Microscopic observation device and method for blocking single fracture by inducing calcium carbonate precipitation through microorganisms

Abstract

The invention discloses a microcosmic observation device and method for blocking a single fracture by inducing calcium carbonate precipitation through microorganisms, and relates to the technical field of geotechnical engineering and environmental microorganisms, the observation device comprises a main body, the main body is provided with a fracture, and the two ends of the main body are further provided with a first overflow groove and a second overflow groove, inner cavities of the first overflow groove and the second overflow groove are communicated with the crack, the first overflow groove is provided with a water inlet, the second overflow groove is provided with a water outlet, and a plurality of through holes communicated with the crack are formed in one side of the main body and one side of the first overflow groove and used for obtaining crack parameters. According to the method, a microcamera is used for shooting the precipitation generation process of calcium carbonate induced by microorganisms in a rough single fracture, and the relevance research of a microcosmic precipitation mechanism and a macroscopic seepage characteristic in a small fracture is realized in combination with the electrical resistivity, potential difference and inlet and outlet water pressure of a solution in the fracture.

Description

Technical Field

[0001] The present invention relates to the field of geotechnical engineering and environmental microbiology technology, and in particular to a microscopic observation device and method for microorganism-induced calcium carbonate precipitation to seal a single crack. Background Art

[0002] Microbial induced calcium carbonate precipitation (MICP), which uses microbial urease to catalyze the hydrolysis of urea to produce calcium carbonate precipitation, has important applications in geotechnical reinforcement, fracture sealing, and environmental remediation. However, its development faces multiple limitations. Existing monitoring methods suffer from a data gap between microscopic morphology observations and macroscopic seepage parameters (such as permeability and water pressure), making it difficult to reveal the mechanisms by which precipitation dynamics influence engineering performance. For example, in traditional two-electrode resistivity measurements, the metal electrodes are susceptible to polarization or corrosion, leading to long-term measurement errors. Sensor size and wiring limitations in narrow fracture environments (e.g., 1.2 mm aperture) further exacerbate data distortion. Although previous studies have attempted to combine resistivity and permeability testing or employ transparent models to observe precipitation morphology, most suffer from complex designs and lack of simultaneous correlation of multiple parameters, hindering process parameter optimization and the development of engineering prediction models. Summary of the Invention

[0003] Based on the technical problems existing in the background technology, the present invention proposes a microscopic observation device and method for microbial-induced calcium carbonate precipitation to plug single fissures. A microscope camera is used to capture the precipitation process of microbial-induced calcium carbonate in a rough single fissure. Combined with the resistivity, potential difference, and inlet and outlet water pressure of the solution in the fissure, the correlation between the microscopic precipitation mechanism and the macroscopic seepage characteristics in small fissures is studied.

[0004] The present invention proposes a microbial-induced calcium carbonate precipitation and single-crack plugging microscopic observation device, comprising a main body, a crack provided on the main body, and a first overflow trough and a second overflow trough with one end open provided at both ends of the main body. The inner cavities of the first overflow trough and the second overflow trough are connected to the crack, the first overflow trough has a water inlet, and the second overflow trough has a water outlet. Several through holes connected to the crack are provided on one side of the main body and the first overflow trough for obtaining crack parameters.

[0005] Preferably, the through holes include a first through hole, a second through hole, a third through hole, a fourth through hole, a fifth through hole and a sixth through hole provided on the main body and a seventh through hole provided on the first overflow trough; each through hole is provided with a detection electrode.

[0006] Preferably, the first through hole and the sixth through hole are connected to voltage electrodes; the second through hole and the fifth through hole are connected to current electrodes; and the seventh through hole, the third through hole and the fourth through hole are connected to Ag / AgCl electrodes.

[0007] Preferably, both the water outlet and the water inlet are provided with water pressure sensors.

