Method and device for evaluating shale oil core adsorbed oil

Abstract

The application discloses a shale oil core adsorbed and bound oil evaluation method and device, which comprises the following steps: preparing a shale oil core sample and marking a bedding direction; sequentially performing crude oil saturation, mobile free oil removal by displacement and organic solvent extraction treatment to obtain a residual oil state after displacement and an oil-free state core after extraction; collecting multi-polarization terahertz time domain signals of the two state samples in parallel and perpendicular directions of the bedding direction; calculating absorption coefficients, refractive indexes and complex dielectric constants, constructing spectral difference features and multi-polarization anisotropy difference indexes; and quantitatively outputting adsorbed oil and bound oil saturation, volume fraction, bound oil response index, adsorbed oil enrichment index and spatial distribution results based on a complex dielectric difference inversion model.The application has the beneficial effects that the background interference of shale mineral matrix, organic skeleton and bedding structure is effectively eliminated through a difference spectrum technology, multi-polarization response is utilized to reveal anisotropy characteristics of adsorbed oil and bound oil, and the accuracy and reliability of the evaluation results are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of shale oil reservoir core fluid occurrence state detection and unconventional oil and gas reservoir evaluation technology, and more specifically to a method and apparatus for evaluating adsorbed and bound oil in shale oil cores. Background Technology

[0002] Shale oil reservoirs are typically characterized by low porosity, low permeability, strong heterogeneity, and pronounced bedding structures, resulting in a complex state of crude oil occurrence. Unlike conventional oil reservoirs, where movable oil is primarily found in larger pores or fractures, shale oil, in addition to some existing in a free state, also contains a significant portion in adsorbed, bound, or microporous residual states on organic matter surfaces, mineral surfaces, nanopores, and micropore throats. This type of adsorbed and bound oil is jointly controlled by organic matter adsorption, mineral surface effects, pore size effects, and bedding structures. Even after waterflooding or conventional displacement, it tends to remain within the core, exhibiting weak flowability and significant difficulty in extraction. Therefore, accurately identifying and quantitatively evaluating adsorbed and bound oil in shale oil cores is crucial for analyzing immovable oil, evaluating remaining oil, identifying sweet spots, and assessing development potential in shale oil reservoirs.

[0003] Currently, common methods for evaluating adsorbed and bound oil in shale oil cores include solvent extraction, weighing, nuclear magnetic resonance (NMR), pyrolysis analysis, scanning electron microscopy (SEM), fluorescence microscopy, and low-temperature nitrogen adsorption. Solvent extraction and weighing can estimate residual oil content from the perspective of mass change, but they typically only provide overall mass information and are insufficient to reflect the spatial distribution of oil phases and differences in bedding orientation within the core. NMR can utilize short T2 components to assist in identifying bound fluids or microporous fluids, but its results are easily affected by pore structure, wettability, fluid properties, and mineral background, and it is difficult to directly obtain spectral response differences along bedding orientations. SEM and fluorescence microscopy can observe local oil phase distribution or microscopic pore structure, but the testing area is limited, making rapid quantitative evaluation at the core scale difficult. Therefore, existing methods still have shortcomings in the non-destructive identification, directional characterization, spatial distribution evaluation, and quantitative inversion of adsorbed and bound oils.

[0004] Terahertz time-domain spectroscopy (TDS) offers advantages such as non-contact operation, wide bandwidth, sensitivity to medium polarization and molecular vibrational responses, and the ability to simultaneously acquire amplitude and phase information. It can be used to analyze the absorption, refraction, and complex dielectric responses of multiphase composite media, including rocks, fluids, and organic matter, in the terahertz frequency band. However, existing terahertz detection methods often focus on material identification, moisture detection, or overall oil-bearing status assessment. They typically analyze spectral responses based on a single state or polarization direction, making it difficult to effectively distinguish the contributions of shale mineral matrix, organic matter framework, bedding structure background, and adsorbed and bound oil responses. Especially for adsorbed and bound oil remaining after waterflooding, their responses are often superimposed with those of the rock framework, organic matter, and residual water. Without state difference analysis, polarization contrast analysis, and complex dielectric inversion mechanisms, accurate extraction and quantitative evaluation are difficult.

[0005] Therefore, there is an urgent need for a specialized evaluation method and apparatus for adsorbed and bound oil in shale oil cores. This method involves constructing residual oil states after displacement and de-oiled states after extraction, utilizing the differences in terahertz absorption coefficient, refractive index, and complex dielectric constant between the two to subtract the background responses of mineral matrix, organic framework, and bedding structure. Simultaneously, multi-polarization tests parallel and perpendicular to the bedding direction are combined to extract the anisotropic differential characteristics of adsorbed and bound oil. Furthermore, a complex dielectric differential inversion model is used to quantitatively evaluate the saturation, enrichment index, bound oil response index, and spatial distribution of adsorbed and bound oil. This method overcomes the shortcomings of existing technologies in distinguishing background responses, reflecting differences in bedding direction, and quantitatively evaluating adsorbed and bound oil, providing a new technical means for the analysis of immovable oil in shale oil and the identification of reservoir sweet spots. Summary of the Invention

[0006] This invention overcomes the shortcomings of the prior art and provides a method and apparatus for evaluating adsorbed and bound oil in shale oil cores.

[0007] The evaluation method for adsorbed and bound oil in shale oil cores includes the following specific steps: S1. Obtain shale oil core samples, preprocess the shale oil core samples, and identify and mark the bedding orientation of the shale oil core samples. S2. The same shale oil core sample is subjected to crude oil saturation treatment, and the crude oil saturated shale oil core sample is subjected to displacement treatment to remove the mobile free oil in the crude oil saturated shale oil core sample to obtain the residual oil core sample after displacement. S3. Organic solvent extraction is performed on the residual oil core sample after displacement to remove adsorbed oil, bound oil or residual oil in micropores from the residual oil core sample after displacement, so as to obtain the oil-free core sample after extraction. S4. Multi-polarization terahertz time-domain spectroscopy was performed on the residual oil core sample after displacement and the oil-depleted core sample after extraction to obtain the terahertz time-domain signals in the direction parallel to the bedding and perpendicular to the bedding. S5. Calculate the absorption coefficient, refractive index and complex dielectric constant of the residual oil core sample after displacement and the oil-free core sample after extraction under different polarization directions based on the terahertz time-domain signal obtained in S4. S6. Based on the differences in absorption coefficient, refractive index, complex dielectric constant, and multipolarization response between the residual oil core sample after displacement and the oil-free core sample after extraction, construct the differential feature vectors of adsorbed oil and bound oil. S7. Substitute the differential eigenvectors of adsorbed oil and bound oil obtained in S6 into the complex dielectric differential inversion model to establish the complex dielectric differential inversion model and output the evaluation results of adsorbed oil and bound oil.

[0008] The differential characteristics of adsorbed and bound oils in S6 include absorption differential spectrum, refractive index differential spectrum, real part differential spectrum of complex dielectric constant, and imaginary part differential spectrum of complex dielectric constant. The expression for the absorption difference spectrum is:

[0009] The expression for the refractive index difference spectrum is:

[0010] The expression for the difference spectrum of the real part of the complex permittivity is as follows:

[0011] The expression for the difference spectrum of the imaginary part of the complex permittivity is:

[0012] In the formula, For frequency Differential absorption spectra of adsorbed and bound oils; The absorption coefficient of the residual oil-bearing core sample after displacement; The absorption coefficient of the oil-free core sample after extraction; It is a refractive index difference spectrum; The refractive index spectrum of the residual sample; The refractive index spectrum of the extracted sample; The difference spectrum of the real part of the complex permittivity; The difference spectrum of the imaginary part of the complex permittivity; The spectrum of the imaginary part of the dielectric constant of the residual sample; The spectrum of the imaginary part of the dielectric constant of the sample after extraction; The frequency of terahertz electromagnetic waves; This is the polarization angle.

