A non-destructive and efficient shale dispersion method

Abstract

The application provides a mudstone non-destructive and efficient dispersion method and relates to the technical field of mudstone dispersion. The mudstone non-destructive and efficient dispersion method comprises the following steps: step 1: sample grading pretreatment: according to the mudstone cementation strength, a grading crushing strategy is implemented, wherein high cementation strength mudstone is crushed to 0.1-0.2 cm granular, low cementation strength mudstone is crushed to 0.2-0.3 cm granular; a sample with a particle size deviation of no more than 0.05 cm is screened, after the sample surface impurities are removed by using deionized water, the sample is placed in a 50-70 DEG C constant temperature environment for drying for 10-14 hours to remove free water until the constant weight. The application constructs a three-stage composite salt solution gradient from low concentration to high concentration to balanced concentration, and is supplemented with a pulse vacuum negative pressure to break the mudstone pore gas lock effect; the first stage is to build a channel by shallow wetting, the second stage is to maximize the salt loading by near-saturation concentration, and the third stage is to utilize the chemical potential gradient by concentration adjustment to drive the surface microcrystals to diffuse inward, avoid the surface crust blockage and ensure the uniform penetration of the salt solution into the mudstone.

Description

Technical Field

[0001] This invention belongs to the field of geological sample pretreatment and rock and mineral analysis technology, specifically involving a non-destructive and efficient dispersion method for mudstone. It is suitable for the single-mineral particle dissociation treatment of mudstone samples before high-precision experiments such as laser particle size analysis, scanning electron microscopy observation, and geochemical detection. It can be directly applied to related fields such as geological exploration, unconventional oil and gas development, environmental geological engineering, and CO2 geological storage, and can effectively ensure the accuracy and reliability of subsequent experimental results. Background Technology

[0002] Shale and mudstone are among the most widely distributed sedimentary rocks globally, serving as crucial geological carriers for shale gas development, CO2 geological sequestration, and major infrastructure construction. Accurate detection of core geological parameters such as mineral composition, pore structure, and particle morphology is essential for scientific research and engineering practice in related fields. Mudstone, as the core rock type of shale and mudstone, is primarily composed of fine-grained clay minerals. These particles are tightly bound together by cements such as calcareous, siliceous, and ferrous materials, forming a dense micro-nano-scale porous structure. Complete dissociation of these particles under natural conditions is extremely difficult. Sufficient and non-destructive dispersion of mudstone samples is a necessary prerequisite for conducting high-precision experiments such as laser particle size analysis, scanning electron microscopy, and geochemical detection, directly determining the accuracy and reliability of subsequent test results.

[0003] Existing mudstone dispersion techniques are insufficient to meet the practical technical requirements of non-destructive, efficient, and thorough dispersion in geological sample pretreatment; all methods have significant technical shortcomings. 1. Physical dispersion method: Natural weathering has a long processing cycle and extremely low efficiency, which cannot meet the needs of batch sample processing; mechanical grinding is prone to destroying the mineral crystal structure and original particle morphology, resulting in mineral crystal damage and particle morphology distortion, which in turn leads to experimental data distortion; the single freeze-thaw method can only act on the surface layer and shallow pores of the sample, and has limited ability to dissociate the deep cemented structure of strongly cemented mudstone, and cannot achieve effective particle dissociation in the core area of ​​mudstone.

[0004] 2. Chemical dispersion method: When strong acid and strong base reagents are used to dissociate cement, they will corrode the clay mineral lattice and change the geochemical composition of the sample. This method cannot achieve the core requirement of "non-destructive" dispersion and is not suitable for the pretreatment of samples for high-precision geochemical detection.

[0005] 3. Existing single ultrasonic dispersion method: Traditional ultrasonic dispersion often adopts a continuous high-power mode, which can easily lead to local overheating of the solution and cause the collapse of the interlayer structure of clay minerals. At the same time, ultrasonic energy is difficult to penetrate the deep dense cemented structure of mudstone, which can easily lead to the heterogeneous phenomenon of "over-dispersion on the surface and lack of dissociation in the deep layer", affecting the representativeness of experimental data.

[0006] 4. Existing combined dispersion method: It often uses a salt solution with fixed parameters in combination with freeze-thaw process. Especially in the salt solution infiltration stage, if the concentration is not properly controlled, it is very easy for the surface pores of mudstone to crystallize prematurely due to oversaturation, forming a "salt crust" that blocks the infiltration channels and leads to failure of deep infiltration. In addition, static vacuum infiltration has low efficiency and is difficult to overcome the airlock effect of micro and nano pores, making it impossible to achieve effective infiltration of salt solution into the core area of ​​mudstone.

