space of shale wettability 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 lipid-soluble fluorescent tracer is Nile red, with an excitation wavelength of 552 nm and an emission wavelength of 636 nm.

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

6. The method for characterizing the pore space of shale wettability according to claim 1, characterized in that, Laser confocal microscopy analysis was performed on submerged shale samples to obtain three-dimensional visualization models of pore spaces with different wettability, specifically including: Laser confocal analysis was performed using an excitation wavelength of 490 nm and a fluorescence collection wavelength of 520 nm to collect a three-dimensional spatial distribution map of the water-wetting pore space. Laser confocal testing and analysis were performed using an excitation wavelength of 552 nm and a fluorescence acquisition wavelength of 636 nm to obtain a three-dimensional spatial distribution map of the oil-wetting pore space. Using image processing software, a three-dimensional visualization model of pore space with different wettability is constructed based on the three-dimensional spatial distribution map of water-wetting pore space and the three-dimensional spatial distribution map of oil-wetting pore space.

7. The method for characterizing the pore space of shale wettability according to claim 1, characterized in that, The wettability characteristics of the pore space in shale samples were determined based on the volume of the fluorescence scanning region, the volume of oil-wetting pores, and the volume of water-wetting pores. Specifically, these characteristics included: The ratio of oil-wetting pores to the total sample volume and the ratio of water-wetting pores to the total sample volume are calculated based on the volume of the fluorescence scanning region, the volume of oil-wetting pores, and the volume of water-wetting pores. When the proportion of oil-wetting pores to the total volume of the sample is less than the proportion of water-wetting pores to the total volume of the sample, the pore space wettability of the shale sample is oil-wetting. When the proportion of water-wetted pores to the total volume of the sample is less than that of oil-wetted pores, the pore space wettability of the shale sample is water-wettable.

8. The method for characterizing the pore space of shale wettability according to claim 7, characterized in that, The method for characterizing the pore space of shale wettability also includes: The oil-water wettability pore volume ratio is calculated based on the volume of the fluorescence scanning region, the volume of oil-wetting pores, and the volume of water-wetting pores.

9. The method for characterizing the pore space of shale wettability according to claim 1, characterized in that, The image processing software is Imaje J.

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