[0013] In S6, under multiple polarization conditions, the absorption differential spectra of adsorbed oil and bound oil in the direction parallel to the layering and perpendicular to the layering were constructed respectively. The differential absorption spectra of adsorbed and bound oils parallel to the stratification direction are expressed as follows.

[0014] The differential absorption spectrum expressions for adsorbed and bound oils perpendicular to the stratification direction are as follows.

[0015] In the formula, The absorption differential spectra of adsorbed and bound oils along the parallel stratification direction are shown. The absorption coefficient of the residual oil-bearing core sample after displacement along the parallel bedding direction; The absorption coefficient of the sample after extraction along the parallel stratification direction; The absorption differential spectra of adsorbed and bound oils perpendicular to the stratification direction are shown. The absorption coefficient of the residual oil-bearing core sample after displacement perpendicular to the bedding direction; The absorption coefficient of the sample after extraction perpendicular to the stratification direction.

[0016] In S6, an anisotropy index for absorption differential spectra is constructed based on the absorption differential spectra of adsorbed and bound oils parallel to and perpendicular to the layering direction. The expression for the anisotropy index for absorption differential spectra is as follows:

[0017] In the formula, As a protection constant, It is a positive number that approaches 0.

[0018] The multi-polarization response difference in S6 includes the absorption anisotropy difference index, the expression of which is:

[0019] In the formula, The anisotropy index of absorption of residual oil after displacement; This is an anisotropy index of absorption in the oil-free state after extraction.

[0020] The expression for the complex permittivity differential inversion model in S7 is:

[0021] In the formula, The equivalent complex dielectric differential response caused by adsorbed and bound oil; The equivalent complex permittivity of the residual oil state after displacement; It represents the equivalent complex permittivity of the oil-free state after extraction.

[0022] In S7, the saturation of adsorbed and bound oils is determined by comparing the difference between the measured complex dielectric differential response and the model-predicted complex dielectric differential response. , The function expression is,

[0023] In the formula, To find the minimum value of the optimized variable; The difference spectrum of the complex permittivity at the i-th frequency point is obtained by actual measurement. For the i-th frequency point, the model The calculated complex permittivity difference spectrum; N is the number of frequency points involved in the inversion; For the i-th frequency point participating in the inversion, is the weighting coefficient for the i-th frequency point.

[0024] Considering the influence of residual water, the residual water saturation or residual water response correction term in the residual oil state after displacement is used as an auxiliary correction parameter in the inversion. The expression for the objective function is:

[0025] In the formula, This is a correction term for the residual water saturation or residual water response in the residual oil state after displacement.

[0026] The evaluation results of adsorbed and bound oils in S7 include the saturation of adsorbed and bound oils. Volume fraction of adsorbed oil and bound oil The bound oil response index (SBOI), the adsorbed oil enrichment index (AOI), and the anisotropy difference index of adsorbed and bound oils. Or one or more of the spatial distribution results of adsorbed oil and bound oil; The expressions for the volume fractions of adsorbed oil and bound oil are as follows:

[0027] In the formula, Porosity of shale oil core samples; The expression for the SBOI (Self-Boarding Index) of the binding oil is:

[0028] In the formula, The absorption difference spectrum of adsorbed oil and bound oil at the i-th frequency point; Let be the difference spectrum of the imaginary part of the complex permittivity at the i-th frequency point; and These are the weighting coefficients; The expression for the Adsorbed Oil Enrichment Index (AOI) is:

[0029] In the formula, As a protection constant, It is a positive number that approaches 0.

[0030] Shale oil core adsorption-bound oil evaluation device, including: Terahertz pulse transmitting module, used to generate broadband terahertz pulses; Terahertz pulse detection module is used to receive terahertz time-domain signals after passing through shale oil core samples; The time delay module is used to scan terahertz time-domain waveforms; The polarization modulation module is used to adjust the direction of the terahertz electric field so that the direction of the terahertz electric field is parallel to the shale bedding direction and perpendicular to the shale bedding direction, respectively. The sample carrying and positioning reset module is used to carry shale oil core samples to ensure that the residual oil core samples after displacement and the oil-free core samples after extraction are tested in the same test area for terahertz testing. The fluid displacement module is used to displace crude oil saturated shale oil core samples to remove mobile free oil and form residual oil core samples after displacement. The solvent extraction module is used to extract organic solvents from residual oil-bearing core samples after displacement to form oil-free core samples. The data acquisition and differential inversion processing module is used to calculate the absorption coefficient, refractive index and complex dielectric constant based on the terahertz time-domain signals of the residual oil-bearing core samples after displacement and the deoiled core samples after extraction. It outputs the evaluation results of adsorbed oil and bound oil based on the spectral difference between the residual oil-bearing core samples after displacement and the deoiled core samples after extraction.

[0031] The beneficial effects of this invention are as follows: Based on the terahertz spectral difference method for residual oil and de-oiled states in the same shale oil core, this invention can effectively eliminate background interference from core minerals, pores, organic matter, and bedding structures, accurately separating the specific spectral responses of adsorbed and bound oils, overcoming the drawbacks of traditional techniques such as the superposition of multi-component signals and the difficulty in distinguishing oil phase information. Simultaneously, this invention integrates terahertz amplitude and phase information to construct a multi-dimensional differential evaluation system encompassing absorption, refractive index, and complex dielectric properties, overcoming the limitations of single-parameter evaluation and effectively improving the accuracy and stability of quantitative inversion of adsorbed and bound oils.

[0032] This scheme introduces multi-polarization terahertz detection to establish an anisotropic differential evaluation index. This index can quantitatively characterize the enrichment degree of adsorbed and bound oil, and accurately depict the directional occurrence characteristics of oil phases along bedding planes, pore throats, and organic matter bands. It can effectively distinguish between the inherent anisotropy of the rock and the polarization response of the oil phase, avoiding evaluation misjudgments caused by structural interference and overcoming the limitation of existing technologies in characterizing the spatial distribution differences of oil phases. Simultaneously, through a complex dielectric differential inversion model, terahertz spectral data can be converted into quantitative reservoir parameters such as oil phase saturation and volume fraction, providing reliable quantitative basis for shale oil residual oil evaluation, sweet spot identification, and development potential analysis.

[0033] This invention employs a precise repositioning and positioning testing method, ensuring uniform testing conditions, significantly reducing the impact of systematic errors and core heterogeneity, and improving the repeatability of test results. Combined with multi-point and two-dimensional scanning testing, it enables visualization of the spatial distribution of oil phases, providing a direct representation of the heterogeneous occurrence characteristics of the core. This invention focuses on the specialized evaluation of immobile oils such as adsorbed and bound oils after waterflooding, complementing conventional mobile oil detection techniques. It is highly targeted, practical, and possesses significant engineering application value. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0035] Example 1 like Figure 1 As shown, the evaluation method for adsorbed and bound oil in shale oil cores includes the following specific steps: S1. Obtain shale oil core samples, preprocess the shale oil core samples, and identify and mark the bedding orientation of the shale oil core samples.

[0036] S1 is used to obtain shale oil core samples with well-defined dimensions, bedding orientation, and a stable initial state. In this embodiment, the same core sample was sequentially subjected to drying, brine saturation, crude oil saturation, brine displacement, and solvent extraction. Using the same core sample for multi-state testing can reduce the influence of differences in mineral composition, pore structure, and organic matter content between different cores on the test results, thus ensuring that subsequent terahertz spectral differences primarily reflect changes in the fluid's occurrence state.

