Microfluidic chip preparation method and system based on real core vertical heterogeneity characteristics

Abstract

The application provides a microfluidic chip preparation method and system based on real core vertical heterogeneity characteristics, and belongs to the field of real core simulation. In order to solve the problems that the existing microfluidic chip technology has obvious deficiencies in the realness of pore structure, the simulation accuracy of heterogeneity, the consideration of gravity effect and the application of geological data. The application comprises layer division, core sampling, pore throat characteristic parameter extraction, vertical heterogeneity quantitative modeling and combination, and microfluidic chip design and processing. The application combines real pore structure extraction and vertical heterogeneity modeling, and prepares a microfluidic chip which can accurately restore the heterogeneity characteristics of the reservoir, so as to provide an effective experimental method for studying the microflow law of the heterogeneous reservoir.

Description

Technical Field

[0001] This invention relates to the field of real core simulation methods, and more specifically, to a microfluidic chip fabrication method and system based on the vertical heterogeneity characteristics of real cores. Background Technology

[0002] In existing reservoir engineering, reservoir heterogeneity is a key factor affecting oil and gas recovery, remaining oil distribution, and oilfield development effectiveness. Traditional reservoir seepage experiments mostly rely on macroscopic analysis, making it difficult to reveal the changes in seepage characteristics caused by differences in permeability among different layers within the reservoir from a microscopic perspective. In particular, there is a lack of effective physical experimental verification of the impact of vertical heterogeneity on reservoir development.

[0003] As oil and gas field development increasingly focuses on complex, heterogeneous reservoirs, traditional core displacement experiments have shown limitations in terms of visualization and depth of mechanism revelation. Microfluidic chip technology, with its visualization capabilities and precise scale control, offers a new technical approach for studying multiphase flow at the microscale, demonstrating promising application prospects in the field of oil and gas flow mechanism research. However, existing microfluidic chip technology still has significant shortcomings in simulating real reservoir environments. Current technical solutions in this field mainly suffer from the following limitations:

[0004] 1. The problem of idealizing pore structure.

[0005] Existing microfluidic chips mostly employ regular geometric patterns to construct pore networks, such as circular or rectangular channels. While this design is simple to fabricate, it differs significantly from the complex pore structure formed by geological processes in real rock cores. Real reservoirs exhibit irregular pore morphology, uneven size distribution, and complex connectivity, and the idealized designs of existing technologies cannot accurately reflect these characteristics, leading to discrepancies between experimental results and actual reservoir conditions.

[0006] 2. Insufficient simulation of heterogeneity.

[0007] Existing technologies typically employ simple layered structures or parallel channels to simulate heterogeneity. This approach can only reflect macroscopic interlayer differences and cannot reproduce the vertical heterogeneity characteristics controlled by sedimentary rhythms in real reservoirs. In actual oil reservoirs, channel sand bodies usually exhibit continuous physical property variations vertically, such as typical positive rhythmic distributions. This continuous heterogeneity has a significant impact on fluid migration, but existing technologies struggle to effectively simulate these fine vertical variation patterns.

[0008] 3. The influence of gravity is not adequately considered.

[0009] Current microfluidic experiments often employ horizontal placement, neglecting the influence of gravity on the seepage process. In actual reservoir development, the gravitational differentiation effect, combined with reservoir heterogeneity, significantly affects the distribution and migration of fluids in different permeability zones. Existing technologies struggle to effectively simulate this coupling effect of gravity and reservoir heterogeneity, leading to discrepancies between experimental results and actual production dynamics.

[0010] 4. Insufficient geological data support.

[0011] Existing microfluidic models often rely on theoretical assumptions for their design parameters, lacking support from real geological data. The models fail to fully utilize actual geological data such as core samples and well logs, resulting in a weak correlation between the model and the geological characteristics of the target reservoir, thus reducing the representativeness and practicality of the experimental results.

[0012] In summary, existing microfluidic chip technology has significant shortcomings in terms of pore structure realism, heterogeneous simulation accuracy, gravity effect consideration, and geological data application. Therefore, it is necessary to develop a new microfluidic chip fabrication method that can better reproduce real reservoir characteristics and improve the accuracy and practicality of experimental results. Summary of the Invention

[0013] The technical problem to be solved by this invention is:

[0014] To address the significant shortcomings of existing microfluidic chip technology in terms of pore structure realism, heterogeneous simulation accuracy, gravity effect consideration, and geological data application.

