A method for preparing a visual model of a simulated geological fracture in a simulated rock reservoir

Abstract

The application discloses a kind of rock reservoir profiling imitated lubricated geological fissure visual model preparation methods, it is related to deep unconventional oil and gas exploration and development and rock reservoir percolation experimental technical field, obtains the three-dimensional topography of rock primary fissure using low-temperature imaging characterization technology, constructs geometric template after image processing;Micro-processing technology is used to prepare microfluidic model in high-fidelity replication rock primary fissure structure on transparent substrate in batches;According to the test results of target reservoir rock in-situ wettability, the inner wall of model microchannel is quantitatively modified, so that its surface wettability is accurately matched with reservoir rock, and finally the profiling imitated lubricated integrated fissure visual model is obtained, the present application realizes the super-high-fidelity replication of rock primary fissure structure and the accurate regulation and control of reservoir in-situ wettability for the first time, and provides a reliable and controllable physical experimental carrier for the study of deep rock reservoir gas-liquid two-phase percolation mechanism.

Description

Technical Field

[0001] This invention relates to the field of deep unconventional oil and gas exploration and development and rock reservoir seepage experiment technology, specifically to a method for preparing a visualization model of geological fractures in rock reservoirs based on shape and moisture. Background Technology

[0002] Deep unconventional oil and gas is a core replacement area for increasing reserves and production of unconventional oil and gas resources. Deep rock reservoirs are located in complex geological environments with high temperature and pressure. The internal pore-fracture network geometry and rock surface wettability are the two core controlling factors that determine the gas-liquid two-phase flow patterns and oil and gas production efficiency. Indoor physical simulation experiments are the core means to reveal the gas-water migration mechanism of reservoirs and optimize development process parameters. The reliability and accuracy of the experimental results directly depend on the degree to which the model reproduces the real geological and interface characteristics of the reservoir.

[0003] Currently, natural rock cores are commonly used for displacement experiments. Natural rocks are taken from the target reservoir and retain their inherent properties, but they also have inherent drawbacks: natural rocks are highly heterogeneous, making it impossible to obtain parallel samples with completely consistent pore and fracture structures and mineral compositions, making it difficult to conduct comparative experiments with strict single-variable control; during the experiment, the cores are easily contaminated by fluids, resulting in irreversible changes such as pore blockage and altered wettability, making them unusable, leading to long experimental cycles, high costs, and poor parallelism and repeatability of results; at the same time, natural rocks are opaque media, only macroscopic seepage parameters can be obtained, and it is impossible to directly observe microscopic behaviors such as gas-liquid interface migration at the pore and fracture scale, making it difficult to reveal the intrinsic control mechanism of seepage laws.

[0004] To address the visualization challenges, microfluidic technology has been introduced into the study of oil and gas reservoir seepage. Microchannel networks can be fabricated on transparent substrates using photolithography and etching, enabling high-resolution observation of the seepage process. Existing microfluidic models are mainly divided into two categories: one is a simplified model based on regular pore-throat structures, which is simple to fabricate and has good repeatability, but differs significantly from the complex fracture networks, irregular pore-throat topologies, and rough wall morphologies of natural rocks, resulting in poor reservoir applicability of experimental results; the other is a conformal microfluidic model based on the characterization of rock microstructure, using core structure data obtained through CT scanning, electron microscopy, etc., as a geometric template, and this is currently the mainstream technological direction. However, this type of contour model still faces many technical bottlenecks: In terms of structural characterization, conventional CT resolution is insufficient to accurately capture micro- and nano-scale fractures and pore throats that control seepage. At room temperature, focused ion beam scanning electron microscopy characterization is prone to causing thermal damage to rock samples, collapse of micropores and primary fractures, making it difficult to reproduce the morphology of primary fractures with high fidelity, resulting in geometric distortion of the model. In terms of wettability reproduction, existing models mostly only replicate the geometric structure, ignoring the decisive role of wettability. Moreover, surface modification technology can only achieve simple qualitative control of hydrophilicity or hydrophobicity, and cannot accurately quantitatively match the results of in-situ wettability tests of reservoirs. The modified layer has poor stability under high temperature and pressure, making it difficult to simulate the dynamic evolution of wettability at different temperature and pressure stages. In addition, structural replication and surface modification are usually separate processes, and the connection process is prone to microchannel damage or contamination, making it difficult to simultaneously ensure geometric and interface authenticity. Furthermore, there is a lack of standardized batch preparation platforms, resulting in poor model structural consistency and failing to meet the needs of multiple parallel comparison experiments.

[0005] In summary, existing technologies suffer from several key problems, including the inability to perform parallel comparisons of heterogeneous natural cores, difficulties in high-fidelity non-destructive characterization of primary fractures, lack of wettability and insufficient quantitative control of conformal models, poor modification stability, and difficulties in the batch preparation of integrated structure-wetting materials. Summary of the Invention

[0006] To address the shortcomings of existing natural rock experiments and contour-mimicking microfluidic modeling techniques, such as strong heterogeneity, low fidelity in structural characterization, inability to accurately match wettability, difficulty in integrated preparation, and non-reproducibility of experiments, this invention aims to overcome these limitations and provide a method for preparing a contour-mimicking and wettability-simulating geological fracture visualization model of rock reservoirs, comprising the following steps: Based on rock samples, three-dimensional morphological data of native rock fractures were obtained using low-temperature imaging characterization technology. After image processing and three-dimensional reconstruction, a geometric template for microfluidic processing was constructed. Based on geometric templates, microfluidic models replicating the original fracture structure of rocks were mass-produced on transparent substrates using micromachining technology. Based on the in-situ wettability test results of the target reservoir rock, the surface of the microchannel inner wall of the microfluidic model is quantitatively modified to match the surface wettability with the in-situ wettability of the target reservoir rock, thus obtaining a shape- and wettability integrated fracture visualization model.

