Ellipsometry-based method and device for quantitatively characterizing surface wettability of oil shale

Abstract

This invention discloses a method and apparatus for quantitative characterization of the wettability of oil shale surfaces based on ellipsometric measurement, relating to the field of oil and gas field development. The method includes: acquiring ellipsometric measurement data of a stable liquid film on a sample surface under different incident conditions, and establishing an interface optical measurement dataset; based on a multilayer thin-film optical model, iteratively fitting the measured ellipsometric angle and phase difference data by setting initial liquid film thickness parameters to obtain a fitted value for the liquid film thickness; calculating the effective coverage of the liquid film on the shale surface based on the effective medium theory and the equivalent refractive index of the composite medium layer obtained by inversion from the measurement data; constructing a comprehensive wettability evaluation index, and determining the wettability category of the shale surface based on the index threshold range. The advantages of this invention are: simultaneously acquiring liquid film thickness and effective coverage based on ellipsometric measurement, constructing a comprehensive wettability evaluation index, and achieving rapid, non-destructive, and quantitative characterization of shale surface wettability.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development, specifically to a method and apparatus for quantitative characterization of the surface wettability of petroleum shale based on ellipticity measurement. Background Technology

[0002] Wettability is a crucial factor influencing oil and gas seepage behavior and recovery rates, determining the distribution pattern of oil and water in rock pores, flow resistance, and displacement efficiency. In petroleum engineering, the water-wetness or neutral wettability of rocks directly affects the recovery rates of waterflooding, gasflooding, and chemical flooding. Therefore, accurate characterization of wettability is of great significance for improving oil and gas extraction efficiency. However, existing wettability characterization methods mainly rely on macroscopic contact angle measurements. These methods indirectly infer wetting characteristics based on the static equilibrium morphology of droplets on solid surfaces, making it difficult to obtain the true structural parameters of liquid films at the micro-nano scale. Furthermore, they are highly sensitive to surface roughness and chemical heterogeneity, failing to achieve non-destructive, dynamic, and precise quantitative characterization of nanoscale liquid film thickness. For example, Chinese Patent CN202210359694A discloses a method and system for determining rock wettability based on multi-droplet contact angle measurement correction. This method involves forming multiple droplets in a rock sample in an oil-water environment and correcting the contact angles at different shooting angles to obtain contact angle data for characterizing rock wettability. The contact angle method is based on the principle that when a liquid reaches mechanical equilibrium on a solid surface, the interfacial tensions of the solid-liquid-gas three phases jointly determine the geometry of the droplet. It reflects the wetting characteristics of the solid surface by measuring the interfacial angle. Furthermore, the droplet scale on which this method relies is usually much larger than the pore scale of rock, making it difficult to directly reflect the true wetting state when a fluid forms a liquid film or adsorption layer on the walls of micro- and nano-pores.

[0003] Existing wettability measurement methods mostly rely on macroscopic methods such as contact angle and adsorption-displacement experiments, which make it difficult to obtain nanoscale structural information of liquid films on solid surfaces. They also cannot achieve high-precision, non-destructive, and real-time quantitative characterization of liquid film thickness under dynamic conditions, thus limiting a deeper understanding of the wettability formation mechanism and the microscopic evolution of interfaces. Summary of the Invention

[0004] To address the aforementioned technical problems, this paper provides a method and apparatus for quantitative characterization of wettability of petroleum shale surface based on ellipticity measurement. This technical solution solves the problem mentioned in the background that existing wettability measurement methods mostly rely on macroscopic methods such as contact angle and adsorption-displacement experiments, which make it difficult to obtain nanoscale structural information of liquid film on solid surface and also cannot achieve high-precision, non-destructive, and real-time quantitative characterization of liquid film thickness under dynamic conditions.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A quantitative characterization method for the surface wettability of petroleum shale based on ellipticity measurement includes: Based on the contact process between shale samples and liquid media, ellipticity measurement data of the stable liquid film on the sample surface under different incident conditions were obtained, and an interface optical measurement dataset was established. Based on the multilayer thin film optical model, the liquid film thickness fitting value is obtained by iteratively fitting the measured ellipticity and phase difference data by setting the initial thickness parameter of the liquid film; Based on the effective medium theory and combined with the equivalent refractive index of the composite medium layer obtained by inversion from the measurement data, the effective coverage of the liquid film on the shale surface is calculated. Based on the fitted value of liquid film thickness and effective coverage, a comprehensive wettability evaluation index is constructed, and the wettability category of shale surface is determined according to the index threshold range.

