Method and device for preparing salt rock-mudstone interface model sample

Abstract

The present application discloses a method and device for preparing a salt rock-mudstone interface model sample, comprising the following steps: loading a mudstone layer and a salt powder layer in a mold, wherein the salt powder layer is located on the upper part of the mudstone layer; heating the mold loaded with the mudstone and salt powder until the salt powder reaches a molten state; then cooling the mold to allow the molten salt to slowly cool and grow and recrystallize, and by controlling the temperature curve of the slow cooling growth of the molten salt, the crystallization process of the molten salt at the interface position between the mudstone layer and the salt powder layer is controlled to prepare a salt rock-mudstone interface model sample that matches the actual rock structure; the present application grows salt rock crystals similar to the natural layered salt rock structure on the mudstone surface by melting and slow cooling crystallization, ensuring that the mechanical and permeability properties of the model sample at the salt rock-mudstone interface are close to real conditions, thereby providing an experimental basis for conducting long-term stability and airtightness research on salt cavern energy storage systems.

Description

Technical Field

[0001] The present application relates to the field of geotechnical engineering technology, and in particular to a method and device for preparing a salt rock-mudstone interface model sample. Background Art

[0002] Currently, underground salt caverns are a key energy storage facility, widely used in compressed air energy storage, hydrogen energy storage, and crude oil storage. Salt caverns are constructed within salt rock layers primarily composed of sodium chloride, offering excellent sealing properties and long-term stability. However, most salt rock in China is lacustrine, layered salt deposited within these layers, interbedded with mudstone. This results in numerous salt-mudstone interfaces within the surrounding rock mass of the salt caverns. These interfaces inherently have weak tensile and shear strengths, making them susceptible to slippage failure when uncoordinated displacement occurs between the two rock types. This ineffectively anchors the interlayers, which suppress creep in the surrounding rock, reducing the cavern's usable volume and compromising its mechanical stability. Furthermore, when the interface between the two rock types is damaged or even slipped, cracks form. Once this interlayer crack network develops sufficiently, it becomes a leakage channel for the stored medium, compromising the energy storage efficiency of the salt cavern. Leaked stored medium can also cause accidents such as groundwater contamination and surface fires.

[0003] Therefore, conducting mechanical and permeability experiments on the interface of salt rock and mudstone is very important for evaluating the energy storage reliability of salt caverns. However, due to the poor mechanical properties of the interface, during the process of drilling and coring, the interface is often damaged by drilling mechanical forces, stress release, etc., making it difficult to obtain complete and sufficient interface rock samples. To solve this problem, the most commonly used method in academia is to artificially prepare salt rock-mudstone interface model samples, using cement slurry or cement mortar as an alternative material. After the cement slurry or cement mortar is cast in layers, it is pressed using positive stress to achieve bonding between the interfaces. This method utilizes the plasticity of cement slurry and cement mortar, has the advantages of convenient preparation and homogeneous finished products, and can achieve batch preparation of model samples. However, this method has many defects:

[0004] 1. Differences in material properties: The simulated material formed after cement curing has significant differences in crystal structure and void distribution from real salt rock and mudstone. Therefore, the prepared rock model is difficult to simulate the mechanical properties and permeability of the actual layered salt rock-interlayered mudstone body and the interface between them.

[0005] 2. Different diagenetic mechanisms: The compression effect during sample preparation is significantly different from the natural formation process of the layered rock structure of salt rock and mudstone. In particular, during the sedimentary diagenesis of layered salt rock, the salt rock on one side of the interface will undergo complex melting, dissolution, and crystallization processes under the action of stress and temperature, making the cementation effect of the interface more complex and difficult to simulate through simple compression. As a result, the experimental results of the interface model cannot accurately reflect the actual situation.

