A method, system, and apparatus for preferential mobilization of a shale oil reservoir horizon containing mobile crude oil

Abstract

The application discloses a shale oil reservoir layer position containing movable crude oil optimization method, system and device, relates to the unconventional oil and gas resource exploration and development technical field, and the method comprises the following steps: collecting core samples of different layers of the interlayer type shale oil reservoir; optimizing the three-dimensional pore structure reconstruction of the natural core sample with the pore structure type and pore parameter being favorable to seepage, so as to realize quantitative evaluation of the pore structure; performing two-dimensional nuclear magnetic resonance experiment on the oil-containing core sample of each pore structure type, obtaining a two-dimensional relaxation spectrum distribution map, and extracting the oil content of crude oil in each component fluid; detecting the crude oil occurrence state in the oil-containing region of the core sample with the oil content being higher than a threshold value, so as to realize quantitative evaluation of the crude oil occurrence state; and further optimizing the layer position with the movable crude oil being higher than a preset value; the method is used for optimizing the well position and layer position with good development potential, and has practical application value for formulating the development plan of the interlayer type shale oil reservoir.

Description

Technical Field

[0001] This invention relates to the field of unconventional oil and gas resource exploration and development technology, specifically to a method, system, and apparatus for optimizing the stratigraphic position of shale oil reservoirs containing movable crude oil. Background Technology

[0002] Interbedded shale oil, as a transitional unconventional resource, forms under conditions of source rock and reservoir separation, exhibiting strong fluid mobility and good reservoir properties. These reservoirs consist of interbedded mudstone and shale with sandstone / tuff, and the reservoir space is multi-scale and highly heterogeneous. Shale oil exists in free, adsorbed, and dissolved states within nano- to micron-sized pores, resulting in complex and diverse pore and fracture structures and intricate hydrocarbon enrichment mechanisms. This leads to a significant gap between current actual shale oil production and its enormous resource reserves. Interbedded shale oil has become a research hotspot in recent years, but the quantitative coupling relationship between its pore-fracture structure and fluid mobility remains insufficiently understood.

[0003] For the study of the microstructure of porous media, the following three types of technical means are mainly used: (1) Qualitative characterization techniques, mainly including scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM), focused ion beam scanning electron microscopy (FIB-SEM), hydrogen ion polishing scanning electron microscopy and X-ray computed tomography (X-CT), etc.; This type of technique can intuitively reflect the morphological characteristics and spatial distribution of pores and fractures by performing high-resolution imaging on thin sections of rocks or sample surfaces, but it is usually difficult to obtain quantitative structural parameters such as pore connectivity and pore throat size relationship, and it is difficult to use it to accurately evaluate the reservoir permeability; (2) Quantitative characterization techniques, mainly including high pressure mercury intrusion, constant rate mercury intrusion, gas adsorption method and helium porosity determination, etc. These techniques analyze the intrusion, adsorption or displacement behavior of fluid in porous media, invert pore size distribution, pore volume and partial connectivity characteristics, and thus obtain statistical parameters of reservoir pore structure. However, these methods generally have the problems of being somewhat destructive to rock samples, the experimental results being easily affected by the integrity of the sample and experimental conditions, and the measurement error being relatively large. (3) Nuclear magnetic resonance technology, which can measure the relaxation characteristics of fluid in pores without significantly damaging the rock core, thereby inverting pore size distribution, porosity and fluid occurrence state.

[0004] However, for shale oil reservoirs, especially interlayered shale oil reservoirs, the complex sedimentary and diagenetic evolution processes, diverse lithological combinations, and highly heterogeneous distribution of pore types and scales significantly increase the difficulty of pore structure characterization. Current methods are usually only applicable to pores within a specific scale range, neglecting the systematic analysis of the synergistic effects of pores at different scales. This makes it difficult to achieve continuous characterization of the reservoir's multi-scale pore structure, resulting in inaccurate evaluation of the overall reservoir permeability space structure and making it impossible to determine the optimal interlayered shale oil reservoir layers containing movable crude oil. Summary of the Invention

[0005] To address the shortcomings of existing technologies in achieving continuous and systematic characterization of the multi-scale pore structure of reservoirs, which leads to inaccurate evaluation of the overall reservoir permeability space structure, this invention proposes a method, system, and apparatus for optimal selection of strata in shale oil reservoirs containing movable crude oil. By establishing quantitative detection of pore structure, connectivity, and fluid occurrence state at each level, this invention solves the problems existing in the prior art.

[0006] A method for selecting the stratigraphic position of a shale oil reservoir containing movable crude oil includes the following steps: Core samples were collected from different layers of interlayered shale oil reservoirs; Core samples were prepared into cast thin sections; scanning electron microscopy was used to stitch and scan the cast thin sections, simultaneously acquiring secondary electron images and backscattered electron images to obtain images with a resolution higher than a first preset value; the acquired images were imported into image analysis software, and image stitching and alignment, grayscale correction and filtering to remove noise, separation of pores and mineral skeleton based on grayscale histograms, and binarization processing to number and label each individual pore were performed to generate a pore binary image; pore structure parameters including pore throat coordination number, average pore size, homogeneity coefficient, and pore throat ratio were extracted from the pore binary image; and the pore structure type of interlayered shale oil reservoirs was classified according to the pore structure parameters. Core samples with fracture connectivity in pore structure higher than the second preset value after classification were selected, and the three-dimensional pore structure of the selected core samples was reconstructed at the nanoscale to extract the three-dimensional pore structure parameters. The multi-scale pore size distribution of the selected core samples was obtained based on low-temperature nitrogen adsorption and high-pressure mercury intrusion experiments, and the usable pore structure in the selected core samples was determined by combining the three-dimensional pore structure parameters. Two-dimensional nuclear magnetic resonance experiments were conducted on oil-bearing core samples of different pore structure types after classification to generate two-dimensional relaxation spectrum distribution maps. Based on the two-dimensional relaxation spectrum distribution maps, core samples with oil content higher than the threshold were selected and oil-bearing areas were identified. The occurrence state of crude oil in the oil-bearing areas was detected to determine the proportion of bound, semi-bound, and free crude oil, thereby obtaining a quantitative evaluation result of the proportion of movable crude oil under each pore structure type. Based on the quantitative evaluation results of the usable pore structure and the proportion of movable crude oil under each pore structure type in the core samples, the optimal layer containing movable crude oil in interlayered shale oil reservoirs was determined.