[0006] Preferably, the step of acquiring ellipsometric measurement data of the stable liquid film on the sample surface under different incident conditions based on the contact process between the shale sample and the liquid medium, and establishing an interface optical measurement dataset includes: The surface of the shale sample was brought into full contact with deionized water, and the excess liquid phase was removed by centrifugation, forming a continuous liquid film structure with stable thickness on the sample surface. An ellipticity measurement system was used to collect ellipticity angle and phase difference data of reflected light from the air-liquid film-shale three-layer interface within a preset incident angle and wavelength scanning range. The collected elliptic deflection angle and phase difference data are denoised and wavelength aligned to form an interface optical measurement dataset.

[0007] Preferably, the step of obtaining the liquid film thickness fitting value by iteratively fitting the measured ellipticity angle and phase difference data based on the multilayer thin film optical model and by setting the initial thickness parameter of the liquid film includes: A multilayer thin-film optical model is established, which consists of a three-layer structure: a top air layer, a middle liquid film layer, and a bottom shale substrate. The multilayer thin-film optical model treats the shale substrate as an absorbing medium with complex refractive index and adopts the Fresnel reflection coefficient formula applicable to the absorbing substrate. Based on the refractive indices of air, liquid film, and shale substrate, and combined with the angle of incidence, the angle of light propagation in each layer is calculated using the complex form of Snell's law. Based on the complex form of the Fresnel reflection coefficient formula, the vertical and parallel light reflection coefficients of air-liquid film-shale are calculated respectively. Set an initial value for the liquid film thickness, and calculate the phase difference generated by the propagation of light waves in the liquid film layer based on this initial value; Based on the superposition formula of multilayer film reflectance coefficients, and combined with the reflectance coefficients and phase differences of each interface, the theoretical elliptic angle and theoretical phase difference under the current set thickness are calculated. An error evaluation function is established between the theoretical ellipticity parameters and the measured ellipticity parameters. The liquid film thickness value is adjusted by the least squares optimization algorithm until the error function value converges to the preset value. The corresponding thickness value is then used as the fitted value of the liquid film thickness.

[0008] Preferably, the calculation of the effective coverage of the liquid film on the shale surface based on the effective medium theory and the equivalent refractive index of the composite medium layer obtained by inversion from measurement data includes: The liquid film on the shale surface and the air in the uncovered area are considered as a composite medium layer with a uniform equivalent refractive index; Based on the effective medium approximation model, a quantitative relationship is established between the equivalent refractive index and the effective coverage of the liquid film, the air refractive index, and the liquid film refractive index. Based on the fitted value of the liquid film thickness, the refractive index of the liquid film in the multilayer thin film optical model is replaced with the equivalent complex refractive index to be fitted, and the equivalent refractive index of the composite medium layer is obtained from the ellipsometric measurement data using the same least squares optimization algorithm. Based on the equivalent refractive index of the composite medium layer, and using an approximate model of the effective medium, the effective coverage of the liquid film on the shale surface is calculated.

[0009] Preferably, the construction of a comprehensive wettability evaluation index based on the liquid film thickness fitting value and effective coverage, and the determination of the wettability category of the shale surface according to the index threshold range, includes: By using the fitted value of liquid film thickness and effective coverage as two independent input dimensions, a comprehensive wettability evaluation index expression is constructed, which is the product of liquid film thickness and non-coverage rate. Based on the statistical characteristics of historical data, set threshold ranges for indicators; When the comprehensive wettability evaluation index is less than or equal to the lower limit of the index threshold range, it is judged as strong wettability. When the comprehensive wettability evaluation index is greater than or equal to the upper limit of the index threshold range, it is judged as weak wettability. When the comprehensive wettability evaluation index is between the lower limit and the upper limit, it is judged as medium wettability.

