Study on Dynamic Response Characteristics of Electrical Resistivity of Gas Bearing Coal in Spontaneous Imbibition Process
Abstract
1. Introduction
2. Materials and Methods
2.1. Coal Sample Preparation
2.2. Test Equipment
2.3. Test Process
2.3.1. Resistivity Method
- (1)
- Instrument connection: Put the coal sample tank in the experimental system, connect each pipeline-interface of the system, confirm that all valves of the system are closed, connect each test electrode with the resistance tester, and turn on the main power supply of the equipment. The electrode connection is shown in the following Figure 3.
- (2)
- Constant temperature and loading: Set the temperature of the incubator at 16 °C, open the suction valve of the axial pressure loading pump, close the suction valve after suction, and load the axial pressure 10 MPa on the control panel.
- (3)
- Air tightness test: Open the helium bottle to fill the coal sample tank with helium of about 1 MPa, then close the air inlet valve and read the pressure gauge reading of the coal sample tank after the reading is stable. If the pressure does not drop within half an hour, it indicates that the air tightness is good. Otherwise, soap water should be used for leak detection. Open the exhaust valve to release helium in the coal sample tank after ensuring that the air tightness is good;
- (4)
- Dead volume calibration: Fill the calibration tank with helium at a certain pressure, read the gas pressure in the tank after the indication is stable, then connect the calibration tank with the coal sample tank and reread the balance pressure after the indication is stable. The dead volume of the coal sample tank can be obtained according to Formula (2). Repeat the operation three times and take the average to reduce the experimental error:
- (5)
- Vacuum pumping: Open the exhaust valve to release the gas in the coal sample tank and close all valves. After that, open the connecting valve between the coal sample tank and the vacuum pump and start the vacuum pump for vacuum degassing of the coal sample tank; when the reading of the vacuum gauge drops below 20 Pa, close the connecting valve between the coal sample tank and the vacuum pump and close the vacuum pump switch.
- (6)
- Gas adsorption: Open the switch of the methane cylinder and the inlet valve in turn, let a small amount of methane enter the coal sample tank many times, and make the coal sample adsorb and balance under the pressure of 0.74 Mpa.
- (7)
- Quantitative water adding: Open the water inlet valve of the advection pump and piston container, input the flow rate and water injection volume of the advection pump on the control panel, then start the advection pump and close the advection pump and water inlet valve after adding water.
- (8)
- Resistivity measurement: Open the isobaric valve and water injection valve between the piston container and the coal sample tank to allow water to infiltrate into the coal naturally. At the same time, quickly open the resistance tester to record the resistivity of the coal sample in real time.
2.3.2. Slice Drying Method
- (1)
- When the coal sample is pretreated, only the first layer of electrode is arranged in the briquette pressing stage, which is located in the middle of the briquette. At the same time, in order to reduce the difference in moisture content at different heights of the briquette, the height of the briquette should be reduced as much as possible.
- (2)
- A certain amount of water is injected into the water injection container and the spontaneous imbibition test of coal is carried out. To thoroughly wet the coal with water and facilitate the later determination of water content, the test time is set at 48 h.
- (3)
- After the test, the electrode wire is pulled out, and the briquette is completely withdrawn using the calibration block built into the tank and the servo press. The moisture content of the briquette is then measured using the slice drying method. First, the briquette is equally cut into two coal slices from the middle, and the two coal slices are circumferentially cut according to the way shown in Figure 4.
- (4)
- Each coal slice is weighed after cutting, its initial mass mij is measured, its residual mass is measured mij after it is put into the drying oven for full drying, and the moisture content of each coal slice after cutting is calculated.
- (5)
- The data are sorted, the resistance value between the collected two measuring points is converted into the resistivity value, the difference of moisture content measured by the slice drying method and the resistivity method is analyzed, and the reliability of moisture content measured by the resistivity method is also examined.
3. Results and Analysis
3.1. Feasibility Verification Based on Slice Drying Method
3.2. Measurement of Coal Resistivity Under Different External Moisture Conditions
3.3. Temporal and Spatial Distribution Characteristics of Electrical Resistivity of Gassy Coal
3.4. Corresponding Relationship Between Coal Resistivity and Moisture Content
4. Conclusions
- (1)
- Taking the 3% added water test group as an example, the final resistivity values of each measurement section in the coal body after a long-term imbibition process are within a certain range, and the average stable resistivity value is 1756.39 Ω ·m. The equivalent moisture content of the plane of the electrode measurement section obtained by the slice drying method is 2.92%. Compared with the measurement results of the resistivity method, the relative error between the two is only 2.67%, indicating that the resistivity method can be used for the measurement and research of coal moisture content.
- (2)
- With the increase in imbibition time, the resistivity of coal shows a downward trend, and its change process can be divided into three stages: rapid change, gradual change, and stability. With the increase in water content, the average mutation time point and average resistivity stability value of coal resistivity gradually decrease. Under the condition of the duplicate water content, the resistivity curves of different sections have the phenomenon of crossing.
