A quantitative classification method for pore wettability in different pore size intervals of shale

Abstract

The present invention belongs to the technical field of oil and gas geological exploration, and specifically relates to a method for quantitatively dividing pore wettability in different pore size intervals of shale. The method is based on nitrogen physical adsorption and contrast-transformed small-angle neutron scattering technology. First, the pore volume of connected pores in the rock is determined by nitrogen physical adsorption. Then, the total pore volume, the pore volume of water-accessible pores, and the pore volume of oil-accessible pores are determined by contrast-transformed small-angle neutron scattering technology. Finally, a calculation model for the wettability of shale pores in different pore size intervals is established to quantitatively divide pores with different wettabilities, evaluate the wettability of shale reservoirs, accurately predict the volume proportions of pores with different wettabilities, and determine the wettability of pores in any pore size interval. This method solves the problem that the existing technology can only qualitatively and semi-quantitatively evaluate the overall wettability of shale, quantifies the heterogeneity of the wettability of shale reservoirs, provides a basis for predicting the flow patterns and occurrence locations of shale oil and formation water, and effectively improves the success rate of shale oil exploration and development.

Description

Technical field:

[0001] The present invention belongs to the technical field of oil and gas geological exploration, and specifically relates to a method for quantitatively dividing the wettability of pores in different pore size intervals of shale. Based on nitrogen physical adsorption and contrast-transformed small-angle neutron scattering technology, the method determines the wettability differences of pores of different sizes and quantifies the pore volumes with different wettabilities. Background technology:

[0002] Wettability controls the distribution and flow of fluids in rocks and is the result of fluid-rock interactions. Due to the inherent complexity of mineralogy, organic matter characteristics, and pore structure, the wettability of organic-rich shales is even more complex than that of conventional reservoir rocks, making determination of shale wettability extremely challenging. Numerous methods exist in the petroleum industry for determining rock wettability, but traditional methods such as Amott and USBM, designed for conventional reservoirs, are not suitable for characterizing shale wettability. Contact angle measurement, spontaneous imbibition, and flotation methods are currently widely used to determine shale wettability. Contact angle measurement, due to its simplicity and rapidity, has become a common method for characterizing shale wettability. However, shale has complex surface properties and pore structure, resulting in significant heterogeneity, which leads to significant variations in sample contact angles. This requires extensive contact angle measurements across different three-phase contact areas. Furthermore, initial exposure of shale samples to oil or brine can distort the final liquid-liquid contact angle measurements. Furthermore, contact angle experiments require polished sample surfaces. This sample processing destroys the microscopic heterogeneity of actual reservoir rocks, such as orientation and surface roughness, potentially leading to discrepancies between wettability assessments and actual shale wettability. Compared to contact angle measurements, spontaneous imbibition reflects the overall wettability of shale samples. The imbibition slope or volume is the primary parameter for evaluating shale wettability. However, imbibition experiments are primarily used to qualitatively characterize shale wettability. A more representative and reliable quantitative wettability index has yet to be established and requires further research. Flotation methods, based on the differences in wettability of various mineral surfaces, measure wettability by introducing shale particle samples into a mixture of immiscible solvents (such as water or oil). While this method can semi-quantitatively characterize the wettability of micron-scale shale samples, it is not suitable for mixed-wetting shales containing multi-wettability pore networks. Furthermore, many new surfaces of dominant minerals may be generated through crushing and pulverization and do not represent pore wetting properties. It can be seen that the understanding of shale wettability based on contact angle measurement, spontaneous imbibition and flotation methods is still too macroscopic and lacks quantitative characterization of the wettability differences at the pore level within shale.

