Structural Characteristics of the Turning End of the Kaiping Syncline and Its Influence on Coal Mine Gas
<p>Kaiping syncline structure diagram (<b>a</b>) and No.1 section diagram (<b>b</b>).</p> "> Figure 2
<p>Tectonic outline map of the study area (<b>a</b>); grid division diagram (<b>b</b>); contour map of stratigraphic dip angle at the turning end of the Kaiping syncline (<b>c</b>); scatter plot of stratigraphic dip angle in each structural zone (<b>d</b>). Notes: <math display="inline"><semantics> <mrow> <mstyle scriptlevel="0" displaystyle="true"> <mfrac> <mrow> <mi mathvariant="normal">x</mi> <mo>~</mo> <mi mathvariant="normal">y</mi> </mrow> <mrow> <mi>z</mi> </mrow> </mfrac> </mstyle> </mrow> </semantics></math>, x: minimum value; y: maximum value; z: average value.</p> "> Figure 3
<p>Ideal stratigraphic distribution model diagram (<b>a</b>) and strata dip angle calculation model diagram (<b>b</b>).</p> "> Figure 4
<p>Gas content contour map of the Kaiping syncline turning end. (<b>a</b>) No.7 coal seam gas content contour map; (<b>b</b>) No.9 coal seam gas content contour map; (<b>c</b>) No.12 coal seam gas content contour map.</p> "> Figure 5
<p>The absolute gas emission and relative gas emission line diagram of the mine. (<b>a</b>) Zhaogezhuang mining area; (<b>b</b>) Linxi mining area.</p> "> Figure 6
<p>The contour map of gas emission at the turning end of the Kaiping syncline. (<b>a</b>) No. 7 coal seam gas emission contour map; (<b>b</b>) No. 9 coal seam gas emission contour map; (<b>c</b>) No. 12 coal seam gas emission contour map.</p> "> Figure 7
<p>Burial–hydrocarbon history of the Kaiping oblique coal seam (according to Huang and Li, 2023, modification [<a href="#B26-applsci-14-12035" class="html-bibr">26</a>]). (<b>a</b>) Sedimentary and burial history diagram of the Kaiping syncline; (<b>b</b>) “Three Histories” configuration diagram of the Kaiping syncline. Notes: C: Carboniferous; P: Permian; T: Triassic; J: Jurassic; K: Cretaceous; E: Paleogene; N: Neogene.</p> "> Figure 8
<p>Geologic sketch of coal mine gas in coal—endowed areas of North China (according to Wang et al., 2021, modification [<a href="#B31-applsci-14-12035" class="html-bibr">31</a>]).</p> "> Figure 9
<p>Schematic diagram of gas distribution in the Kaiping Xiangxi mine.</p> "> Figure 10
<p>Plane distribution map of gas content at the turning end of Kaiping syncline: (<b>a</b>) No. 7 coal seam gas content plane distribution map; (<b>b</b>) No. 9 coal seam gas content plane distribution map; (<b>c</b>) No. 12 coal seam gas content plane distribution map.</p> "> Figure 11
<p>The relationship diagram of structure, buried depth, and gas content of No. 9 coal seam: (<b>a</b>) Zhaogezhuang mining area; (<b>b</b>) Linxi mining area.</p> ">
Abstract
:1. Introduction
2. Geological Overview of the Study Area
3. Structural and Gas Distribution Characteristics of the Kaiping Syncline Turning End
3.1. Geological Structural Distribution Characteristics at the Turning End
3.2. Gas Content Distribution Characteristics at the Turning End
3.3. Gas Emission Characteristics at the Turning End
4. Structural Control Mechanisms on Coal and Gas Occurrence in Mines
4.1. Structural Evolution and Gas Generation
4.2. Stepwise Structural Control of Gas Occurrence
4.2.1. North China Craton’s Control on Regional Gas Generation, Migration, and Preservation
4.2.2. Kaiping Syncline’s Control on Gas Occurrence in the Kailuan Mining Area
4.2.3. Structural Control of Gas Occurrence at the Turning End of the Kaiping Syncline
4.3. Structure-Controlled Gas Prevention and Mitigation Measures
- (1)
- Minimize the number of times that roadways expose (or intersect) outburst-prone coal seams. The locations for exposing (or intersecting) such coal seams should reasonably avoid geological structural zones, especially areas with compressive-shear faults and well-developed fractures.