[0037] In this embodiment, the shale oil core samples were cut, ground, polished, and dried. The preferred drying temperature was 60-105℃, and the preferred drying time was 6-24 hours to reduce the volatilization of light organic components in the shale oil cores. Parallel and perpendicular bedding directions were distinguished and marked using microscopic observation, X-ray imaging, core photographs, thin section images, or bedding texture identification methods. The basic parameters of the shale oil core samples are shown in Table 1.

[0038] Table 1 Basic parameters of core samples

[0039] S2. The same shale oil core sample is subjected to crude oil saturation treatment, and the crude oil-saturated shale oil core sample is subjected to displacement treatment to remove the mobile free oil in the crude oil-saturated shale oil core sample to obtain the residual oil core sample after displacement.

[0040] Furthermore, in step S2, the displacement treatment uses simulated formation water, brine, or other displacement fluids. When the oil phase content in the outlet liquid is lower than a set threshold, or the oil phase content at the outlet does not change significantly over multiple consecutive sampling periods, or the oil-water ratio at the outlet reaches a stable state, it is considered that the mobile free oil has been sufficiently displaced, and a residual oil-bearing core sample is obtained after displacement. This embodiment provides specific preparation processes for different fluid occurrence states, as shown in Table 2 below.

[0041] Table 2. Preparation conditions for evaluating the state of adsorbed and bound oils.

[0042] In this embodiment, the dried and marked shale oil core sample was placed in a high-temperature and high-pressure saturation device and saturated with shale crude oil from the target block for 24 hours at 60°C and 25 MPa. After the crude oil was saturated, it was transferred to a core holder, and a confining pressure of 30 MPa and a pore pressure of 15 MPa were set. Simulated formation water displacement was carried out at a constant flow rate of 0.05 mL / min. The outlet fluid was continuously collected to monitor the change in oil phase content. Displacement was stopped when any termination condition was met, and the free liquid on the sample surface was wiped off to obtain the residual oil core sample after displacement.

[0043] S3. Organic solvent extraction is performed on the residual oil core sample after displacement to remove adsorbed oil, bound oil or residual oil in micropores from the residual oil core sample after displacement, so as to obtain the oil-free core sample after extraction.

[0044] Furthermore, in S3, the organic solvent includes toluene, dichloromethane, n-hexane, chloroform, petroleum ether, or mixtures thereof. The endpoint of the organic solvent extraction treatment is determined based on at least one of the following conditions: First, the change in sample mass between two consecutive weighings is less than a set threshold; second, the oil phase content in the extract is lower than a set threshold; third, the color change of the extract tends to stabilize; fourth, the change in the absorption coefficient of the core sample at a selected terahertz frequency point before and after extraction is less than a set threshold.

[0045] S4. Multi-polarization terahertz time-domain spectroscopy was performed on the residual oil core samples after displacement and the oil-depleted core samples after extraction to obtain terahertz time-domain signals in the direction parallel to the bedding and perpendicular to the bedding.

[0046] Furthermore, in S4, when performing multi-polarization terahertz time-domain spectroscopy tests on residual oil-bearing core samples after displacement and deoiled core samples after extraction, the same test area, the same terahertz spot position, the same polarization direction, the same optical path conditions, and the same acquisition parameters are maintained.

[0047] Furthermore, in S4, after the residual oil-bearing core sample is tested, the same core sample is marked with its location, recorded with its coordinates, or recorded with its image. When testing the deoiled core sample after extraction, the core sample is reset to the same test area according to the location marking, coordinate recording, or image recording.

[0048] In this embodiment, a terahertz time-domain testing system was constructed with an effective frequency range of 0.1-3.0 THz, and 0.2-1.5 THz was preferred for data analysis. Nitrogen gas was continuously introduced into the testing chamber to reduce interference from water vapor on terahertz absorption. During the test, both types of core samples maintained the same testing area, the same spot position, the same polarization angle, and unified optical path and acquisition parameters.

[0049] To obtain the influence of shale bedding orientation on the terahertz response of adsorbed and bound oil, at least two sets of polarization tests were conducted on the residual oil state after displacement and the oil-removed state after extraction.

[0050] In the first set of tests, the polarization modulation module was adjusted so that the terahertz electric field direction was parallel to the shale bedding direction, and sample signals were collected in the residual oil state after displacement and in the direction parallel to the bedding direction. And the sample signals after extraction in the oil-free state and parallel to the stratification direction. .

[0051] In the second set of tests, the polarization direction was rotated by 90° so that the terahertz electric field direction was perpendicular to the shale bedding direction. Sample signals were collected from the residual oil state after displacement and from samples perpendicular to the bedding direction. And the sample signals in the oil-free state and perpendicular to the stratification direction after extraction. .

[0052] Where res: residual, the oil residue after displacement; ext: extracted, the oil-free state after extraction. Parallel to the bedding direction; It is perpendicular to the bedding direction.

[0053] The terahertz time-domain spectroscopy test conditions in this embodiment are shown in Table 3 below.

[0054]

[0055] Table 3. Terahertz time-domain spectroscopy test conditions for evaluating adsorbed and bound oils. S5. Based on the terahertz time-domain signal obtained in S4, calculate the absorption coefficient, refractive index, and complex permittivity of the residual oil-bearing core sample after displacement and the oil-depleted core sample after extraction under different polarization directions.

[0056] S5 is used to convert the multi-polarized terahertz time-domain signals of the residual oil state after displacement and the oil-removed state after extraction, which were collected in S4, into frequency-domain parameters that can reflect the optical and dielectric responses of the core samples.

[0057] The specific steps include: first, performing Fourier transform on the reference signal, the residual oil sample signal after displacement, and the oil-free sample signal after extraction to obtain a complex frequency domain signal; then, based on the amplitude and phase differences between the frequency domain signals of each sample and the reference frequency domain signal, calculating the absorption coefficient, refractive index, extinction coefficient, and complex dielectric constant respectively.

[0058] The time-domain to frequency-domain conversion function is:

[0059] In the formula, t is the terahertz time-domain delay time; The frequency is terahertz. Terahertz reference time-domain signals acquired under conditions of no sample, empty sample stage, empty clamp, or reference medium; The time-domain signal of the sample was collected after the terahertz wave passed through the residual oil-bearing shale core sample after displacement. This is the time-domain signal of the sample collected after terahertz waves pass through the extracted oil-bearing shale core sample. , , This is the frequency domain complex signal obtained after the corresponding time-domain signal undergoes a Fast Fourier Transform (FFT). Distinguishing residual oil state After extraction, the oil is removed. and no sample state ; Distinguishing parallel With vertical polarization .

[0060] The frequency domain transfer function is:

[0061] In the formula, For residual oil samples after displacement at frequency Terahertz frequency domain transfer function; For the oil-free sample after extraction at frequency The terahertz frequency domain transfer function.

[0062] The formula for calculating refractive index is:

[0063] In the formula, For the sample at frequency The refractive index below; The speed of light in a vacuum; This represents the phase difference between the sample frequency domain signal and the reference frequency domain signal. The frequency is terahertz. The thickness of the shale core sample; Pi is the mathematical constant of a circle.

[0064] The formula for calculating the absorption coefficient is:

[0065] In the formula, For the sample at frequency The absorption coefficient at the specified depth; The thickness of the shale core sample is shown.

[0066] The formula for calculating the extinction coefficient is:

[0067] In the formula, Extinction coefficient; The speed of light in a vacuum; The absorption coefficient; It is a terahertz frequency.

[0068] The formula for calculating the complex permittivity is:

[0069]

[0070] In the formula, is the real part of the complex permittivity, representing the energy storage capacity of the dielectric. This represents the imaginary part of the complex permittivity, indicating the dielectric loss capability. The real part of the refractive index; is the extinction coefficient, used to characterize the attenuation of terahertz waves in a sample.