[0007] 5. Lack of medium replenishment during freeze-thaw process: Existing freeze-thaw technology usually does not intervene after the initial soaking. However, each expansion of ice in the freeze-thaw cycle will generate new microcracks. If residual air in the cracks forms an "air cushion", it will buffer the expansion stress of the next freezing. Moreover, there is no active solution refill mechanism after melting, which leads to the decrease in efficiency of subsequent freeze-thaw cycles with the increase of the number of cycles and incomplete deep dissociation.

[0008] 6. The endpoint determination process has scientific flaws: Existing methods mostly rely on single index determination or parallel detection modes, lacking a systematic hierarchical screening mechanism; the verification step of "dispersion stability" is missing, and the endpoint is often determined solely based on the D50 value of a single particle size analysis, which can easily lead to insufficient processing (incomplete dissociation of internal cementation) or over-processing (mineral particle damage), thus affecting the accuracy of subsequent experimental results; in addition, laser particle size detection is costly and time-consuming, and if particle size detection is directly carried out on all samples in the processing stage, it will cause unnecessary waste of resources. Summary of the Invention

[0009] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a non-destructive and efficient mudstone dispersion method, which solves the problem that existing mudstone dispersion technologies have many limitations and cannot meet the actual needs of non-destructive, efficient, and thorough dispersion.

[0010] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: a non-destructive and efficient dispersion method for mudstone, the method comprising the following steps: Step 1: Sample grading pretreatment A graded crushing strategy was implemented based on the cementation strength of the mudstone. Mudstone with high cementation strength was crushed to 0.1-0.2 cm particles, and mudstone with low cementation strength was crushed to 0.2-0.3 cm particles. Samples with a particle size deviation of no more than 0.05 cm were screened. After washing the sample surface with deionized water to remove impurities, the samples were dried in a constant temperature environment of 50-70℃ for 10-14 hours to remove free water until constant weight was achieved. This eliminated the barrier effect on the permeation of the salt solution and laid a good foundation for subsequent gradient permeation. Step 2: Gradient salt solution pulsed vacuum-assisted osmosis A multi-stage gradient permeation system was constructed by using a composite salt solution of sodium sulfate and sodium chloride (Na2SO4-NaCl) to construct a system from low concentration to high concentration and then to equilibrium concentration. The system was then driven by pulsed vacuum negative pressure to accelerate the permeation of the salt solution into the micro-nano pores inside the mudstone, ensuring that the salt is uniformly loaded into the pores inside the mudstone. The ambient temperature during the entire permeation process is controlled at 15-30℃ (normal temperature range). Permeation is carried out in three stages, and the sodium sulfate concentration is controlled below the saturation concentration at this temperature to ensure that it remains completely dissolved throughout the entire permeation stage, preventing surface pre-crystallization from clogging the pores and ensuring unobstructed permeation channels. Step 3: Programmed temperature freeze-thaw cycle, vacuum, and ultrasonic-assisted depolymerization and dynamic monitoring The sample that has completed gradient infiltration, together with the salt solution, is placed in a temperature-controlled vacuum environment for freeze-thaw cycle treatment. A dynamic monitoring mechanism is introduced to track the degree of dispersion in real time to avoid over-treatment or under-treatment until the mudstone sample reaches the preset dispersion standard. Step 4: Final washing and particle collection The deagglomerated mudstone particle suspension was diluted, subjected to low-power secondary ultrasonication, sieving, and centrifugation. A combination of centrifugation and ultrasonic washing was used to remove residual salts from the sample surface and pores until sulfate ions (SO42-) were removed from the filtrate. 2- ) and chloride ions (Cl - The concentration should be lower than the detection limit (i.e., no corresponding ion reaction) to avoid residual salt affecting subsequent experimental results; the final product after washing should be freeze-dried and then sealed for storage.

[0011] Preferably, in step 2, the first stage of shallow wetting involves placing the sample in a vacuum permeation device and adding an 8-12 wt% composite salt solution (preferably 8 wt% Na2SO4 + 2 wt% NaCl). Under a vacuum negative pressure of -0.07 to -0.09 MPa, the device is maintained in pulse mode (evacuating for 20-40 minutes, releasing to atmospheric pressure for 5-10 minutes, and repeating this cycle) for 15-25 hours. This process removes gas from the mudstone pores, breaks the gas-lock effect, and constructs surface permeation channels for the salt solution, creating conditions for deep permeation.

[0012] Preferably, in step 2, the second stage of deep loading involves: draining the first-stage salt solution and adding a high-concentration composite salt solution to make the Na2SO4 component concentration reach more than 90% of the saturation concentration at that temperature (preferably 16wt% Na2SO4 + 5wt% NaCl at 20℃). This is maintained for 20-30 hours in pulse mode under a vacuum of -0.085 to -0.098 MPa. During this stage, the sodium sulfate concentration is 90%-98% of the saturation concentration at that temperature, maximizing the salt loading in the pores, providing maximum potential energy for subsequent crystallization expansion, and ensuring the effective breaking down of the deep cemented structure.