[0006] From the above analysis, it can be seen that the existing layered rock preparation technology has many shortcomings in simulating the mechanical and permeability properties of the layered salt rock-mudstone interface. The present application provides a method and device for preparing a salt rock-mudstone interface model sample, aiming to solve the above-mentioned defects of the existing technology. Summary of the Invention

[0007] To address the above-mentioned issues, the present application provides a method and apparatus for preparing a salt rock-mudstone interface model sample. By melting and slowly cooling and crystallizing, salt rock crystals with a structure similar to that of natural layered salt rock are grown on the mudstone surface, ensuring that the mechanical and permeability properties of the model sample at the salt rock-mudstone interface are close to those of real conditions. The technical solution is as follows:

[0008] In a first aspect, the present application provides a method for preparing a salt rock-mudstone interface model sample, comprising the following steps: loading a mudstone layer and a salt powder layer in a mold, wherein the salt powder layer is located on the upper part of the mudstone layer; heating the mold loaded with mudstone and salt powder until the salt powder reaches a molten state; then cooling the mold to allow the molten salt to slowly cool and grow and recrystallize, and by controlling the temperature curve of the slow cooling growth of the molten salt, controlling the crystallization process of the molten salt at the interface position between the mudstone layer and the salt powder layer, a salt rock-mudstone interface model sample matching the actual rock structure is prepared.

[0009] For example, in the method for preparing the salt rock-mudstone interface model sample provided in one embodiment, when heating the mold loaded with mudstone and salt powder, the heating rate is controlled to be 5-10° C. / min.

[0010] For example, in the preparation method of the salt rock-mudstone interface model sample provided in one embodiment, after the mold loaded with mudstone and salt powder is heated to the melting point of the salt powder, it is kept warm so that the salt powder layer is fully melted and sufficient ion diffusion occurs. The holding time is determined according to the amount of salt powder.

[0011] For example, in the method for preparing the salt rock-mudstone interface model sample provided in one embodiment, slow cooling is adopted when cooling the mold, and the temperature is controlled to gradually drop to 600-650°C to adjust the supercooling degree, thereby controlling the crystal growth rate.

[0012] For example, in the method for preparing the salt rock-mudstone interface model sample provided in one embodiment, slow cooling is adopted when cooling the mold, and the temperature is controlled to gradually drop to 638° C. to form a crystal nucleus with a stable crystal phase.

[0013] For example, in the method for preparing the salt rock-mudstone interface model sample provided in one embodiment, after the mold temperature drops below 600° C., the cooling rate is controlled to 1-3° C. / min to ensure a uniform grain structure.

[0014] For example, in the preparation method of the salt rock-mudstone interface model sample provided in one embodiment, the upper surface of the mudstone layer is a flat surface with a certain roughness to serve as a crystallization bed of molten salt, and the salt powder layer is laid on the upper surface of the mudstone layer and covers the upper surface of the mudstone layer.

[0015] For example, in the method for preparing the salt rock-mudstone interface model sample provided in one embodiment, the salt powder layer is high-purity sodium chloride salt powder, and the salt powder particle size is above 200 mesh.

[0016] For example, in the preparation method of the salt rock-mudstone interface model sample provided in one embodiment, quartz sand high-temperature resistant granular material is added to the salt powder layer as a seed crystal to improve the nucleation efficiency and cementation strength at the interface position between the mudstone layer and the salt powder layer.

[0017] A second aspect of the present application provides a device for preparing a salt rock-mudstone interface model sample, comprising a mold and a high-temperature melting furnace, wherein the mold is used to load a mudstone layer and a salt powder layer, and the salt powder layer is located on the upper part of the mudstone layer; the high-temperature melting furnace is used to heat and cool the mold loaded with the mudstone layer and the salt powder layer, a temperature sensor is provided in the high-temperature melting furnace for monitoring the temperature in the furnace, and a temperature program control system electrically connected to the temperature sensor is provided on the high-temperature melting furnace to adjust the temperature change rate and time, and set the temperature curves of the heating, insulation and cooling stages to ensure the temperature accuracy of the salt powder during the melting and crystallization process.

[0018] The beneficial effects of a method and apparatus for preparing a salt rock-mudstone interface model sample provided in some embodiments of the present application are as follows: Compared with the traditional cement pressing sample preparation method, the present application adopts a melting salt rock method, which grows salt rock crystals with a structure similar to natural layered salt rock on the mudstone surface through melting and slow cooling crystallization. This ensures that the mechanical and permeability properties of the model sample at the salt rock-mudstone interface are close to those under real conditions, and has the following significant advantages:

[0019] (1) Improving the matching degree of the main material properties of the model: This application uses real mudstone and sodium chloride salt as raw materials for preparation. The prepared mudstone-salt rock composite structure is closer to natural salt rock and mudstone in terms of the rock body, thereby improving the similarity of the mechanical and seepage properties of the rock model.