[0071] S6. Based on the differences in absorption coefficient, refractive index, complex dielectric constant, and multipolarization response between the residual oil core sample after displacement and the oil-free core sample after extraction, construct differential feature vectors for adsorbed oil and bound oil.

[0072] In S6, the residual oil spectral parameters after displacement are subtracted from the oil-free spectral parameters after extraction to construct four types of basic difference spectra in sequence. Then, two sets of polarization-specific absorption difference spectra are calculated separately. Based on the difference spectra, two-level anisotropy indices are further derived. Finally, all features are integrated to form adsorbed oil and bound oil feature vectors, which are used as the input dataset for the inversion model.

[0073] Furthermore, in S6, feature vectors for adsorbed oil and bound oil are constructed. These feature vectors include one or more of the following: absorption difference spectrum, refractive index difference spectrum, real part difference spectrum of complex dielectric constant, imaginary part difference spectrum of complex dielectric constant, absorption difference spectrum parallel to the stratification direction, absorption difference spectrum perpendicular to the stratification direction, refractive index anisotropy difference index, absorption anisotropy difference index, dielectric anisotropy difference index, absorption difference spectrum anisotropy index, and comprehensive anisotropy difference index.

[0074] Furthermore, the differential characteristics of adsorbed and bound oils in S6 include absorption differential spectrum, refractive index differential spectrum, real part differential spectrum of complex dielectric constant, and imaginary part differential spectrum of complex dielectric constant. The expression for the absorption difference spectrum is:

[0075] The expression for the refractive index difference spectrum is:

[0076] The expression for the difference spectrum of the real part of the complex permittivity is as follows:

[0077] The expression for the difference spectrum of the imaginary part of the complex permittivity is:

[0078] In the formula, For frequency Differential absorption spectra of adsorbed and bound oils; The absorption coefficient of the residual oil-bearing core sample after displacement; The absorption coefficient of the oil-free core sample after extraction; It is a refractive index difference spectrum; The refractive index spectrum of the residual sample; The refractive index spectrum of the extracted sample; The difference spectrum of the real part of the complex permittivity; The difference spectrum of the imaginary part of the complex permittivity; The spectrum of the imaginary part of the dielectric constant of the residual sample; The spectrum of the imaginary part of the dielectric constant of the sample after extraction; The frequency of terahertz electromagnetic waves; This is the polarization angle.

[0079] Furthermore, in S6, under multiple polarization conditions, the absorption differential spectra of adsorbed oil and bound oil in the direction parallel to the layering and perpendicular to the layering were constructed respectively. The differential absorption spectra of adsorbed and bound oils parallel to the stratification direction are expressed as follows.

[0080] The differential absorption spectrum expressions for adsorbed and bound oils perpendicular to the stratification direction are as follows.

[0081] In the formula, The absorption differential spectra of adsorbed and bound oils along the parallel stratification direction are shown. The absorption coefficient of the residual oil-bearing core sample after displacement along the parallel bedding direction; The absorption coefficient of the sample after extraction along the parallel stratification direction; The absorption differential spectra of adsorbed and bound oils perpendicular to the stratification direction are shown. The absorption coefficient of the residual oil-bearing core sample after displacement perpendicular to the bedding direction; The absorption coefficient of the sample after extraction perpendicular to the stratification direction.

[0082] Furthermore, in S6, an absorption differential spectrum anisotropy index is constructed based on the absorption differential spectra of adsorbed and bound oils parallel to and perpendicular to the stratification direction. The expression for the absorption differential spectrum anisotropy index is as follows:

[0083] In the formula, As a protection constant, It is a positive number that approaches 0.

[0084] Furthermore, the multi-polarization response difference in S6 includes an absorption anisotropy differential index, the expression of which is:

[0085] In the formula, The anisotropy index of absorption of residual oil after displacement; This is an anisotropy index of absorption in the oil-free state after extraction.

[0086] Furthermore, based on the aforementioned difference spectrum and anisotropic difference index, feature vectors for adsorbed oil and bound oil are constructed:

[0087] In the formula, These are the feature vectors of adsorbed and bound oils; For the first Selected frequency points; For frequency Differential absorption spectra of adsorbed and bound oils; For frequency The refractive index difference spectrum of adsorbed oil and bound oil; For frequency Difference spectra of the real part of the dielectric constant of adsorbed and bound oils; For frequency The difference spectrum of the imaginary part of the dielectric constant of adsorbed oil and bound oil; The absorption differential spectra of adsorbed and bound oils along the parallel stratification direction are shown. The absorption differential spectra of adsorbed and bound oils perpendicular to the stratification direction are shown. It is a differential index of refractive index anisotropy; To absorb the anisotropic difference index; The dielectric constant is an anisotropic differential index; Anisotropy of the absorption differential spectra of adsorbed and bound oils; The anisotropy difference index is used to comprehensively measure the adsorbed and bound oils.

[0088] Preferably, a frequency point is selected. Located in the range of 0.2-1.5THz, several representative frequency points with high signal-to-noise ratios and significant differences between the residual oil state after displacement and the oil-free state after extraction can be selected, such as 0.5THz, 1.0THz and 1.5THz.

[0089] In this embodiment, three representative frequency points, 0.5THz, 1.0THz and 1.5THz, were selected to calculate the absorption anisotropy index, and the results are shown in Table 4 below.

[0090] Table 4. Multipolarization absorption coefficients of residual oil after displacement and oil-free state after extraction, and anisotropic difference index of adsorbed oil.

[0091] in, Anisotropy is absorbed by residual oil. Anisotropic absorption in the deoiled state; The anisotropy index is calculated based on the absorption differential spectra of adsorbed and bound oils. .

[0092] As shown in Table 4, the residual oil phase after displacement exhibits a higher absorption coefficient parallel to the bedding plane than perpendicular to it at all three representative frequency points, indicating that the residual oil phase retained after displacement has a certain dominant response in the bedding plane direction. The de-oiled phase after extraction also shows some absorption anisotropy, but its anisotropy index is significantly lower than that of the residual oil phase after displacement, suggesting that the polarization differences remaining after extraction mainly originate from the rock skeleton, organic matter bands, and the bedding structure itself.

[0093] Further comparison reveals that, The values ​​are positive at 0.5 THz, 1.0 THz, and 1.5 THz, indicating that the adsorbed and bound oils contribute more to absorption in the direction parallel to the bedding plane than in the direction perpendicular to the bedding plane. Meanwhile, The value is also positive, indicating that the adsorbed oil and bound oil responses obtained based on the differential absorption spectra of residual oil and de-oiled states have obvious directionality.

[0094] These results indicate that adsorbed and bound oils are likely more concentrated in organic matter bands, nanopores, or micropore throats that develop along the bedding direction. By constructing anisotropic differential indices for adsorbed and bound oils, the misinterpretation of the bedding anisotropy of the shale skeleton itself as an adsorbed oil response can be avoided, thereby improving the accuracy of adsorbed and bound oil evaluation.

[0095] Based on the original dual-polarization terahertz time-domain signal collected by S4, the absorption coefficient, refractive index, and complex dielectric fundamental spectral parameters obtained by S5, and combined with the layered polarization difference spectrum constructed by S6 and the two-level anisotropy index, a joint calculation was completed. All spectral differences and polarization response differences were integrated to calculate a complete set of characteristic parameters of adsorbed oil and bound oil. The anisotropy characteristic calculation results corresponding to multiple frequency points are shown in Table 5.

[0096] Table 5 Examples of differential spectra and anisotropic characteristics of adsorbed and bound oils.