[0010] Furthermore, this solution proposes a quantitative characterization device for the surface wettability of oil shale based on ellipsometric measurement, used to realize the quantitative characterization method for the surface wettability of oil shale based on ellipsometric measurement as described above, including: A sample carrier module is used to fix the shale sample to be tested and maintain stable contact between the sample surface and the liquid medium. An ellipticity measurement module is used to emit polarized light to a sample under preset incident conditions and collect data on the ellipticity angle and phase difference of the reflected light. The data processing module is used to fit and calculate the ellipticity and phase difference data based on the multilayer thin film optical model, obtain the liquid film thickness and coverage, and obtain the comprehensive wettability evaluation index.

[0011] Preferably, the ellipticity measurement module specifically includes: A light source unit, the light source unit being used to generate an incident light beam having a continuous wavelength range; A polarizing unit is disposed at the emission end of the light source unit and is used to convert the incident light beam into linearly polarized light; A compensation unit is disposed between the polarization unit and the sample, and is used to modulate the polarization state of the incident light and the reflected light. A polarization analyzer, disposed after the compensation unit, is used to selectively transmit the polarization component of the reflected light. A detection unit is disposed at the output end of the polarizer unit and is used to receive reflected light and convert it into an electrical signal.

[0012] Preferably, the data processing module specifically includes: The data acquisition unit is used to receive the elliptic deviation angle and phase difference data output by the elliptic deviation measurement module, and perform normalization and alignment processing. The model fitting unit is used to calculate the liquid film thickness and the effective coverage of the liquid film based on the multilayer thin film optical model and the effective medium approximation model. The wettability evaluation unit is used to construct a comprehensive wettability evaluation index based on the liquid film thickness and coverage, and output the wettability category of the shale surface.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: This scheme proposes a quantitative characterization method for the wettability of petroleum shale surfaces based on ellipsometric measurement. Using ellipsometric measurement and a multilayer thin-film optical model, the nanometer-scale thickness of the liquid film is directly obtained through iterative fitting, achieving non-destructive and high-precision quantitative measurement. This avoids the dependence of traditional contact angle methods on droplet morphology and surface smoothness. Furthermore, this scheme introduces effective medium theory to invert the liquid film coverage and integrates thickness and coverage to construct a comprehensive wettability evaluation index. This overcomes the one-sidedness and indirectness of evaluation based on a single geometric parameter, effectively improving the physical rigor and accuracy of wettability judgment. Secondly, this scheme has a simple experimental procedure and is easy to operate, requiring only routine ellipsometric measurement and simple sample pretreatment. No manual interpretation is needed, resulting in high measurement efficiency and good repeatability. It can adapt to the characterization needs of different solid surfaces and dynamic wetting processes, providing a reliable and efficient technical tool for interfacial characteristic research in fields such as oil and gas reservoir development. Attached Figure Description

[0014] Figure 1 This is a flowchart of the quantitative characterization method for surface wettability of petroleum shale based on ellipticity measurement according to the present invention. Figure 2 The flowchart of the present invention is shown below, which iteratively fits the measured ellipticity and phase difference data to obtain the liquid film thickness fitting value. Figure 3 This invention provides a flowchart for calculating the effective coverage of a liquid film on a shale surface based on the effective medium theory and the equivalent refractive index of the composite medium layer obtained by inversion from measurement data. Figure 4 The flowchart of the present invention describes the construction of a comprehensive wettability evaluation index based on the fitting value of liquid film thickness and effective coverage, and the determination of the wettability category of shale surface according to the threshold range of the index. Figure 5 This is a schematic diagram of the structure of the solid surface wettability quantitative characterization device based on ellipticity measurement according to the present invention. Detailed Implementation

[0015] The following description is intended to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art.

[0016] Example 1 Reference Figure 1 As shown, a quantitative characterization method for the surface wettability of petroleum shale based on ellipticity measurement includes: Based on the contact process between shale samples and liquid media, ellipticity measurement data of the stable liquid film on the sample surface under different incident conditions were obtained, and an interface optical measurement dataset was established. Based on the multilayer thin film optical model, the liquid film thickness fitting value is obtained by iteratively fitting the measured ellipticity and phase difference data by setting the initial thickness parameter of the liquid film; Based on the effective medium theory and combined with the equivalent refractive index of the composite medium layer obtained by inversion from the measurement data, the effective coverage of the liquid film on the shale surface is calculated. Based on the fitted value of liquid film thickness and effective coverage, a comprehensive wettability evaluation index is constructed, and the wettability category of shale surface is determined according to the index threshold range.