[0015] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0016] This invention provides a method for fabricating a microfluidic chip based on the vertical heterogeneity of real rock cores, comprising the following steps:

[0017] S100, stratigraphic division and core sampling: The reservoir is vertically divided into several stratigraphic layers according to permeability differences and sedimentary characteristics; representative core samples are selected for each stratigraphic layer.

[0018] S200. Pore throat structure extraction: After washing, vacuuming and saturating epoxy resin, the core samples of each layer obtained in step S100 are cut and polished to form cast thin sections; then the cast thin sections are image acquired to obtain pore throat characteristic parameters.

[0019] S300, Quantitative modeling and combination of vertical heterogeneity: The pore throat characteristic parameters of the multi-layer core samples obtained in step S200 are normalized and then quantitatively combined to establish a continuously changing vertical heterogeneous distribution model.

[0020] S400 Microfluidic chip design and fabrication: Based on the vertical heterogeneous distribution model obtained in step S300, microfluidic chips are fabricated using photolithography-etching processes.

[0021] Furthermore, the microfluidic chip is used for studying the evolution of dominant seepage channels, evaluating the effectiveness of profile control and water shut-off, analyzing interlayer crossflow characteristics, or studying chemical flooding to enhance oil recovery.

[0022] Furthermore, in studying the evolution of dominant seepage channels, the formation mechanism of dominant channels was revealed by observing the fluid transport paths in different permeability zones in real time.

[0023] When evaluating the effectiveness of profile control and water shut-off, the sealing effect is observed after the plugging agent is injected, and the sealing mechanism of the plugging agent in different permeability ranges is studied.

[0024] When conducting interlayer crossflow characteristic analysis, the interlayer crossflow volume is quantitatively analyzed using tracer technology to study the conditions for crossflow occurrence.

[0025] In chemical flooding studies to enhance oil recovery, it is used to evaluate the oil displacement effect and residual oil distribution of different displacement agents in heterogeneous reservoirs.

[0026] Furthermore, in step S100, the reservoir is vertically divided into 3-6 layers, with the permeability difference between each layer being 2-10 times.

[0027] Further, in step S200, the thickness of the cast sheet is 0.3mm-0.5mm.

[0028] Furthermore, in step S200, the image processing employs a method combining threshold segmentation and morphological processing, achieving a pore recognition accuracy of 1 μm.

[0029] Furthermore, in step S400, the chip design uses AutoCAD software, and the channel depth is 10-100 μm.

[0030] Furthermore, in step S400, the etching depth error is controlled within ±2μm.

[0031] A microfluidic chip fabrication system based on the vertical heterogeneity of real core samples is provided. This system has program modules corresponding to the above steps and executes the steps in the above-described microfluidic chip fabrication method based on the vertical heterogeneity of real core samples during runtime.

[0032] A computer-readable storage medium storing a computer program configured to, when invoked by a processor, implement steps of a microfluidic chip fabrication method based on the vertical heterogeneity characteristics of a real core sample.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] 1. Improved accuracy in reconstructing geological features.

[0035] This invention, based on the extraction technology of real core castings, achieves accurate replication of micron-level pore networks, effectively solving the technical challenge of the fundamental difference between traditional regularized pore networks and real geological structures. Employing a geostatistically driven layered modeling method, it achieves quantitative characterization of continuous physical property changes, overcoming the technical limitation of simple layered models in simulating the rhythmic changes of actual reservoirs.

[0036] 2. Optimization of experimental simulation technical indicators.

[0037] This invention significantly improves the precision of microchannel fabrication, noticeably enhances surface quality, and yields superior optical performance. It also improves the precision of the experimental control system and the quality of data acquisition. Furthermore, it increases experimental preparation efficiency, shortens the cycle time for a single experiment, extends chip lifespan, and further enhances data acquisition efficiency.

[0038] 3. High fit to heterogeneous structures.