[0007] Furthermore, low-temperature imaging characterization technology was used to obtain three-dimensional morphological data of primary rock fractures. After image processing and three-dimensional reconstruction, a geometric template for microfluidic fabrication was constructed, specifically including: Rock samples were cryogenically frozen to rapidly freeze the internal pore fluids in order to preserve the original pore and fracture state. While maintaining a low temperature environment, the target observation area of ​​the rock sample was continuously sliced ​​and imaged layer by layer to obtain a sequence of tomographic images; Alignment, denoising, and segmentation of sequential tomographic images are performed to complete three-dimensional digital core reconstruction and extract the core geometric feature parameters of the original rock fractures; Based on the core geometric feature parameters, the core fracture network region controlling the seepage is selected, and after two-dimensional projection and structural adaptation optimization, a two-dimensional geometric vector template suitable for photolithography is generated.

[0008] Furthermore, the low-temperature imaging characterization technique is one or more of the following: low-temperature focused ion beam scanning electron microscopy, low-temperature transmission electron microscopy, high-resolution micro-CT, or atomic force microscopy.

[0009] Furthermore, based on the geometric template, microfluidic models replicating the original fracture structure of rocks are mass-produced on a transparent substrate using microfabrication techniques, specifically including: Provide a transparent substrate and perform a cleaning pretreatment on it; Photoresist is coated on the pretreated transparent substrate, and photolithography and development are performed using a geometric template to transfer the geometric structure pattern of the original rock fissures to the photoresist layer. Using the photoresist retained after development as an etching protective layer, the exposed transparent substrate area is etched to form a microchannel structure; Remove residual photoresist to complete the fabrication of the substrate with the cracked structure; A substrate with a slit structure is irreversibly bonded to a transparent cover plate to form a closed microfluidic model. Using the same geometric template and standardized process parameters, repeat the above steps to achieve batch fabrication of microfluidic models with consistent structures.

[0010] Furthermore, the materials of the transparent substrate and the transparent cover are one of borosilicate glass, quartz glass, COP / COC resin, PDMS, or tempered glass; the irreversible bonding method is one of high-temperature hot-press bonding, anodic bonding, UV-cured adhesive bonding, or low-temperature glass solder bonding.

[0011] Furthermore, based on the in-situ wettability test results of the target reservoir rock, the inner wall surface of the microchannel in the microfluidic model was quantitatively modified, specifically including: Determine the target wettability parameter, which is the in-situ contact angle value of the rock in the target reservoir under different pressure and temperature conditions; The inner wall surface of the microchannel in the microfluidic model was pretreated with hydroxylation to introduce active hydroxyl groups; Based on the target wettability parameters, a modified solution with corresponding concentration and composition is prepared, and the pretreated model is brought into contact with the modified solution for reaction. Corresponding functional groups are grafted onto the inner wall surface of the microchannel to achieve quantitative control of surface wettability. The modified model is cleaned and cured to complete the lubrication modification.

[0012] Furthermore, the quantitative control of surface wettability is achieved by adjusting the modification process parameters of multiple models with completely identical geometry in the same batch, thus preparing a series of models with different wettability gradients to meet the requirements of comparative experiments with single-variable control.

[0013] Furthermore, the deviation between the contact angle of the modified model inner wall and the in-situ contact angle of the target reservoir rock is controlled within 3°.

[0014] Furthermore, it also includes a step of performance verification of the prepared integrated contour-mimicking and wettability-mimicking crack visualization model. The performance verification includes at least one of the following: geometric structure fidelity verification, wettability matching degree verification, high temperature and high pressure stability verification, sealing verification, and optical performance verification.

[0015] Furthermore, the rock reservoir is a deep unconventional oil and gas reservoir. The prepared integrated fracture visualization model based on shape and wettability was used to simulate the gas-liquid two-phase flow experiment under the dynamic evolution of reservoir wettability at different mining stages.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: 1. This invention achieves ultra-high fidelity replication of the morphology of native rock fractures, breaking through the limitations of existing structural characterization techniques. Employing low-temperature focused ion beam scanning electron microscopy, it achieves non-destructive imaging of rock samples in a liquid nitrogen temperature environment, completely avoiding the thermal damage and structural collapse problems of conventional techniques. It can acquire the three-dimensional structure of native fractures at nanometer-level resolution, accurately reproducing the micro- and nano-pore throats and wall roughness morphology that control seepage, ensuring a high degree of consistency between the model's geometry and the actual seepage channels in the rock.

[0017] 2. This invention pioneers an integrated system for preparing visual fracture models of rock reservoirs that simulates both shape and wettability, overcoming the core bottleneck of traditional models that only replicate geometric structures and cannot reproduce interfacial wetting characteristics. It simultaneously achieves high-fidelity replication of the original fracture geometry and precise matching of in-situ reservoir wettability, ensuring a high degree of consistency between the model's microscopic seepage behavior and the actual reservoir, significantly enhancing the engineering guidance value of the experimental results.