- (2)
- For areas predicted to be free of outburst risk, regional prediction can be performed block by block using measured coal seam gas parameters, coal seam occurrence, and geological structures within the section.
- (3)
- Based on coal seam occurrence characteristics, geological structure conditions, outburst distribution patterns in the mined areas, and detection and prediction results of coal seam geological structures in the forecasted areas, the gas geological analysis method is applied to delineate outburst hazard zones. If the distribution of outburst points or locations with significant warning signs is directly associated with a structural belt, the extended position of this structure and the coal seam within a specific range on both sides are classified as outburst hazard zones. Otherwise, within the same geological unit, the coal seam extending 20 m (vertical depth) above and below the outburst point or location with significant warning signs is also classified as an outburst hazard zone.
- (4)
- Inspection and testing points in each study area should be located in regions with lower borehole density, wider borehole spacing, and shorter pre-drainage times. These points should be positioned as far as possible from pre-drainage gas boreholes or equidistant from surrounding boreholes, where feasible, to avoid the discharge range of excavation roadways and the pre-drainage advance distance of working faces. In geologically complex areas, the number of inspection and testing points should be appropriately increased, with special attention to closed faults (e.g., compressive or compressive-shear faults), which act as barriers, obstruct gas emissions, and seal against gas dissipation.
- (5)
- For every 10–50 m of working face advancement—or every 30 m in geologically complex areas or pre-drainage gas regions using non-directional drilling rigs—at least two regional verifications must be performed. Comprehensive records of engineering design, construction, and performance inspections must be meticulously preserved. Continuous regional verifications should be conducted in structurally damaged zones to analyze fault zone characteristics, including fault fillings, fracture development, and the properties of rock layers contacting the coal seam on the opposite fault block.
- (6)
- Before exposing outburst-prone coal seams in roadways, it is critical to determine the coal seam horizon, occurrence parameters, and geological structures, with special attention to areas where coal seam thickness varies. These areas are often locations where in situ stress varies and concentrates, resulting in elevated gas content and pressure, which makes the coal seam prone to gas outbursts or gas accumulation.
- (7)
- When the coal roadway heading face encounters geological structural damage zones or abrupt changes in coal seam occurrence conditions, and the original design measures cannot be applied, boreholes must be drilled to determine coal seam conditions. Gas should then be discharged through boreholes with diameters ranging from 42 to 50 mm.
- (8)
- Where technically feasible, an integrated surface and underground gas prevention and control approach should be implemented. Gas control primarily employs a long-term hydraulic fracturing extraction strategy through surface horizontal wells, supplemented by underground in-seam boreholes, to mitigate outburst hazards. During protective seam mining, gas extraction is conducted using surface mining-induced wells and surface L-shaped wells to drain pressure-relief gas from the protected seam. During the retreat of the working face, gas from adjacent seams is extracted through surface L-shaped wells and long underground directional boreholes.
5. Conclusions
- (1)
- The structural distribution of the Kaiping syncline hinge zone shows pronounced north–south differentiation. The strata on the northwestern limb are steeply inclined, with locally vertical or overturned sections, and dip angles generally ranging from 60° to 85°. Conversely, the strata on the southeastern limb are relatively gentle, with dip angles ranging from 10° to 30°, further complicated by a series of subordinate folds trending in the same direction. Based on the geological data of the syncline hinge zone, the degree of structural development, and the dip angles of the strata, the area can be roughly categorized into six structural zones: west wing fault structure area, wellhead open syncline area, Kaiping syncline structural zone, monoclinal tectonic zone, Dujunzhuang Anticline structure area, and Heiyazi Syncline structure area. Additionally, the variation in the dip angles of the strata shows a strong correlation with the development of faults and folds within the study area.