[0013] Preferably, in step 2, the third stage of balancing and preventing blockage involves using a composite salt solution with a concentration slightly lower than that in the second stage (preferably 14wt% Na2SO4 + 3wt% NaCl at 20°C), and maintaining the solution under normal or slightly negative pressure for 15-25 hours, during which gentle mechanical vibration is applied. In this stage, the total concentration of the composite salt solution is reduced by 10%-20% compared to the second stage. The concentration difference is used to diffuse the microcrystals precipitated on the surface inward, preventing crystallization blockage at the pore inlets, ensuring a uniform distribution of the ion concentration field inside the mudstone, and guaranteeing the uniformity of subsequent freeze-thaw polymerization.

[0014] Preferably, the freeze-thaw cycle treatment in step 3 includes the following: 1) Freeze-thaw cycle: Freeze at -30 to -40℃ for 3-5 hours, utilizing the volume expansion of salt solution crystals in the mudstone pores and the effect of ice expansion to generate micro-compression force, destroying the cemented structure between particles; then thaw in a water bath at 75-85℃ for 0.5-1.5 hours, utilizing the thermal expansion and contraction effect to generate thermal stress fatigue, causing microcracks to open. 2) Pulsed vacuum fracture reinjection: After the melting step is completed, when the salt solution temperature naturally cools to 40℃ or below, turn on the pulse vacuum system and control the vacuum degree to -0.05 to -0.07MPa (lower than the permeation vacuum degree in step 2 to prevent the solution from boiling at low pressure). Use pulse mode (vacuum for 5-10 minutes, release to normal pressure for 2-5 minutes, cycle 3-5 times) and maintain for 30-60 minutes. Technical principle: This step uses negative pressure to force the salt solution into the newly generated microcracks in the freeze-thaw cycle and to expel the residual gas released by the melting ice in the pores; it eliminates the "air lock" and "air cushion" effects in the cracks, provides sufficient liquid-phase coupling medium for subsequent ultrasonic treatment, ensures that the ultrasonic cavitation microjets can directly act on the cemented surface deep in the cracks, and reserves medium for the next round of freeze-thaw expansion. 3) Intermittent ultrasonic synergy: After vacuum refilling, keep the sample immersed in the salt solution and apply intermittent ultrasonic oscillation with a power of 80-120W and a frequency of 35-45kHz. The duration of each oscillation is 10-20 minutes. The intermittent working mode adopts a working time to pause time ratio of 1:1 to 2:1. It uses the liquid that has filled into the crack to conduct ultrasonic energy, peel off the particles that have been weakened by freeze-thaw, and avoid local overheating and mineral lattice damage caused by continuous ultrasound. 4) Dynamic monitoring and endpoint determination: Set a fixed detection interval. When approaching the dispersion endpoint, it is recommended to conduct a test after each freeze-thaw cycle and ultrasonic cycle, and take samples to test the dispersion degree of mudstone. The test should follow the order of visual inspection, microscopy and particle size analyzer. When all levels of testing meet the standards and the particle size analyzer test meets the stability requirements, the cycle should be terminated to ensure thorough dispersion and no damage to mineral particles.

[0015] Preferably, the determination of the preset dispersion standard in step 3 follows the following sequence, with hierarchical screening: Level 1: Visual inspection. The sample is completely loose and powdery, with no visible non-single-particle clumps. If it meets the standard, proceed to Level 2 testing. If it does not meet the standard, continue the cycle. Level 2: Observation under an optical microscope, randomly selecting no fewer than 3 fields of view, with no obvious aggregates in each field of view; if the standard is met, proceed to Level 3 detection; if the standard is not met, continue the cycle. Level 3: Laser particle size analyzer detection; Initial testing: Once the optical microscope meets the initial standard, the first laser particle size analyzer test is performed, and the D10, D50, and D90 values ​​are recorded as the initial comparison values. The cycle continues (subsequent data needs to be obtained to verify the dispersion stability). Subsequent testing: Compare the current test results with the previous test results. If the relative deviation of the characteristic particle size parameters between the two consecutive tests is less than the preset deviation threshold (indicating that the particle size distribution is stable before and after the last freeze-thaw cycle, with no hidden agglomeration or excessive breakage), and the D50 value of the most recent test meets the threshold required for the target analysis, it is determined that the dispersion meets the standard; if the relative deviation of the characteristic particle size parameters is not less than the preset deviation threshold, it is determined that the standard is not met, and the cycle continues.

[0016] Preferably, the characteristic particle size parameters include at least two of D10, D50, and D90; the preset deviation threshold is 3%-10%; and the relative deviation calculation formula is: in, This is the feature particle size value from the previous detection. These are the characteristic particle size values ​​detected in this study; For common mudstones, the typical threshold reference value is D50≤15μm, which is adjusted according to the original grain size characteristics of mudstones and actual experimental requirements.