[0017] Specifically, based on the contact process between shale samples and liquid media, ellipsometric measurement data of the stable liquid film on the sample surface under different incident conditions were obtained, and an interface optical measurement dataset was established, including: The surface of the shale sample was brought into full contact with deionized water, and the excess liquid phase was removed by centrifugation, forming a continuous liquid film structure with stable thickness on the sample surface. An ellipticity measurement system was used to collect ellipticity angle and phase difference data of reflected light from the air-liquid film-shale three-layer interface within a preset incident angle and wavelength scanning range. The collected elliptic deflection angle and phase difference data are denoised and wavelength aligned to form an interface optical measurement dataset.

[0018] To ensure the consistency of the initial state of the liquid film, this scheme uses centrifugation to form a uniform and stable thin liquid film on the shale surface. By controlling the centrifugation speed and time, excess liquid phase can be effectively removed without destroying the continuity of the liquid film. The ellipsometry measurement system obtains ellipsometry angle and phase difference data that are extremely sensitive to film thickness by collecting the polarization state changes of reflected light at multiple wavelengths. The dataset formed after denoising and wavelength alignment provides high-quality input data for subsequent model inversion.

[0019] Reference Figure 2 As shown, the measured ellipticity angle and phase difference data are iteratively fitted to obtain the fitted values ​​for the liquid film thickness, including: A multilayer thin-film optical model is established, which consists of a three-layer structure: a top air layer, a middle liquid film layer, and a bottom shale substrate. The multilayer thin-film optical model treats the shale substrate as an absorbing medium with complex refractive index and adopts the Fresnel reflection coefficient formula applicable to the absorbing substrate. Based on the refractive indices of air, liquid film, and shale substrate, and combined with the angle of incidence, the angle of light propagation in each layer is calculated using the complex form of Snell's law. Based on the complex form of the Fresnel reflection coefficient formula, the vertical and parallel light reflection coefficients of air-liquid film-shale are calculated respectively. Set an initial value for the liquid film thickness, and calculate the phase difference generated by the propagation of light waves in the liquid film layer based on this initial value; Based on the superposition formula of multilayer film reflectance coefficients, and combined with the reflectance coefficients and phase differences of each interface, the theoretical elliptic angle and theoretical phase difference under the current set thickness are calculated. An error evaluation function is established between the theoretical ellipticity parameters and the measured ellipticity parameters. The liquid film thickness value is adjusted by the least squares optimization algorithm until the error function value converges to the preset value. The corresponding thickness value is then used as the fitted value of the liquid film thickness.

[0020] This scheme establishes a forward optical model from liquid film thickness to ellipsometric measurement parameters, and solves for the thickness through inverse optimization. The principle is as follows: Incident light emitted from the ellipsometer illuminates the air-liquid film interface at an incident angle from the air layer. Part of the light is reflected back to the air layer at this interface, while the other part is refracted into the liquid film layer. The refracted light propagates to the liquid film-shale interface and undergoes reflection and refraction again. The reflected light returns to the liquid film layer and finally passes through the air-liquid film interface into the air layer, where it is received by the detector. Because the shale substrate has absorption characteristics in the visible-near-infrared band (i.e., the extinction coefficient is not equal to 0), the traditional Fresnel formula based on real refractive index is no longer applicable. Therefore, this scheme adopts the Fresnel formula in the form of complex refractive index, as follows: The angle of refraction of light in a liquid film is determined by the complex Snell's law: In the formula, The angle of refraction of light in the liquid film layer. The refractive index of air, The refractive index of the liquid film, The incident angle of the light source of the ellipsometer; Calculate the reflection coefficients of perpendicular and parallel light between each interface: The formula for calculating the air-liquid film interface is: The formula for calculating the liquid film-shale interface is: In the formula, , These are the reflectance coefficients of perpendicular and parallel light at the air-liquid film interface, respectively. , These are the vertical and parallel light reflectance coefficients at the liquid film-shale interface, respectively. Let the complex refractive index of the shale basement satisfy: ,in, For the real part of the refractive index of shale, Extinction coefficient, The imaginary unit, Let be the complex angle of refraction of light in the shale matrix, satisfying: i.e. ; The angle of refraction of light in a shale matrix is ​​determined by the complex Snell's law, which is in complex form. Its real part corresponds to the direction of propagation, and its imaginary part corresponds to absorption and attenuation. The expression for the phase difference produced by light waves propagating in a liquid film layer is: In the formula, For phase difference, Where is the wavelength of the incident light. The thickness of the liquid film; The expression for calculating the theoretical elliptic deflection angle and theoretical phase difference under the current set thickness is as follows: In the formula, , These are the total reflectance coefficients for perpendicular and parallel light, respectively. For the theoretical elliptic declination angle, The theoretical phase difference, Argument operator for complex numbers; The expression for the error evaluation function between the theoretical ellipsoidal parameters and the measured ellipsoidal parameters is as follows: In the formula, The mean square error evaluation function value is... and Let be the theoretical ellipticity and the theoretical phase difference at the i-th wavelength, respectively. and Let be the ellipticity and phase difference measured experimentally at the i-th wavelength, respectively. This represents the number of wavelength scan points.