[0007] Furthermore, the method for obtaining the multi-scale pore size distribution of the selected core sample based on low-temperature nitrogen adsorption and high-pressure mercury intrusion porosimetry specifically includes the following steps: Core samples with pore structure and fracture connectivity higher than a second preset value were divided into two parallel samples. One sample underwent a low-temperature nitrogen adsorption experiment, and the other underwent a high-pressure mercury intrusion porosimetry experiment. The low-temperature nitrogen adsorption experiment included: crushing the core sample to the target particle size and then degassing it under vacuum to remove moisture and volatiles; measuring the adsorption-desorption isotherm at liquid nitrogen temperature using nitrogen as the adsorption medium; and calculating the micropore-mesopore size distribution in the pore size range of 2nm-50nm based on the adsorption-desorption isotherm. The high-pressure mercury intrusion porosimetry experiment included: drying the selected plunger rock sample to constant weight; using a fully automated mercury intrusion porosimetry instrument, injecting mercury into the rock sample under vacuum conditions, gradually increasing the pressure and recording the mercury injection volume corresponding to each pressure point; and converting the pressure into the pore throat radius according to the Washburn equation to obtain the mesopore-macropore size distribution with a pore size greater than 50nm. By splicing and coupling analysis of micropore-mesopore size distribution data obtained from low-temperature nitrogen adsorption experiments and mesopore-macropore size distribution data obtained from high-pressure mercury intrusion experiments, multi-scale pore size distribution curves from nanometer to micrometer scales were obtained.

[0008] Furthermore, the nanoscale three-dimensional pore structure of the selected core samples was reconstructed using focused ion beam scanning electron microscopy, specifically including the following steps: The surface of the core sample was ion polished and a gold or platinum conductive layer was sputtered and deposited on the sample surface. The sample with the conductive layer deposited was placed in the sample chamber of a focused ion beam scanning electron microscope (FIE) and subjected to high-energy GaN microscopy. + The sample is milled layer by layer by an ion beam; after each layer is milled, a secondary electron image or backscattered electron image of the cross section of that layer is immediately acquired using a scanning electron microscope. After multiple milling and imaging processes, a continuous sequence of two-dimensional pore images was obtained. Multiple two-dimensional pore images are superimposed to generate a three-dimensional stereomicroscope image, thereby establishing a three-dimensional digital model of the nanoscale pore structure.

[0009] Furthermore, the selected oil-bearing core samples with different pore structures were subjected to two-dimensional nuclear magnetic resonance experiments. Specifically, this involved using a Neomai MR Cores-XX high-precision benchtop nuclear magnetic resonance unconventional core analyzer at a magnetic resonance frequency of 20 MHz. By inverting the echo train measured in the core, a two-dimensional relaxation spectrum distribution map of T1-T2 was obtained, and the content of each component fluid was extracted.

[0010] Furthermore, the multi-scale pore size distribution obtained from the low-temperature nitrogen adsorption and high-pressure mercury intrusion experiments exhibits a bimodal structure.

[0011] Furthermore, the three-dimensional pore structure parameters include the radius distribution and three-dimensional connectivity parameters of the pores and the radius distribution and three-dimensional connectivity parameters of the throat.

[0012] Furthermore, the step of selecting core samples with oil content higher than the threshold based on the two-dimensional relaxation spectrum distribution map specifically includes the following steps: Based on the distribution range of different fluids in rocks shown in the two-dimensional relaxation spectrum distribution diagram, the oil content of crude oil in each component fluid is extracted; Based on the oil content of crude oil in each component fluid, core samples with oil content higher than a preset threshold are selected.

[0013] The present invention also includes a shale oil reservoir site selection system containing movable crude oil, comprising: The acquisition module is used to collect core samples from different layers of interlayered shale oil reservoirs; The classification module is used to prepare core samples into cast thin sections; to perform stitched scanning of the cast thin sections using a scanning electron microscope, simultaneously acquiring secondary electron images and backscattered electron images to obtain images with a resolution higher than a first preset value; to import the acquired images into image analysis software, and sequentially perform image stitching and alignment, grayscale correction and filtering to remove noise, separation of pores and mineral skeletons based on grayscale histograms, and binarization processing to number and label each individual pore, generating a pore binary image; to extract pore structure parameters including pore throat coordination number, average pore size, homogeneity coefficient, and pore throat ratio from the pore binary image; and to classify the pore structure type of interlayered shale oil reservoirs according to the pore structure parameters. The pore structure quantitative evaluation module is used to select core samples whose pore structure fracture connectivity is higher than the second preset value after classification, and to reconstruct the three-dimensional pore structure of the selected core samples at the nanoscale to extract the three-dimensional pore structure parameters. Based on low-temperature nitrogen adsorption and high-pressure mercury intrusion experiments, the multi-scale pore size distribution of the selected core samples is obtained, and combined with the three-dimensional pore structure parameters, the usable pore structure in the selected core samples is determined. The crude oil occurrence state quantitative evaluation module is used to select oil-bearing core samples of various pore structure types after classification for two-dimensional nuclear magnetic resonance experiments to generate two-dimensional relaxation spectrum distribution maps; based on the two-dimensional relaxation spectrum distribution maps, core samples with oil content higher than the threshold are selected and oil-bearing areas are determined; the crude oil occurrence state in the oil-bearing areas is detected to determine the proportion of bound, semi-bound, and free crude oil, thereby obtaining the quantitative evaluation results of the proportion of movable crude oil under each pore structure type; The optimization module is used to determine the optimal layer containing movable crude oil in interlayered shale oil reservoirs based on the quantitative evaluation results of the usable pore structure and the proportion of movable crude oil under each pore structure type in the core sample.