[0017] Preferably, for mudstones of different lithologies, the sodium sulfate-sodium chloride composite salt solution is optimized with optional components. The specific adaptation strategy is as follows: 1) For high organic mudstone with a total organic carbon content ≥0.8wt%, a surfactant was added to the composite salt solution to improve the wettability of the salt solution on the mudstone sample; 2) For calcareous cemented mudstone with a calcium carbonate content ≥10wt%, a complexing agent is added to the composite salt solution to weaken the calcareous cement strength. 3) For mudstone with high silt content, adjust the proportion of sodium chloride in the composite salt solution and optimize the osmotic pressure to match the dispersion characteristics of silt particles.

[0018] Preferably, the surfactant is a conventional nonionic or anionic surfactant, and the complexing agent is a conventional complexing reagent of sodium citrate; the amount of surfactant and complexing agent added is 0.1%-0.5% of the total mass of the composite salt solution.

[0019] (III) Beneficial Effects This invention provides a non-destructive and efficient method for dispersing mudstone. It has the following beneficial effects: 1. A three-stage composite salt solution gradient was constructed, ranging from low concentration to high concentration and then to equilibrium concentration. Pulsed vacuum negative pressure was used to break the air-locking effect in the mudstone pores. The first stage was shallow wetting to build channels. The second stage was near-saturation concentration to maximize salt loading. The third stage was concentration adjustment to utilize the chemical potential gradient to drive the surface microcrystals to diffuse inward, avoiding surface crusting and blockage, and ensuring that the salt solution penetrates evenly into the mudstone interior.

[0020] 2. During the infiltration stage, high negative pressure pulsed vacuum breaks the initial airlock; during the freeze-thaw stage, medium and low pressure pulsed vacuum is used for crack reinjection, which forces the salt solution into the newly generated microcracks, removes residual gas, and eliminates the air cushion effect, ensuring that each freeze-thaw cycle can achieve the maximum physical fragmentation efficiency and reduce the number of freeze-thaw cycles.

[0021] 3. Vacuum reinjection first fills the new fractures with salt solution to create a high-efficiency liquid-solid acoustic wave coupling channel, allowing the ultrasonic cavitation effect to penetrate deep into the micro-nano pores inside the mudstone, improving the efficiency of deep cementation dissociation, while avoiding the secondary backfilling of voids by fine particles caused by ultrasonic treatment followed by vacuum.

[0022] 4. First, the cementation bonds of mudstone are weakened by freeze-thaw stress. Then, in a low-temperature environment of 40℃ and below, intermittent ultrasound (working-pause ratio 1:1-2:1) is used to avoid local overheating damage to the mineral lattice by continuous ultrasound, thus preserving the original morphology and geochemical composition of the minerals.

[0023] 5. Employ a grading and detection method that combines visual inspection, optical microscopy, and laser particle size analyzer to prioritize low-cost screening of substandard samples; use the relative deviation (3%-10%) of characteristic particle size (D10 / D50 / D90) as the quantitative standard, combined with the D50 target threshold, to ensure stable dispersion and avoid under-processing (hidden agglomeration) or over-processing (mineral damage).

[0024] 6. For mudstones with high organic matter, calcareous cementation, and high silt content, the composite salt solution can be optimized by selectively adding surfactants / complexing agents and optimizing the NaCl ratio to adapt to the dispersion characteristics of different lithologies and improve the versatility of the method. Attached Figure Description

[0025] Figure 1 This is a scanning electron microscope (SEM) image of the dispersed mudstone mineral particles in Example 1. Figure 2 This is a schematic diagram of the overall process flow of the method of the present invention. Detailed Implementation

[0026] 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.

[0027] Example 1 (Typical clay-rich mudstone) In this embodiment, a calcareous cemented clay-rich mudstone with a calcium carbonate content of 12 wt% was selected as the target sample. The laboratory ambient temperature was controlled at 20±2℃, and the method of this invention was strictly followed. The specific steps are as follows: Sample pretreatment: The target mudstone was crushed into 0.1-0.2cm particles, and the particle size deviation was screened to be no more than 0.05cm. The samples were dried in a constant temperature environment of 60℃ for 12 hours to remove free water until constant weight was achieved, so as to avoid water from hindering the penetration of salt solution.

[0028] Gradient salt solution pulsed vacuum-assisted osmosis: Phase 1: A 10wt% composite salt solution (8wt% Na2SO4 + 2wt% NaCl) is used, with optional addition of 0.3wt% sodium citrate (to suit the calcareous cementing properties). A vacuum of -0.08 MPa is applied using a pulsed "30min evacuation - 5min pause" mode for 20 hours to effectively expel gas from the pores and construct surface permeation channels.

[0029] Second stage: Use a 20wt% composite salt solution (16wt% Na2SO4 + 5wt% NaCl), with optional addition of 0.3wt% sodium citrate. Vacuum degree -0.095MPa, using the same pulse mode, for 24 hours to maximize the salt loading in the pores.