[0018] 3. This invention completely solves the problem that traditional core experiments cannot conduct parallel comparison experiments. Based on standardized geometric templates and fully controllable processing technology, models with completely identical structures can be prepared in batches. Combined with quantitative control of wettability, it enables comparative experiments with strict single-variable control, avoiding the dispersion of experimental results caused by the heterogeneity of natural rocks. The models can be cleaned and reused, significantly reducing experimental costs and shortening the experimental cycle.

[0019] 4. This invention achieves precise and stable control of wettability, adapting to the experimental requirements of deep reservoirs. Based on in-situ wettability test results, quantitative modification can accurately match the dynamic wettability characteristics of rocks under different temperature and pressure conditions. The modified surface exhibits excellent long-term stability under high temperature and high pressure environments, meeting the requirements of long-term seepage experiments in deep reservoirs.

[0020] 5. This invention provides a novel visualization technology platform for the study of seepage mechanisms. The model has excellent optical transparency and can realize the observation of the entire process of gas-liquid interface transport at the nanometer to micrometer scale of cracks, supporting cross-scale research from microscopic interface behavior to macroscopic seepage laws. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of rock fracture characterization and imaging based on low-temperature focused ion beam scanning electron microscopy. Figure 2 A schematic diagram of the batch fabrication process for high borosilicate glass microfluidic models; Figure 3 A schematic diagram of the precise surface modification process for a microfluidic model; Figure 4 A schematic diagram of the performance verification and quality control process for the integrated contour and lubrication model; Figure 5 This is a schematic diagram of coal and rock fracture structure extraction. Figure 6 This is a schematic diagram of the geometric template for a microfluidic model. Figure 7 The curve of contact angle as a function of pressure for a coal sample from a certain basin; Figure 8 Vapor phase breakthrough characteristic diagrams and pressure response curves for different wettability models; Figure 9The following are statistical diagrams of residual liquid phase distribution under different wettability conditions, where (a) is model A (θ=97.6°), (b) is model B (θ=79.3°), and (c) is model C (θ=66.7°). Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] This invention addresses the core needs of research on the gas-liquid two-phase seepage mechanism in deep rock reservoirs and the limitations of traditional experimental methods by proposing a visualization model preparation technology for geological fractures in rock reservoirs based on shape and wettability.

[0024] First, low-temperature focused ion beam scanning electron microscopy is used to perform non-destructive continuous slice imaging of rock samples in a liquid nitrogen low-temperature environment. After image preprocessing and three-dimensional reconstruction, the three-dimensional morphology and geometric features of the micro-nano scale fracture network of the rock are accurately obtained. Then, a standardized geometric template that can be used for microfluidic processing is constructed to ensure the geological authenticity of the model from the source.

[0025] In addition to the specified 3D reconstruction software, image reconstruction software platforms with image alignment, denoising, segmentation, and reconstruction functions, such as Avizo, Fiji, ImageJ, and MATLAB custom programs, can also be used to realize 3D digital modeling of fracture structures.

[0026] In addition to using low-temperature focused ion beam scanning electron microscopy, other equipment with micro- and nano-scale characterization capabilities, such as low-temperature transmission electron microscopy, high-resolution micro-CT, and atomic force microscopy, can also be used to obtain the three-dimensional structure of primary rock fractures, achieving equivalent structural characterization results.

[0027] Second, based on the geometric template, a standardized microfluidic preparation process of photolithography-wet etching-hot pressing bonding is adopted, and high borosilicate glass is used as the substrate to prepare transparent microfluidic models that completely replicate the original fracture structure of rocks in batches. This solves the industry problem of strong heterogeneity of natural rock cores and non-reproducible experiments, and provides a physical experimental platform with consistent structure and reusability for seepage experiments.

[0028] For microfluidic model substrates, in addition to borosilicate glass, transparent materials with high transparency, high temperature and pressure resistance, and chemical stability such as quartz glass, COP / COC resin, PDMS, and tempered glass can also be used, all of which can meet the requirements of visual percolation experiments. For bonding processes, in addition to high temperature hot pressing bonding, anodic bonding, UV curing adhesive bonding, and low temperature glass solder bonding can also be used to achieve a sealed bond between the glass substrate and the cover plate, ensuring the sealing performance of the model under high temperature and pressure conditions.

[0029] Preferably, the cryogenic fixation of rock samples can be achieved by external pre-freezing with liquid nitrogen and constant temperature on a cryogenic stage, or by high-pressure freezing fixation, propane cryogenic freezing, etc., which can avoid sample structure shrinkage and collapse. Preferably, in addition to hydrofluoric acid-ammonium fluoride buffered wet etching, precision micromachining methods such as inductively coupled plasma dry etching, femtosecond laser etching, and reactive ion etching can also be used to achieve high-precision etching of microchannels in cracks. For surface modification, in addition to silane coupling agent liquid-phase grafting modification, atomic layer deposition, chemical vapor deposition, plasma polymerization, and vapor-phase silanization can also be used to quantitatively control the wettability of the model surface, all of which can achieve stable and uniform simulated wetting effects.