[0097] As shown in Table 5, both adsorbed and bound oils exhibit resolvable absorption differential, refractive index differential, and complex dielectric differential responses at three representative frequency points: 0.5 THz, 1.0 THz, and 1.5 THz. Among these, the absorption differential spectrum... The increase with increasing frequency indicates that adsorbed and bound oils exhibit a more significant contribution to energy attenuation at higher terahertz frequencies.

[0098] Both the real and imaginary part difference spectra of the dielectric are positive, indicating that the adsorbed and bound oils not only change the absorption of terahertz waves by the sample, but also change the sample's dielectric energy storage capacity and loss capacity.

[0099] Absorbed anisotropic difference and absorption differential spectrum anisotropy All values ​​are positive, indicating that the adsorbed and bound oils in the sample respond more strongly in the direction parallel to the stratification than in the direction perpendicular to the stratification, which may be related to the organic matter bands, nanopores or micropore throats developed along the stratification direction.

[0100] Therefore, the results in Table 5 show that, based on the differential spectrum of the residual oil state and the de-oiled state, as well as the multi-polarization anisotropy differential index, the adsorbed oil and bound oil response in shale oil cores can be characterized from multiple perspectives, including amplitude, phase, dielectric, and directionality.

[0101] S7. Substitute the differential eigenvectors of adsorbed and bound oil obtained in S6 into the complex dielectric differential inversion model to establish the complex dielectric differential inversion model and output the evaluation results of adsorbed and bound oil. Perform multi-point testing or two-dimensional scanning testing on shale oil core samples to obtain the saturation of adsorbed and bound oil, the bound oil response index, the adsorbed oil enrichment index, and the anisotropy differential index at multiple testing points, and generate spatial distribution maps of adsorbed and bound oil.

[0102] Furthermore, the expression for the complex permittivity differential inversion model in S7 is as follows:

[0103] In the formula, The equivalent complex dielectric differential response caused by adsorbed and bound oil; The equivalent complex permittivity of the residual oil state after displacement; It represents the equivalent complex permittivity of the oil-free state after extraction.

[0104] Furthermore, in S7, the saturation of adsorbed and bound oils is solved by comparing the difference between the measured complex dielectric differential response and the model-predicted complex dielectric differential response. , The function expression is,

[0105] In the formula, To find the minimum value of the optimized variable; The difference spectrum of the complex permittivity at the i-th frequency point is obtained by actual measurement. For the i-th frequency point, the model The calculated complex permittivity difference spectrum; N is the number of frequency points involved in the inversion; For the i-th frequency point participating in the inversion, is the weighting coefficient for the i-th frequency point.

[0106] Furthermore, considering the influence of residual water, the residual water saturation or residual water response correction term in the residual oil state after displacement is used as an auxiliary correction parameter in the inversion. The expression for the objective function is:

[0107] In the formula, This is a correction term for the residual water saturation or residual water response in the residual oil state after displacement.

[0108] Furthermore, the evaluation results of adsorbed oil and bound oil in S7 include the saturation of adsorbed oil and bound oil. Volume fraction of adsorbed oil and bound oil The bound oil response index (SBOI), the adsorbed oil enrichment index (AOI), and the anisotropy difference index of adsorbed and bound oils. Or one or more of the spatial distribution results of adsorbed oil and bound oil; The volume fraction expressions for adsorbed oil and bound oil are as follows:

[0109] In the formula, Porosity of shale oil core samples; The expression for the SBOI (Self-Boarding Index) of the binding oil is:

[0110] In the formula, The absorption difference spectrum of adsorbed oil and bound oil at the i-th frequency point; Let be the difference spectrum of the imaginary part of the complex permittivity at the i-th frequency point; and These are the weighting coefficients; The expression for the Adsorbed Oil Enrichment Index (AOI) is:

[0111] In the formula, As a protection constant, It is a positive number that approaches 0.

[0112] Furthermore, by conducting multi-point testing or two-dimensional scanning testing on shale oil core samples, the saturation of adsorbed and bound oil at multiple testing points was obtained. Volume fraction of adsorbed oil and bound oil The bound oil response index (SBOI), the adsorbed oil enrichment index (AOI), and the anisotropy difference index of adsorbed and bound oils. Spatial distribution map of adsorbed oil and bound oil generated.

[0113] In this embodiment, the adsorbed oil and bound oil feature vectors Vao constructed in S6 are input into the complex dielectric differential inversion model to solve for the saturation of adsorbed oil and bound oil. The inversion results are shown in Table 6.

[0114] Table 6. Inversion results of adsorbed and bound oil from shale oil cores.

[0115] As shown in Table 6, the saturation of adsorbed and bound oil in this sample is 0.31, indicating that a certain proportion of oil phase remains in the shale core as adsorbed oil, bound oil, or residual oil in micropores after water flooding. Based on porosity... =0.086, from which the volume fractions of adsorbed oil and bound oil can be obtained. =0.0267.

[0116] The bound oil response index (SBOI) is 0.74, indicating that the sample exhibits a significant bound oil response in terms of terahertz absorption difference and dielectric loss difference. The adsorbed oil enrichment index (AOI) is 0.31, indicating that adsorbed and bound oil constitute a certain proportion in the pore system of this sample.

[0117] It should be noted that the residual water correction item in Table 6 is used to reduce the influence of residual water after displacement on the inversion results of adsorbed oil and bound oil, and is not considered as the main evaluation output of this invention; the core output of this invention is the saturation of adsorbed oil and bound oil, the bound oil response index, and the adsorbed oil enrichment index.

[0118] Furthermore, to verify the rationality of the adsorbed oil and bound oil saturation results obtained in S7 based on the terahertz complex permittivity differential inversion method, this embodiment further employs a weighing method to perform auxiliary verification on the same sample. The weighing method estimates the mass of adsorbed oil and bound oil removed during the extraction process by comparing the mass change between the residual oil state after displacement and the oil-free state after extraction.

[0119] The weighing method estimates the mass of adsorbed and bound oil by recording the mass changes of core samples in the residual oil state after displacement and in the oil-free state after extraction. This method reflects the content of oil phase remaining in the sample after waterflooding and that can be extracted and removed from the macroscopic mass change perspective, and can be used as an auxiliary verification method for terahertz inversion results.

[0120] To verify the rationality of the terahertz inversion results, a weighing method was used to verify the same sample. The mass of the residual oil state after displacement and the oil-free state after extraction were recorded separately, and the mass of the dried state and the saturated state of crude oil were also recorded as auxiliary references. The results are shown in Table 7.

[0121] Table 7 Sample mass under different conditions

[0122] It should be noted that the core mass difference verified by the weighing method of this invention is m. r -m e This refers to the mass difference between the residual oil state after displacement and the oil-free state after extraction. The mass of the dry state and the saturated state of crude oil can be used as auxiliary references, but are not necessary parameters for verifying the weighing of adsorbed and bound oil.

[0123] Based on the data in Table 7, the mass of adsorbed oil and bound oil can be calculated:

[0124] Substitute the data from this embodiment:

[0125] in, This indicates the mass of adsorbed and bound oil removed by extraction from the residual oil state after displacement. This mass includes adsorbed and bound oil adsorbed on the surface of organic matter, mineral surfaces, nanopores, and micropore throats, as well as some residual oil in micropores.

[0126] To facilitate comparison between different core samples, the adsorbed oil and bound oil content per unit core mass can be further calculated:

[0127] Substitute the data from this embodiment:

[0128] It is also possible to calculate the enrichment indices of adsorbed and bound oil relative to pore volume or porosity:

[0129] The above indicators can be used to compare the enrichment of adsorbed and bound oil in different core samples, different layers, or different measuring points.