[0014] The present invention also includes a computer device for selecting the stratigraphic position of a shale oil reservoir containing movable crude oil, comprising: a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the method for selecting the stratigraphic position of a shale oil reservoir containing movable crude oil.

[0015] The present invention also includes a readable storage medium storing a computer program, the computer program including program instructions, which, when executed by a processor, are used to perform the steps of the method for selecting the stratigraphic position of the shale oil reservoir containing movable crude oil.

[0016] This invention provides a method for selecting the optimal stratigraphic position of shale oil reservoirs containing movable crude oil, which has the following beneficial effects: This invention systematically integrates multi-scale pore size distribution acquisition, three-dimensional pore structure reconstruction, two-dimensional nuclear magnetic resonance fluid quantitative analysis, and crude oil occurrence state detection. For the first time, it achieves the continuous characterization of multi-scale pore structure from nanometer to centimeter scale and the quantitative evaluation of fluid mobility, overcoming the shortcomings of single-scale characterization methods that cannot fully depict the strong heterogeneity of interlayered shale oil reservoirs. At the same time, by establishing a progressive quantitative evaluation chain of "pore structure - oil content - occurrence state - mobility", it can accurately identify the favorable occurrence pore size domains and connectivity conditions of mobile crude oil from the microscopic mechanism, thereby effectively selecting layers with high mobile oil content. This provides a scientific and quantifiable decision-making basis for the formulation of development plans for interlayered shale oil reservoirs, significantly improving the accuracy of reservoir evaluation and the reliability of sweet spot prediction. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of core thin section scanning in an embodiment of the present invention; Figure 1 (a) to (f) are schematic diagrams of large-field-of-view maps scanning of cast thin sections of samples with different structural types; Figure 2 This is a schematic diagram of the core pore size distribution of a sandwich-type oil reservoir in an embodiment of the present invention; Figure 2(a) to (d) in the figure represent the schematic diagrams of the pore size distribution of cores from different strata with natural fractures. Figure 3 This is a schematic diagram of a three-dimensional reconstructed pore network model in an embodiment of the present invention; Figure 3 (a) to (d) in the figure represent schematic diagrams of the three-dimensional pore network model obtained by FIB scanning of cores from different strata with natural fractures. Figure 4 This is a schematic diagram of the pore radius distribution curve in an embodiment of the present invention; Figure 4 (a) to (d) in the figure represent schematic diagrams of the pore radius distribution detection results obtained by FIB scanning of cores from different strata with natural fractures; Figure 5 This is a schematic diagram of the throat radius distribution curve in an embodiment of the present invention; Figure 5 (a) to (d) in the figure represent schematic diagrams of throat radius distribution detection results obtained by FIB scanning of cores from different strata with natural fractures; Figure 6 This is a histogram of coordination number distribution in an embodiment of the present invention; Figure 6 In the figure, (a) to (d) represent histograms of pore throat coordination number distribution obtained by FIB scanning of cores from different stratigraphic levels with natural fractures. Figure 7 This is a schematic diagram of the two-dimensional nuclear magnetic resonance T1-T2 spectrum of the core fluid in an embodiment of the present invention; Figure 7 In the figure, (a) and (b) represent the state of oil and water in the core pores of the sandstone and shale with foliation fractures in the upper part of the reservoir, respectively; Figure 8 This is a schematic diagram illustrating the oil and water occurrence state in the pores of a shale core containing foliation fractures in the middle part of an oil reservoir, as described in an embodiment of the present invention. Figure 9 This is a schematic diagram of the two-dimensional nuclear magnetic resonance T1-T2 spectrum of the core fluid in an embodiment of the present invention; Figure 9 In the figure, (a) and (b) represent the state of oil and water in the pores of shale cores with and without foliation fractures in the lower part of the reservoir, respectively; Figure 10 This is a local true-color transmission fluorescence superimposed image of a rock thin section in an embodiment of the present invention; Figure 10 In the figure, (a) and (b) are schematic diagrams of fluorescence scanning images of thin sections of shale core castings with foliation fractures; Figure 11 This is a statistical histogram of laser confocal detection results of crude oil distribution in natural rock cores in this embodiment of the invention; Figure 11 (a) and (b) in the figure represent the proportions of crude oil in different occurrence states in shale cores with foliation fractures, respectively. Figure 12This is a schematic diagram of the process for optimizing the stratigraphic position of an interlayered shale oil reservoir containing movable crude oil in an embodiment of the present invention. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0019] This invention proposes a method for optimizing the stratigraphic position of interlayered shale oil reservoirs containing movable crude oil. This method optimizes the optimal stratigraphic position containing movable crude oil in interlayered shale oil reservoirs by establishing a quantitative relationship between pore structure, connectivity and fluid occurrence state step by step.

[0020] like Figure 12 As shown, the method specifically includes the following steps: S1. Shale oil reservoir classification based on large field-of-view cast thin section scanning.