[0030] Third, addressing the technical bottleneck of existing models being unable to match the in-situ wettability of reservoirs, based on the in-situ wettability test results of the target reservoir rocks, the surface hydroxylation pretreatment and silane coupling agent grafting modification are used to achieve precise quantitative control of the model surface wettability, making the model interface characteristics highly consistent with the real reservoir rocks, forming a fracture visualization physical model that integrates shape and wettability simulation.

[0031] Fourth, the model underwent comprehensive performance verification, including geometric accuracy, wettability matching, and high-temperature and high-pressure stability, to ensure that the model meets the experimental requirements of deep reservoirs. Through multiple sets of gas-liquid two-phase displacement experiments, the seepage law under different flow rates and wettability conditions was revealed, providing theoretical basis and technical support for the efficient development of deep unconventional oil and gas.

[0032] Example 1 The specific steps of the method for preparing a visualization model of geological fractures in rock reservoirs using contour imitation and wettability in this embodiment are as follows: (1) Acquisition of three-dimensional morphology and geometric template construction of primary rock fractures based on low-temperature focused ion beam scanning electron microscopy like Figure 1 As shown, the core of this step is to obtain the original micro-nano-scale fracture morphology and three-dimensional structure of rock samples non-destructively through low-temperature cryo-fixation and automated continuous slicing scanning, and to construct a high-precision geometric template that can be used for microfluidic processing.

[0033] Representative rock samples from the target reservoir were selected and cut into block-shaped samples suitable for focused ion beam scanning electron microscopy and cryogenic transport systems. The observation surfaces were gently polished with fine sandpaper to remove the surface damage layer caused by mechanical processing, ensuring that the observation surfaces were flat and clean.

[0034] The pretreated rock sample was placed in a rapid sample loader and pre-frozen externally with liquid nitrogen to rapidly freeze the pore fluid inside the rock, preserving the original pore and fracture state to the maximum extent. The pre-frozen sample was then transferred to the low-temperature sample stage inside the electron microscope along with the rapid loader. The -160°C low-temperature environment was continuously maintained by liquid nitrogen circulation to ensure that the sample did not undergo structural shrinkage or collapse during the entire test.

[0035] By spraying a gold or platinum conductive layer onto the surface of rock samples at low temperatures, the conductivity of the sample surface is improved, ensuring high-resolution imaging quality. Real-time imaging with a scanning electron microscope is then used to locate target observation areas that are representative of the reservoir, preparing for subsequent slice imaging.

[0036] Adjust the angle between the focused ion beam and the scanning electron beam to 54° to ensure that the slice direction is perpendicular to the surface of the target observation area. Set a fixed slice thickness and start the automated program to continuously slice and image the target area layer by layer to obtain a complete sequence of tomographic images. Maintain a low temperature throughout the process to avoid altering the original fracture structure of the rock during the imaging process.

[0037] The acquired sequential tomographic images underwent standardized preprocessing. Dedicated image analysis software was used for automatic inter-layer alignment to eliminate positional deviations caused by probe jitter. Resampling was employed to unify the Z-axis resolution, improving the accuracy of 3D reconstruction. Masking was used to remove invalid edge regions, retaining only the effective observation areas containing pores and fractures. Median filtering was used to remove image noise and improve segmentation accuracy. Based on this, image segmentation was used to distinguish between the solid matrix and the pore / fracture space, completing 3D digital core reconstruction and extracting core geometric features such as pore throat size, fracture orientation, wall roughness, and topological connectivity.

[0038] Based on the reconstructed and extracted geometric features of the original rock fractures, the core fracture network region controlling seepage is selected. After two-dimensional projection and structural adaptation optimization, a two-dimensional geometric vector template suitable for photolithography is generated. The optimization process fully preserves the core topological features of the fracture network and the pore throat size relationship, ensuring a high-fidelity match between the geometric template and the original rock structure. Finally, a standardized photolithography vector paper is output, completing the construction of the digital blueprint for contouring.

[0039] (2) Batch fabrication of microfluidic fracture models of borosilicate glass based on real fracture structure like Figure 2As shown, this step, based on the aforementioned constructed geometric template, employs a positive photoresist etching method and microfluidic precision machining process to mass-produce transparent glass models that faithfully replicate the original fracture structure of rocks. The specific implementation steps are as follows: High borosilicate glass was selected as the model substrate, which has excellent optical transparency, high temperature and high pressure resistance and chemical stability, and can meet the harsh environmental requirements of deep reservoir simulation experiments. The glass substrate was cleaned, polished and dried. The RCA standard cleaning process was used to thoroughly remove organic impurities, inorganic contaminants and particulate impurities from the surface to ensure the accuracy and effect of subsequent photolithography and etching processes.

[0040] Positive photoresist is uniformly coated onto the pretreated glass substrate surface. The photoresist thickness is precisely controlled through a spin coating process. After soft baking to remove the internal solvent of the photoresist, a photolithography machine is used with a standardized geometric template vector paper as a mask for precise ultraviolet exposure. During the exposure process, the positive photoresist in the rock's original fracture network region corresponding to the mask decomposes under ultraviolet light, while the photoresist in the non-fracture region remains unexposed, thus completely transferring the original rock fracture geometry to the photoresist layer. After exposure, the glass substrate undergoes precise development. The developer dissolves and removes the exposed and decomposed photoresist in the crack areas, exposing the glass surface to be etched. The unexposed photoresist in the non-crack areas is retained and serves as an etching protective layer. After development, a rigorous hardening process is performed to enhance the bonding strength between the residual photoresist and the glass surface, ensuring the edge accuracy and structural integrity of the pattern during subsequent etching.

