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倾斜煤层群覆岩“三场”非对称特征及靶向抽采机制

Asymmetric characteristics of “three-field” in overburden of inclined coal seam groups and target extraction mechanism

  • 摘要: 倾斜煤层群“三场”(应力场、位移场和裂隙场)演化规律较为复杂,对卸压瓦斯运移和储集具有重要意义。为了探究倾斜煤层群“三场”演化规律,研究以新疆1930煤矿为对象,开展了倾斜煤层群多重采动相似模拟实验。分析了上覆岩层垮落形态,获得了覆岩应力演化特征,分析了覆岩位移分布和移动方向特征,阐明了采动裂隙分布特征。进而探究了三场演化规律对瓦斯运移的影响,并开展了定向钻孔瓦斯抽采现场试验进行验证。研究结果表明:倾斜煤层群多重采动下,采动裂隙矩形梯台呈现明显的非对称特征。低位侧覆岩应力变化较大,随开采次数增加,卸压效应更为明显,而高位侧覆岩应力变化较小;结合重力−倾角效应,高位侧覆岩更易破坏,垮落次序优先,呈非对称特征。覆岩位移分布呈非对称特征,高位侧位移显著且移动方向变化较大。高位侧裂隙区网格内采动裂隙频数明显高于低位侧;高位侧裂隙区破断裂隙分布更多,且开度较大;采动裂隙呈“高位扩展−低位压缩”的非对称特征。多重采动使得“三场”非对称特征更为显著。此外,覆岩贯通度存在“慢速减小−快速减小”的现象。基于“三场”演化特征和瓦斯运移的关系,揭示了瓦斯抽采靶向优选机制。结合试验结果,构建了基于“三场”演化规律的裂隙带瓦斯抽采靶点区判定流程。现场瓦斯抽采效果良好,保证了工作面安全高效回采。研究结果为倾斜煤层群卸压瓦斯精准抽采提供了理论参考,旨在提高倾斜煤层群瓦斯抽采量,防止上隅角瓦斯超限,实现倾斜煤层群安全高效开采。

     

    Abstract: The three-field (stress, displacement and fracture field) evolution laws of the inclined coal seam group are complex, which are important for the transport and storage of pressure-relief gas. In order to investigate the three-field evolution law of inclined coal seam group, the study carried out a similar simulation experiment of multiple mining in inclined coal seam group with the 1930 coal mine in Xinjiang as an object. The collapse pattern of the overlying strata was analyzed, the stress evolution characteristics of overlying strata was obtained, the overlying strata displacement distribution and movement direction characteristics were analyzed, and the characteristics of mining-induced fracture distribution were elucidated. The influence of the three-field evolution law on gas migration was further investigated, and a directional borehole gas extraction field test was carried out for veri-fication. The study results shown that, the rectangular ladder platform of mining-induced fracture shown obvious asymmetric characteristics under multiple mining of inclined coal seam group. The overlying strata stress of the lower side was more variable, and the pressure-relief effect was more obvious with increasing mining frequency, while the overlying strata stress of the higher side was less variable. Combined with the gravity-dip effect, the overlying strata of the higher side was more prone to be damaged, and the collapse order was preferred with asymmetric characteristics. The displacement distribution of overlying strata was asymmetric, with significant displacement on the high side and large changes in the movement direction. The frequency of mining-induced fractures in the high side fractured area was significantly higher than that in the low side. The high side fracture area had more fracture distribution and fracture aperture was bigger. The mining-induced fractures shown the asymmetric characteristics of “high expansion-low compression”. The multiple mining made the asymmetric characteristics of three-field more significant. In addition, there was a “slow decreasing-fast decreasing” in the overlying strata penetration. Based on the relationship between three-field evolution characteristics and gas mi-gration, the mechanism of preferential gas extraction targeting was revealed. Combined with the experimental results, the process of determining the target area for gas extraction in the fractured zone based on the three-field evolution law was constructed. The gas extraction effect in the field was great, which ensured the safe and efficient recovery of the working face. The results of this study provide a theoretical reference for the accurate extraction of pressure-relief gas in the inclined coal seam group, aiming to improve the gas extraction from the inclined coal seam group, prevent gas overlimit in the upper corner, and achieve safe and efficient mining of the inclined coal seam group.

     

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