[0021] Core samples were prepared into cast thin sections and subjected to large-area, high-resolution scanning under a scanning electron microscope (e.g., using MAPS technology). This yielded stitched images of the thin sections in secondary electron microscopy (SE2) and backscattered electron microscopy (BSE) modes, and key pore structure parameters were extracted using image analysis. This yielded indicators such as porosity (thin section porosity), average pore size, pore-throat coordination number, and pore-throat ratio. These parameters are used to qualitatively and quantitatively assess the development and connectivity characteristics of pores in different lithofacies. For example, the average coordination number directly characterizes the number of throats connected to a single pore and is an important indicator for evaluating the connectivity of the pore-throat network; the pore-throat ratio reflects the relative relationship between pore and throat sizes and indicates the resistance to fluid flow through the throat. Through thin section scanning, the reservoir was initially classified into different pore structure types (e.g., matrix-pore-dominant, pore-fracture composite, and fracture-dominant). Cores from the pore-fracture composite and fracture-dominant types, which are conducive to seepage, were selected. Figure 1 As shown in (b), (c), (d), (f) and Table 1, core samples with seepage advantages are selected for pore size distribution detection of samples of different structural types in step S2; representative selection of sample cores for FIB-SEM three-dimensional reconstruction in step S3 is provided; and initial core physical property parameters are provided for structural interpretation of mobility differences in steps S4 and S5.

[0022] Table 1. Quantitative Analysis Results of Cast Thin Sheets

[0023] S2. Full-scale pore size distribution analysis based on low-temperature nitrogen adsorption and high-pressure mercury intrusion: Rock samples were subjected to low-temperature nitrogen adsorption (liquid nitrogen at 77 K, using nitrogen as the adsorption medium) and high-pressure mercury intrusion experiments. First, low-temperature nitrogen adsorption was used to obtain the structural characteristics of micropores and mesopores with pore sizes ranging from 2 nm to 50 nm. Before testing, the samples were degassed under vacuum at 110 °C to remove moisture and volatiles. Then, adsorption-desorption isotherms were measured using a surface area and pore size analyzer, and the micropore specific surface area, pore volume, and pore size distribution were calculated. Subsequently, high-pressure mercury intrusion experiments were conducted, with pressures reaching up to 200 MPa, allowing mercury to penetrate mesopores and macropores with pore sizes greater than 50 nm. Based on the relationship between mercury intrusion volume and pressure during mercury intrusion, the radius distribution of larger pore throats and the connectivity threshold pressure were inverted. Combining the nitrogen adsorption curves with the mercury intrusion curves yielded multi-scale pore size distribution parameters from the nanometer to the micrometer scale. For example, by coupling the two methods, a bimodal structure (nanoscale micropore peaks and hundred-nanometer-micrometer scale macropore peaks) in the reservoir pore size distribution can be identified, and the differences in the proportion of pores of different scales in the total pore volume can be determined. Figure 2 As shown.

[0024] S3. Reconstruction of nanoscale three-dimensional pore structures based on focused ion beam scanning electron microscopy (FIB-SEM).

[0025] Small cubic samples (approximately 1 mm³) were extracted from typical rock samples, and their microstructure was reconstructed in three dimensions using FIB-SEM. Specifically, the sample surface was first ion-polished and coated with a conductive layer, and then high-energy... Ion beam milling of the sample layer by layer, with SEM images acquired after each layer is removed. After hundreds of cycles, a continuous sequence of two-dimensional pore slices is obtained. This image sequence is then imported into 3D reconstruction software (such as Avizo) for image preprocessing (tilt correction, median filtering, FFT denoising, etc.) and threshold segmentation to reconstruct a 3D digital model of the rock mineral framework and pores. This model allows for direct observation of the connectivity of nanoscale pores in three-dimensional space, extracting parameters such as connected pore volume, specific surface area, and 3D connectivity. FIB-SEM 3D reconstruction overcomes the limitation of thin-section scanning, which only allows for two-dimensional observation, enabling in-depth analysis of the spatial distribution and interconnection of nanopores and microcracks within the matrix, providing direct evidence for assessing the connectivity of the pore network. Figure 3 , Figure 4 , Figure 5 , Figure 6 As shown in Table 2, this step performs a three-dimensional authenticity verification of the connectivity judgment obtained based on the two-dimensional thin slice in step S1, and serves as the "authenticity verification" of the pore structure.

[0026] Table 2. Quantitative analysis results of core micro / nanoscale FIB-SEM scanning.

[0027] S4. Quantitative analysis of pore fluid mobility based on two-dimensional nuclear magnetic resonance experiments.

[0028] Using the same samples as in the previous step, pore fluid distribution was determined using the Numaimai MR Cores-XX high-precision benchtop nuclear magnetic resonance (NMR) unconventional core analyzer. Low-field two-dimensional NMR utilizes the concept of 2DNMR in NMR spectroscopy. By inverting the echo train from the core measurements, a T1-T2 two-dimensional relaxation spectrum distribution map is obtained, which can display the distribution range of different fluids in the rock and extract the content of each component fluid. Based on the oil content of crude oil in each component fluid, core samples with oil content higher than a preset threshold were selected. True-color fluorescence scanning was used to determine the oil-bearing region of the selected core samples. Laser confocal microscopy was used to detect the crude oil occurrence state in the oil-bearing region, determining the proportions of bound, semi-bound, and free crude oil to achieve a quantitative evaluation of the crude oil occurrence state.

[0029] S5. Based on the quantitative evaluation results of the pore structure and crude oil occurrence state of the core samples, the layers in the interlayered shale oil reservoir with movable crude oil exceeding the preset value are selected.

[0030] Experimental conditions: 25℃, magnetic resonance frequency 20MHz.