[0041] A hydrofluoric acid-ammonium fluoride buffer etching system is used to perform precise and controllable wet etching on the developed glass substrate. Only the exposed crack areas of the glass are etched to form microchannels, while the non-crack areas remain flat due to the protection of photoresist. The etching time, etching temperature, and etching rate are precisely controlled according to the target crack depth to etch a crack microchannel structure on the glass substrate surface that is completely consistent with the geometric template, thus completely replicating the wall morphology and throat size characteristics of the rock crack. After etching, all residual photoresist is removed using photoresist stripping solution, and then residual etching solution and impurities are thoroughly removed through a cleaning process. The substrate is then cleaned and dried to complete the preparation of a substrate with native crack structure.

[0042] Based on the connection requirements of the experimental setup, ultrafast laser drilling technology was used to process the fluid inlet and outlet at the corresponding positions on the etched glass substrate. The aperture and depth of the holes were precisely controlled to ensure the smooth flow of fluid in and out and the reliability of the subsequent sealing connection.

[0043] The substrate with the crack structure is precisely aligned and bonded to a blank glass cover plate, and then placed in a high-temperature bonding furnace for programmed temperature rise and hot pressing bonding. By precisely controlling the bonding temperature, pressure, heating rate and holding time, a high-strength permanent bond between the two glass plates is achieved, forming a closed crack microfluidic model, and completing the basic preparation of a transparent and visualized model.

[0044] Based on the same set of geometric templates and standardized process parameters, the above-mentioned photolithography, development, etching, and bonding processes are repeated to achieve batch preparation of microfluidic models with completely consistent structures. The dimensional accuracy, channel depth, and bonding sealing of each batch of models are sampled and tested to ensure that the geometric consistency deviation of the batch-prepared models is controlled within 5%.

[0045] (3) Precise surface modification of the model based on in-situ wettability test results like Figure 3 As shown, this step, based on the in-situ wettability test results of the target reservoir rock, employs a surface grafting modification method to precisely control the wettability of the batch-prepared glass models, ensuring that the surface wettability characteristics of the models match the actual wettability characteristics of the reservoir rock. The specific implementation steps are as follows: S31. Determination of target wettability parameters The in-situ contact angle test results of rocks in the target reservoir under different pressure and temperature conditions were obtained to clarify the gas-liquid-solid three-phase contact angle values ​​of rocks at different reservoir evolution stages, which were then used as the target values ​​for model wettability control.

[0046] S32. Model surface hydroxylation pretreatment The prepared glass microfluidic model was cleaned and purified. High-density active hydroxyl groups were introduced into the inner wall surface of the glass microchannel by oxygen plasma treatment or hydroxylation solution immersion process. This provides uniform active reaction sites for subsequent surface grafting modification and enhances the bonding strength between the modified layer and the substrate.

[0047] S33. Implementation of surface grafting modification process Based on the target contact angle value, a silane coupling agent modification solution with corresponding concentration and composition is prepared. The pretreated glass model is completely immersed in the modification solution. By precisely controlling the concentration of the modification solution, the reaction temperature and the reaction time, the corresponding functional groups are grafted onto the inner wall surface of the microchannel of the model, so as to achieve quantitative and uniform control of the wettability of the model surface.

[0048] S34. Post-modification curing and post-treatment After the grafting reaction is completed, the model is removed and the microchannels and model surface are rinsed alternately with anhydrous ethanol and deionized water to thoroughly remove unreacted modifying reagents and impurities. Then, the model is placed in a constant temperature drying oven for gradient temperature curing to further improve the bonding stability between the grafted functional groups and the glass surface, thus completing the "lubrication" modification treatment of the model.

[0049] S35. Preparation of Multiple Differential Models To meet the requirements of comparative experiments, a series of models with different wettability gradients were prepared by adjusting the modification process parameters based on models with completely identical geometry from the same batch, in order to meet the requirements of comparative experiments controlled by a single variable.

[0050] (4) Performance verification and quality control of the integrated contour-following and lubrication-following fracture model like Figure 4 As shown, this step verifies the core performance of the prepared model to ensure it meets the requirements of subsequent seepage experiments. The specific implementation steps are as follows: Geometric structure fidelity verification: The microchannel structure of the model was scanned and imaged using a laser confocal microscope and a white light interferometer. Key parameters such as crack width, depth and wall roughness were measured and compared with the original geometric features of the rock obtained by a low-temperature focused ion beam scanning electron microscope to verify the accuracy of the geometric structure replication.

[0051] Wettability matching verification: Using a high-temperature and high-pressure contact angle measuring instrument, the gas-liquid contact angle of the inner wall of the modified model was tested under simulated reservoir temperature and pressure conditions. The test results were compared with the in-situ contact angle data of the target rock to ensure that the contact angle deviation was controlled within 3° to meet the requirements of accurate wettability matching.

[0052] Temperature and pressure stability verification: The model was placed in a high temperature and high pressure environment simulating a deep reservoir, and long-term immersion and fluid scouring experiments were carried out. The contact angle change was detected periodically to evaluate the wetting stability of the modified surface and ensure that it did not significantly decay during the experimental period.