[0021] Reference Figure 3 As shown, based on the effective medium theory and the equivalent refractive index of the composite medium layer obtained by inversion from measurement data, the effective coverage of the liquid film on the shale surface is calculated as follows: The liquid film on the shale surface and the air in the uncovered area are considered as a composite medium layer with a uniform equivalent refractive index; Based on the effective medium approximation model, a quantitative relationship is established between the equivalent refractive index and the effective coverage of the liquid film, the air refractive index, and the liquid film refractive index. Based on the fitted value of the liquid film thickness, the refractive index of the liquid film in the multilayer thin film optical model is replaced with the equivalent complex refractive index to be fitted, and the equivalent refractive index of the composite medium layer is obtained from the ellipsometric measurement data using the same least squares optimization algorithm. Based on the equivalent refractive index of the composite medium layer, and using an approximate model of the effective medium, the effective coverage of the liquid film on the shale surface is calculated.

[0022] When the liquid film fails to completely cover the shale surface, ellipsometric measurements perceive the effective optical response after the liquid film mixes with air. This scheme employs an effective medium approximation model to describe the equivalent refractive index of this mixed medium. This model equates the microscopic non-uniform distribution to a homogeneous medium layer through volume-weighted averaging, with its equivalent refractive index falling between the air refractive index and the liquid film refractive index. In this model, the effective liquid film coverage is the volume fraction of the liquid. Therefore, given the air refractive index, the liquid film refractive index, and the equivalent refractive index obtained from ellipsometric data, the effective liquid film coverage on the shale surface can be uniquely determined. The specific implementation details are as follows: The approximate expression for the effective medium is: In the formula, For the effective coverage of the liquid film, The equivalent refractive index of the composite dielectric layer; Given the air refractive index, liquid film refractive index, and the equivalent refractive index obtained from ellipsometric data, the effective coverage of the liquid film can be obtained by solving the approximate model expression of the effective medium. When the liquid film on the shale surface is not completely covered, i.e., the liquid film coexists with air, its microstructure is non-uniformly distributed. According to the effective medium theory, this non-uniform mixed layer can be optically equivalent to a single medium layer with a uniform equivalent refractive index, between the air refractive index and the liquid film refractive index. The geometric thickness of this equivalent layer is the liquid film thickness value obtained by fitting the assumed pure liquid film refractive index. The specific method for inverting the equivalent refractive index is as follows: based on the obtained liquid film thickness fitting value, the liquid film refractive index in the multilayer thin film optical model is replaced with the equivalent complex refractive index to be fitted. The real part corresponds to the optical response, and the imaginary part corresponds to the absorption / scattering loss. The equivalent refractive index of the composite medium layer is obtained by inverting from the ellipsometric measurement data using the same least squares optimization. For weakly absorbing or transparent liquid films, the imaginary part can be ignored, and only the real part is fitted.

[0023] Reference Figure 4 As shown, based on the fitted values ​​of liquid film thickness and effective coverage, a comprehensive wettability evaluation index is constructed, and the wettability category of the shale surface is determined according to the index threshold range, including: By using the fitted value of liquid film thickness and effective coverage as two independent input dimensions, a comprehensive wettability evaluation index expression is constructed, which is the product of liquid film thickness and non-coverage rate. Based on the statistical characteristics of historical data, set threshold ranges for indicators; When the comprehensive wettability evaluation index is less than or equal to the lower limit of the index threshold range, it is judged as strong wettability. When the comprehensive wettability evaluation index is greater than or equal to the upper limit of the index threshold range, it is judged as weak wettability. When the comprehensive wettability evaluation index is between the lower limit and the upper limit, it is judged as medium wettability.