- (2)
- The Kaiping syncline hinge zone is classified into Structural Zone I (Zhaogezhuang Mine) and Structural Zone II (Linxi Mine) based on variations in coal thickness, strata dip angles, and hydrogeological conditions. The study reveals that in Structural Zone I, the gas content ranges from 4.8 to 12.0 m3/t, the relative gas emission ranges from 5.68 to 12.63 m3/t, and the absolute gas emission ranges from 19.19 to 35.1 m3/min. In Structural Zone II, the gas content ranges from 2.8 to 6.6 m3/t, the relative gas emission ranges from 3.74 to 6.87 m3/t, and the absolute gas emission ranges from 9.27 to 14.86 m3/min. Overall, both gas content and gas emissions show a significant increase with coal seam depth. Gas content and gas emissions on the northern limb of the hinge zone are notably higher than those in the southern structural zone, suggesting that structural complexity plays a significant role in influencing gas distribution and emission.
- (3)
- The coal-bearing strata in the Kailuan mining area have undergone structural burial, thermal evolution, and hydrocarbon generation, with subsequent preservation conditions ultimately determining the characteristics of gas occurrence in the coal. The burial history of the coal seams on both limbs of the Kaiping syncline is approximately “V-shaped”, with a turning point in the Late Indosinian period. The coal seams in the study area have undergone multiple cycles of subsidence, hydrocarbon generation, and dissipation, resulting in varied current states of gas occurrence. Through quantitative analysis of the evolution of the “three histories” and coal seam characteristics, the complete process of gas generation, occurrence, and migration in the study area has been revealed. This process is divided into five stages: the initial generation stage, the deep burial and enrichment stage, the stagnation and dissipation stage, the intense accumulation and reservoir formation stage, and the dissipation and stabilization stage.
- (4)
- Gas occurrence in the study area is stepwise, controlled by geological structures. North China Craton governs regional gas generation, migration, and preservation, while the Kaiping syncline plays a dominant role in controlling gas occurrence in the Kailuan mining area. The structural differences and burial depths on the two limbs of the turning end are the main factors influencing the variation in gas occurrence between the two limbs.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
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Mine | Reverse Fault (Article) | Normal Fault (Article) | The Proportion of Reverse Faults | The Proportion of Normal Faults |
---|---|---|---|---|
Zhaogezhuang Mine | 13 | 11 | 54.17% | 45.83% |
Linxi Mine | 3 | 10 | 23.08% | 76.92% |
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Chen, Z.; Zhu, Y.; Zhang, H.; Li, J. Structural Characteristics of the Turning End of the Kaiping Syncline and Its Influence on Coal Mine Gas. Appl. Sci. 2024, 14, 12035. https://doi.org/10.3390/app142412035
Chen Z, Zhu Y, Zhang H, Li J. Structural Characteristics of the Turning End of the Kaiping Syncline and Its Influence on Coal Mine Gas. Applied Sciences. 2024; 14(24):12035. https://doi.org/10.3390/app142412035
Chicago/Turabian StyleChen, Zhenning, Yanming Zhu, Hanyu Zhang, and Jin Li. 2024. "Structural Characteristics of the Turning End of the Kaiping Syncline and Its Influence on Coal Mine Gas" Applied Sciences 14, no. 24: 12035. https://doi.org/10.3390/app142412035
APA StyleChen, Z., Zhu, Y., Zhang, H., & Li, J. (2024). Structural Characteristics of the Turning End of the Kaiping Syncline and Its Influence on Coal Mine Gas. Applied Sciences, 14(24), 12035. https://doi.org/10.3390/app142412035