[0031] Experimental standard: SY / T 6490-2014 Laboratory measurement specifications for nuclear magnetic resonance parameters of rock samples.

[0032] Experimental procedure: 1) Set the corresponding two-dimensional NMR acquisition parameters according to the sample conditions; 2) Place the original sample into the NMR instrument and verify whether the parameters are correct before acquiring the NMR signal; 3) Use the accompanying software to invert the acquisition results; 4) Divide the region and interpret the quantitatively based on the inversion results.

[0033] Two-dimensional NMR can further distinguish the influence of pore structure on fluid behavior, enabling quantitative assessment of reservoir movable oil saturation (generally, crude oil in medium and large pores is considered movable crude oil). Figure 7 , Figure 8 , Figure 9 As shown in Table 3.

[0034] Table 3 shows the crude oil distribution in centimeter-sized core samples and the results of two-dimensional NMR analysis.

[0035] S5. Quantification of crude oil occurrence state based on laser scanning confocal microscopy: Core samples were prepared into polished thin sections, and three-dimensional fluorescence imaging of oil-bearing pores was obtained using laser confocal microscopy to visually observe the occurrence and distribution of different crude oil components within the pores. Oil-bearing natural cores were taken, and sample preparation was performed according to the following process: slicing → gelling → polishing → gluing → thin section preparation → labeling. Soaking in organic solvents was prohibited before slide preparation. Slide preparation required that oil-bearing rock samples be prepared under frozen conditions during drilling and slicing. True-color fluorescence mapping was used to locate the oil-bearing areas in the core, and then laser confocal microscopy was performed on these areas to obtain a quantitative description of the crude oil distribution. Figure 10 As shown; the conditions for the laser confocal analyzer are: the instrument model is LEICA SP8, and it needs to be warmed up for 0.5 to 1 hour after powering on; the laser intensity and the selection of the grating are very important; the number of image scans should be determined comprehensively based on the amount of data and the image effect, generally 7 to 10 times is sufficient; when detecting micropores and organic matter, a larger magnification is generally selected for the objective lens, such as 10, 20 and 50 times.

[0036] During sample preparation, the sample is impregnated with fluorescent dye or utilizes the inherent fluorescence of the oil to distinguish between light components (such as saturated hydrocarbons and aromatic hydrocarbons) and heavy components (such as gums and asphaltenes). By adjusting the laser excitation wavelength and detection channel, the fluorescence signals of different components are displayed in different colors in the confocal image. Quantitative analysis of the acquired three-dimensional fluorescence images allows for the extraction of fluorescence intensity values ​​of crude oil in different occurrence states within typical regions, thereby calculating the proportion (percentage) of crude oil in different occurrence states, such as... Figure 11 As shown in Table 4, this provides micro-level support for the final reservoir selection and development potential evaluation.

[0037] Table 4. Results of laser confocal analysis of crude oil distribution.

[0038] This method allows for the qualitative classification of pore structure, the quantitative parameters of connectivity, and the correlation between pore size distribution characteristics and the occurrence morphology and mobile oil saturation of crude oil, enabling a systematic evaluation at multiple scales.

[0039] The method of this invention integrates multiple experimental techniques to achieve a systematic evaluation of the pore structure characteristics, crude oil occurrence state, and mobility of interlayered shale oil reservoirs. Its technical effectiveness is significantly superior to any previous single experimental method or simple combination thereof, specifically: (1) Through thin section scanning and FIB-SEM reconstruction, this method, for the first time, simultaneously quantifies the connectivity structure of the pore-fracture network in interlayered shale oil reservoirs at both the macroscopic thin section scale and the microscopic nanoscale. Figure 1 , Figure 4 , Figure 5 , Figure 6As shown in Tables 1 and 2, the shale reservoirs in the study area can be divided into three types. The matrix-organic pore-dominated type has reservoir space highly concentrated in organic matter pores, with numerous isolated or terminal pores exhibiting extremely poor connectivity. It possesses a huge specific surface area and adsorption capacity, but the matrix permeability is extremely low, and its natural seepage capacity is poor (e.g., ...). Figure 1 (a) and (e) in the text). Fracture-pore composite reservoirs are mainly distributed in foliation fractures or natural fractures, with a small amount of pores in the matrix, mainly intergranular pores, edge pores, and organic pores. They have a moderate coordination number and exhibit a composite characteristic of fractures providing core flow channels and matrix pores supplementing the reservoir space. Figure 1 (b), (c), and (d)). In fracture-dominated reservoirs, almost all the storage space is located within foliation fractures or natural fractures, with very little matrix porosity. This type has an average pore size of 39.00 µm, a coordination number of 1.76, and a pore-throat ratio as low as 1.99, forming a highly interconnected microfracture seepage system. Figure 1 (f) The excellent connectivity of the pore-fracture network makes it a key channel for obtaining oil and gas from the surrounding matrix, representing a potential high-yield sweet spot. Experimental results show that there are significant differences in connectivity among different lithologies and pore types: in sandy interlayers, although macroscopic porosity is high, seepage is still limited if the coordination number is low, while in argillaceous matrix, even with low total porosity, a well-developed interconnected fracture network can provide efficient seepage channels. This invention characterizes the quality of the interconnected network using parameters such as coordination number and pore-throat ratio, revealing that porosity is not a sufficient condition to determine mobility; the degree of interconnection of the pore-fracture network is the key controlling factor. In contrast, traditional schemes rely solely on porosity or permeability indices, failing to identify this difference in interconnected structure.