[0003] The shale wettability evaluation methods in the prior art can only qualitatively and semi-quantitatively evaluate the overall wettability of micron-centimeter-scale shale samples, and cannot reflect the differences in wettability inside shale pores. The obtained wettability results are inaccurate, which affects the mechanistic understanding of the location and flow patterns of shale oil and formation water in shale reservoirs. For example, Chinese Patent 202110701030.5 discloses a method for quantitatively characterizing shale wettability using small-angle neutron scattering, which includes the following five steps: Step 1, preparing multiple shale samples to be tested; Step 2, performing small-angle neutron scattering experiments on each shale sample to be tested, respectively, obtaining the proportion of accessible pores at different original pore size distributions of each shale sample to be tested, and respectively obtaining the first shale pore volume and pore size distribution diagram; step 3, respectively prepare a mixed solution that matches the average scattering length density value of the shale sample to be tested required by the experiment; step 4, place the shale sample to be tested in the prepared mixed solution, and fully infiltrate each shale sample to be tested; step 5, perform a small-angle neutron scattering experiment on each fully infiltrated shale sample to be tested, respectively obtain the accessible pore ratio of each shale sample to be tested on different pore size distributions after wetting, and respectively obtain a second pore volume and pore size distribution diagram for each shale sample to be tested; compare and analyze the experimental results in each corresponding first shale pore volume and pore size distribution diagram with the experimental results in the second pore volume and pore size distribution diagram, and quantitatively characterize the shale wettability of each shale sample to be tested. Chinese Patent No. 202211519538.4 discloses a shale wettability evaluation method comprising the following five steps: Step 1: Sampling shale samples and measuring their wetting angles; Step 2: Performing total organic carbon, rock pyrolysis, and mineral content analysis experiments on the shale samples; Step 3: Correlating the parameters obtained in Step 2 with the shale wetting angles to determine the shale wettability sensitive parameters and constructing a "wettability comprehensive evaluation factor F" we "; Step 4: Conduct low-temperature nitrogen physical adsorption experiments on shale samples to obtain the fractal dimension D; Step 5: Establish the fractal dimension D and F weThe relationship between the fractal dimension D and the wettability of shale is evaluated. A method for fine characterization of shale wettability based on nuclear magnetic resonance is disclosed in Chinese Patent 202310244501.3, which includes the following 11 steps in sequence: (1) Obtaining a crude oil sample of shale, calibrating the hydrogen index HI of the crude oil for subsequent signal correction, that is, performing nuclear magnetic resonance T2 spectrum scanning on 1 mL of crude oil and 1 mL of deionized water, and determining the hydrogen index by the signal peak area ratio; (2) Cutting the middle of a shale standard plunger sample to obtain two core samples A1 and A2 of the same nature; (3) Polishing the end face of the core, using crude oil and ground (4) Prepare compound formation water with the same salinity as the formation water using heavy water; (5) Place core sample A1 in a pressure vessel filled with crude oil and soak it at normal pressure for 72 hours; Place core sample A2 in a pressure vessel filled with formation water and soak it at normal pressure for 72 hours. After the self-imbibition of the two cores is completed, perform nuclear magnetic resonance T2 spectrum scanning respectively; (6) Place core sample A1 in a pressure vessel filled with crude oil and pressurize it for 72 hours; Place core sample A2 in a pressure vessel filled with crude oil and soak it at normal pressure for 72 hours. The core samples A1 and A2 were placed in a pressure vessel filled with compound formation water and saturated for 72 hours. After the saturation was completed, the two cores were scanned by nuclear magnetic resonance T2 spectrum. (7) The core sample A1 was placed in a pressure vessel filled with compound formation water and soaked at normal pressure for 72 hours. The core sample A2 was placed in a pressure vessel filled with compound fluoride solution and soaked at normal pressure for 72 hours. After the self-imbibition of the two cores was completed, the core sample A1 was placed in a pressure vessel filled with compound formation water and saturated for 72 hours. The core sample A2 was placed in a pressure vessel filled with compound fluoride solution and soaked at normal pressure for 72 hours. After the self-imbibition of the two cores was completed, the core sample A2 was placed in a pressure vessel filled with compound formation water and saturated for 72 hours. h, after the pressure saturation is completed, the two cores are scanned with NMR T2 spectra; (9) based on the high-pressure mercury injection test results of core samples A1 and A2, the relaxation time and pore throat radius are converted; (10) based on the peak area of ​​the relaxation time corresponding to the NMR T2 spectra of different saturation processes, the macroscopic wettability index I of the shale core is obtained; (11) based on the NMR T2 spectra of different saturation processes, after determining the pore size distribution range of pure oil wet and pure water wet, the pore size distribution range of mixed wet is further determined, thereby calculating the wettability index corresponding to each level of mixed wet pores. Based on the discussion of the above three related patents, it is urgent to develop a quantitative classification method for the wettability of pores in different pore size intervals of shale to solve the key problem that the overall wettability of shale samples can only be evaluated qualitatively and semi-quantitatively. Summary of the invention:

[0004] The purpose of the present invention is to overcome the defects of the existing technology and develop a method for quantitatively dividing the pore wettability of shale in different pore size intervals, so that the shale wettability evaluation can accurately reflect the heterogeneity of shale wettability at the pore level.