[0030] Third stage: Use a 17wt% compound salt solution (14wt% Na2SO4 + 3wt% NaCl). Soak at normal pressure for 20 hours, during which a slight mechanical agitation is applied every 4 hours to prevent surface crust formation and ensure uniform internal ion concentration.

[0031] Freeze-thaw-vacuum-ultrasound coordinated depolymerization and dynamic monitoring: Freeze-thaw cycle: Perform a freeze-thaw cycle of freezing at -35℃ for 4 hours and thawing in a water bath at 80℃ for 1 hour, utilizing crystallization expansion and thermal stress fatigue to weaken the cemented structure.

[0032] Pulsed vacuum refill (mandatory for each cycle): After each melting, allow the solution to cool to 35°C, then initiate pulsed vacuum treatment. Maintain a vacuum level of -0.06 MPa, using a "5 min pump - 3 min stop" cycle, repeating 5 times for a total duration of 40 minutes. This step ensures the salt solution fills the new fractures.

[0033] Intermittent ultrasonic synergy: After vacuum treatment, ultrasonic oscillation treatment is started with an ultrasonic power of 100W and a frequency of 40kHz. The intermittent mode of "working for 5 seconds and pausing for 5 seconds" is adopted, and the duration of a single ultrasonic treatment is 15 minutes to avoid mineral damage.

[0034] Endpoint determination process: When approaching the expected endpoint, perform one test per cycle, strictly following the grading determination criteria. The particle size analyzer determination criteria are: D50≤15μm, and the relative deviations of the characteristic particle size parameters (D10, D50, D90) in two consecutive tests are all less than 10%, and the arithmetic mean of the relative deviations of the three parameters is less than 5%.

[0035] After the 9th cycle: visual inspection shows that the standard is met, then optical microscopy is used to observe that obvious aggregates are present (the standard is not met), and the standard is determined to be unmet, so the cycle continues.

[0036] After the 11th cycle: Visual observation shows that the standard is met; optical microscopy shows no obvious agglomerates (meets the standard). Then, a laser particle size analyzer is used to detect the particle size distribution. D50 = 8.5 μm (reaching the threshold of clay-rich mudstone), D10 = 2.6 μm, D90 = 24.5 μm. The calibration values ​​are recorded, and the standard is not met (stability needs to be verified). The cycle continues.

[0037] After the 12th cycle: visual inspection and optical microscopy observation both met the standards; laser particle size analyzer detection showed D50=7.0μm, D10=2.2μm, D90=22.1μm; the average relative deviation of particle size parameters from the 11th cycle was (17.65%+15.38%+9.80%) / 3≈14.28%, which was deemed unacceptable, and the cycle continued.

[0038] After the 13th cycle: visual inspection and optical microscopy showed that the particle size distribution met the standards; laser particle size analyzer showed that D50=7.0μm, D10=2.1μm, and D90=20.9μm; the average relative deviation of the particle size parameters from the 12th cycle was (0%+4.76%+5.43%) / 3≈3.40%, indicating that the dispersion met the standards, and the cycle was terminated.

[0039] Final washing and particle collection: The depolymerized suspension was diluted, subjected to low-power (50W) secondary ultrasonication, sieving, and centrifugation. A centrifugation-ultrasonic alternating washing method was used to remove residual salts until no SO4 was found in the filtrate. 2- and Cl - The reaction proceeds; after freeze-drying, the product is sealed with a desiccant to prevent moisture absorption and agglomeration.

[0040] Evaluation of results: The entire mudstone dispersion process in this embodiment took 18 days, which is more than 50% shorter than the traditional single freeze-thaw method, and the dispersion efficiency was significantly improved. SEM observation showed that the mudstone mineral particles had clear edges and no obvious traces of dissolution, damage or lattice distortion, achieving non-destructive dispersion and fully meeting the requirements of high-precision experiments.

[0041] Figure 1 This is a scanning electron microscope (SEM) image of the dispersed mudstone mineral particles in Example 1 (showing that the mineral crystal edges are intact and undamaged). Table 1 shows the data on the change of particle size D50 with the number of freeze-thaw-ultrasonic cycles during the dynamic monitoring process of Example 1.

[0042] Example 2 (High-cementation-strength mudstone) This embodiment selects mudstone samples with strong siliceous cementation and high dispersion difficulty. The implementation steps, composite salt solution concentration composition, and process parameters are completely consistent with those in Example 1, except that the cementation strength of the samples is different. This is used to verify the adaptability of the method of the present invention to mudstone with high cementation strength.

[0043] Process record: 15th cycle test: Visually acceptable, but still shows obvious agglomerates under an optical microscope (not acceptable). The particle size analyzer test is terminated directly, and the cycle continues to avoid wasting resources.