[0024] Neither liquid film thickness nor coverage rate alone is sufficient to fully describe the water wetting state of a shale surface. For example, a thick but discontinuous water film corresponds to a weak water wetting state, while a thin but completely covering water film corresponds to a strong water wetting state. This scheme multiplies the fitted value of the liquid film thickness with the effective coverage rate to construct a comprehensive water wetting evaluation index. The physical meaning of this index is that the stronger the water wetting ability of the shale surface, the easier it is to form a thin and continuous water film. Therefore, the smaller the water film thickness and the lower the coverage rate, the smaller the index value. Conversely, the weaker the water wetting ability, the easier it is to form a thick and discontinuous droplet-like distribution. Therefore, the larger the water film thickness and the higher the coverage rate, the larger the index value. By pre-calibrating standard samples with known water wetting levels, the threshold range for distinguishing different water wetting levels is determined. For unknown samples, after calculating their comprehensive water wetting evaluation index, it is compared with the threshold range to automatically output the water wetting level. The expression for the comprehensive wettability evaluation index is: In the formula, This is a comprehensive wettability evaluation index value; Several standard shale samples with known wettability grades were collected, including three categories: highly wettable, moderately wettable, and weakly wettable. The comprehensive wettability evaluation index values ​​for each category were measured. The arithmetic mean and standard deviation of each category were calculated. The upper limit boundary value of the index for highly wettable samples was defined as the mean plus twice the standard deviation for highly wettable samples; the lower limit boundary value of the index for moderately wettable samples was defined as the mean minus twice the standard deviation for moderately wettable samples. The arithmetic mean of these two boundary values ​​was used as the dividing line between highly wettable and moderately wettable samples. Similarly, the upper limit boundary value of the index for moderately wettable samples and the lower limit boundary value of the index for weakly wettable samples were used as the dividing line between moderately wettable and weakly wettable samples. If the two boundary values ​​overlapped, the ROC curve analysis method was used, and the index value corresponding to the maximum Youden index was taken as the optimal dividing line. The calibrated index threshold ranges were solidified into the data processing system for automatic wettability determination of unknown samples.

[0025] Example 2 Based on Example 1, this embodiment further illustrates the above-mentioned method for determining wettability by using a simulated example for explanation: The shale samples were cleaned with deionized water to remove dust and contaminants, and dried in a 60℃ constant temperature oven until the quality was stable. The sample size and number were recorded. The dried shale was completely immersed in deionized water for 12 hours to allow the water to spread fully on the surface of the shale. After soaking in water, the shale is fixed in the centrifuge fixture, with the surface to be tested facing upwards. The speed is set to 1000 rpm and centrifuged for 5 minutes to allow the excess water on the surface to be discharged under the action of centrifugal force, forming a water film structure of stable thickness. The shale was fixed on the ellipsometer sample stage, the incident angle was set to 70° and the measurement wavelength range was 400-800nm, and the measurement parameters were initialized. Ellipticity measurements were performed on the shale surface to be tested, and the corresponding ellipticity angle and phase difference data were collected. Based on a three-layer thin-film optical model of air-water film-shale, the thickness of the water film is obtained by fitting and calculating the elliptic angle and phase difference data. Based on the effective medium theory and the equivalent refractive index of the composite medium layer obtained by inversion from the measurement data, the effective coverage of the water film on the shale surface is calculated. The water wettability grade of the shale sample is determined by comparing the comprehensive wettability evaluation index with the pre-calibrated index threshold range.