[0005] The specific process flow of the method for quantitatively dividing pore wettability of different pore size intervals in shale disclosed by the present invention comprises the following steps:

[0006] S1. Pretreatment of shale samples

[0007] The shale was prepared into three sets of parallel samples: powder, granules and rock slices, which were then Soxhlet extracted and dried.

[0008] Among them, the shale sample specifications are selected according to the instrument test requirements, and the thickness of the rock slice is less than 0.8mm to avoid multiple scattering during the small-angle neutron scattering test.

[0009] S2. Calculate the scattering length density

[0010] Calculate the scattering length density (SLD) of shale samples;

[0011] S3. Prepare water / oil wettability solution

[0012] A water-wettable mixed solution and an oil-wettable mixed solution having the same SLD as the shale sample were prepared respectively;

[0013] S4. Soaking shale samples

[0014] At room temperature, two rock slab shale samples were immersed in two mixed solutions and sealed.

[0015] S5. Determine the volume of connected pores

[0016] Test granular shale samples to determine the pore volume of connected pores at different pore size intervals;

[0017] S6. Determine the total pore volume

[0018] Testing of thin rock shale samples to determine the pore volume of different pore size intervals of total pores;

[0019] S7. Determine water / oil accessible pore volume

[0020] The soaked rock thin section shale samples were tested separately to determine the pore volume of water / oil accessible pores;

[0021] S8. Establishment of quantitative model of pore wettability in different pore size intervals

[0022] A pore size interval is selected, and the water-wet pore volume, oil-wet pore volume, mixed-wet pore volume, and effective wettability of shale to a certain wettability fluid are calculated based on the connected pore volume, total pore volume, and water / oil accessible pore volume in this pore size interval.

[0023] In step S2 of the present invention, the calculation method of the scattering length density of the shale sample is as follows: XRD and TOC tests are performed on the powdered shale sample, and the types of minerals and the mass fractions of minerals and organic matter in the shale sample are determined based on the test results. The mass fractions are normalized to volume fractions based on the density, and the formula is used: Calculated;

[0024] Where vol%(i) is the volume percentage of each component in the shale matrix; SLD(i) is the SLD of each component (mineral or organic matter) in the shale matrix; i represents one component; and n is the total number of all components.

[0025] In step S3 of the present invention, the method for preparing the water / oil wettability solution is as follows: water-wettable and oil-wettable fluids and their corresponding deuterated fluids are selected, and the required molar percentage of each fluid is calculated based on the SLD of the shale sample and the inherent SLD of the fluid. The required mass of each fluid is then calculated by converting the density of the fluid into a mass percentage.

[0026] In step S7 of the present invention, the method for calculating the water / oil accessible pore volume is as follows: selecting a pore size interval;

[0027] The water-accessible pore volume was obtained by subtracting the water-inaccessible pore volume from the total pore volume;

[0028] The oil-accessible pore volume was obtained by subtracting the oil-inaccessible pore volume from the total pore volume.

[0029] In step S8 of the present invention, the calculation process of the quantitative model of pore wettability in different pore size intervals is:

[0030] Based on the formula: V water-wet =V connected -V oil-access Calculate the water-wettable pore volume V water-wet ;

[0031] Based on the formula: V oil-wet =V connected -V water-access Calculate the oil-wet pore volume V oil-wet ;

[0032] Based on the formula: V mixed-wet =V water-access +V oil-access -V connected Calculation of mixed wettability pore volume V mixed-wet ;

[0033] Based on the formula: I w =V liuiqd-access / V connected×100% Calculate the effective wettability of shale to a certain wettability fluid I w , where V liuiqd-access is the water accessible pore volume V water-access Or oil accessible pore volume V oil-access ;

[0034] The calculation principle is:

[0035] Based on the fact that the total pores are composed of connected pores and non-connected pores, the total pore volume is: V total =V connected +V closed #

[0036] Where V closed is the pore volume of non-connected pores;

[0037] Based on the fact that the connected pores are composed of water-wet pores, oil-wet pores and mixed-wet pores, the volume of the connected pores is:

[0038] V connected =V water-wet +V oil-wet +V mixed-wet #

[0039] The water-accessible pores determined based on small-angle neutron scattering consist of water-wettable pores and mixed-wettable pores, and the water-accessible pore volume is:

[0040] V water-access =V water-wet +V mixed-wet #

[0041] The oil-accessible pores determined based on small-angle neutron scattering are composed of oil-wet pores and mixed-wet pores. The oil-accessible pore volume is:

[0042] V oil-access =V oil-wet +V mixed-wet #

[0043] Based on V connected =V water-wet +V oil-wet +V mixed-wet #and

[0044] V oil-access =V oil-wet +V mixed-wet #, the water-wettable pore volume is:

[0045] V water-wet =V connected -(V oil-wet +V mixed-wet )=V connected -V oil-access#

[0046] Based on V connected =V water-wet +V oil-wet +V mixed-wet #and

[0047] V water-access =V water-wet +V mixed-wet #, the oil-wet pore volume is:

[0048] V oil-wet =V connected -(V water-wet +V mixed-wet )=V connected -V water-access #

[0049] Based on V water-access =V water-wet +V mixed-wet #、V water-wet =V connected -(V oil-wet +V mixed-wet )=V connected -V oil-access # and V oil-wet =V connected -(V water-wet +V mixed-wet )=V connected -V water-access #,

[0050] The mixed wettability pore volume is:

[0051] V mixed-wet =V water-access +V oil-access -V connected #.

[0052] Compared with the existing technology, the present invention is based on nitrogen physical adsorption and contrast-transformed small-angle neutron scattering technology. First, nitrogen physical adsorption is used to determine the pore volume of connected pores in the rock. Then, contrast-transformed small-angle neutron scattering technology is used to determine the total pore volume, the pore volume of water-accessible pores and oil-accessible pores. Finally, a calculation model for the wettability of shale pores in different pore size intervals is established to quantitatively divide pores with different wettabilities, evaluate the wettability of shale reservoirs, accurately predict the volume proportion of pores with different wettabilities, and determine the wettability of pores in any pore size interval. Wet ratio solves the problem that existing technologies can only qualitatively and semi-quantitatively evaluate the overall wettability of shale, quantifies the heterogeneity of shale reservoir wettability, provides a basis for predicting the flow patterns and occurrence locations of shale oil and formation water, and effectively improves the success rate of shale oil exploration and development. Its principle is scientific and reliable, and can accurately determine the wettability differences of pores of different sizes, quantify the pore volumes with different wettabilities, and determine and accurately calculate the wettability of pores in any pore size range with a pore size less than 100nm in shale samples, as well as the pore volumes with different wettabilities. Description of the drawings:

[0053] Figure 1 It is a process flow chart of the present invention.

[0054] Figure 2 This is a histogram of the pore volumes of water-wettable, oil-wettable and mixed-wettable pores in different pore size intervals of the shale sample 1 involved in the present invention.

[0055] Figure 3 This is a histogram of the pore volumes of water-wettable, oil-wettable and mixed-wettable pores in different pore size intervals of the shale sample 2 involved in the present invention. Specific implementation method:

[0056] The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings.

[0057] Example 1:

[0058] The specific process flow of the method for quantitatively dividing the pore wettability of different pore size intervals in shale involved in this embodiment includes the following steps:

[0059] S1. Pretreatment of shale samples

[0060] The shale samples were prepared into three sets of parallel samples: 200 mesh powder, 20-35 mesh particles and three 15mm×9mm×0.8mm rock slices. After Soxhlet extraction, they were dried at 60℃ for 48 hours.

[0061] S2. Calculate the scattering length density

[0062] The scattering length density (SLD) of shale samples is calculated based on the mineral type, mass fraction of minerals and organic matter, and density;

[0063] S3. Prepare water / oil wettability solution

[0064] A water-wettable mixed solution and an oil-wettable mixed solution having the same SLD as the shale sample were prepared respectively;

[0065] Among them, the water-wetting mixed solution is prepared from pure water (H2O) and heavy water (D2O);

[0066] The oil wettability mixed solution is composed of n-decane (C 10 H 22 ), toluene (C7H8), deuterated n-decane (C 10 D 22 ) and deuterated toluene (C7D8), and can also be made of dodecane (C 12 H 26 ) and deuterated dodecane (C 12 D 26 ), an oil-wetting mixed solution of n-decane, toluene and deuterated compounds, which can simulate the high content of saturated hydrocarbons and aromatic hydrocarbons in shale oil;

[0067] S4. Soaking shale samples

[0068] The two mixed solutions were injected into two quartz cuvettes with an inner cavity thickness of 1 mm, and two rock thin-section shale samples were completely immersed in the fluid of the quartz cuvettes and sealed. They were then soaked at a temperature of 25°C for 24 hours.