[0044] 18th cycle test: Visual inspection met the standard, no obvious agglomerates were found under optical microscope (meeting the standard), laser particle size analyzer was used for the first time, D50=14.8μm, D10=4.1μm, D90=39.4μm, the data was recorded, and the stability was verified by continuing the cycle.

[0045] 19th cycle of testing: laser particle size analyzer test, D50=14.5μm, D10=3.7μm, D90=35.6μm; compared with the 18th test, the average deviation = (2.03%+9.76%+9.64%) / 3≈7.14%>5%, continue the cycle.

[0046] 20th cycle test: Laser particle size analyzer test, D50=14.5μm, D10=3.8μm, D90=34.2μm; Compared with the 19th test, the average deviation is (0%+2.70%+3.93%) / 3≈2.21%<5%, the cycle is terminated, and the dispersion is judged to meet the standard.

[0047] Note: This embodiment fully demonstrates that the method of the present invention, through the graded detection process of "visual inspection, microscope, and particle size analyzer", can effectively avoid invalid particle size detection and save detection costs; at the same time, through the quantitative determination of particle size parameters, it can ensure that high-cementation-strength mudstone is thoroughly dispersed, which is suitable for the treatment needs of difficult-to-disperse mudstone.

[0048] Example 3 (containing silty mudstone) In this embodiment, a mudstone sample with a high silt content (approximately 35 wt%) was selected. The implementation steps were basically the same as in Example 1, except that the proportion of NaCl in the composite salt solution was selectively adjusted according to the adaptation strategy for mudstone with high silt content (adjusted to 13 wt% Na2SO4 + 7 wt% NaCl in the second stage). All other process parameters were the same as in Example 1, verifying the adaptability of the method of the present invention to special lithologies.

[0049] Process Record: After 15 freeze-thaw-ultrasonic cycles, visual and optical microscopic observations showed that the particle size distribution met the standards. Initial laser particle size analyzer measurements showed D50 = 22.5 μm (reaching the adjusted threshold), D10 = 6.7 μm, and D90 = 43.8 μm. Cycling was continued to verify stability. After the 16th cycle, laser particle size analyzer measurements showed D50 = 22.4 μm, D10 = 6.5 μm, and D90 = 43.1 μm. The average deviation of particle size parameters between two consecutive measurements was (0.44% + 2.99% + 1.60%) / 3 ≈ 1.68% < 5%. Based on the preset dispersion standard of this invention, which requires "no abnormal agglomerates and stable particle size distribution," the sample was determined to have met the dispersion requirements, and the cycle was terminated.

[0050] Note: This embodiment demonstrates that the method of the present invention does not blindly pursue excessively low D50 values, respects the primary mineral grain size characteristics of mudstone samples, avoids damage to silt particles due to over-processing, and can be adapted to silty mudstones through parameter adjustment, thus exhibiting strong versatility.

[0051] Comparative Example 1 (Traditional Static Vacuum Osmosis) The comparative example is completely identical to the sample, composite salt solution concentration composition, and process parameters of Example 1. The core difference is that the vacuum-assisted permeation in step 2 adopts a static vacuum maintenance mode (continuous vacuuming without releasing pressure), and step 3 does not include the pulsed vacuum fissure recharge step. All other operations are the same as in Example 1.

[0052] Results: The penetration phase took the same amount of time, but after 20 subsequent freeze-thaw cycles, obvious aggregates could still be observed under the microscope (only 13 cycles were required to complete the dispersion in Example 1), and the dispersion efficiency was significantly reduced. This indicates that pulsed vacuum can effectively break the airlock effect, and vacuum re-injection during the freeze-thaw phase is crucial for maintaining efficient dissociation.

[0053] Comparative Example 2 (without third-stage balanced blocking) Compared with Example 1, this comparative example omits the third-stage balancing and anti-blocking step. After the second stage, a freeze-thaw cycle is performed directly. All other operations are the same as in Example 1. This is used to verify the necessity of the third stage.

[0054] Results: During the experiment, a white salt crust formed on the surface of some samples, hindering internal water exchange and ion diffusion, resulting in uneven dispersion of mudstone samples and incomplete dissociation of some particles, leading to poor dispersion. This result demonstrates that the third-stage "concentration adjustment" design is crucial for preventing surface crusting and ensuring uniform dispersion, and is one of the core innovations of this invention.

[0055] Comparative Example 3 (Single Particle Size Threshold Determination) Compared with Example 1, the endpoint determination in this comparative example only uses the single criterion of "D50≤15μm" in step 3, does not require the particle size distribution curve to be stable, and does not have the order of detection of "visual inspection, microscope, particle size analyzer". All other operations are the same as in Example 1, which is used to verify the scientific nature of the endpoint determination process of the present invention.