[0008] The present invention proposes an observation method for a microscopic observation device for plugging a single fissure by microbial-induced calcium carbonate precipitation. The observation device is as described above, and the method steps are as follows:

[0009] S1: Inject Bacillus pasteurianus liquid into the crack;

[0010] S2: Fill the cracks treated in S1 with a mixture of urea and calcium chloride;

[0011] S3: The precipitation process in the cracks is captured by a microscopic camera and transmitted to the analysis software to extract the crystal size, distribution density and coverage;

[0012] S4: measuring the voltage difference and natural potential difference of the crack by electrodes set in the through-hole;

[0013] S5: Measure the water pressure at the water inlet and outlet and calculate the permeability.

[0014] Preferably, the calculation formula for permeability is:

[0015]

[0016] Where Q is the volume flow rate; A is the cross-sectional area of ​​the fracture; K is the permeability coefficient; μ is the dynamic viscosity; ΔP is the pressure difference between the inlet and outlet water pressures; and L is the lateral length along the flow direction.

[0017] Preferably, the molar ratio of urea to calcium chloride is 1:0.5-1.5.

[0018] Preferably, the fractures are randomly generated by Synfrac software.

[0019] Beneficial technical effects of the present invention:

[0020] (1) The present invention can monitor the process of microbial induced calcium carbonate precipitation (MICP) in small cracks, capture the precipitation morphology (such as crystal size and distribution density) in real time, and combine the multi-parameter collaborative analysis of resistivity, potential difference, water pressure and microscopic imaging to realize the correlation study between microscopic precipitation mechanism and macroscopic seepage characteristics.

[0021] (2) The present invention adopts a four-electrode method to measure the resistivity of the solution, wherein the electrodes of the second through hole and the fifth through hole are power supply electrodes, and the electrodes of the first through hole and the sixth through hole are pressure measuring electrodes. Compared with the two-electrode method for calculating the resistivity, this method effectively eliminates the influence of the electrode / solution interface contact on the measurement results, and significantly improves the resistivity measurement accuracy.

[0022] (3) The Ag / AgCl electrodes provided in the third through hole, the fourth through hole and the seventh through hole of the present invention can monitor the abnormal electric field area in real time through the potential difference data, and assist in verifying the reliability of the resistivity measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic structural diagram of the microscopic observation device for plugging a single fissure by microbial-induced calcium carbonate precipitation proposed in the present invention.

[0024] In the figure: 1-main body, 11-first through hole, 12-second through hole, 13-third through hole, 14-crack, 15-fourth through hole, 16-fifth through hole, 17-sixth through hole, 2-first overflow groove, 21-seventh through hole, 3-second overflow groove. DETAILED DESCRIPTION

[0025] The present invention will be further explained below with reference to specific embodiments.

[0026] Example 1

[0027] Reference Figure 1 The present invention proposes a microbial-induced calcium carbonate precipitation and single-crack plugging microscopic observation device, which includes a main body 1, a crack 14 is provided on the main body 1, and a first overflow trough 2 and a second overflow trough 3 with one end open are provided at both ends of the main body 1. The inner cavity of the first overflow trough 2 and the second overflow trough 3 is connected with the crack 14, the first overflow trough 2 has a water inlet, and the second overflow trough 3 has a water outlet. A plurality of through holes connected with the crack 14 are provided on one side of the main body 1 and the first overflow trough 2 for obtaining crack parameters.

[0028] Specifically, the through holes include a first through hole 11, a second through hole 12, a third through hole 13, a fourth through hole 15, a fifth through hole 16 and a sixth through hole 17 provided on the main body 1 and a seventh through hole 21 provided on the first overflow tank 2; each through hole is provided with a detection electrode.

[0029] The first through hole 11 and the sixth through hole 17 are connected to voltage electrodes; the second through hole 12 and the fifth through hole 16 are connected to current electrodes; the seventh through hole 21 , the third through hole 13 and the fourth through hole 15 are connected to Ag / AgCl electrodes.

[0030] In addition, water pressure sensors are installed at both the outlet and the inlet. The water pressure sensors are PS1 products of Shanghai Pengzan Biotechnology Co., Ltd., which are respectively arranged at the front and rear ends of the device and connected to the inlet and outlet with hoses to measure the water pressure at the inlet and outlet in real time. The water pressure sensor has a measurement range of 0-7kPa and a measurement accuracy of 0.5%. The sedimentation process in the cracks can also be obtained through a microscope camera.