[0026] Example 3 This embodiment, based on Embodiment 1, provides a quantitative characterization device for solid surface wettability based on ellipticity measurement, including a sample carrying module, an ellipticity measurement module, and a data processing module, as described above. Figure 5 As shown: The sample carrying module includes a sample carrying platform 4, a horizontal adjustment button 9, and a fixing clamp 8. The sample carrying platform 4 is used to carry the rock core and is mounted on the device base. The horizontal adjustment button 9 is located below the sample carrying platform 4 and is used to adjust the horizontal state of the sample carrying platform 4. The fixing clamp 8 is located on the left and right sides of the sample carrying platform 4 and is used to position and clamp the rock core to ensure the stability of the sample position during the measurement process. The ellipticity measurement system includes a light source 1, a polarizer 2, a first compensator 3, a second compensator 5, an analyzer 6, and a detector 7. It is used to emit polarized light to the sample under a preset incident angle and collect the ellipticity angle and phase difference of the reflected light from the interface, thereby obtaining raw measurement data describing the optical properties of the interface. Light source 1 is used to generate an incident light beam with a predetermined wavelength or wavelength range; polarizer 2 is disposed on the emission side of light source 1 to convert the incident light beam into linearly polarized light; first compensator 3 is disposed between polarizer 2 and sample platform 4 to adjust the polarization state of the incident light so that the incident light meets the incident conditions for ellipsometric measurement; sample platform 4 is used to fix and position the core to be tested so that the incident light irradiates the sample to be tested at a predetermined incident angle and generates reflected light; second compensator 5 is disposed between sample platform 4 and analyzer 6 to adjust the polarization state of the reflected light; analyzer 6 is used to perform polarization selection on the reflected light and obtain the corresponding light intensity signal; detector 7 is disposed on the emission side of analyzer 6 to receive the reflected light and convert it into an electrical signal and output it to the data processing system. The data processing module includes a computer 10, a processor, and a storage unit. The storage unit is used to store ellipsometric measurement data and model parameters. The processor is used to calculate the ellipsometric parameters based on the multilayer thin film optical model to obtain liquid film thickness, coverage, and wettability evaluation results.

[0027] In summary, the advantages of this invention are: based on elliptic measurement, the liquid film thickness and effective coverage are obtained simultaneously, and a comprehensive wettability evaluation index is constructed to achieve rapid, non-destructive, and quantitative characterization of the wettability of shale surfaces.

[0028] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

Claims

1. A quantitative characterization method for the surface wettability of petroleum shale based on ellipticity measurement, characterized in that, include: Based on the contact process between shale samples and liquid media, ellipticity measurement data of the stable liquid film on the sample surface under different incident conditions were obtained, and an interface optical measurement dataset was established. Based on the multilayer thin film optical model, the liquid film thickness fitting value is obtained by iteratively fitting the measured ellipticity and phase difference data by setting the initial thickness parameter of the liquid film; Based on the effective medium theory and combined with the equivalent refractive index of the composite medium layer obtained by inversion from the measurement data, the effective coverage of the liquid film on the shale surface is calculated. Based on the fitted value of liquid film thickness and effective coverage, a comprehensive wettability evaluation index is constructed, and the wettability category of shale surface is determined according to the index threshold range.

2. The method for quantitative characterization of surface wettability of petroleum shale based on ellipticity measurement according to claim 1, characterized in that, The process of obtaining ellipsometric measurement data of the stable liquid film on the sample surface under different incident conditions based on the contact process between the shale sample and the liquid medium, and establishing an interface optical measurement dataset, includes: The surface of the shale sample was brought into full contact with deionized water, and the excess liquid phase was removed by centrifugation, forming a continuous liquid film structure with stable thickness on the sample surface. An ellipticity measurement system was used to collect ellipticity angle and phase difference data of reflected light from the air-liquid film-shale three-layer interface within a preset incident angle and wavelength scanning range. The collected elliptic deflection angle and phase difference data are denoised and wavelength aligned to form an interface optical measurement dataset.

3. The method for quantitative characterization of surface wettability of petroleum shale based on ellipticity measurement according to claim 2, characterized in that, The method based on the multilayer thin-film optical model involves iteratively fitting the measured ellipticity and phase difference data by setting initial liquid film thickness parameters to obtain the liquid film thickness fitting value, including: A multilayer thin-film optical model is established, which consists of a three-layer structure: a top air layer, a middle liquid film layer, and a bottom shale substrate. The multilayer thin-film optical model treats the shale substrate as an absorbing medium with complex refractive index and adopts the Fresnel reflection coefficient formula applicable to the absorbing substrate. Based on the refractive indices of air, liquid film, and shale substrate, and combined with the angle of incidence, the angle of light propagation in each layer is calculated using the complex form of Snell's law. Based on the complex form of the Fresnel reflection coefficient formula, the vertical and parallel light reflection coefficients of air-liquid film-shale are calculated respectively. Set an initial value for the liquid film thickness, and calculate the phase difference generated by the propagation of light waves in the liquid film layer based on this initial value; Based on the superposition formula of multilayer film reflectance coefficients, and combined with the reflectance coefficients and phase differences of each interface, the theoretical elliptic angle and theoretical phase difference under the current set thickness are calculated. An error evaluation function is established between the theoretical ellipticity parameters and the measured ellipticity parameters. The liquid film thickness value is adjusted by the least squares optimization algorithm until the error function value converges to the preset value. The corresponding thickness value is then used as the fitted value of the liquid film thickness.