[0069] S5. Determine the volume of connected pores

[0070] The 20-35 mesh shale samples were tested by nitrogen adsorption to determine the pore volume V of the connected pores in different pore size intervals. connected ;

[0071] S6. Determine the total pore volume

[0072] Small-angle neutron scattering was used to test a thin shale rock sample to determine the pore volume V of different pore size intervals of total pores. total ;

[0073] During the small-angle neutron scattering test, shale samples, air, standard samples (a mixture of polystyrene and deuterated styrene), transmittance, and detector efficiency were tested. The relative scattering intensity of the shale sample was corrected to absolute scattering intensity. The IRENA macro plug-in in the Igor Pro software was used to fit the corrected absolute scattering intensity using the maximum entropy method. The pore volume V of the shale sample in different pore size intervals was calculated based on the polydisperse sphere model. total ;

[0074] S7. Determine water / oil accessible pore volume

[0075] Small-angle neutron scattering was used to test thin-section shale samples immersed in different fluids to determine the water / oil accessible pore volume V water-access / V oil-access ;

[0076] Water accessible pore volume V water-access is the total pore volume V total Pore ​​volume inaccessible to water V water-inaccess The difference:

[0077] Oil accessible pore volume V oil-access is the total pore volume V total Pore ​​volume inaccessible to water V oil-inaccess The difference.

[0078] S8. Establishment of quantitative model of pore wettability in different pore size intervals

[0079] Select the pore size interval, and calculate the connected pore volume V of the pore size interval. connected , total pore volume V total , water accessible pore volume V water-access and oil accessible pore volume V oil-access , calculate the water-wettable pore volume V water-wet , oil-wet pore volume V oil-wet and mixed wettability pore volume V mixed-wet , and the effective wettability of shale I;

[0080] Water-wettable pore volume V water-wet is the volume of connected pores V connected Oil accessible pore volume V oil-access The difference between

[0081] Oil-wet pore volume V oil-wet is the volume of connected pores V connected Pore ​​volume accessible to water V water-access The difference between

[0082] Mixed wettability pore volume V mixed-wetis the water accessible pore volume V water-access Oil accessible pore volume V oil-access The sum of the connected pore volume V connected The difference between

[0083] Effective wettability of shale I w is the pore volume V of water / oil accessible pores water-access / V oil-access The volume of connected pores V connected percentage.

[0084] Example 2:

[0085] This embodiment involves a quantitative classification method for pore wettability of different pore size intervals in shale, which quantitatively classifies the pore wettability of different pore size intervals in the Lucaogou Formation shale in the Jimusar Sag of the Junggar Basin. The specific process steps are as follows:

[0086] S1. Prepare samples

[0087] Two shale samples from the Lucaogou Formation in the Jimusar Sag of the Junggar Basin were selected. The samples were prepared into 200-mesh powder, 20-35-mesh particles, and three 15 mm × 9 mm × 0.8 mm rock slices, respectively. After Soxhlet extraction, the samples were dried in a drying oven at 60°C for 48 hours.

[0088] S2. Calculate the scattering length density

[0089] The 200-mesh powder shale samples were tested by XRD and TOC tests to obtain the mineral types, mass fractions of minerals and organic matter of the two shale samples. The mass fractions were normalized to volume fractions according to the density of minerals and organic matter, and the formula was used: The SLD of two shale samples was calculated, and the results are shown in Table 1:

[0090]

[0091]

[0092] S3. Prepare water / oil wettability solution

[0093] The SLD of the two shale samples calculated according to Table 1;

[0094] Based on the intrinsic SLD of pure water and heavy water, the mole fraction is calculated and converted into a mass fraction, thereby calculating the mass of pure water and heavy water. Pure water and heavy water are fully mixed to form a water-wetting mixed solution;

[0095] n-decane (C 10 H 22 ), toluene (C7H8), deuterated n-decane (C 10 D22 ) and deuterated toluene (C7D8) are fully mixed to form an oil-wetting mixed solution, and the preparation process is the same as that of the water-wetting mixed solution;

[0096] S4. Soaking shale samples

[0097] The water-wetting solution and the oil-wetting solution were injected into two quartz cuvettes with an inner cavity thickness of 1 mm, respectively. The two rock slices were completely immersed in the solutions in the quartz cuvettes. The openings of the quartz cuvettes were sealed and placed at room temperature (25°C) for 24 hours.

