A high temperature and high pressure micro-displacement method based on a dual-pore microfluidic model with equal porosity

Abstract

This invention discloses a high-temperature and high-pressure micro-displacement method based on an isoporosity dual-pore microfluidic model. Addressing the issues of irreversible diagenesis and the difficulty in obtaining paired samples before and after evolution, a baseline model A and an experimental model B are constructed. Isoporosity constraints are used to eliminate interference from reservoir property differences, enabling a quantitative evaluation of the influence of dissolution pore structure on seepage patterns. The method includes: S1, extracting the primary intergranular pore skeleton and secondary dissolution pore characteristics from typical core thin sections of the same stratum; S2, constructing the baseline model A; S3, embedding dissolution pore units within its topological space and using an equivalent volume compensation algorithm to adaptively scale the intergranular channels to form model B; S4, verifying the porosity accuracy of the completed baseline model A and experimental model to ensure that the pore volume deviation between the two models does not exceed 5%; S5, conducting comparative displacement experiments under real high-temperature and high-pressure conditions.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development and seepage mechanics physical simulation technology, specifically to a high-temperature and high-pressure micro-displacement method based on an equal porosity dual-pore microfluidic model. Background Technology

[0002] Microscopic displacement experiments are an important tool for studying reservoir seepage mechanisms and evaluating oil and gas recovery rates. With the increasing demand for the development of unconventional and complex heterogeneous oil and gas reservoirs, dissolution reservoirs have attracted much attention because secondary dissolution during diagenesis alters the topological connectivity of primary intergranular pores, thus significantly affecting the fluid occurrence state and displacement efficiency.

[0003] Existing microphysical simulation techniques have significant limitations in studying dissolution reservoirs: Firstly, the irreversibility of diagenetic evolution means that paired samples of the same core before and after dissolution cannot be obtained in actual sampling. This results in a lack of baseline samples from the same source, making it difficult to clarify the process by which dissolution modifies pores. Secondly, severe variable coupling occurs; in traditional core comparison experiments, porosity, permeability, and wettability between samples are usually mutually variable and coupled, leading to significant differences in displacement patterns that are difficult to attribute to specific topological changes. Thirdly, a lack of single-factor control methods exists; existing model reconstruction techniques lack single-factor control methods for the influence of topological structures. Although dissolution causes changes in formation porosity during actual formation evolution, in laboratory mechanism studies, if both total porosity and pore topology change simultaneously, the reasons for differences in seepage patterns cannot be clearly identified.

[0004] Therefore, how to construct a microscopic physical simulation method for a single variable under the actual temperature and pressure conditions of the reservoir and through the constraint of equal porosity has become an important research topic for exploring the seepage mechanism of complex heterogeneous reservoirs and improving the accuracy of recovery rate evaluation. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a high-temperature and high-pressure micro-displacement method based on an equal-porosity dual-pore microfluidic model.

[0006] The purpose of this invention is to overcome the difficulty of quantitatively evaluating the independent contribution of dissolution pores to the seepage law in the existing technology, and thus provide a high-temperature and high-pressure micro-displacement method based on a dual-pore microfluidic model with equal porosity.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: The provided high-temperature and high-pressure microscopic displacement device mainly includes: an inlet displacement pump, an intermediate container, a confining pressure pump, a high-temperature and high-pressure microscopic visualization experimental platform, a parameter control console, and an outlet displacement pump. The high-temperature and high-pressure microscopic visualization experimental platform is self-heating, pressurized by the displacement pump, and can house a microfluidic chip. The microfluidic chip includes a baseline model A and an experimental model B. The fabrication method of the baseline model A specifically includes the following steps: converting the original intergranular pore mesh framework extracted from a real rock core into a vectorized topology; based on the pore size distribution parameters of the real rock core casting thin section, setting the solid wall boundary, and reconstructing the vectorized topology into a digital pore model with equivalent flow characteristics; based on micro-nano fabrication technology, etching the digital pore model onto the substrate material to obtain the baseline model A. The fabrication method of the experimental model B is identical to that of the baseline model A, except for the difference in the vectorized topology characterization step. The vectorized topology characterization step specifically involves: embedding the typical secondary dissolution pore units into the topological space of the reference model A; and calculating the initial total pore volume of the primary intergranular channels in the reference model A. V initial ;Calculate the newly added dissolution pore volume in experimental model B after embedding the secondary irregular dissolution pore unit. ΔV Using the total pore volume as a constraint, calculate the target volume of the primary intergranular channels in the experimental model. V target =V initial -ΔV Based on the target volume V target By using adaptive scaling, the final total pore volume of the experimental model B is made to deviate from the absolute value of the reference model A by ≤5%, and finally the vectorized topology of the experimental model B is obtained.