4. The method for quantitative characterization of surface wettability of petroleum shale based on ellipticity measurement according to claim 3, characterized in that, The calculation of the effective coverage of the liquid film on the shale surface, based on the effective medium theory and the equivalent refractive index of the composite medium layer obtained by inversion from measurement data, includes: The liquid film on the shale surface and the air in the uncovered area are considered as a composite medium layer with a uniform equivalent refractive index; Based on the effective medium approximation model, a quantitative relationship is established between the equivalent refractive index and the effective coverage of the liquid film, the air refractive index, and the liquid film refractive index. Based on the fitted value of the liquid film thickness, the refractive index of the liquid film in the multilayer thin film optical model is replaced with the equivalent complex refractive index to be fitted, and the equivalent refractive index of the composite medium layer is obtained from the ellipsometric measurement data using the same least squares optimization algorithm. Based on the equivalent refractive index of the composite medium layer, and using an approximate model of the effective medium, the effective coverage of the liquid film on the shale surface is calculated.

5. The method for quantitative characterization of surface wettability of petroleum shale based on ellipticity measurement according to claim 4, characterized in that, The comprehensive wettability evaluation index is constructed based on the liquid film thickness fitting value and effective coverage, and the wettability category of the shale surface is determined according to the index threshold range, including: By using the fitted value of liquid film thickness and effective coverage as two independent input dimensions, a comprehensive wettability evaluation index expression is constructed, which is the product of liquid film thickness and non-coverage rate. Based on the statistical characteristics of historical data, set threshold ranges for indicators; When the comprehensive wettability evaluation index is less than or equal to the lower limit of the index threshold range, it is judged as strong wettability. When the comprehensive wettability evaluation index is greater than or equal to the upper limit of the index threshold range, it is judged as weak wettability. When the comprehensive wettability evaluation index is between the lower limit and the upper limit, it is judged as medium wettability.

6. A quantitative characterization device for the surface wettability of petroleum shale based on ellipticity measurement, characterized in that, A method for quantitative characterizing the surface wettability of petroleum shale based on ellipticity measurement as described in any one of claims 1-5, comprising: A sample carrier module is used to fix the shale sample to be tested and maintain stable contact between the sample surface and the liquid medium. An ellipticity measurement module is used to emit polarized light to a sample under preset incident conditions and collect data on the ellipticity angle and phase difference of the reflected light. The data processing module is used to fit and calculate the ellipticity and phase difference data based on the multilayer thin film optical model, obtain the liquid film thickness and coverage, and obtain the comprehensive wettability evaluation index.

7. The device for quantitative characterization of surface wettability of petroleum shale based on ellipticity measurement according to claim 6, characterized in that, The ellipticity measurement module specifically includes: A light source unit, the light source unit being used to generate an incident light beam having a continuous wavelength range; A polarizing unit is disposed at the emission end of the light source unit and is used to convert the incident light beam into linearly polarized light; A compensation unit is disposed between the polarization unit and the sample, and is used to modulate the polarization state of the incident light and the reflected light. A polarization analyzer, disposed after the compensation unit, is used to selectively transmit the polarization component of the reflected light. A detection unit is disposed at the output end of the polarizer unit and is used to receive reflected light and convert it into an electrical signal.

8. The quantitative characterization device for the surface wettability of petroleum shale based on ellipticity measurement according to claim 7, characterized in that, The data processing module specifically includes: The data acquisition unit is used to receive the elliptic deviation angle and phase difference data output by the elliptic deviation measurement module, and perform normalization and alignment processing. The model fitting unit is used to calculate the liquid film thickness and the effective coverage of the liquid film based on the multilayer thin film optical model and the effective medium approximation model. The wettability evaluation unit is used to construct a comprehensive wettability evaluation index based on the liquid film thickness and coverage, and output the wettability category of the shale surface.

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