[0040] (2) This method combines the multi-peak pore size distribution obtained by nitrogen adsorption and mercury injection with the crude oil occurrence characteristics, and finds that the pore size distribution in the study area generally exhibits a "bimodal" structure. Figure 2The shale matrix is ​​dominated by 5nm micropores, while the sandstone interlayers have a peak pore size of around 100nm, indicating larger pores. Sandy interlayers not only expand reservoir space but also reduce the pore-throat ratio and improve connectivity, significantly increasing the movable oil volume fraction. This microscopic mechanism explains why interlayered shale oil layers have better macroscopic mobility than pure shale layers, providing a structural basis for improving shale oil production capacity. Previous methods lacked this multi-scale pore size correlation analysis, making it difficult to quantitatively explain the differences in movable oil from a pore size perspective. The pore size distribution is bimodal in both shale layers, with peak values ​​around 5nm and 50-60nm, indicating a higher proportion of small pores. In sandstone layers, peak values ​​are around 5nm and 100nm, indicating a higher proportion of large pores, suggesting that under certain conditions, shale oil has a higher movable proportion. The pore size distribution in sandstone interlayers contributes significantly more pore volume in the >50nm range, with the second peak shifting towards around 100nm. This indicates that the thin sandstone layers in interlayered reservoirs not only serve as reservoir space themselves, but more importantly, they provide a higher proportion of movable oil-bearing large-pore areas. The superiority of layered shale oil lies not only in the increased reservoir space, but also in its optimized pore structure, significantly increasing the volume ratio of the easily flowable "movable pore domain" throughout the reservoir. This is the root cause of the superior macroscopic mobility of interlayered reservoirs compared to pure shale in terms of microscopic physical properties.

[0041] (3) By combining two-dimensional nuclear magnetic resonance and laser confocal microscopy experiments, this invention achieves quantitative characterization of the occurrence morphology of oil products (e.g., Figure 7 , Figure 8 , Figure 9 , Figure 11 (As shown in Tables 3 and 4). Quantitative analysis using laser confocal fluorescence revealed a higher proportion of free-state crude oil (over 50%) in fracture-dominated reservoirs, indicating that high connectivity enhances the proportion of mobile oil. Conversely, poorly connected sections are dominated by adsorbed and film-like oils, exhibiting low mobility and severe heavy oil retention. These innovative findings demonstrate that this method can quantitatively reveal the law governing how pore and fracture structure types determine the microscopic morphology of oil: fracture-type sections are predominantly composed of "free-to-semi-bound" oils, composite reservoirs exhibit a coexistence of "adsorbed-to-free" oils, and matrix-type reservoirs primarily consist of "adsorbed-to-film" oils. This structure-fluid coupling relationship is difficult to obtain using previous single-technical methods.

[0042] The proportion of large and medium-pore oil is a key indicator for assessing the mobility potential of crude oil (Table 3). This indicator varies significantly among different samples. Although the total oil yield of sample #1 is as high as 11.449 μL / g, its proportion of large and medium-pore oil is only 28.95%, indicating a complex reservoir pore structure with pores of multiple scales, resulting in large reserves but difficulty in extraction. While large pores provide some movable oil, over 70% of the crude oil is trapped in micropores, significantly increasing the difficulty of economically effective extraction. Well #2 (2319.22m depth) is a typical high-reservoir, low-production reservoir with a total oil yield of 9.117 μL / g, but its proportion of large and medium-pore oil is only 29.06%. Good reservoir properties do not equate to good crude oil mobility; high porosity mainly stems from an extremely well-developed micropore system. These micropores provide vast reservoir spaces, but due to limited pore-throat connectivity, the permeability is relatively low compared to conventional reservoirs, and the crude oil mobility is extremely poor, meaning that the abundant crude oil is mainly confined within nanoscale micropores. Fracture-dominated or well-connected samples generally have a higher proportion of large and medium-pore oil.

[0043] The core contradiction in mobility differences lies in the physical constraint of pore and fracture structure on crude oil. Well-connected strata often correspond to a higher proportion of "free oil," which, along with "fracture-type" structures and the "proportion of large and medium-sized pores," points to pore and fracture structure as the primary controlling factor in mobility differences.

[0044] (4) The comprehensive evaluation results obtained using this method clearly identify fracture network reservoirs with high coordination numbers and low pore-throat ratios as high-quality sweet spot sections, characterized by high mobile oil saturation and abundant light hydrocarbons, thus possessing greater production potential. In contrast, matrix-dominated sections, while having large resource reserves, mostly contain oil in a bound state, making development difficult and requiring auxiliary stimulation measures. These conclusions provide a scientific basis for the classification and development of shale oil reservoirs, demonstrating the significant improvement in evaluation accuracy and applicability of the method described in this invention compared to traditional analysis.

[0045] The advantages of this invention lie in its organic integration of geological, rock physics, and hydrocarbon chemistry testing, enabling a comprehensive and systematic evaluation of the characteristics and mobility of interlayered shale oil reservoirs, achieving a synergistic effect. The results of each experiment corroborate each other, improving the reliability of the analytical conclusions. Compared to conventional single-test methods, this invention significantly improves evaluation accuracy and depth, but also correspondingly increases implementation costs and technical barriers. These are directions to consider for further optimization. Overall, the innovation and systematic nature of this method far surpass existing technologies, providing a new approach to unconventional reservoir evaluation, and its advantages significantly outweigh any potential shortcomings.

[0046] Based on the obtained three-dimensional pore network model, computer numerical simulation (such as direct flow simulation or the Lattice-Boltzmann method) is introduced to simulate and calculate the flow of crude oil in multi-scale pores. Numerical experiments can estimate macroscopic flow parameters such as equivalent permeability and initiation pressure gradient, and verify the accuracy of the relationship between movable oil saturation and pore structure measured in this invention. This improvement is expected to link static structural characterization with dynamic flow behavior, further enhancing the predictive ability of reservoir recoverability. This invention can also be integrated with other advanced testing methods, such as field emission SEM to obtain higher resolution pore images, helium ion microscopy to characterize organic nanopores, or NMR imaging and μ-CT to achieve four-dimensional monitoring of in-situ saturation-displacement processes. The introduction of these related technologies will enrich the characterization methods of this approach, making the evaluation results more comprehensive and accurate.