[0020] (2) Restoring the real diagenetic process: This application uses the melting method to simulate the deposition and phase transformation mechanism of layered salt rock in nature by adjusting the temperature curve. By adjusting the supercooling and grain density of the crystallization process, the crystal structure of the rock model is matched with the real salt rock. The crystal growth, cementation and other processes at the interface between salt rock and mudstone are reproduced from the crystallographic level to ensure the similarity of the mechanical, seepage and other properties of the interface of the rock model with the natural interface.

[0021] (3) Ensure the stability and repeatability of experimental samples: Through a controllable melting-crystallization process, a stable and uniform rock model is prepared to provide repeatable and reliable experimental results, providing an experimental basis for conducting long-term stability and airtightness research on salt cavern energy storage systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of this specification or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 This is a schematic diagram of the overall structure of the salt rock-mudstone interface model sample preparation device of this application;

[0024] Figure 2 This is a schematic diagram of the mold structure of the salt rock-mudstone interface model sample preparation device of this application. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0026] Unless otherwise defined, the technical or scientific terms used in this disclosure should have the usual meanings understood by persons of ordinary skill in the field to which this disclosure belongs. The words "first", "second" and similar terms used in this disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "include" or "comprise" mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0027] In view of the shortcomings of existing layered rock preparation technology in simulating the mechanical and permeability properties of layered salt rock-mudstone interface, this application proposes a method and device for preparing salt rock-mudstone interface model specimens, aiming to solve the following key technical problems:

[0028] 1. Inaccurate interface mechanics and permeability characteristics: Traditional preparation methods often use cement mortar or cement paste to simulate layered interfaces. Although this method is convenient, the mechanical properties and permeability characteristics of cement materials are significantly different from those of real salt rock and mudstone. As a result, the prepared model cannot truly reflect the mechanical behavior and seepage characteristics of the natural interface, affecting the accuracy of the experimental results.

[0029] 2. The interface bonding mechanism of the model is not restored: The cement-based interface material is formed through a pressing process, but the interface bonding strength formed is relatively weak. Moreover, the interface after pressing cannot effectively simulate the complex thermal history and physical and chemical bonding formed by mineral recrystallization during the sedimentary diagenesis process of real salt rock, resulting in unstable mechanical and seepage properties.

[0030] 3. The simulation accuracy and uniformity of the samples are not high: In the existing technology, the pressing effects at different positions during the pressing process of cement samples may be different, resulting in large differences in the repeatability and accuracy of the experimental results of the prepared samples, and it is impossible to provide consistent and reliable experimental data.

[0031] In view of this, the present application provides a method and device for preparing a salt rock-mudstone interface model sample. By melting and slow cooling crystallization, salt rock crystals similar to the natural layered salt rock structure are grown on the mudstone surface, ensuring that the mechanical and permeability properties of the model sample at the salt rock-mudstone interface are close to real conditions.

[0032] The salt rock-mudstone interface model sample preparation device of this application is as follows Figure 1-2As shown, it includes: a mold 3 and a high-temperature melting furnace 1, the mold 3 is used to load a mudstone layer 6 and a salt powder layer 5, and the salt powder layer 5 is located on the upper part of the mudstone layer 6; the high-temperature melting furnace 1 is used to heat and cool the mold 3 loaded with the mudstone layer 6 and the salt powder layer 5, and a temperature sensor 2 is provided in the high-temperature melting furnace 1 for monitoring the temperature in the furnace, and a temperature program control system 4 electrically connected to the temperature sensor 2 is provided on the high-temperature melting furnace 1 to accurately adjust the temperature change rate and time, and set the temperature curves of the heating, insulation and cooling stages to ensure the temperature accuracy of the salt powder during the melting and crystallization process.

[0033] Among them, the high-temperature melting furnace 1 is a high-temperature muffle furnace, which is used to heat the salt powder to its molten state (the temperature reaches above 801°C) and control the subsequent cooling and crystallization process; the mold 3 is used to load mudstone and salt powder, has high-temperature thermal shock resistance, and maintains minimal deformation at high temperatures. At the same time, a special coating is applied on the inner surface of the mold 3 to ensure that the salt rock-mudstone interface model sample can be smoothly demolded after preparation and molding.