[0039] This invention employs an integrated construction method combining geological data, digital models, and physical chips. Based on thin sections of real rock core castings, pore throat parameters are extracted and manually calibrated. Combined with vertical heterogeneous stratigraphic division and quantitative combination models, manual intervention is used for pore throat correction, optimizing the connectivity model and enabling visualized observation of multiphase flow processes under gravity. Compared to existing technologies, this significantly improves the accuracy of pore structure reconstruction and the realism of vertical heterogeneous simulation, enhances the reliability of experimental data, simplifies the conversion process from geological features to physical models, and improves experimental efficiency.

[0040] 4. The application benefits have been significantly improved.

[0041] This invention improves the ability to identify seepage channels, enhances the effectiveness of profile control and water shut-off measures, strengthens the control of inter-layer crossflow, and improves the accuracy of recovery rate prediction. It reduces experimental costs, increases the efficiency of development scheme optimization, and reduces the number of field tests, which is expected to improve the final recovery rate. It is applicable to various development methods and provides key technical support for the construction of digital oilfields. Attached Figure Description

[0042] Figure 1 This is a flowchart of a microfluidic chip fabrication method based on the vertical heterogeneity of real rock cores in an embodiment of the present invention;

[0043] Figure 2 This is a schematic diagram of pore structure extraction and calibration in an embodiment of the present invention;

[0044] Figure 3This is a schematic diagram of vertical heterogeneous modeling in an embodiment of the present invention;

[0045] Figure 4 This is a schematic diagram of the vertical experimental device in an embodiment of the present invention. Detailed Implementation

[0046] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0047] Specific Implementation Plan 1: Combining Figure 1 As shown, this invention provides a method for fabricating a microfluidic chip based on the vertical heterogeneity of real rock cores, comprising the following steps:

[0048] S100, Stratigraphic Division and Core Sampling: Based on the target reservoir logging interpretation results and core analysis data, the reservoir is vertically divided into several stratigraphic layers according to permeability differences and sedimentary characteristics. For each stratigraphic layer, representative core samples are selected to ensure that the sample physical properties accurately reflect the reservoir characteristics of that layer. Specifically, the reservoir is vertically divided into 3-6 segments, with permeability differences between each segment ranging from 2 to 10 times.

[0049] S200, precise extraction of pore-throat structure: After washing the core sample and vacuum-saturating it with epoxy resin, the core sample is cut and polished into cast thin sections. High-resolution core cast thin section digitization technology (cast thin sections: core samples prepared after resin impregnation and staining, pores identified under a microscope, and pore structure extracted using pore digitization tools such as ImageJ) is employed. This involves extracting pore-throat feature parameters from the thin section image using image processing software; fine depiction of the pore-throat structure is performed in CAD software, with manual adjustments made when necessary (for some actually connected pores, but those extracted by the software are not connected, manual modification is required, and the size and roughness of different pores are adjusted to ensure consistency with the actual core characteristics), ensuring that the extracted pore shape factor, throat width-to-length ratio, and coordination number parameters are consistent with the actual core characteristics. The core samples are from representative core wells of the target reservoir, and the cast thin section thickness is 0.3mm-0.5mm. The image processing uses a combination of threshold segmentation and morphological processing, achieving a pore identification accuracy of 1μm.

[0050] S300, vertical heterogeneous quantitative modeling and combination, normalize the thickness of each layer, and quantitatively combine them in CAD software based on the extracted pore throat parameters; ensure the pore connectivity between each layer through manual adjustment, restore the heterogeneous characteristics of the real strata to the greatest extent, and establish a continuously changing vertical heterogeneous distribution model.

[0051] The S400 microfluidic chip design and fabrication employs a photolithography-etching process to transfer the final model, after quantitative assembly, onto a chip substrate. By optimizing mask design, exposure parameters, and etching conditions using existing methods, the channel fabrication accuracy is controlled, ensuring a high degree of consistency between the microchannels and the design model. The chip design utilizes AutoCAD, with channel depths ranging from 10 to 100 μm. The substrate is a silicon wafer, glass, or polydimethylsiloxane (PDMS), with etching depth errors controlled within ±2 μm.