[0130] The mass of adsorbed and bound oil obtained by the weighing method was 0.0289 g, and the saturation of adsorbed and bound oil obtained by terahertz inversion was [missing value]. =0.31. The two values ​​have different dimensions; the former is the result of mass change, while the latter is the equivalent saturation result obtained based on the terahertz complex permittivity differential response. Therefore, the values ​​do not need to be completely identical.

[0131] However, both indicate that adsorbed and bound oils still exist in the residual oil sample after displacement and can be extracted and removed. The results of the weighing method can be used to verify, calibrate, or correct the trend of the terahertz inversion model.

[0132] The difference lies in the fact that the weighing method reflects the overall mass change of the sample, while the terahertz method reflects the electromagnetic response under the combined influence of fluids, minerals, organic matter, and bedding structure within the core. Terahertz inversion results are also affected by the spatial distribution of oil phases, local bedding, pore structure, and the degree of organic matter enrichment. Therefore, in practical applications, the weighing method results can be used to calibrate the terahertz inversion model, but the weighing method is not a necessary step in the method of this invention.

[0133] To further verify the adsorbed and bound oil results obtained from terahertz inversion, nuclear magnetic resonance T2 spectroscopy tests can be performed on the same sample. Generally, shorter T2 components mainly correspond to adsorbed fluids, bound fluids, or microporous fluids, and therefore can serve as auxiliary verification criteria for the evaluation results of adsorbed and bound oils. Longer T2 components mainly correspond to mobile fluids or fluids in larger pores, and in this invention, they are only used as auxiliary references and not as the core evaluation object.

[0134] In this embodiment, the comparison between the terahertz inversion results and the NMR short T2 component-assisted results is shown in Table 8.

[0135] Table 8 Comparison of Terahertz Inversion Results and T2-Assisted NMR Results

[0136] As shown in Table 8, the results of adsorbed oil and bound oil obtained by terahertz inversion have a consistent trend with the NMR short T2 components, indicating that the method of the present invention can be used to identify adsorbed oil, bound oil or microporous residual oil that is still retained after water flooding in shale oil cores.

[0137] It should be noted that the terahertz inversion result is the equivalent saturation or response intensity obtained based on the complex dielectric difference and multipolarization response, while the NMR short T2 component is the bound fluid proportion obtained based on the relaxation time distribution. The two have different physical meanings, so the values ​​are not required to be completely equal.

[0138] To demonstrate that the method of the present invention can not only obtain the overall evaluation results of adsorbed and bound oil in the sample, but also reflect the heterogeneous distribution characteristics of adsorbed and bound oil inside the sample, three measuring points were selected on the core surface for single-point multi-polarization terahertz testing.

[0139] Among them, measuring point P1 is located near the organic matter enrichment zone, measuring point P2 is located in the stratification development zone, and measuring point P3 is located in the relatively rich mineral matrix area. The above measuring points represent different organic matter contents, stratification development degrees, and mineral matrix backgrounds, and can be used to verify the response ability of adsorbed oil and bound oil evaluation results to heterogeneity.

[0140] Table 9 Evaluation results of adsorbed and bound oils at different measuring points

[0141] As shown in Table 9, there are significant differences in the saturation of adsorbed and bound oil, the bound oil response index, and the comprehensive anisotropy difference index at different measuring points.

[0142] The P1 measuring point is located in the organic matter enrichment zone. Both SBOI and SBOI are high, indicating that areas rich in organic matter are more prone to the formation of adsorbed and bound oils.

[0143] The P2 measuring point is located in a region with well-developed stratification, although Lower than P1, but The higher value indicates that the adsorbed and bound oil in this region is more significantly controlled by the stratification direction, and may be directionally distributed along the stratification direction, organic matter bands, or interlayer nanopores.

[0144] The P3 measuring point is located in a mineral matrix enrichment area. SBOI and The values ​​are all low, indicating that the contribution of adsorbed and bound oils in this area is relatively weak.

[0145] The results show that the method of the present invention can reflect the heterogeneous occurrence characteristics of adsorbed and bound oil inside shale oil cores, and can further identify differences in organic matter-controlled, bedding-controlled, and mineral matrix-controlled types.

[0146] In a preferred embodiment, the above-described single-point test can be extended to a two-dimensional scanning test. By setting a two-dimensional scanning grid on the core surface or core slice, the results at each scanning point are obtained. , SBOI, AOI and Further, saturation distribution maps of adsorbed oil and bound oil, distribution maps of bound oil response index, and distribution maps of adsorbed oil anisotropy difference are generated.

[0147] Two-dimensional distribution maps can intuitively identify areas rich in adsorbed and bound oils, areas controlled by bedding direction, and areas with strong heterogeneity, providing data support for the evaluation of adsorbed oils in shale oil reservoirs, analysis of immovable oils, and selection of sweet spots.

[0148] Example 2 Shale oil core adsorption-bound oil evaluation device, including: A terahertz pulse emission module is used to generate broadband terahertz pulses. This module generates terahertz pulses and directs them into the effective testing area of ​​shale oil core samples. The terahertz pulses preferably cover a frequency range of 0.1–3.0 THz, with the data analysis band preferably ranging from 0.2–1.5 THz, to obtain the absorption, phase, and complex dielectric response of adsorbed and bound oils in the terahertz frequency band. The terahertz pulse emission module can employ a photoconductive antenna, a nonlinear crystal, a femtosecond laser-excited terahertz source, or other devices capable of generating terahertz pulses.

[0149] The terahertz pulse detection module is used to receive terahertz time-domain signals after passing through shale oil core samples, and to obtain sample signals in the residual oil state after displacement and the oil-free state after extraction. The terahertz pulse detection module can record the main peak amplitude, phase delay, and waveform broadening information of the terahertz time-domain waveform, providing a basis for subsequent calculations of the absorption coefficient, refractive index, and complex permittivity. The terahertz pulse detection module can employ photoconductive detection, electro-optic sampling detection, or other terahertz time-domain detection methods.

[0150] The time delay module is used to scan the terahertz time-domain waveform. It modifies the time delay between the terahertz pulse and the probe pulse to obtain the complete terahertz time-domain waveform. The time delay module uses the same scanning range and sampling interval in both the residual oil state test after displacement and the oil-free state test after extraction, improving the comparability of time-domain signals and frequency-domain parameters in the two states.

[0151] The polarization modulation module is used to adjust the direction of the terahertz electric field, making it parallel to and perpendicular to the shale bedding direction, respectively. The polarization modulation module includes a terahertz polarizer, a rotating stage, a polarization controller, or a combination thereof. Through the polarization modulation module, the time-domain signals of the residual oil state after displacement in the direction parallel to and perpendicular to the bedding direction, as well as the time-domain signals of the oil-free state after extraction in the same direction, can be obtained. The polarization modulation module is not only used to obtain the anisotropic response of the shale bedding structure, but also to construct anisotropic differential indices for adsorbed and bound oil, thereby identifying the dominant occurrence characteristics of adsorbed and bound oil along the bedding direction, organic matter bands, nanopores, or micropore throats.

[0152] The sample carrying and positioning reset module is used to carry shale oil core samples, ensuring that residual oil-bearing core samples after displacement and oil-free core samples after extraction are tested in the same test area using terahertz technology.

[0153] Furthermore, the sample carrying and positioning reset module includes one or more of the following: sample stage, positioning fixture, layer direction marking mechanism, coordinate calibration mechanism, and image recording unit.

[0154] The sample carrying and positioning reset module is used to carry shale oil core samples and ensure that the same core sample has the same or reproducible test position when tested in the residual oil state after displacement and the oil-free state after extraction.