[0056] Results: The D50 of the sample reached 11.5 μm for the first time during the 10th cycle, and the experiment was terminated according to a single criterion. Scanning electron microscopy revealed that some areas still contained hidden agglomerates, indicating that the internal cementation was not completely disintegrated and the dispersion effect was incomplete. This result proves that the "stable particle size distribution" criterion and grading judgment process of this invention can effectively avoid insufficient treatment and ensure thorough dispersion, demonstrating significant scientific merit and superiority.

[0057] Comparative Example 4 (no vacuum reinjection during freeze-thaw phase) Compared with Example 1, the parameters of the infiltration stage in step 2 are the same in this comparative example, but the "pulse vacuum fissure reinjection" step is omitted in step 3. After melting and cooling, ultrasonic treatment is performed directly. All other operations are the same as in Example 1.

[0058] Results: The samples required 19 freeze-thaw cycles to achieve the same dispersion standard (D50 ≤ 15 μm and stable), 6 more cycles than in Example 1, increasing the total time by approximately 5 days. SEM observation showed that some deep particles remained encapsulated in microagglomerates. These results demonstrate that pulsed vacuum refilling during the freeze-thaw phase effectively fills new cracks, eliminates the air cushion effect, and significantly improves the dissociation efficiency per cycle.

[0059] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising a reference structure" does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0060] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A non-destructive and efficient method for dispersing mudstone, characterized in that: The method includes the following steps: Step 1: Sample grading pretreatment A graded crushing strategy was implemented based on the cementation strength of the mudstone. Mudstone with high cementation strength was crushed to 0.1-0.2 cm particles, and mudstone with low cementation strength was crushed to 0.2-0.3 cm particles. Samples with a particle size deviation of no more than 0.05 cm were screened. After cleaning the sample surface with deionized water to remove impurities, the samples were dried in a constant temperature environment of 50-70℃ for 10-14 hours to remove free moisture until constant weight was achieved. Step 2: Gradient salt solution pulsed vacuum-assisted osmosis A multi-stage gradient infiltration system was constructed by using a sodium sulfate and sodium chloride composite salt solution, ranging from low concentration to high concentration and then to equilibrium concentration. This system was then supplemented with pulsed vacuum negative pressure to accelerate the infiltration of the salt solution into the micro-nano pores inside the mudstone, ensuring that the salt is uniformly loaded into the pores inside the mudstone. The ambient temperature during the entire permeation process is controlled at 15-30℃. The permeation is carried out in three stages, and the sodium sulfate concentration is controlled below the saturation concentration at this temperature to ensure that it remains completely dissolved throughout the entire permeation process. Step 3: Programmed temperature freeze-thaw cycle, vacuum, and ultrasonic-assisted depolymerization and dynamic monitoring The sample that has completed gradient infiltration, together with the salt solution, is placed in a temperature-controlled vacuum environment for freeze-thaw cycle treatment. A dynamic monitoring mechanism is introduced to track the degree of dispersion in real time to avoid over-treatment or under-treatment until the mudstone sample reaches the preset dispersion standard. Step 4: Final washing and particle collection The deagglomerated mudstone particle suspension was diluted, subjected to low-power secondary ultrasonication, sieving, and centrifugation. A centrifugation and ultrasonic alternating washing method was used to remove residual salts from the sample surface and pores until the concentrations of sulfate and chloride ions in the filtrate were lower than the detection limit to avoid residual salts affecting subsequent experimental results. The final product after washing was freeze-dried and then sealed for storage.

2. The method for non-destructive and efficient dispersion of mudstone according to claim 1, characterized in that: In step 2, the first stage of shallow wetting involves placing the sample in a vacuum permeation device, adding 8-12 wt% composite salt solution, and maintaining the device in a pulse mode for 15-25 hours under a vacuum negative pressure of -0.07 to -0.09 MPa to expel gas from the mudstone pores, break the gas-lock effect, and construct a surface permeation channel for the salt solution, thus creating conditions for deep permeation.

3. The non-destructive and efficient dispersion method for mudstone according to claim 2, characterized in that: In step 2, the second stage of deep loading involves draining the first-stage salt solution and adding a high-concentration composite salt solution to bring the Na2SO4 component concentration to more than 90% of the saturation concentration at that temperature. This is maintained for 20-30 hours under a vacuum of -0.085 to -0.098 MPa using a pulsed mode. During this stage, the sodium sulfate concentration is 90%-98% of the saturation concentration at that temperature, maximizing the salt loading within the pores and providing maximum potential energy for subsequent crystallization expansion, thus ensuring the effective breaking down of the deep cemented structure.

4. The method for non-destructive and efficient dispersion of mudstone according to claim 3, characterized in that: In step 2, the third stage of balancing and preventing blockage involves using a composite salt solution with a lower concentration than that in the second stage, and maintaining the solution under normal or slightly negative pressure for 15-25 hours, during which gentle mechanical vibration is applied. In this stage, the total concentration of the composite salt solution is reduced by 10%-20% compared to the second stage. The concentration difference is used to diffuse the microcrystals precipitated on the surface inward, preventing crystallization blockage at the pore inlets, ensuring a uniform distribution of the ion concentration field inside the mudstone, and guaranteeing the uniformity of subsequent freeze-thaw polymerization.