[0098] S5. Determine the pore volume of connected pores with different pore size intervals

[0099] 2g of 20-35 mesh shale sample was placed in In the VacPrep 061 sample degassing system, the sample was degassed at 110°C for 24 hours and then cooled to room temperature. The nitrogen adsorption test was performed using the ASAP 2460 surface area and pore size analyzer. The nitrogen adsorption data was analyzed using the BJH model to calculate the pore volume V of the connected pores in different pore size intervals. connected , the results are shown in Table 2:

[0100]

[0101] S6. Determine the pore volume of different pore size intervals of the total pores

[0102] Small-angle neutron scattering was used to test dry rock slices, standard samples (a mixture of polystyrene and deuterated polystyrene), air, transmittance, and detector efficiency. The relative scattering intensity of the shale sample was corrected to absolute scattering intensity. The IRENA macro plug-in in Igor Pro software was used to fit the corrected absolute scattering intensity using the maximum entropy method. The pore volume V of the shale sample in different pore size intervals was calculated based on the polydisperse sphere model. total , the results are shown in Table 3:

[0103]

[0104] S7. Determine the pore size distribution and pore volume of pores with different wettability

[0105] The soaked rock slices were tested separately using small-angle neutron scattering. The testing and processing procedures were the same as step S6. The pore volumes of water-inaccessible / oil-inaccessible pores of the two shale samples in different pore size ranges were obtained.

[0106] According to the water accessible pore volume V water-access is the total pore volume V totalPore ​​volume inaccessible to water V water-inaccess The difference between the oil accessible pore volume V oil-access is the total pore volume V total Pore ​​volume inaccessible to water V oil-inaccess The difference between the water and oil accessible pore volume V is calculated. water-access / V oil-access , the results are shown in Table 4 and Table 5:

[0107]

[0108] S8. Establish a quantitative model for pore wettability in different pore size ranges

[0109] Divide the aperture interval according to

[0110] V water-wet =V connected -(V oil-wet +V mixed-wet )=V connected -V oil-access #

[0111] 、V oil-wet =V connected -(V water-wet +V mixed-wet )=V connected -V water-access and V mixed-wet =V water-access +V oil-access -V connected Calculate the water-wet pore volume, oil-wet pore volume and mixed-wet pore volume respectively, according to I w =V liuiqd-access / V connected ×100% to calculate the effective wetting rate. The results are shown in Table 6:

[0112]

[0113] The pore wettability quantification model for different pore size ranges can quantify the water-wet pore volume, oil-wet pore volume and mixed-wet pore volume in different pore size ranges. Figure 2 and Figure 3 As shown, the effective water wettability and effective oil wettability of the shale sample are obtained, and the wettability of the shale pores to oil is greater;

[0114] This shows that the quantitative model of pore wettability in different pore size intervals can quantitatively determine the wettability of shale and the heterogeneity of wettability in different pore size intervals.

Claims

1. A quantitative classification method for pore wettability of different pore size intervals in shale, characterized by: The specific process includes the following steps: S1. Calculate scattering length density Calculate the scattering length density of shale samples; S2. Prepare water / oil wettability solution A water-wettable mixed solution and an oil-wettable mixed solution having the same SLD as the shale sample were prepared respectively; S3. Soaking shale samples At room temperature, two rock slab shale samples were immersed in two mixed solutions and sealed. S4. Determine the volume of connected pores Test granular shale samples to determine the pore volume of connected pores at different pore size intervals; S5. Determine the total pore volume Testing of thin rock shale samples to determine the pore volume of different pore size intervals of total pores; S6. Determine the water / oil accessible pore volume The soaked rock thin-section shale samples were tested separately to determine the water / oil accessible pore volume; S7. Establishment of a quantitative model for pore wettability in different pore size intervals A pore size interval is selected, and the water-wet pore volume, oil-wet pore volume, mixed-wet pore volume, and effective wettability of shale to a certain wettability fluid are calculated based on the connected pore volume, total pore volume, and water / oil accessible pore volume in this pore size interval.