[0053] Sealing and optical performance verification: Pressure resistance tests were conducted on the model to confirm that it has good sealing performance and no leakage within the experimental design pressure range; at the same time, the optical transparency of the model was checked to ensure that it meets the imaging requirements of visualization experiments such as high-speed photography and microscopic observation.

[0054] Example 2 This embodiment takes a low-rank coalbed methane reservoir in a certain coal-bearing area as the application object. The high-fidelity microfluidic model is constructed using the integrated contour and wettability simulation preparation method of the present invention. The dynamic evolution of reservoir wettability at different mining stages is simulated, and gas-liquid two-phase displacement experiments are carried out to verify the technical feasibility and application effect of the present invention.

[0055] 1. Acquisition of 3D morphology of primary rock fractures and construction of geometric templates Fresh coal and rock samples from the target reservoir were selected and cut into standard blocks of 15mm × 15mm × 10mm. After being polished stepwise with sandpaper ranging from 800 to 2000 grit, they underwent chemical mechanical polishing using a 0.025μm diamond suspension to obtain a smooth observation surface with a surface roughness Ra ≤ 0.1μm. The samples were pre-frozen in liquid nitrogen to -160℃ and then transferred to a cryogenic focused ion beam scanning electron microscope (CFFEM) stage. The cryogenic environment was maintained throughout to prevent structural collapse. After depositing a 5nm platinum conductive layer, the angle between the ion beam and the electron beam was adjusted to 54°, and automated continuous slicing imaging was performed with a fixed thickness of 50nm.

[0056] like Figure 5 The image shows the process of extracting coal and rock fracture structures. Figure 5 (a) is the original grayscale image of the primary fractures in coal and rock directly obtained by low-temperature FIB-SEM, with a scale bar of 500 μm, which clearly shows the distribution and connectivity of natural fractures inside the coal and rock. Figure 5 (b) shows the data representation of the fractures after binarization. The gray area represents the solid coal matrix, and the black area represents the pore fracture space, which is used for subsequent three-dimensional reconstruction and geometric parameter extraction.

[0057] After aligning, denoising, and segmenting the sequence images, the core parameters of the fracture network were extracted through 3D reconstruction: the target region contains 30 pore throat units, with an average shape factor of 0.43, a probability entropy of 0.9, and a fractal dimension of 1.63. A two-dimensional geometric vector template was generated by selecting the core region controlling seepage, fully preserving the true dimensions and topological relationships of the inlet channels inlet 1 (85μm), inlet 2 (60μm), inlet 3 (20μm) and outlet channels outlet 1 (50μm) and outlet 2 (125μm).

[0058] like Figure 6 The diagram shows the final generated microfluidic model geometric template. The overall structure, from left to right, consists of the inlet area, injection chamber, core fracture observation area, and outlet area. The total length of the model channel is 28.5 mm. The middle 2.5 mm × 2.5 mm area is a replicated original coal and rock fracture network, which is the main observation area for gas-liquid two-phase flow. The diagram clearly marks the positions of 3 inlet channels and 2 outlet channels, corresponding to the main flow paths of real coal and rock fractures.

[0059] 2. Batch fabrication of microfluidic models and precise control of surface wettability Using 1.1mm thick high borosilicate glass as the substrate, models were mass-produced using a positive photoresist etching method combined with a hydrofluoric acid-ammonium fluoride buffer etching process. After RCA cleaning, photolithography, and development, a 100μm deep crack channel was formed by etching at 25℃ for 120 min. After laser processing of the fluid inlet and outlet, the models were hot-pressed and bonded to blank cover plates at 620℃ and 0.5MPa for 4 h to obtain a closed transparent model. Based on the same template and standardized process, 15 models with identical structures were mass-produced, and the geometric consistency deviation was ≤3.2% after sampling inspection.

[0060] To simulate the evolution of wettability caused by reservoir pressure decrease during extraction, the model was differentiated using quantitative grafting technology with silane coupling agents, based on in-situ contact angle test results of the target reservoir. For example... Figure 7 As shown, the curve of contact angle of coal samples in a certain basin varies with pressure. The horizontal axis represents the reservoir pressure p (MPa), with a test range of 0~15MPa, covering the pressure changes throughout the entire coalbed methane extraction cycle. The vertical axis represents the three-phase contact angle θ (°) of coal-rock gas-liquid-solid, reflecting the wettability characteristics of the coal surface. The black curve is the fitting curve of the experimental test data, with the fitting equation being θ=-35.3e^(-0.14p)+102.1 and the fitting degree R²=0.93, which can accurately and quantitatively characterize the dynamic change law of reservoir wettability at different mining stages. The overall trend shows that as the reservoir pressure decreases, the contact angle gradually decreases, and the coal surface gradually changes from weakly hydrophobic to strongly hydrophilic.

[0061] Three models corresponding to the early, middle and late stages of mining were finally prepared, as shown in Table 1. The measured values ​​of the modified contact angles deviated from the target values ​​by ≤1.5°, which met the requirements for accurate matching.

[0062] Table 1. Model wettability parameters at different mining stages 3. Experimental setup and procedure The experiment employed a high-temperature, high-pressure microfluidic displacement visualization system, consisting of a dual-channel injection pump, a high-precision pressure sensor, an inverted microscope, and a high-speed camera. This system enables simultaneous quantitative fluid injection, real-time pressure monitoring, and microscopic imaging of seepage behavior. Nitrogen was used to simulate methane, and methylene blue-stained deionized water was used to simulate formation water. The experimental temperature was maintained at 318 K throughout the experiment, with an outlet back pressure of 5 mbar.