[0031] In this embodiment, COMSOL Multiphysics software is used to construct a single crack numerical model, and polymethyl methacrylate (PMMA) material is selected as the base material. The single crack model is accurately prepared by high-precision 3D printing technology.

[0032] The rough fracture surface of the single fracture model (main body) was randomly generated using Synfrac software. The generation method was Brown, the random number was Park & ​​Miller, and the model size was 50 mm. In this invention, the fracture surface dimensions were 5 cm × 5 cm, with an average fracture opening of approximately 1.2 mm. The generated fracture surface was then embedded into the main body of the model using COMSOL.

[0033] The overflow trough is a triangular prism with a total side length of approximately 12.07 cm and a height of 0.7 cm, located at the front and rear ends of the single-fracture model. The water inlet and outlet are located at the bottom of the front and rear overflow troughs, respectively, 1.2 cm away from the single-fracture model, and are connected to the overflow trough. They are 0.5 cm long cylinders (inner diameter 2 mm, outer diameter 4 mm).

[0034] The seventh through hole is located above the first overflow trough, and the first through holes to the sixth through holes are located above the single crack model. Figure 1 Taking the top view of the through hole as an example, the brass electrodes set in the first through hole and the sixth through hole are pressure measuring electrodes (respectively marked as M and N electrodes), which are located above the upper part of the single crack model, with a distance of 2 cm between the two electrodes; the brass electrodes set in the second through hole and the fifth through hole are power supply electrodes (respectively marked as A and B electrodes), which are located above the middle part of the single crack model, with a distance of 4.5 cm between the two electrodes; the Ag / AgCl electrodes of the seventh through hole, the third through hole and the fourth through hole are marked as P1, P2 and P3 respectively, and the non-polarized electrodes P2 and P3 are located above the lower part of the single crack model, with a distance of 2 cm between the non-polarized electrodes P2 and P3.

[0035] The non-polarized electrodes P1, P2, and P3 were prepared by immersing silver bars in a 5% sodium hypochlorite solution for 2 hours to form Ag / AgCl electrodes. The electrodes had a diameter of 1.8 mm and a length of 2 cm.

[0036] The present invention can monitor the production process of microbially induced calcium carbonate precipitation (MICP) in small cracks, capture the precipitation morphology (such as crystal size and distribution density) in real time, and combine multi-parameter collaborative analysis of resistivity, potential difference, water pressure and microscopic imaging to realize the correlation study between microscopic precipitation mechanism and macroscopic seepage characteristics.

[0037] The present invention uses a four-electrode method to measure the resistivity of the solution, wherein the electrodes of the second and fifth through holes are power supply electrodes, and the electrodes of the first and sixth through holes are pressure measuring electrodes. Compared with the two-electrode method for calculating resistivity, this method effectively eliminates the influence of electrode / solution interface contact on the measurement results, significantly improving the resistivity measurement accuracy.

[0038] The Ag / AgCl electrodes provided in the third through hole, the fourth through hole and the seventh through hole of the present invention can monitor the abnormal electric field area in real time through the potential difference data, and assist in verifying the reliability of the resistivity measurement result.

[0039] Example 2

[0040] In the microscopic observation of microbial-induced calcium carbonate precipitation plugging of single fissures, the microorganism used was Bacillus pasteurianus (Sporosarcina pasteurii). The culture medium was prepared by mixing 10 g / L ammonium sulfate, 15.7 g / L trihydroxymethane, 20 g / L yeast powder, and 1000 mL deionized water to prepare a nutrient solution. The culture medium was sterilized in a 120°C high-pressure steam cooker for 30 min. After cooling, the culture medium was removed and placed on a sterile operating table for inoculation to form a Bacillus pasteurian culture solution. The culture medium was then placed in a constant temperature shaking incubator set at 30°C and a rotation speed of 120 r / min for 48 hours to obtain a Bacillus pasteurian culture solution.