[0034] The method for preparing a salt rock-mudstone interface model sample using the salt rock-mudstone interface model sample preparation device of the present application is as follows:

[0035] 1. Material preparation

[0036] Mudstone: Select natural mudstone and cut it into the required sample size. Ensure that the selected mudstone has strong thermal stability under high temperature conditions to avoid excessive deformation or cracking.

[0037] Salt powder: Use high-purity sodium chloride salt powder to avoid excessive impurities that could affect the stability of the crystallization process. The salt powder particle size should be controlled above 200 mesh to ensure a rapid and uniform melting process. High-temperature resistant granular materials such as quartz sand can also be added to the salt powder as seed crystals to improve the bonding strength at the interface between the mudstone layer 6 and the salt powder layer 5.

[0038] 2. Material loading

[0039] 2.1 Mudstone preparation and loading: The prepared natural mudstone is placed at the bottom of the mold 3. The surface of the mudstone layer 6 should have a certain degree of roughness while being flat as a whole, so as to provide a good crystallization environment for the molten salt and ensure that the molten salt can be evenly distributed on its surface.

[0040] 2.2 Salt powder filling: Sodium chloride salt powder is evenly spread on the surface of the mudstone layer 6. The thickness of the salt powder layer 5 is determined according to the specifications of the model sample to ensure that the molten salt can cover the surface of the mudstone layer 6 and the composite sample after preparation can meet the required specifications.

[0041] 3. Sample preparation process

[0042] 3.1 Melting process

[0043] Heating stage: The temperature is gradually raised to above 801°C by the high-temperature melting furnace 1. This process requires precise control of the heating rate to avoid temperature fluctuations causing damage to the mudstone layer 6, the mold 3 and the structure of the high-temperature melting furnace 1. The heating rate is generally controlled to be 5-10°C / min.

[0044] Holding stage: The temperature is maintained above the melting point of the sodium chloride salt to allow it to fully melt and allow for sufficient ion diffusion. The holding time is determined by the amount of salt powder and is generally 1-2 hours. Because the density of the salt powder is lower than that of the mudstone, it will always remain on top of the mudstone.

[0045] 3.2 Slow cooling growth

[0046] The recrystallization of molten salt requires a certain degree of supercooling, that is, the actual phase change (crystallization) temperature must be lower than the phase change temperature (801°C) in the equilibrium state. This difference is the supercooling. Supercooling is the driving force for the crystallization of molten salt. The size and change process of supercooling will affect the grain density and microstructure of the crystallized salt.

[0047] Slow cooling: During the cooling phase, the temperature is gradually lowered to 600-650°C to control the crystal growth rate. By regulating the degree of supercooling, the sodium chloride salt gradually crystallizes, forming a crystal nucleus density and crystal structure similar to natural salt rock.

[0048] Crystallization control: After the temperature drops below 600°C, crystals gradually grow. During this process, the temperature drop rate is controlled at 1-3°C / min to ensure a uniform grain structure and avoid the formation of oversized grains or structural defects.

[0049] The preparation of the salt rock-mudstone interface model sample has been completed. The prepared salt rock-mudstone interface model can be used for mechanical experiments (such as uniaxial compression and shear strength tests) and permeability experiments to simulate the geological conditions in the salt cavern energy storage system.

[0050] Among them, the magnitude and change process of supercooling will directly affect the grain density and microstructure of the crystalline salt, so the slow cooling growth stage is the key step of this application.

[0051] Under conditions of rapid cooling and a large degree of undercooling, the faster the crystallization rate, the more crystallization centers are formed. The nucleation rate (the number of crystal nuclei formed per unit time and per unit volume) increases faster than the rate of nucleus growth. When crystals grow around multiple crystallization centers, they are less likely to grow, resulting in finer grains and a higher grain density. Conversely, the slower the crystallization rate, the fewer crystallization centers in the system, which is more conducive to crystal growth and results in more coarse-grained crystals. Therefore, it is important to ensure that the temperature drop rate allows the number of crystal nuclei to match that of real salt rock, while also ensuring that the rough surface of the mudstone serves as the dominant interface for the crystal bed, and that the crystal density and cementation strength at that interface are maintained.