2. The method for quantitatively dividing pore wettability of shale with different pore size intervals according to claim 1 is characterized in that: Before step S1, the shale sample is pretreated: the shale is prepared into three sets of parallel samples of powder, granules and rock slices, and each is subjected to Soxhlet extraction and then dried.

3. The method for quantitatively dividing pore wettability of shale with different pore size intervals according to claim 2 is characterized in that: The thickness of the rock slice is less than 0.8 mm.

4. The method for quantitatively dividing pore wettability of shale with different pore size intervals according to claim 1 is characterized in that: In step S1, the scattering length density of the shale sample is calculated by performing XRD and TOC tests on the powdered shale sample, determining the type of minerals and the mass fractions of minerals and organic matter in the shale sample based on the test results, and normalizing the mass fractions to volume fractions based on the density, using the formula: Calculated.

5. The method for quantitatively dividing pore wettability of shale with different pore size intervals according to claim 4 is characterized in that: Vol%(i) is the volume percentage of each component in the shale matrix; SLD(i) is the SLD of each component in the shale matrix; i represents one component; and n is the total number of all components.

6. The method for quantitatively dividing pore wettability of shale with different pore size intervals according to claim 1, characterized in that: In step S2, the method for preparing the water / oil wettability solution is as follows: water-wettable and oil-wettable fluids and their corresponding deuterated fluids are selected, and the required molar percentage of each fluid is calculated based on the SLD of the shale sample and the inherent SLD of the fluid. The required mass of each fluid is then calculated by converting the density of the fluid into a mass percentage.

7. The method for quantitatively dividing pore wettability of shale with different pore size intervals according to claim 1, characterized in that: In step S6, the water / oil accessible pore volume is calculated as follows: Select the aperture interval; The water-accessible pore volume was obtained by subtracting the water-inaccessible pore volume from the total pore volume; The oil-accessible pore volume was obtained by subtracting the oil-inaccessible pore volume from the total pore volume.

8. The method for quantitatively dividing pore wettability of shale with different pore size intervals according to claim 1 is characterized in that: In step S7, the calculation process of the quantitative model of pore wettability in different pore size intervals is as follows: Based on the formula: V water-wet =V connected -V oil-access Calculate the water-wettable pore volume V water-wet ; Based on the formula: V oil-wet =V connected -V water-access Calculate the oil-wet pore volume V oil-wet ; Based on the formula: V mixed-wet =V water-access +V oil-access -V connected Calculation of mixed wettability pore volume V mixed-wet ; Based on the formula: I w =V liuiqd-access / V connected ×100% Calculate the effective wettability of shale to a certain wettability fluid I w , where V liliqd-access is the water accessible pore volume V water-access Or oil accessible pore volume V oill-access .

9. The method for quantitatively dividing pore wettability of shale with different pore size intervals according to claim 8, characterized in that: The calculation principle is: Based on the fact that the total pores are composed of connected pores and non-connected pores, the total pore volume is: V total =V connected +V closed # Where V closod is the pore volume of non-connected pores; Based on the fact that the connected pores are composed of water-wet pores, oil-wet pores and mixed-wet pores, the volume of the connected pores is: V connected =V water-wet +V oil-wet +V mixed-wet # The water-accessible pores determined based on small-angle neutron scattering consist of water-wettable pores and mixed-wettable pores, and the water-accessible pore volume is: V water-access =V water-wet +V mixed-wet # The oil-accessible pores determined based on small-angle neutron scattering are composed of oil-wet pores and mixed-wet pores. The oil-accessible pore volume is: V oil-access =V oil-wet +V mixed-wet # Based on V connected =V water-wet +V oil-wet +V mixed-wet #and V oil-access =V oil-wet +V mixed-wet #, the water-wettable pore volume is: V water-wet =V connnected -(V oil-wet +V mixed-wet )=V connected -V oil-access # Based on V connected =V water-wet +V oil-wet +V mixed-wet # and V water-access =V water-wet +V mixed-wet #, the oil-wet pore volume is: V oil-wet = V connected -(V water-wet + V mixed-wet ) = V connnected - V water-access # Based on V water-access = V water-wet + V mixed-wet #, V water-wet = V connected - (V oil-wet + V mixed-wet ) = V connected - V oil-access # and V oil-wet =V connected -(V water-wet +V mixed-wet )=V connected -V water-access #, The mixed wettability pore volume is: V mixed-wet =V water-access +V oil-access -V connected #。

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