[0052] S500, experimental applications: The fabricated chip is placed vertically to conduct various percolation experiments, including:

[0053] ① Study on the evolution of dominant seepage channels: By observing the fluid transport paths in different permeability sections in real time, the formation mechanism of dominant channels is revealed;

[0054] ② Evaluation of profile control and water shut-off effect: After injecting the plugging agent, observe the sealing effect and study the sealing mechanism of the plugging agent in different permeability zones;

[0055] ③ Interlayer flow characteristics analysis: The interlayer flow rate is quantitatively analyzed using tracer technology to study the conditions under which flow occurs;

[0056] ④ Chemical flooding to enhance oil recovery: Evaluate the oil displacement effect of different displacement agents in heterogeneous reservoirs and the distribution of residual oil.

[0057] Specific implementation scheme two: A microfluidic chip fabrication system based on the vertical heterogeneity of real rock cores. The system has program modules corresponding to the above steps, and executes the steps in the above-mentioned microfluidic chip fabrication method based on the vertical heterogeneity of real rock cores when running.

[0058] The other combinations and connections in this implementation scheme are the same as in Specific Implementation Scheme 1.

[0059] Specific Implementation Scheme 3: A computer-readable storage medium storing a computer program configured to implement, when called by a processor, the steps of a microfluidic chip fabrication method based on the vertical heterogeneity characteristics of a real core sample.

[0060] The other combinations and connections in this implementation scheme are the same as in Specific Implementation Scheme 1.

[0061] Example 1: Preparation and application of microfluidic chip in a river sand reservoir of an oilfield, combined with... Figures 2 to 4 As shown.

[0062] (1) Core sampling and processing.

[0063] Representative core samples from the target formation of the target oilfield were selected, and the reservoir was vertically divided into four layers (0-0.2, 0.2-0.4, 0.4-0.8, and 0.8-1.0) based on well logging interpretation results. Representative core samples (25 mm in diameter) were selected from each layer, washed with oil, vacuum-saturated with blue epoxy resin, and then cut and polished to produce 0.3 mm thick cast sheets.

[0064] (2) Image acquisition and processing.

[0065] Digital images of thin sections were acquired using a high-resolution scanner (2400 dpi) and image processing was performed using Image-Pro Plus software. Pore network parameters were extracted by grayscale thresholding, with average pore diameters ranging from 15 μm to 40 μm and coordination numbers from 2 to 4. Manual calibration was performed in AutoCAD software, focusing on correcting throat widths and pore morphology to ensure consistency with the characteristics of the actual core samples.

[0066] (3) Vertical heterogeneous modeling.

[0067] A vertically heterogeneous quantitative model was established: the permeability of the top 0-0.2 layer was 100 mD, the permeability of the middle 0.2-0.4 layer was 600 mD, the permeability of the lower middle 0.4-0.8 layer was 1500 mD, and the permeability of the bottom 0.8-1.0 layer was 2500 mD. After normalizing the thickness of each layer, quantitative combinations were performed in CAD software, and manual adjustments were made to ensure the connectivity of pores between layers.

[0068] (4) Chip processing and manufacturing.

[0069] Silicon-based chips are fabricated using a photolithography-etching process: ① Coating with 20μm thick SU-8 photoresist; ② Exposure through a mask (ultraviolet light, wavelength 365nm, exposure time 45 seconds); ③ Development to form a pattern; ④ ICP etching to form microchannels with a depth of 50μm; ⑤ Anodic bonding and encapsulation with a glass substrate; ⑥ Fabrication of injection and exit holes with a diameter of 1mm.

[0070] (5) Application in water drive experiments.

[0071] The chip was placed vertically, and an injection pump was connected to the bottom: ① saturated simulated oil (viscosity 3.2 mPa·s); ② dyed water was injected from the bottom at a flow rate of 0.05 mL / min; ③ the displacement process was observed under a microscope. Experimental results: the water exposure time in the bottom high-permeability layer was advanced by about 35%, the sweep efficiency in the middle section increased by about 25%, and the remaining oil saturation in the top low-permeability layer was relatively high.

[0072] Example 2: Experiment evaluating the effect of profile control and water plugging.