[0063] Before the experiment, the model was tested for airtightness. A pressure decay of less than 1% after stabilizing at 100 mbar for 20 minutes was considered acceptable. After vacuuming, stained water was injected at a flow rate of 1 μL / min until the model was completely saturated. Then, nitrogen was used for displacement at a rate of 50 μL / min, and pressure data and microscopic images were collected simultaneously. The experiment was repeated with models of different wettability to complete multiple comparisons of single variables.

[0064] 4. Experimental Results and Analysis like Figure 8 As shown, this figure is a gas phase breakthrough characteristic diagram and pressure response curve for different wettability models. The figure is divided into two parts, upper and lower, containing three sub-figures, which correspond to model C (θ=66.7°, strong hydrophilicity), model B (θ=79.3°, weak hydrophilicity), and model A (θ=97.6°, weak hydrophobicity) from left to right. The upper part is the pressure phase diagram at the moment of gas phase breakthrough; the three middle diagrams show the distribution of the gas and liquid phases at the moment of breakthrough. The blue area is the fracture channel occupied by the water phase, the white area is the fracture channel occupied by the gas phase, the red arrow indicates the dominant seepage path of gas phase formation, the scale bar of 0.6 mm is the actual size of the core fracture observation area, and the numbers in the figure are the time (in seconds) from the start of gas phase entering the fracture to the formation of breakthrough; the lower part is the inlet pressure change curve corresponding to the breakthrough process. The horizontal axis is time Δt (s), with the start of gas phase entering the fracture structure as the zero point of timing, and the vertical axis is the inlet pressure (mbar), which is the value monitored in real time by the high-precision pressure sensor. The black solid line is the curve of inlet pressure changing with time, and the peak value of the curve is the gas phase breakthrough pressure. The numbers in the figure are marked with the specific values ​​of gas phase initiation pressure, breakthrough pressure and breakthrough time.

[0065] Under different wettability conditions, the breakthrough behavior and dominant path evolution of the gas phase in the fracture network show significant differences. In the weakly hydrophobic model A, capillary force is the driving force. At 23.79 mbar, the gas phase preferentially enters through the narrowest inlet 3, and at 25.88 mbar, it breaks through through outlet 2, forming a single dominant path from inlet 3 to outlet 2, with a final gas phase saturation of 24.1%. In the weakly hydrophilic model B, the influence of capillary force is weakened, and the gas phase enters simultaneously through inlets 1 and 2. At 27.62 mbar, it breaks through through both outlets simultaneously, forming two dominant paths, with a gas phase saturation of 72.6% and the highest displacement efficiency. In the strongly hydrophilic model C, capillary force becomes a strong drag, and the gas phase breakthrough pressure rises to 36.15 mbar, allowing only a single outlet 1 to break through, with a gas phase saturation of 40.7%.

[0066] like Figure 9 The figure shows the statistical distribution of residual liquid phase under different wettability conditions. The horizontal axis represents the throat width (μm), with a statistical range of 0~210μm, covering the size range of all throats in the model. The vertical axis represents the residual water saturation (%), which is the proportion of the residual water volume in the corresponding throat size to the total volume of the throat. The orange curve represents the trend of trench water saturation with throat width, the blue curve represents the trend of broken water saturation with throat width, and the pink curve represents the trend of dead end water saturation with throat width. The three sub-figures correspond to three wettability conditions: Model A (θ=97.6°), Model B (θ=79.3°), and Model C (θ=66.7°).

[0067] After the gas-phase breakthrough, the distribution and saturation of residual water within the fractures changed significantly with wettability. The residual water mainly existed in three forms: channel water, fractured water, and dead-end water. Channel water adhered to the fracture walls, with a higher proportion depending on the strength of the hydrophilicity. Fractured water formed at channel intersections, related to the selection of the dominant path. Dead-end water was found in blind-end fractures and exhibited the highest stability. Under strong hydrophilic conditions, fractured and dead-end water essentially disappeared, leaving only channel water, with the opening of the localized blocking throats concentrated between 21.3 and 90.4 μm.

[0068] This embodiment fully verifies the technical advantages of the integrated contour and wettability simulation preparation method of the present invention: through low-temperature FIB-SEM non-destructive characterization and standardized micro-machining process, high-fidelity replication of the nanoscale morphology of primary coal and rock fractures is achieved, with geometric consistency deviation of ≤3.2% for models in the same batch; the quantitative modification technology based on the in-situ wettability test results of the reservoir can accurately simulate the dynamic evolution of wettability at different mining stages, with contact angle deviation ≤1.5°.

[0069] The prepared model can clearly observe microscopic behaviors such as gas-liquid interface migration, dominant path evolution, and residual water trapping, and can quantitatively obtain key parameters such as breakthrough pressure and residual water saturation. Compared with traditional natural core experiments, the model of this invention can be prepared in batches and reused, shortening the experimental cycle by 70% and reducing costs by 60%, completely solving the industry problems of strong heterogeneity, non-reproducibility, and lack of visualization of natural cores. The experimental data are highly consistent with field production patterns, providing reliable support for the study of seepage mechanisms and the optimization of development processes in deep unconventional oil and gas reservoirs. The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0070] The above embodiments are merely illustrative examples and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a visualization model of geological fractures in a rock reservoir using contour imitation and wettability techniques, characterized in that, Includes the following steps: Based on rock samples, three-dimensional morphological data of native rock fractures were obtained using low-temperature imaging characterization technology. After image processing and three-dimensional reconstruction, a geometric template for microfluidic processing was constructed. Based on geometric templates, microfluidic models replicating the original fracture structure of rocks were mass-produced on transparent substrates using micromachining technology. Based on the in-situ wettability test results of the target reservoir rock, the surface of the microchannel inner wall of the microfluidic model is quantitatively modified to match the surface wettability with the in-situ wettability of the target reservoir rock, thus obtaining a shape- and wettability integrated fracture visualization model.