- (3)
- In the axial direction, with the infiltration of water layer by layer from shallow to deep, the sudden change time of resistivity is delayed with the deepening of the layer. The resistivity of each layer drops suddenly when the water reaches, and then the rate of decline slows down and tends to be stable. The stable value of resistivity increases gradually with the depth of the layer. Radially, the abrupt change time of resistivity in the section near the center of the coal body is slightly earlier than that far away from the center of the coal body, indicating that in the same plane, water first migrates to the center of the coal body and then spreads around.
- (4)
- The stable value of coal resistivity decreases with the increase in water content, but the downward trend gradually slows down. When the water content exceeds 10%, the resistivity basically does not change with the change in water content, and the stable value of coal resistivity ρ and water content w satisfy the exponential function relationship.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
- Xie, H.; Wu, L.; Zheng, D. Prediction on the energy consumption and coal demand of China in 2025. J. China Coal Soc. 2019, 44, 1949–1960. [Google Scholar]
- Wang, G.; Ren, S.; Pang, Y.; Qu, S.; Zheng, D. Development achievements of China’s coal industry during the 13th Five-Year Plan period and implementation path of “dual carbon” target. Coal Sci. Technol. 2021, 49, 1–8. [Google Scholar]
- Cheng, Y.; Yu, Q.; Yuan, L.; Li, P.; Liu, Y.; Tong, Y. Experimental Research of Safe and High-Efficient Exploitation of Coal and Pressure Relief Gas in Long Distance. J. China Univ. Min. Technol. 2004, 02, 8–12. [Google Scholar]
- Qian, M.; Xu, J.; Wang, J. Further on the sustainable mining of coal. China Coal Soc. 2018, 43, 1–13. [Google Scholar]
- Yuan, L. Strategic thinking of simultaneous exploitation of coal and gas in deep mining. J. China Coal Soc. 2016, 41, 1–6. [Google Scholar]
- Xie, H. Research review of the state key research development program of China: Deep rock mechanics and mining theory. China Coal Soc. 2019, 44, 1283–1305. [Google Scholar]
- Jiang, Y.; Pan, Y.; Jiang, F.; Dou, L.; Ju, Y. State of the art review on mechanism and prevention of coal bumps in China. China Coal Soc. 2014, 39, 205–213. [Google Scholar]
- Lei, D.; Liu, L.; Jia, Z.; Liu, N. Experimental study on the complex electrical dispersion response characteristics of coal during hydraulic fracturing. J. Henan Polytech. Univ. (Nat. Sci.) 2025, 44, 42–50. [Google Scholar]
- Ma, S.; Wang, Z.; Sun, Y.; Chen, Y.; Han, P.; Zhang, S.; Li, S. Study on the difference of gas drainage effect between cross-measure borehole and inseam borehole hydraulic punching. Phys. Fluids 2024, 36, 126610. [Google Scholar] [CrossRef]
- Sun, Q.; Guo, Y.; Chen, J.; Yan, X.; Yan, X.; Hu, X.; Guo, L.; Jin, Y. Theoretical model and experimental verification of seepage-transition-spontaneous imbibition in water migration of water-injected coal. Sci. Rep. 2025, 15, 9007. [Google Scholar] [CrossRef]
- Yue, J.; Xu, J.; Zhang, J.; Shi, B.; Zhang, M.; Li, Y.; Wang, C. Gas displacement characteristics during the water wetting process of gas-bearing coal and microscopic influence mechanism. Sci. Total Environ. 2024, 949, 175034. [Google Scholar] [CrossRef] [PubMed]
- Yang, M.; Xu, J.; Gao, J.; Zhang, X.; Liu, J.; Zhang, T.; Ma, J. Study on water seepage law of confined coal body and optimization of water injection parameters. Fuel 2023, 352, 129152. [Google Scholar] [CrossRef]
- Chen, X.; Cheng, Y.; He, T.; Li, X. Water injection impact on gas diffusion characteristic of coal. J. Min. Saf. Eng. 2013, 30, 443–448. [Google Scholar]
- Yuan, L.; Lin, B.; Yang, W. Research progress and development direction of gas control with mine hydraulic technology in China coal mine. Coal Sci. Technol. 2015, 43, 45–49. [Google Scholar]
- Shi, T.; Pan, Y.; Zheng, W.; Wang, A. Influence of Water Injection Pressure on Methane Gas Displacement by Coal Seam Water Injection. Geofluids 2022, 2022, 6208923. [Google Scholar] [CrossRef]
- Zhou, H.; Liu, Z.; Sun, X.; Ren, W.; Zhong, J.; Zhao, J.; Xue, D. Evolution characteristics of seepage channel during water infusion in deep coal samples. J. China Coal Soc. 2021, 46, 867–875. [Google Scholar]