[0047] Based on the same inventive concept, this invention also proposes a shale oil reservoir stratigraphic selection system containing movable crude oil, comprising: The acquisition module is used to collect core samples from different layers of interlayered shale oil reservoirs.

[0048] The classification module is used to prepare core samples into cast thin sections; to perform stitched scanning of the cast thin sections using a scanning electron microscope, simultaneously acquiring secondary electron images and backscattered electron images to obtain images with a resolution higher than a first preset value; to import the acquired images into image analysis software, and sequentially perform image stitching and alignment, grayscale correction and filtering to remove noise, separation of pores from the mineral skeleton based on grayscale histograms, and binarization processing to number and label each individual pore, generating a pore binary image; to extract pore structure parameters including pore throat coordination number, average pore diameter, homogeneity coefficient, and pore throat ratio from the pore binary image; and to classify the pore structure type of interlayered shale oil reservoirs according to the pore structure parameters.

[0049] The pore structure quantitative evaluation module is used to select core samples whose pore structure fracture connectivity is higher than the second preset value after classification, and to reconstruct the three-dimensional pore structure of the selected core samples at the nanoscale to extract the three-dimensional pore structure parameters. Based on low-temperature nitrogen adsorption and high-pressure mercury intrusion experiments, the multi-scale pore size distribution of the selected core samples is obtained, and combined with the three-dimensional pore structure parameters, the usable pore structure in the selected core samples is determined.

[0050] The crude oil occurrence state quantitative evaluation module is used to select oil-bearing core samples of various pore structure types after classification for two-dimensional nuclear magnetic resonance experiments to generate two-dimensional relaxation spectrum distribution maps; based on the two-dimensional relaxation spectrum distribution maps, core samples with oil content higher than the threshold are selected and oil-bearing areas are determined; the crude oil occurrence state in the oil-bearing areas is detected to determine the proportion of bound, semi-bound, and free crude oil, thereby obtaining quantitative evaluation results of the proportion of movable crude oil under each pore structure type.

[0051] The optimization module is used to determine the optimal layer containing movable crude oil in interlayered shale oil reservoirs based on the quantitative evaluation results of the usable pore structure and the proportion of movable crude oil under each pore structure type in the core sample.

[0052] The present invention also includes a computer device for selecting the stratigraphic position of a shale oil reservoir containing movable crude oil, comprising: a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the method for selecting the stratigraphic position of a shale oil reservoir containing movable crude oil.

[0053] The present invention also includes a readable storage medium storing a computer program, the computer program including program instructions, which, when executed by a processor, are used to perform the steps of a method for selecting the stratigraphic position of a shale oil reservoir containing movable crude oil.

[0054] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for optimal selection of shale oil reservoir stratigraphic positions containing movable crude oil, characterized in that, Includes the following steps: Core samples were collected from different layers of interbedded shale oil reservoirs; Core samples were prepared into cast thin sections; the cast thin sections were then scanned using a scanning electron microscope, simultaneously acquiring secondary electron images and backscattered electron images to obtain images with a resolution higher than a first preset value; the acquired images were imported into image analysis software, and sequentially image stitching and alignment, grayscale correction and filtering to remove noise, separation of pores from the mineral skeleton based on grayscale histograms, and binarization processing to number and label each individual pore, generating a pore binary image; pore structure parameters, including pore throat coordination number, average pore size, homogeneity coefficient, and pore throat ratio, were extracted from the pore binary image; and the pore structure type of interlayered shale oil reservoirs was classified according to the pore structure parameters. Core samples with pore structure and fracture connectivity higher than the second preset value were selected after classification, and the three-dimensional pore structure of the selected core samples was reconstructed at the nanoscale to extract the three-dimensional pore structure parameters. The multi-scale pore size distribution of the selected core samples was obtained based on low-temperature nitrogen adsorption and high-pressure mercury intrusion experiments, and the usable pore structure in the selected core samples was determined by combining the three-dimensional pore structure parameters. Two-dimensional nuclear magnetic resonance experiments were conducted on oil-bearing core samples of different pore structure types after classification to generate two-dimensional relaxation spectrum distribution maps. Based on the two-dimensional relaxation spectrum distribution map, core samples with oil content higher than the threshold were selected and oil-bearing areas were identified. The occurrence state of crude oil in the oil-bearing areas was detected to determine the proportion of bound, semi-bound, and free crude oil, thereby obtaining a quantitative evaluation result of the proportion of movable crude oil under each pore structure type. Based on the quantitative evaluation results of the usable pore structure and the proportion of movable crude oil under each pore structure type in the core sample, the optimal layer containing movable crude oil in the interlayered shale oil reservoir was determined. The method for obtaining the multi-scale pore size distribution of selected core samples based on low-temperature nitrogen adsorption and high-pressure mercury intrusion porosimetry specifically includes the following steps: Selected core samples with pore structure and fracture connectivity higher than a second preset value after classification are divided into two parallel samples; one sample undergoes a low-temperature nitrogen adsorption experiment, and the other undergoes a high-pressure mercury intrusion porosimetry experiment. The low-temperature nitrogen adsorption experiment includes: pulverizing the core sample to the target particle size, followed by vacuum degassing to remove moisture and volatiles; measuring the adsorption-desorption isotherm at liquid nitrogen temperature using nitrogen as the adsorption medium; and calculating the micropore-mesopore size distribution in the 2nm-50nm range based on the adsorption-desorption isotherm. The high-pressure mercury intrusion porosimetry experiment... The mercury intrusion porosimetry (MIP) experiment included: drying the selected plunger rock sample to constant weight; using a fully automated MIP apparatus, injecting mercury into the rock sample under vacuum conditions, gradually increasing the pressure and recording the mercury injection volume corresponding to each pressure point; converting the pressure into pore throat radius according to the Washburn equation to obtain a mesopore-macropore pore size distribution with a pore size greater than 50 nm; performing data splicing and coupling analysis on the micropore-mesopore pore size distribution data obtained from the low-temperature nitrogen adsorption experiment and the mesopore-macropore pore size distribution data obtained from the high-pressure MIP experiment to obtain a multi-scale pore size distribution curve from the nanometer to the micrometer scale; the multi-scale pore size distribution obtained from the low-temperature nitrogen adsorption and high-pressure MIP experiments exhibited a bimodal structure. The nanoscale three-dimensional pore structure of selected core samples was reconstructed using focused ion beam scanning electron microscopy (FIE). The specific steps included: ion polishing the sample surface and sputtering a gold or platinum conductive layer onto the sample surface; placing the sample with the conductive layer in the FIE sample chamber and using high-energy... The sample is milled layer by layer by an ion beam. After each layer is milled, a secondary electron image or backscattered electron image of the cross section of that layer is immediately acquired using a scanning electron microscope. After multiple milling and imaging operations, a sequence of continuously arranged two-dimensional pore images is obtained. Multiple two-dimensional pore images are superimposed to generate a three-dimensional stereomicroscope image, thereby establishing a three-dimensional digital model of the nanoscale pore structure.