[0155] After the residual oil state test following displacement is completed, the positioning and resetting module records the test area, spot position, bedding direction, and sample orientation of the core sample. During the de-oiled state test after extraction, the core sample is repositioned to the same test area based on the recorded information. The sample bearing and positioning and resetting module reduces differential errors caused by test position offsets, bedding direction deviations, or sample orientation changes, ensuring that the terahertz response difference between the residual oil state after displacement and the de-oiled state after extraction mainly originates from the removal of adsorbed and bound oil.

[0156] The core clamping and environmental control module is used to fix core samples during terahertz testing and provides temperature, confining pressure, pore pressure or sealing environment control as needed.

[0157] Preferably, the core holding module includes a core holder with a terahertz transmission window, which is made of high-density polyethylene, quartz, polytetrafluoroethylene or other low-loss terahertz materials.

[0158] Preferably, the environmental control module is used to simulate reservoir temperature and pressure conditions, enabling terahertz testing of residual oil-bearing core samples after displacement under near-formation conditions. For deoiled samples after extraction, testing can also be conducted at room temperature and pressure or in a dry nitrogen environment to obtain a stable deoiled matrix response.

[0159] The fluid displacement module is used to displace crude oil-saturated shale oil core samples to remove mobile free oil and form residual oil-bearing core samples after displacement. The fluid displacement module includes a displacement fluid storage tank, an injection pump, a pressure sensor, a flow controller, an outlet fluid collection unit, and an oil phase content monitoring unit.

[0160] In this embodiment, the displacing fluid can be simulated formation water, brine, or other displacing fluid that matches the experimental purpose. By controlling the displacing flow rate, confining pressure, pore pressure, and displacing time, the mobile free oil in the crude oil-saturated core sample is fully displaced.

[0161] When the oil phase content in the outlet liquid is lower than the set threshold, or the oil phase content in the outlet does not change significantly over multiple consecutive sampling periods, or the oil-water ratio in the outlet reaches a stable state, it is considered that the mobile free oil has been fully displaced, and at this time, the residual oil core sample after displacement is obtained.

[0162] It should be noted that the fluid displacement module in this invention is mainly used to construct the residual oil state after displacement required for the evaluation of adsorbed and bound oils, rather than to output the free oil saturation or mobile oil index.

[0163] The solvent extraction module is used to extract organic solvents from residual oil-bearing core samples after displacement to form de-oiled core samples.

[0164] Furthermore, the solvent extraction module includes one or more of the following: extraction container, solvent storage tank, circulation pump, temperature control unit, extractant collection unit, extractant oil phase monitoring unit, and sample drying unit.

[0165] Furthermore, the solvent extraction module also includes an extraction endpoint determination unit, which is used to determine whether the extraction is complete based on the change in mass of two consecutive weighings, the oil phase content in the extract, the color change of the extract, or the change in the absorption coefficient at a selected terahertz frequency point.

[0166] The data acquisition and differential inversion processing module is used to calculate the absorption coefficient, refractive index and complex dielectric constant based on the terahertz time-domain signals of the residual oil-bearing core samples after displacement and the deoiled core samples after extraction. It outputs the evaluation results of adsorbed oil and bound oil based on the spectral difference between the residual oil-bearing core samples after displacement and the deoiled core samples after extraction.

[0167] Furthermore, the data acquisition and differential inversion processing module includes a time-domain signal acquisition unit, a Fourier transform unit, a spectral parameter calculation unit, a residual oil-de-oil differential spectrum calculation unit, a multi-polarization anisotropic differential calculation unit, and a complex dielectric differential inversion unit.

[0168] The data acquisition and differential inversion processing module is used to calculate the following parameters: Differential absorption spectra between the residual oil state after displacement and the oil-free state after extraction; The refractive index difference spectrum between the residual oil state after displacement and the oil-free state after extraction; The difference spectrum of the real part of the complex permittivity between the residual oil state after displacement and the oil-free state after extraction; The difference spectrum of the imaginary part of the complex permittivity between the residual oil state after displacement and the oil-free state after extraction; Anisotropic differential index of adsorbed and bound oil absorption; Anisotropy of the absorption differential spectra of adsorbed and bound oils; Anisotropy difference index of adsorbed oil and bound oil.

[0169] The shale oil core adsorption-bound oil evaluation device also includes a two-dimensional scanning module. This module drives the sample stage or terahertz spot to move two-dimensionally across the surface or cross-section of the shale oil core sample to obtain multi-polarization terahertz responses at multiple measurement points. The two-dimensional scanning module includes a two-dimensional displacement platform, a scanning controller, a coordinate recording unit, and a scanning path setting unit. It uses the same scanning range, scanning step size, and coordinate origin in both post-displacement residual oil testing and post-extraction oil removal testing.

[0170] The shale oil core adsorption and binding oil evaluation device also includes a result output module, which is used to output one or more of the following: adsorption and binding oil saturation, adsorption and binding oil volume fraction, binding oil response index, adsorption oil enrichment index, adsorption and binding oil anisotropy difference index, or adsorption and binding oil spatial distribution map.

[0171] In this embodiment, the specific working steps of the shale oil core adsorption and bound oil evaluation device are as follows: The first step is to obtain shale oil core samples, and complete the cutting, grinding, polishing, and drying processes, and mark the bedding direction. The processed shale oil core samples are then subjected to crude oil saturation treatment to obtain crude oil saturated core samples.

[0172] The second step involves using the built-in fluid displacement module of the device to displace the saturated crude oil core sample, removing the movable free oil inside the sample, and obtaining the residual oil core sample after displacement.

[0173] The third step involves placing the residual oil core sample after displacement into the sample support and positioning module; then activating the terahertz pulse emission module, terahertz pulse detection module, time delay module, and polarization modulation module to acquire terahertz time-domain signals in the direction parallel to and perpendicular to the bedding planes of the terahertz electric field, respectively.

[0174] The fourth step is to remove the residual oil-bearing core sample after displacement and send it to the solvent extraction module for organic solvent extraction to remove adsorbed oil, bound oil and residual oil in micropores, thus obtaining the oil-free core sample after extraction.

[0175] The fifth step involves accurately repositioning the extracted, de-oiled core sample to the original test area using the location markers, coordinate information, and image recording data stored in the sample carrying and positioning reset module. The polarization modulation optical path acquisition process is repeated to obtain the terahertz time-domain signals corresponding to the parallel and perpendicular bedding directions.

[0176] The sixth step involves the data acquisition and differential inversion processing module performing Fourier transforms on the two sets of time-domain signals to calculate the absorption coefficient, refractive index, extinction coefficient, and complex dielectric constant of the residual oil-state core samples after displacement and the oil-depleted core samples after extraction, respectively. Based on the difference in spectral parameters between the two types of samples, absorption difference spectrum, refractive index difference spectrum, real part difference spectrum of complex dielectric constant, imaginary part difference spectrum of complex dielectric constant, and multi-polarization anisotropy difference index are constructed and integrated to obtain the differential feature vectors of adsorbed oil and bound oil.

[0177] Step 7: The differential eigenvectors obtained in step 6 are used as inputs to the complex dielectric differential inversion model for quantitative solution. The final outputs are the saturation of adsorbed and bound oils, the volume fraction of adsorbed and bound oils, the response index of bound oils, the enrichment index of adsorbed oils, the anisotropic differential index of adsorbed and bound oils, and the spatial distribution results of adsorbed and bound oils.