2. The method for preparing a visualization model of geological fractures in rock reservoirs based on the contour and wettability described in claim 1, characterized in that, Three-dimensional morphological data of primary rock fractures were obtained using low-temperature imaging characterization technology. After image processing and 3D reconstruction, a geometric template for microfluidic fabrication was constructed, specifically including: Rock samples were cryogenically frozen to rapidly freeze the internal pore fluids in order to preserve the original pore and fracture state. While maintaining a low temperature environment, the target observation area of ​​the rock sample was continuously sliced ​​and imaged layer by layer to obtain a sequence of tomographic images; Alignment, denoising, and segmentation of sequential tomographic images are performed to complete three-dimensional digital core reconstruction and extract the core geometric feature parameters of the original rock fractures; Based on the core geometric feature parameters, the core fracture network region controlling the seepage is selected, and after two-dimensional projection and structural adaptation optimization, a two-dimensional geometric vector template suitable for photolithography is generated.

3. The method for preparing a visualization model of geological fractures in rock reservoirs according to claim 2, characterized in that, The low-temperature imaging characterization technique is one or more of the following: low-temperature focused ion beam scanning electron microscopy, low-temperature transmission electron microscopy, high-resolution micro-CT, or atomic force microscopy.

4. The method for preparing a visualization model of geological fractures in rock reservoirs based on the contour and wettability of the rock reservoir according to claim 1, characterized in that, Based on the geometric template, microfluidic models replicating the original fracture structure of rocks are mass-produced on transparent substrates using microfabrication processes, specifically including: Provide a transparent substrate and perform a cleaning pretreatment on it; Photoresist is coated on the pretreated transparent substrate, and photolithography and development are performed using a geometric template to transfer the geometric structure pattern of the original rock fissures to the photoresist layer. Using the photoresist retained after development as an etching protective layer, the exposed transparent substrate area is etched to form a microchannel structure; Remove residual photoresist to complete the fabrication of the substrate with the cracked structure; A substrate with a slit structure is irreversibly bonded to a transparent cover plate to form a closed microfluidic model. Using the same geometric template and standardized process parameters, repeat the above steps to achieve batch fabrication of microfluidic models with consistent structures.

5. The method for preparing a visualization model of geological fractures in rock reservoirs according to claim 4, characterized in that, The transparent substrate and transparent cover are made of borosilicate glass, quartz glass, COP / COC resin, PDMS, or tempered glass; the irreversible bonding method is one of high-temperature hot-press bonding, anodic bonding, UV-cured adhesive bonding, or low-temperature glass solder bonding.

6. The method for preparing a visualization model of geological fractures in rock reservoirs based on the contour and wettability of the rock reservoir according to claim 1, characterized in that, Based on the in-situ wettability test results of the target reservoir rock, the surface of the microchannel inner wall of the microfluidic model was quantitatively modified, specifically including: Determine the target wettability parameter, which is the in-situ contact angle value of the rock in the target reservoir under different pressure and temperature conditions; The inner wall surface of the microchannel in the microfluidic model was pretreated with hydroxylation to introduce active hydroxyl groups; Based on the target wettability parameters, a modified solution with corresponding concentration and composition is prepared, and the pretreated model is brought into contact with the modified solution for reaction. Corresponding functional groups are grafted onto the inner wall surface of the microchannel to achieve quantitative control of surface wettability. The modified model is cleaned and cured to complete the lubrication modification.

7. The method for preparing a visualization model of geological fractures in rock reservoirs according to claim 6, characterized in that, Quantitative control of surface wettability is achieved by adjusting the modification process parameters of multiple models with completely identical geometry in the same batch, thus preparing a series of models with different wettability gradients to meet the requirements of comparative experiments with single-variable control.

8. The method for preparing a visualization model of geological fractures in rock reservoirs according to claim 6, characterized in that, The deviation between the contact angle of the inner wall of the modified model and the in-situ contact angle of the target reservoir rock was controlled within 3°.

9. The method for preparing a visualization model of geological fractures in rock reservoirs based on the contour and wettability of the rock reservoir according to claim 1, characterized in that, It also includes a step of performance verification of the prepared integrated crack visualization model with conformal and wettability characteristics. The performance verification includes at least one of the following: geometric structure fidelity verification, wettability matching degree verification, high temperature and high pressure stability verification, sealing verification, and optical performance verification.

10. The method for preparing a visualization model of geological fractures in rock reservoirs based on any one of claims 1-9, characterized in that, The rock reservoir is a deep unconventional oil and gas reservoir. The prepared integrated fracture visualization model based on shape and wettability was used to simulate the gas-liquid two-phase flow experiment under the dynamic evolution of reservoir wettability at different mining stages.

Images