2. The method for selecting the stratigraphic position of a shale oil reservoir containing movable crude oil according to claim 1, characterized in that, The selected oil-bearing core samples with different pore structures were subjected to two-dimensional nuclear magnetic resonance experiments. Specifically, the experiment involved using an unconventional nuclear magnetic resonance core analyzer at a magnetic resonance frequency of 20 MHz to invert the echo train measured in the core, obtain the T1-T2 two-dimensional relaxation spectrum distribution map, and extract the content of each component fluid.

3. The method for selecting the stratigraphic position of a shale oil reservoir containing movable crude oil according to claim 1, characterized in that, The three-dimensional pore structure parameters include the radius distribution and three-dimensional connectivity parameters of the pores and the radius distribution and three-dimensional connectivity parameters of the throat.

4. The method for selecting the stratigraphic position of a shale oil reservoir containing movable crude oil according to claim 1, characterized in that, The selection of core samples with oil content higher than the threshold based on the two-dimensional relaxation spectrum distribution map specifically includes the following steps: Based on the distribution range of different fluids in rocks shown in the two-dimensional relaxation spectrum distribution diagram, the oil content of crude oil in each component fluid is extracted; Based on the oil content of crude oil in each component fluid, core samples with oil content higher than a preset threshold are selected.

5. A shale oil reservoir stratigraphic selection system based on the method for selecting stratigraphic positions of shale oil reservoirs containing movable crude oil as described in claim 1, characterized in that, include: The acquisition module is used to collect core samples from different layers of interlayered shale oil reservoirs; The classification module is used to prepare core samples into cast thin sections; to perform stitched scanning of the cast thin sections using a scanning electron microscope, simultaneously acquiring secondary electron images and backscattered electron images to obtain images with a resolution higher than a first preset value; to import the acquired images into image analysis software, and sequentially perform image stitching and alignment, grayscale correction and filtering to remove noise, separation of pores and mineral skeletons based on grayscale histograms, and binarization processing to number and label each individual pore, generating a pore binary image; to extract pore structure parameters including pore throat coordination number, average pore size, homogeneity coefficient, and pore throat ratio from the pore binary image; and to classify the pore structure type of interlayered shale oil reservoirs according to the pore structure parameters. The pore structure quantitative evaluation module is used to select core samples whose pore structure fracture connectivity is higher than the second preset value after classification, and to reconstruct the three-dimensional pore structure of the selected core samples at the nanoscale to extract the three-dimensional pore structure parameters. The multi-scale pore size distribution of the selected core samples was obtained based on low-temperature nitrogen adsorption and high-pressure mercury intrusion experiments, and the usable pore structure in the selected core samples was determined by combining the three-dimensional pore structure parameters. The crude oil occurrence state quantitative evaluation module is used to select oil-bearing core samples of different pore structure types after classification for two-dimensional nuclear magnetic resonance experiments and generate two-dimensional relaxation spectrum distribution maps. Based on the two-dimensional relaxation spectrum distribution map, core samples with oil content higher than the threshold were selected and oil-bearing areas were identified. The occurrence state of crude oil in the oil-bearing areas was detected to determine the proportion of bound, semi-bound, and free crude oil, thereby obtaining a quantitative evaluation result of the proportion of movable crude oil under each pore structure type. The optimization module is used to determine the optimal layer containing movable crude oil in interlayered shale oil reservoirs based on the quantitative evaluation results of the usable pore structure and the proportion of movable crude oil under each pore structure type in the core sample.

6. A computer device for optimizing the stratigraphic position of a shale oil reservoir containing movable crude oil, characterized in that, include: The memory, the processor, and the computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the method for selecting the stratigraphic position of a shale oil reservoir containing movable crude oil as described in any one of claims 1-4.

7. A readable storage medium, characterized in that, The readable storage medium stores a computer program, which includes program instructions that, when executed by a processor, are used to perform the steps of the method for selecting the stratigraphic position of a shale oil reservoir containing movable crude oil as described in any one of claims 1-4.

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