[0008] Based on the above-mentioned device, the present invention also provides a high-temperature and high-pressure microscopic displacement method, comprising the following steps: S1, extracting typical primary intergranular pore mesh skeleton and secondary irregular dissolution pore unit features from typical core casting thin section images of the same layer; S2, constructing a benchmark model A reflecting the basic structure of the formation based on the primary intergranular pore mesh skeleton; S3, simulating the reservoir dissolution and transformation process by embedding the typical secondary dissolution pore units in the topological space of model A, and then using an equivalent volume compensation algorithm to adaptively scale the intergranular pores in experimental model B; S4, verifying the porosity accuracy of the processed benchmark model A and experimental model B to ensure that the total pore volume of model B deviates from the absolute deviation of benchmark model A by ≤5%; S5, assembling the obtained models A and B into a high-temperature and high-pressure microscopic visualization experimental device, and conducting comparative displacement experiments under real high-temperature and high-pressure conditions of the reservoir.

[0009] Beneficial effects of the invention The beneficial effects of the method provided by this invention are mainly reflected in the following four aspects: 1. Reproducing the true temperature and pressure conditions of the reservoir. Most existing experimental methods use ambient temperature and pressure devices, which are difficult to simulate the actual formation temperature and pressure conditions of oil reservoirs. This leads to a mismatch between experimental results and field development. This invention, based on a constructed experimental platform, ensures high-temperature and high-pressure conditions within the experimental device, and simultaneously achieves stable micro-displacement in conjunction with a displacement pump.

[0010] 2. Single-factor variable control of microscopic seepage experiments was achieved. Through the equivalent volume compensation algorithm, this invention adaptively reduces the original pore volume while introducing the topological features of dissolution pores, ensuring that the absolute deviation of total porosity between the models before and after is ≤5%, successfully eliminating the interference caused by the increase in volume, and realizing a quantitative evaluation of the contribution of dissolution pore structure to the displacement mechanism.

[0011] 3. The problem of non-retrospective comparison of stratigraphic samples was solved. By reconstructing the same primary intergranular pore mesh framework, the diagenetic evolution logic was artificially simulated, overcoming the difficulty of obtaining pore distribution images of the same core sample before and after evolution, making the experimental conclusions more convincing. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the high-temperature and high-pressure microscopic visualization displacement system provided by the present invention. In the figure: 1-inlet displacement pump, 2-intermediate container, 3-containing pressure pump, 4-high-temperature and high-pressure microscopic visualization experimental platform, 5-parameter control console, 6-outlet displacement pump.

[0013] Figure 2 This is a schematic diagram of the overall process of the microscopic displacement method provided by the present invention.