5. The non-destructive and efficient dispersion method for mudstone according to claim 4, characterized in that: The freeze-thaw cycle process in step 3 includes the following: 1) Freeze-thaw cycle: Freeze at -30 to -40℃ for 3-5 hours, utilizing the volume expansion of salt solution crystals in the mudstone pores and the effect of ice expansion to generate micro-compression force, destroying the cemented structure between particles; then thaw in a water bath at 75-85℃ for 0.5-1.5 hours, utilizing the thermal expansion and contraction effect to generate thermal stress fatigue, causing microcracks to open. 2) Pulsed vacuum fracture reinjection: After the melting step is completed, when the temperature of the salt solution cools naturally to 40°C or below, turn on the pulse vacuum system, control the vacuum degree between -0.05 and -0.07 MPa, use pulse mode, and maintain for 30-60 minutes; 3) Intermittent ultrasonic synergy: After vacuum refilling, keep the sample immersed in the salt solution and apply intermittent ultrasonic oscillation with a power of 80-120W and a frequency of 35-45kHz. The duration of each oscillation is 10-20 minutes. The intermittent working mode adopts a working time to pause time ratio of 1:1 to 2:

1. It uses the liquid that has filled into the crack to conduct ultrasonic energy, peel off the particles that have been weakened by freeze-thaw, and avoid local overheating and mineral lattice damage caused by continuous ultrasound. 4) Dynamic monitoring and endpoint determination: Set a fixed detection interval. When approaching the dispersion endpoint, it is recommended to conduct a test after each freeze-thaw cycle and ultrasonic cycle, and take samples to test the dispersion degree of mudstone. The test should follow the order of visual inspection, microscopy and particle size analyzer. When all levels of testing meet the standards and the particle size analyzer test meets the stability requirements, the cycle should be terminated to ensure thorough dispersion and no damage to mineral particles.

6. The non-destructive and efficient dispersion method for mudstone according to claim 5, characterized in that: The determination of the preset dispersion criteria in step 3 follows the following order, with hierarchical screening: Level 1: Visual inspection. The sample is completely loose and powdery, with no visible non-single-particle clumps. If it meets the standard, proceed to Level 2 testing. If it does not meet the standard, continue the cycle. Level 2: Observation under an optical microscope, randomly selecting no fewer than 3 fields of view, with no obvious aggregates in any field of view; If the standard is met, proceed to the third level of testing; If the target is not met, continue the cycle. Level 3: Laser particle size analyzer detection; Initial testing: Once the optical microscope meets the initial standard, the first laser particle size analyzer test is performed, and the D10, D50, and D90 values ​​are recorded as the initial comparison values. The cycle continues. Subsequent testing: Compare the results of this test with the results of the previous test. If the relative deviation of the characteristic particle size parameters between the two consecutive tests is less than the preset deviation threshold, and the D50 value of the most recent test reaches the threshold required for the target analysis, it is determined that the dispersion meets the standard. If the relative deviation of the characteristic particle size parameter is not less than the preset deviation threshold, it is determined to be substandard, and the process continues in a loop.

7. The non-destructive and efficient dispersion method for mudstone according to claim 6, characterized in that: The characteristic particle size parameter includes at least two of D10, D50, and D90; the preset deviation threshold is 3%-10%; The formula for calculating relative deviation is: in, This is the feature particle size value from the previous detection. These are the characteristic particle size values ​​detected in this study; For common mudstones, the typical threshold reference value is D50≤15μm, which is adjusted according to the original grain size characteristics of mudstones and actual experimental requirements.

8. The non-destructive and efficient dispersion method for mudstone according to claim 7, characterized in that: For mudstones of different lithologies, the composition of the sodium sulfate-sodium chloride composite salt solution was optimized. The specific adaptation strategy is as follows: 1) For high organic mudstone with a total organic carbon content ≥0.8wt%, a surfactant was added to the composite salt solution to improve the wettability of the salt solution on the mudstone sample; 2) For calcareous cemented mudstone with a calcium carbonate content ≥10wt%, a complexing agent is added to the composite salt solution to weaken the calcareous cement strength. 3) For mudstone with high silt content, adjust the proportion of sodium chloride in the composite salt solution and optimize the osmotic pressure to match the dispersion characteristics of silt particles.

9. The non-destructive and efficient dispersion method for mudstone according to claim 8, characterized in that: The surfactant is a conventional nonionic or anionic surfactant, and the complexing agent is a conventional complexing reagent of sodium citrate; the amount of surfactant and complexing agent added is 0.1%-0.5% of the total mass of the composite salt solution.

Images