煤矿覆岩主控致灾层位危险识别及现场应用

Identification and on-site application of the main hazard-causing stratum of overlying strata in coal mines

  • 摘要: 针对煤矿地面水力压裂技术施工中工作面覆岩主控致灾层位难以准确辨识的难题,以孟村煤矿401102工作面地面水力压裂工业试验为背景,采用理论分析、微震监测、现场调研等方法,揭示了煤矿厚硬覆岩运动诱发矿震和冲击地压的动力灾害机理,分析了基于载荷三带理论的厚硬覆岩分区运动特征与诱发动力灾害之间的关系,建立了基于关键层运动状态的矿震能量预测模型与采场等效附加应力估算模型,提出了基于K-means聚类算法和肘部法则的煤矿覆岩主控致灾层位识别技术方法,确定了现场压裂施工层位并进行工业试验,根据现场微震监测数据及理论分析结果进行了效果验证,得到结论如下:孟村煤矿401102工作面致冲关键层及矿震关键层均为距离煤层66 m的安定组关键层R9,其初次破断运动采场等效附加扰动应力理论值为7.23 MPa,初次破断运动释放矿震能量理论值为6.08×105 J,致灾危险性较强;震−冲关键层压裂后,矿震能量理论值降幅94%,采场等效附加扰动应力理论值降幅76%,工作面上方5×103 J大能量微震事件出现明显上移趋势,上移量约为15 m;103 J及以上能级微震事件频次占比显著下降,由60.39%降至17.89%,最大微震事件能量由6.65×105 J降至9.75×103 J;102 J及以下能级微震事件频次占比显著上升,由39.61%增至82.11%。

     

    Abstract: In response to the challenging task of accurately identifying the main hazard-causing layer of overlying strata in the coal mine surface hydraulic fracturing construction, this study focuses on the industrial test of ground hydraulic fracturing at the 401102 working face of the Mengcun Coal Mine. The research is conducted using the methods of theoretical analysis, microseismic monitoring, and on-site investigation to reveal the dynamic disaster mechanism of mine earthquakes and rock bursts induced by the movement of thick and hard overlying strata in the coal mines. The relationship between the movement characteristics of thick and hard overlying strata based on a three-zone structure loading model of overlying strata and induced dynamic disasters is analyzed, and a prediction model for mining seismic energy and an estimation model for equivalent additional stress in mining areas based on the movement state of key layers are established. A coal mine identification technology for the main hazard-causing layer of overlying strata is proposed based on the K-means clustering algorithm and the elbow rule. The construction layer for hydraulic fracturing is determined, and an industrial test is carried out on-site. The effectiveness is verified based on the microseismic monitoring data and theoretical analysis results, leading to the following conclusions. In the Mengcun Coal Mine’s 401102 working face, both the key stratum responsible for rock bursts and mine seismic activities can be traced to the R9 key stratum of the Anding Group, situated 66 meters away from the coal seam. The primary fracturing movement of this critical stratum R9 imparts an equivalent supplementary disturbance stress value of 7.23 MPa, with the seismic energy liberated by this initial rupture motion quantifying to 6.08×105 J, thereby indicating a pronounced susceptibility towards catastrophic occurrences. After fracturing the key layer which induces mining earthquakes and rock bursts, the theoretical value of the mine earthquake energy is reduced by 94%, and the theoretical value of the equivalent disturbance stress of the working face is reduced by 76%. High-energy microseismic events above the working face with an energy of 5×103 J show a noticeable upward trend, with an upward movement of approximately 15 m. The frequency ratio of microseismic events with an energy level of 103 J or higher significantly decreases from 60.39% to 17.89%, and the maximum microseismic event energy decreases from 6.65×105 J to 9.75×103 J. The proportion of microseismic events with an energy level of 102 J and below significantly increases from 39.61% to 82.11%.

     

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