[0014] Figure 3 shows the principle of model reconstruction and porosity compensation. In the figure: (a) - benchmark model A, (b) - initial model after embedding dissolution units, (c) - experimental model B after executing the compensation algorithm. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solution of this invention will be clearly and completely described below in conjunction with a preferred embodiment. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0016] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0017] Example: High-Temperature and High-Pressure Micro-Displacement Method Based on Equal Porosity Dual-Porosity Microfluidic Model. This example constructs an equal porosity dual-pore microfluidic model. The construction steps are as follows: A sandstone reservoir in a deep oilfield is selected, with formation conditions of 15 MPa and 90℃. Based on the actual cast thin section image of the reservoir, typical primary intergranular pore mesh skeleton and typical secondary dissolution pore units are extracted. Combining image processing technology, the primary intergranular pore mesh skeleton and typical secondary dissolution pore units are transformed into vectorized topological structures, where the vectorized topological structure of the primary intergranular pore mesh skeleton is the reference model A vector model. Mineral composition identification is performed on the core cast thin section image to delineate the easily soluble regions in the reference model A. The vectorized topological structure of the typical secondary dissolution pore units is embedded into the easily soluble regions in the reference model A, thereby obtaining the vectorized topological structure of the incompletely processed experimental model B. Based on the equivalent volume compensation algorithm, the following calculations are performed: the initial average pore width of the reference model A is 30 μm, the etching depth is 20 μm, and the total pore volume is... V initial The total volume occupied by the two newly added dissolution pit units is 0.4 mm³. ΔV The total pore volume is 0.08 mm³. To ensure that the total pore volume remains constant, the total volume of the original channels in experimental model B is... V target The volume should be compressed to 0.32 mm³. Based on the target volume, the initial vector model containing the newly added dissolution pores was adaptively adjusted using two methods: proportional reduction and local weighted scaling. In the local weighted scaling, since the experimental object was a sandstone reservoir, the parameters used in this embodiment were: α = 1.2; β = 0.85. After algorithm compensation, the average width of the original pores in experimental model B was reduced from the initial 30 μm to 24 μm, thus completing the vector model construction of experimental model B. Finally, after the vector model passed the porosity accuracy verification, it was etched onto a sapphire glass substrate using laser etching technology to obtain the microfluidic chip required for the experiment.

[0018] The specific steps of the high-temperature and high-pressure micro-displacement method based on this model are as follows: S1. System connection and airtightness check: Install the microfluidic chip into the high temperature and high pressure microscopic visualization experimental stage, connect the pipelines at each end, and inject test gas using the inlet displacement pump to observe the pressure change and ensure that the device is airtight. S2. Formation environment loading: Adjust the confining pressure pump to reach a confining pressure of 20MPa, turn on the heating system, and heat the device to 90℃; S3. Fluid Saturation and Initialization: Use the inlet displacement pump to pump the crude oil in the intermediate container into the model, and set the outlet displacement pump to constant pressure receiving mode to ensure that the pressure at both ends of the chip is the same. S4, Displacement: Replace the fluid in the inlet section and displace the fluid through coordinated control of the inlet and outlet pumps; S5, Image collection:全程跟踪模型驱替动态通过参数控制台配套的高速显微镜全程跟踪模型驱替动态;全程跟踪模型驱替动态Track the displacement dynamics of the model throughout the process using a high-speed microscope equipped with the parameter console; The controls involved in this invention are all prior arts and will not be elaborated here.

[0019] The above are only embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or equivalent process transformations made using the content of the specification and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included in the patent protection scope of the present invention.

Claims

1. A high-temperature and high-pressure micro-displacement method based on a dual-pore microfluidic model with equal porosity, characterized in that, Includes the following steps: S1. Extract the features of typical primary intergranular pore mesh framework and secondary irregular dissolution pore units from thin section images of typical core castings in the same layer. S2. Based on the original intergranular pore mesh skeleton, construct a benchmark model A that reflects the basic structure of the formation; S3. By embedding typical secondary dissolution pore units in the topological space of model A, simulate the reservoir dissolution and transformation process, and then use the equivalent volume compensation algorithm to adaptively scale the intergranular pores in experimental model B. S4. Verify the porosity accuracy of the completed benchmark model A and experimental model B to ensure that the total pore volume of model B deviates from the absolute value of benchmark model A by ≤5%; S5. Assemble the obtained models A and B into a high-temperature and high-pressure microscopic visualization experimental device and conduct comparative displacement experiments under real high-temperature and high-pressure conditions in the reservoir.

2. The method according to claim 1, characterized in that, In step S1, the specific process of extracting features includes: performing grayscale and binarization processing on the cast thin section image of the typical rock core to separate the rock matrix and pore space; and extracting the connected typical primary intergranular pore mesh skeleton and secondary irregular dissolution pore units based on image processing technology.