[0041] A 1M urea solution was prepared. The molar mass of urea is known to be approximately 60.06 g / mol. 60.06 g of urea and 1000 mL of deionized water were stirred and mixed. A 1M calcium chloride solution was prepared. The molar mass of calcium chloride is known to be approximately 110.98 g / mol. 110.98 g of calcium chloride and 1000 mL of deionized water were stirred and mixed. The urea solution and the calcium chloride solution were added and mixed in a ratio of 1:1 to obtain a binder.

[0042] The specific observation steps are as follows:

[0043] (1) Injection of bacterial solution and microbial attachment: A microinjection pump was used to inject Bacillus pasteurianus bacterial solution with an OD600 of 1.0 into the model fissure at a constant flow rate of 5 mL / h. The injection volume was 50% of the total pore volume of the fissure. After the injection was completed, the solution was allowed to stand for 30 minutes and maintained at a constant temperature of 30°C to promote the colonization of microorganisms on the fissure surface.

[0044] (2) Mixing and injection of cementing fluid: Prepare 1 M urea and 1 M CaCl2 solution (ratio 1:1), adjust the pH to 9.0 after mixing, and inject the cementing fluid at the same flow rate (5 mL / h) until the remaining pore volume is filled. Monitor the solution conductivity in real time to ensure uniform mixing.

[0045] (3) Microscopic dynamic recording and image analysis: The microscope camera (×100 magnification, 5 μm resolution) was started to capture the precipitation process in the cracks at a frequency of 1 frame per second. The images were transmitted to the analysis software (Image J) in real time to extract the crystal size, distribution density, and coverage, which were used to study the mechanism of microbial-induced calcium carbonate precipitation in small cracks.

[0046] (4) Resistivity and natural potential measurement: A constant current source inputs 1 mA direct current to electrodes A and B, and the voltage difference is measured between electrodes M and N. The resistivity is calculated using an ERT21S (Nanjing University) resistivity meter (sampling frequency 1 Hz). The power is turned off and the natural potential difference between P2 and P3 relative to P1 is recorded (sampling interval 5 seconds). When calcium carbonate precipitation forms in the cracks, the resistivity in the solution increases. The more precipitation, the greater the resistivity increase. The potential difference data between P2 and P3 and P1 can be used to monitor abnormal electric field areas in real time. Uneven precipitation distribution will cause potential difference fluctuations. High-density areas correspond to sudden changes in potential difference, which helps verify the reliability of the resistivity measurement results.

[0047] (5) Water pressure test and permeability calculation: After grouting, deionized water was introduced at a constant flow rate of 1 mL / min, and a high-precision water pressure sensor (±0.5%) was used to record the stable water pressure ΔP. When precipitation formed in the cracks and blocked the dominant flow path, ΔP increased and the permeability (K) decreased. As ΔP increased, K decreased exponentially. The permeability formula is:

[0048]

[0049] Where Q is the volume flow rate; A is the cross-sectional area of ​​the fracture; K is the permeability coefficient; μ is the dynamic viscosity; ΔP is the pressure difference between the inlet and outlet water pressures; and L is the lateral length along the flow direction.

[0050] Repeat the above steps 7 times, with an interval of 48 hours between each grouting, to complete the microscopic observation of single fissure plugging by microbial-induced calcium carbonate precipitation based on multi-parameter coordinated monitoring.

[0051] In addition, before the formal grouting experiment began, deionized water was introduced into the device using a microinjection pump until the device was filled with deionized water.