[0178] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A method for evaluating adsorbed and bound oil in shale oil cores, characterized in that, The specific steps include: S1. Obtain shale oil core samples, preprocess the shale oil core samples, and identify and mark the bedding orientation of the shale oil core samples. S2. The same shale oil core sample is subjected to crude oil saturation treatment, and the crude oil saturated shale oil core sample is subjected to displacement treatment to remove the mobile free oil in the crude oil saturated shale oil core sample to obtain the residual oil core sample after displacement. S3. Organic solvent extraction is performed on the residual oil core sample after displacement to remove adsorbed oil, bound oil or residual oil in micropores from the residual oil core sample after displacement, so as to obtain the oil-free core sample after extraction. S4. Multi-polarization terahertz time-domain spectroscopy was performed on the residual oil core sample after displacement and the oil-depleted core sample after extraction to obtain the terahertz time-domain signals in the direction parallel to the bedding and perpendicular to the bedding. S5. Calculate the absorption coefficient, refractive index and complex dielectric constant of the residual oil core sample after displacement and the oil-free core sample after extraction under different polarization directions based on the terahertz time-domain signal obtained in S4. S6. Based on the differences in absorption coefficient, refractive index, complex dielectric constant, and multipolarization response between the residual oil core sample after displacement and the oil-free core sample after extraction, construct the differential feature vectors of adsorbed oil and bound oil. S7. Substitute the differential eigenvectors of adsorbed oil and bound oil obtained in S6 into the complex dielectric differential inversion model to establish the complex dielectric differential inversion model and output the evaluation results of adsorbed oil and bound oil.

2. The method for evaluating adsorbed and bound oil in shale oil cores according to claim 1, characterized in that: The differential characteristics of adsorbed and bound oils in S6 include absorption differential spectrum, refractive index differential spectrum, real part differential spectrum of complex dielectric constant, and imaginary part differential spectrum of complex dielectric constant. The expression for the absorption difference spectrum is: The expression for the refractive index difference spectrum is: The expression for the difference spectrum of the real part of the complex permittivity is as follows: The expression for the difference spectrum of the imaginary part of the complex permittivity is: In the formula, For frequency Differential absorption spectra of adsorbed and bound oils; The absorption coefficient of the residual oil-bearing core sample after displacement; The absorption coefficient of the oil-free core sample after extraction; It is a refractive index difference spectrum; The refractive index spectrum of the residual sample; The refractive index spectrum of the extracted sample; The difference spectrum of the real part of the complex permittivity; The difference spectrum of the imaginary part of the complex permittivity; The spectrum of the imaginary part of the dielectric constant of the residual sample; The spectrum of the imaginary part of the dielectric constant of the sample after extraction; The frequency of terahertz electromagnetic waves; This is the polarization angle.

3. The method for evaluating adsorbed and bound oil in shale oil cores according to claim 2, characterized in that: In S6, under multiple polarization conditions, the absorption differential spectra of adsorbed oil and bound oil in the direction parallel to the layering and perpendicular to the layering were constructed respectively. The differential absorption spectra of adsorbed and bound oils parallel to the stratification direction are expressed as follows. The differential absorption spectrum expressions for adsorbed and bound oils perpendicular to the stratification direction are as follows. In the formula, The absorption differential spectra of adsorbed and bound oils along the parallel stratification direction are shown. The absorption coefficient of the residual oil-bearing core sample after displacement along the parallel bedding direction; The absorption coefficient of the sample after extraction along the parallel stratification direction; The absorption differential spectra of adsorbed and bound oils perpendicular to the stratification direction are shown. The absorption coefficient of the residual oil-bearing core sample after displacement perpendicular to the bedding direction; The absorption coefficient of the sample after extraction perpendicular to the stratification direction.

4. The method for evaluating adsorbed and bound oil in shale oil cores according to claim 3, characterized in that: In S6, an anisotropy index for absorption differential spectra is constructed based on the absorption differential spectra of adsorbed and bound oils parallel to and perpendicular to the layering direction. The expression for the anisotropy index for absorption differential spectra is as follows: In the formula, As a protection constant, It is a positive number that approaches 0.

5. The method for evaluating adsorbed and bound oil in shale oil cores according to claim 1, characterized in that: The multi-polarization response difference in S6 includes the absorption anisotropy difference index, the expression of which is: In the formula, The anisotropy index of absorption of residual oil after displacement; This is an anisotropy index of absorption in the oil-free state after extraction.

6. The method for evaluating adsorbed and bound oil in shale oil cores according to claim 1, characterized in that, The expression for the complex permittivity differential inversion model in S7 is: In the formula, The equivalent complex dielectric differential response caused by adsorbed and bound oil; The equivalent complex permittivity of the residual oil state after displacement; It represents the equivalent complex permittivity of the oil-free state after extraction.

7. The method for evaluating adsorbed and bound oil in shale oil cores according to claim 6, characterized in that: In S7, the saturation of adsorbed and bound oils is determined by comparing the difference between the measured complex dielectric differential response and the model-predicted complex dielectric differential response. , The function expression is, In the formula, To find the minimum value of the optimized variable; The difference spectrum of the complex permittivity at the i-th frequency point is obtained by actual measurement. For the i-th frequency point, the model The calculated difference spectrum of the complex permittivity; N is the number of frequency points involved in the inversion; For the i-th frequency point participating in the inversion, is the weighting coefficient for the i-th frequency point.

8. The method for evaluating adsorbed and bound oil in shale oil cores according to claim 7, characterized in that: Considering the influence of residual water, the residual water saturation or residual water response correction term in the residual oil state after displacement is used as an auxiliary correction parameter in the inversion. The expression for the objective function is: In the formula, This is a correction term for the residual water saturation or residual water response in the residual oil state after displacement.

9. The method for evaluating adsorbed and bound oil in shale oil cores according to claim 1, characterized in that: The evaluation results of adsorbed and bound oils in S7 include the saturation of adsorbed and bound oils. Volume fraction of adsorbed oil and bound oil The bound oil response index (SBOI), the adsorbed oil enrichment index (AOI), and the anisotropy difference index of adsorbed and bound oils. Or one or more of the spatial distribution results of adsorbed oil and bound oil; The volume fraction expressions for adsorbed oil and bound oil are as follows: In the formula, Porosity of shale oil core samples; The expression for the SBOI (Self-Boarding Index) of the binding oil is: In the formula, The absorption difference spectrum of adsorbed oil and bound oil at the i-th frequency point; Let be the difference spectrum of the imaginary part of the complex permittivity at the i-th frequency point; and These are the weighting coefficients; The expression for the Adsorbed Oil Enrichment Index (AOI) is as follows. In the formula, As a protection constant, It is a positive number that approaches 0.

10. A shale oil core adsorption-bound oil evaluation device, used to perform the shale oil core adsorption-bound oil evaluation method as described in any one of claims 1-9, characterized in that, include: Terahertz pulse transmitting module, used to generate broadband terahertz pulses; Terahertz pulse detection module is used to receive terahertz time-domain signals after passing through shale oil core samples; The time delay module is used to scan terahertz time-domain waveforms; The polarization modulation module is used to adjust the direction of the terahertz electric field so that the direction of the terahertz electric field is parallel to the shale bedding direction and perpendicular to the shale bedding direction, respectively. The sample carrying and positioning reset module is used to carry shale oil core samples to ensure that the residual oil core samples after displacement and the oil-free core samples after extraction are tested in the same test area by terahertz. The fluid displacement module is used to displace crude oil saturated shale oil core samples to remove mobile free oil and form residual oil core samples after displacement. The solvent extraction module is used to extract organic solvents from residual oil-bearing core samples after displacement to form oil-free core samples. The data acquisition and differential inversion processing module is used to calculate the absorption coefficient, refractive index and complex dielectric constant based on the terahertz time-domain signals of the residual oil-bearing core samples after displacement and the deoiled core samples after extraction. It outputs the evaluation results of adsorbed oil and bound oil based on the spectral difference between the residual oil-bearing core samples after displacement and the deoiled core samples after extraction.

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