3. The method according to claim 1, characterized in that, In step S2, the specific process of constructing the benchmark model A includes: converting the original intergranular pore mesh skeleton extracted in step S1 into a vectorized topology; setting the solid wall boundary based on the real pore size distribution parameters of the typical core casting thin section, and reconstructing the vectorized topology into a digital pore model with equivalent flow characteristics; and etching the digital pore model onto the substrate material based on micro-nano fabrication technology.

4. The method according to claim 1, characterized in that, In step S3, the specific implementation process of embedding the typical secondary dissolution pore unit includes: converting the features of the secondary irregular dissolution pore unit extracted in step S1 into a vectorized topological structure; identifying the mineral composition of the core casting thin section in step S1 and dividing the easily soluble region in the benchmark model A; and embedding the vectorized topological structure of the typical secondary dissolution pore unit into the easily soluble region in the benchmark model A.

5. The method according to claim 1, characterized in that, In step S3, the specific implementation process of the equivalent volume compensation algorithm includes: calculating the initial total pore volume of the primary intergranular channels in the benchmark model A. V initial ;Calculate the newly added dissolution pore volume in experimental model B after embedding the secondary irregular dissolution pore unit. ΔV Using the total pore volume as a constraint, calculate the target volume of the primary intergranular channels in the experimental model. V target =V initial -ΔV Based on the target volume V target Adaptive scaling is used to ensure that the total pore volume of the experimental model B deviates from that of the benchmark model A by ≤5%.

6. The method according to claim 4, characterized in that, The adaptive scaling implementation process includes two methods: global proportional scaling and local weighted scaling; the specific implementation process of local weighted scaling is as follows: Let any channel in experimental model B... i The initial width is d i，0 The scaled target width is d i，1 To protect the model's seepage characteristics while compensating for volume, a local adaptive weighting coefficient is introduced. X i Therefore, the formula for calculating the target width is: d i，1= d i，0 ∙(1-λ∙X i ） （1） In the formula, λ The global base scaling factor is determined by the total compensation volume. X i This is a local weighting function, and its expression is related to the hydraulic radius of the orifice. R i The logic of negative correlation: X i= α∙ （2） In the formula, R The average hydraulic radius of the original pore network. α and β The preset lithology-sensitive adjustment constant is used. Based on the above weight function, the algorithm assigns differentiated scaling weights to pores of different specifications according to the original pore-throat ratio and permeability contribution of different regions, and finally scales them uniformly.

7. The method according to claim 1, characterized in that, In step S4, the specific implementation process of the porosity accuracy verification includes: using a stereomicroscope to perform a panoramic scan of the seepage area of ​​the benchmark model A and the experimental model B at the same magnification to obtain a binary mapping map; using image processing software to count the total number of white pixels (pores) in the effective seepage area; comparing the total number of white pixels (pores) of models A and B, if the absolute deviation is ≤5%, the compensation algorithm is determined to be effective.

8. The method according to claim 1, characterized in that, In step S5, the specific implementation conditions of the comparative displacement experiment include: using a heating system to simulate the actual temperature conditions of the reservoir, and using a displacement system to restore the actual formation pressure.

9. The method according to claim 1, characterized in that, In step S5, the evaluation indicators for the comparative displacement experiment include: calculating the differences in residual oil saturation, sweep efficiency, and displacement pressure between the baseline model A and the experimental model B at different injection stages.

10. A high-temperature, high-pressure microscopic displacement device, characterized in that: It mainly includes an inlet displacement pump, an intermediate container, a confining pressure pump, a high-temperature and high-pressure microscopic visualization experimental platform, a parameter control console, and an outlet displacement pump; the high-temperature and high-pressure microscopic visualization experimental platform is self-heating, can be pressurized by means of the displacement pump, and can house a microfluidic chip; the microfluidic chip includes a baseline model A and an experimental model B; the high-temperature and high-pressure microscopic displacement device implements the high-temperature and high-pressure microscopic displacement method as described in any one of claims 1 to 9 when it is in operation.

Images