[0052] During slow cooling growth, it is important to ensure that the critical supercooling for uniform nucleation of sodium chloride is achieved, approximately 163°C. Specifically, the slow cooling growth temperature curve is designed at a baseline level of 638°C, so that the resulting nuclei have a stable crystalline phase. At the same time, during the slow cooling growth process, it is important to ensure that the temperature does not drop too quickly or that the supercooling is too great, otherwise the resulting salt will be amorphous, with strength far inferior to that of crystalline salt rock.

[0053] In summary, the method of the present application was used to prepare a salt rock-mudstone interface model specimen. The crystal growth process was influenced by adjusting the temperature control curve to simulate the crystal structure of salt rocks in different regions. The temperature curve was optimized through multiple experiments, and the nucleation process was designed and adjusted to simulate a crystal structure and grain density at the interface position that was closer to that of natural salt rock.

[0054] The preparation method of the salt rock-mudstone interface model sample of the present application grows salt rock crystals with a structure similar to that of natural layered salt rock on the mudstone surface through melting and slow cooling crystallization, ensuring that the mechanical and permeability properties of the model sample at the salt rock-mudstone interface are close to real conditions; by precisely designing the temperature curve and adjusting the crystal nucleus density, crystal volume and crystal structure by controlling the degree of supercooling, the crystal growth process close to that of natural salt rock is simulated. The present application simulates the diagenetic mechanism of layered salt rock, specifically the melting and recrystallization process of layered salt rock at the interface under the influence of geothermal conditions. The interface model material prepared based on this principle and related experiments will provide a more reliable experimental basis for the long-term reliability of salt cavern energy storage systems.

[0055] Although the implementation scheme of the present application has been disclosed as above, it is not limited to the applications listed in the description and implementation mode. It can be fully applied to various fields suitable for the present application. For those familiar with this field, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present application is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for preparing a salt rock-mudstone interface model sample, characterized in that: The following steps are involved: A mudstone layer and a salt powder layer are loaded into the mold, wherein the salt powder layer is located on the upper part of the mudstone layer; The mold loaded with mudstone and salt powder is heated until the salt powder reaches a molten state, and after the mold loaded with mudstone and salt powder is heated to the melting point of the salt powder, the mold is kept warm; The mold is then cooled to allow the molten salt to slowly cool and grow and recrystallize. By controlling the temperature curve of the slow cooling growth of the molten salt, the molten salt reaches a critical supercooling degree at the interface of the mudstone layer to form a stable crystalline phase. The crystallization process of the molten salt at the interface between the mudstone layer and the salt powder layer is controlled to prepare a salt rock-mudstone interface model sample that matches the actual rock structure.

2. The method for preparing the salt rock-mudstone interface model sample according to claim 1, characterized in that: When heating the mold loaded with mudstone and salt powder, the heating rate is controlled to be 5-10°C / min.

3. The method for preparing the salt rock-mudstone interface model sample according to claim 1, characterized in that: When cooling the mold, slow cooling is adopted to control the temperature to gradually drop to 600-650°C to adjust the supercooling degree and thus control the crystal growth rate.

4. The method for preparing the salt rock-mudstone interface model sample according to claim 3, characterized in that: When cooling the mold, slow cooling is adopted to control the temperature to gradually drop to 638°C to form a crystal nucleus with a stable crystal phase.

5. The method for preparing the salt rock-mudstone interface model sample according to claim 4, characterized in that: When the mold temperature drops below 600°C, control the cooling rate to 1-3°C / min to ensure uniform grain structure.

6. The method for preparing a salt rock-mudstone interface model sample according to claim 1, characterized in that: The upper surface of the mudstone layer is a flat surface with a certain degree of roughness, so as to serve as a crystallization bed of molten salt. The salt powder layer is laid on and covers the upper surface of the mudstone layer.

7. The method for preparing a salt rock-mudstone interface model sample according to claim 1, characterized in that: The salt powder layer is high-purity sodium chloride salt powder, and the salt powder particle size is above 200 meshes.

8. The method for preparing a salt rock-mudstone interface model sample according to claim 1, characterized in that: Quartz sand high temperature resistant granular material is added to the salt powder layer as a seed crystal to improve the nucleation efficiency and cementation strength at the interface between the mudstone layer and the salt powder layer.

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