- Marland, S.; Merchant, A.; Rowson, N. Dielectric properties of coal. Fuel 2007, 80, 1839–1849. [Google Scholar] [CrossRef]
- Li, M.; Liu, S.; Jiang, Z.; Su, B.; Chen, S. Detecting floor geological information bymine DC perspective and 3D inversion. J. China Coal Soc. 2022, 47, 2708–2721. [Google Scholar]
- Chen, P.; Wang, E.; Zhu, Y. Experimental study on resistivity variation regularities of loading coal. J. China Coal Soc. 2013, 38, 548–553. [Google Scholar]
- Meng, L.; Liu, M.; Wang, Y. Study on the rules of electrical resistivity variation of tectonic coal in uniaxial compression experiment. J. China Coal Soc. 2010, 35, 2028–2032. [Google Scholar]
- Zhang, X.; Ye, D.; Gu, F. Investigation on moisture distribution inducing dielectric anisotropy of coal particles. J. Eng. Thermophys. 2004, S1, 185–188. [Google Scholar]
- Wang, Y.; Wei, J. Experimental Research on Electrical Parameters Variation of Loaded Coal. Procedia Eng. 2011, 26, 890–897. [Google Scholar]
- Song, D.; Qiu, L.; Jia, H.; Gao, M.; Zhao, Z.; Liu, M.; Li, X. Response Experiments of Coal and Rock Apparent Resistivity in Hydraulic Fracturing Process. Saf. Coal Mines. 2015, 46, 9–12. [Google Scholar]
- Peng, Y.; Song, D.; Gao, Q. Apparent Resistivity Response Features Analysis of Hydraulic Fracturing in Highly Bursting Coal Seam. Saf. Coal Mines. 2016, 47, 23–26. [Google Scholar]
- Dong, D. Experimental Study on Characteristics of Gas Adsorption-desorption Process on Resistivity of coal. J. Taiyuan Polytech. Univ. 2016. [Google Scholar]
- Wang, B. Study on response characteristics of resistance of gas-free coal to moisture content during water permeability. J. Henan Polytech. Univ. 2020. [Google Scholar]
- GB/T 212-2008 [S]; General Administration of Quality Supervision, Inspection and Quarantine of China, Standardization Administration of China. Proximate Analysis of Coal. Standards Press of China: Beijing, China, 2008.
- Yue, J.; Wang, Z. Imbibition characteristics of remolded coal without gas. China Coal Soc. 2017, 42, 377–384. [Google Scholar]
Sampling Location | Metamorphic Degree | Mad/% | Aad/% | Vdaf/% | Calorific Value (MJ/kg) |
---|---|---|---|---|---|
Guhanshan mine | Anthracite | 1.04 | 10.85 | 7.25 | 19.68 |
First Floor | A1–A2 | A1–A3 | A1–A4 | A1–A5 | A2–A6 | A3–A7 | A4–A8 | A5–A9 |
---|---|---|---|---|---|---|---|---|
Time/min | 216 | 190 | 205 | 246 | 243 | 207 | 235 | 286 |
Second floor | B1–B2 | B1–B3 | B1–B4 | B1–B5 | B2–B6 | B3–B7 | B4–B8 | B5–B9 |
Time/min | 627 | 601 | 621 | 570 | 570 | 694 | 630 | 681 |
Third floor | C1–C2 | C1–C3 | C1–C4 | C1–C5 | C2–C6 | C3–C7 | C4–C8 | C5–C9 |
Time/min | 989 | 986 | 1035 | 1048 | 991 | 1004 | 1150 | 1083 |
Fourth floor | D1–D2 | D1–D3 | D1–D4 | D1–D5 | D2–D6 | D3–D7 | D4–D8 | D5–D9 |
Time/min | 1374 | 1378 | 1448 | 1375 | 1401 | 1475 | 1367 | 1295 |
Different Added Moisture (%) | Average Mutation Time (min) | Average Resistivity Stability Value (Ω m) |
---|---|---|
2 | 389 | 2416.07 |
3 | 365 | 1756.39 |
4 | 332 | 1503.56 |
6 | 299 | 1202.45 |
8 | 218 | 996.68 |
10 | 194 | 886.61 |
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Wang, K.; Wang, Z.; Jia, H.; Ma, S.; Sun, Y.; Wang, L.; Guo, X. Study on Dynamic Response Characteristics of Electrical Resistivity of Gas Bearing Coal in Spontaneous Imbibition Process. Processes 2025, 13, 2028. https://doi.org/10.3390/pr13072028
Wang K, Wang Z, Jia H, Ma S, Sun Y, Wang L, Guo X. Study on Dynamic Response Characteristics of Electrical Resistivity of Gas Bearing Coal in Spontaneous Imbibition Process. Processes. 2025; 13(7):2028. https://doi.org/10.3390/pr13072028
Chicago/Turabian StyleWang, Kainian, Zhaofeng Wang, Hongzhe Jia, Shujun Ma, Yongxin Sun, Liguo Wang, and Xin Guo. 2025. "Study on Dynamic Response Characteristics of Electrical Resistivity of Gas Bearing Coal in Spontaneous Imbibition Process" Processes 13, no. 7: 2028. https://doi.org/10.3390/pr13072028
APA StyleWang, K., Wang, Z., Jia, H., Ma, S., Sun, Y., Wang, L., & Guo, X. (2025). Study on Dynamic Response Characteristics of Electrical Resistivity of Gas Bearing Coal in Spontaneous Imbibition Process. Processes, 13(7), 2028. https://doi.org/10.3390/pr13072028