[0073] A profile-modified water-blocking experiment was conducted using the chip prepared in Example 1:

[0074] (1) First, water drive is carried out until the water content reaches 90%;

[0075] (2) Inject 0.3PV of polymer gel plugging agent (concentration 1500mg / L).

[0076] (3) Subsequent water flooding until the water content of the produced liquid is 98%.

[0077] Experimental results: The plugging agent preferentially enters the high-permeability layer, with a plugging rate of over 85%; the subsequent displacement fluid is directed to the medium- and low-permeability layers, increasing the recovery rate of the low-permeability layer by about 30%; inter-layer crossflow is effectively controlled, delaying the water breakthrough time by about 40%; the final recovery rate is 12% higher than that of waterflooding alone.

[0078] Alternative solutions: PDMS material can be selected as the substrate, and the microstructure can be replicated using soft photolithography; the accuracy of pore extraction can be improved by using a machine learning-based segmentation algorithm; the vertical stratification can be adjusted to a 3-layer or 5-layer mode according to the actual geological features; the experimental fluid can be replaced with polymer solution or foam with different displacing agents.

[0079] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A method for fabricating a microfluidic chip based on the vertical heterogeneity of real rock cores, characterized in that, Includes the following steps: S100, stratigraphic division and core sampling: The reservoir is vertically divided into several stratigraphic layers according to permeability differences and sedimentary characteristics; representative core samples are selected for each stratigraphic layer. The reservoir is vertically divided into 3-6 layers, with permeability differences between the layers ranging from 2 to 10 times. S200. Pore throat structure extraction: After washing, vacuuming and saturating epoxy resin, the core samples of each layer obtained in step S100 are cut and polished to form cast thin sections; then the cast thin sections are image acquired to obtain pore throat characteristic parameters. The thickness of the cast sheet is 0.3mm-0.5mm; The image processing method combines threshold segmentation and morphological processing, achieving a pore recognition accuracy of 1 μm. S300, Quantitative modeling and combination of vertical heterogeneity: The pore throat characteristic parameters of the multi-layer core samples obtained in step S200 are normalized and then quantitatively combined to establish a continuously changing vertical heterogeneous distribution model. S400, Microfluidic chip design and fabrication: Based on the vertical heterogeneous distribution model obtained in step S300, microfluidic chips are fabricated using photolithography-etching process; The microfluidic chip is used for studying the evolution of dominant seepage channels, evaluating the effectiveness of profile control and water shut-off, analyzing interlayer crossflow characteristics, or studying chemical flooding to improve oil recovery.

2. The method for fabricating a microfluidic chip based on the vertical heterogeneity of real rock cores according to claim 1, characterized in that: When studying the evolution of dominant seepage channels, the formation mechanism of dominant channels is revealed by observing the fluid transport paths in different permeability sections in real time. When evaluating the effectiveness of profile control and water shut-off, the sealing effect is observed after the plugging agent is injected, and the sealing mechanism of the plugging agent in different permeability ranges is studied. When conducting interlayer crossflow characteristic analysis, the interlayer crossflow volume is quantitatively analyzed using tracer technology to study the conditions for crossflow occurrence. In chemical flooding studies to enhance oil recovery, it is used to evaluate the oil displacement effect and residual oil distribution of different displacement agents in heterogeneous reservoirs.

3. The method for fabricating a microfluidic chip based on the vertical heterogeneity of real rock cores according to claim 2, characterized in that: In step S400, the chip design uses AutoCAD software, and the channel depth is 10μm-100μm.

4. The method for fabricating a microfluidic chip based on the vertical heterogeneity of real core samples according to claim 3, characterized in that: In step S400, the etching depth error is controlled within ±2μm.

5. A microfluidic chip fabrication system based on the vertical heterogeneity of real rock cores, characterized in that: The system has a program module corresponding to the steps of any one of claims 1-4 above, and executes the steps in the above-described microfluidic chip preparation method based on the vertical heterogeneity characteristics of real rock cores when it is run.

6. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program configured to, when invoked by a processor, implement the steps of the microfluidic chip fabrication method based on the vertical heterogeneity characteristics of real cores as described in any one of claims 1-4.

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