[0052] This invention combines multi-parameter coordinated monitoring (resistivity, natural potential difference, microscopic imaging, and water pressure) with a non-polarizable electrode design, and four-electrode anti-interference measurement to achieve simultaneous monitoring of microscopic precipitation morphology and macroscopic seepage parameters during the microbial-induced calcium carbonate precipitation (MICP) process for plugging single fractures. Its industrial applicability is evident in applications such as geological disaster prevention (e.g., plugging rock fractures caused by landslides and tunnel seepage), oil and gas reservoir remediation (microcrack sealing and permeability restoration), soil reinforcement of contaminated sites (blocking pollutant migration), and seepage control in underground projects (tunnel anti-seepage). Real-time optimization of process parameters such as bacterial solution concentration and injection frequency improves plugging efficiency and reliability. The four-electrode resistivity measurement and automated data acquisition system overcome the electrode / solution interface contact issues, sensor integration difficulties, and data fragmentation associated with traditional two-electrode resistivity measurement in narrow fractures (e.g., 1.2 mm aperture). Furthermore, MICP technology combines environmental friendliness, high-precision monitoring, and engineering adaptability, offering significant economic benefits and broad market potential.

[0053] Although the embodiments of the present application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and spirit of the present application. The scope of the present application is defined by the appended claims and their equivalents, and all should be included in the scope of protection of the present application.

Claims

1. A microscopic observation device for plugging a single fissure by microbial-induced calcium carbonate precipitation, characterized in that: The invention comprises a main body (1), wherein the main body (1) is provided with a fissure (14), and a first overflow groove (2) and a second overflow groove (3) with one end open are provided at both ends of the main body (1), wherein the inner cavities of the first overflow groove (2) and the second overflow groove (3) are communicated with the fissure (14), the first overflow groove (2) is provided with a water inlet, and the second overflow groove (3) is provided with a water outlet, and a plurality of through holes communicated with the fissure (14) are provided on one side of the main body (1) and the first overflow groove (2) for obtaining fissure parameters.

2. The microbial-induced calcium carbonate precipitation and single-crack plugging microscopic observation device according to claim 1, characterized in that: The through holes include a first through hole (11), a second through hole (12), a third through hole (13), a fourth through hole (15), a fifth through hole (16), and a sixth through hole (17) provided on the main body (1), and a seventh through hole (21) provided on the first overflow trough (2); each through hole is provided with a detection electrode.

3. The microbial-induced calcium carbonate precipitation and single-crack plugging microscopic observation device according to claim 2, characterized in that: The first through hole (11) and the sixth through hole (17) are connected to voltage electrodes; the second through hole (12) and the fifth through hole (16) are connected to current electrodes; and the seventh through hole (21), the third through hole (13) and the fourth through hole (15) are connected to Ag / AgCl electrodes.

4. The microbial-induced calcium carbonate precipitation and single-crack plugging microscopic observation device according to claim 1, characterized in that: The water outlet and the water inlet are both provided with water pressure sensors.

5. A method for observing a microscopic observation device for plugging a single fissure by microbial-induced calcium carbonate precipitation, the observation device being as described in any one of claims 1 to 4, characterized in that: The steps are as follows: S1: Inject Bacillus pasteurianus liquid into the crack; S2: Fill the cracks treated in S1 with a mixture of urea and calcium chloride; S3: The precipitation process in the cracks is captured by a microscopic camera and transmitted to the analysis software to extract the crystal size, distribution density and coverage; S4: measuring the voltage difference and natural potential difference of the crack by electrodes set in the through-hole; S5: Measure the water pressure at the water inlet and outlet and calculate the permeability.

6. The observation method of the microbial-induced calcium carbonate precipitation and single-crack plugging microscopic observation device according to claim 5, characterized in that: The formula for calculating permeability is: , Where Q is the volume flow rate; A is the cross-sectional area of ​​the fracture; K is the permeability coefficient; μ is the dynamic viscosity; ΔP is the pressure difference between the inlet and outlet water pressures; and L is the lateral length along the flow direction.

7. The observation method of the microbial-induced calcium carbonate precipitation and single-crack plugging microscopic observation device according to claim 5, characterized in that: The molar ratio of urea to calcium chloride is 1:0.5-1.

5.

8. The observation method of the microbial-induced calcium carbonate precipitation and single-crack plugging microscopic observation device according to claim 5, characterized in that: Fractures were randomly generated using Synfrac software.

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