顶板不同区域压裂程度覆岩采动响应特征

Response characteristics of mining-induced overburden strata under different degrees of regional fracturing on the roof

  • 摘要: 为了获得顶板不同区域压裂程度下覆岩活动规律及其响应特征,进而为区域压裂防治顶板主导型冲击地压提供借鉴。首先根据地面区域压裂施工期间的微震监测结果,刻画了微震缝网的平面扩展形态,并依据微震缝网对工作面的覆盖程度进行区域划分;然后基于理论分析揭示了区域压裂超前释放累积应力和能量、覆岩结构调控控制载荷源以及压裂层自身“缓冲吸能”作用机理;之后分析了不同回采区域的微震事件迁移特征、日总能量频次特征、能量频次核密度分布特征及工作面超前和倾向的采动影响范围;最后对比分析了不同回采区域的矿压显现宏观特征及支架工作阻力变化特征。研究结果表明:① 微震活动时空响应特征与区域压裂程度有着密切联系,压裂充分区、压裂不充分区和未压裂区3个回采区域分别呈现“高频次、低能量”、“高频次、高能量”和“高频次、高能量”微震响应特征,微震能量频次核密度分布与其具有一致性,区域压裂后微震活动度和丛集效应降低,且微震事件分布呈现从工作面前方向工作面后方迁移和聚集的趋势;② 覆岩采动影响范围与区域压裂程度呈反比,区域压裂能够缩小悬臂长度,切断载荷传递路径,从而减小超前和倾向采动影响范围,压裂充分区和压裂不充分区与未压裂区相比,超前采动影响范围分别减小20.6%、14.7%,倾向采动影响范围分别减小21.5%、10%;③ 区域压裂能够有效缓和矿压显现强度,区域压裂对厚硬岩层整体性及其强度进行弱化,使覆岩破断块体减小且能够有序及时垮落,压裂充分区和压裂不充分区与未压裂区相比,周期来压规律不明显、来压强度低,持续来压时间缩短,来压时间间隔增大,来压次数减少。④ 综合不同回采区域覆岩采动响应特征,在针对厚硬顶板开展水平井区域压裂施工时,应确保区域压裂缝网有效覆盖工作面及巷道两侧煤柱区域,且避免在工作面形成未压裂区。

     

    Abstract: To obtain the activity patterns and response characteristics of the overburden strata under different fracturing degrees of the roof, and thereby provide a reference for preventing and controlling roof-dominated rock burst through regional fracturing. Firstly, based on the microseismic monitoring results during the fracturing construction period in the ground area, the planar expansion pattern of the microseismic fracture network was characterized, and the area was divided according to the coverage of the microseismic fracture network on the working face. Then, based on theoretical analysis, the mechanism of regional fracturing leading to the release of accumulated stress and energy, the control of load sources by overlying rock structure regulation, and the self-buffering and energy absorption of the fracturing layer was revealed. Afterwards, the migration characteristics of microseismic events in different regions, the frequency characteristics of daily total energy, the distribution characteristics of energy frequency nuclear density, and the range of influence of mining on the strike direction of the working face were analyzed. Finally, the macroscopic characteristics of mining pressure manifestation and the variation characteristics of support working resistance in different regions were compared. The research results indicate that: ① the synergistic effect of regional fracturing leading to the release of accumulated stress and energy, the control of load sources by overlying rock structure, and the self-buffering and energy absorption of the fracturing layer is closely related to the degree of regional fracturing. The three recovery areas of fracturing filling zone, fracturing non-filling zone, and non-fracturing zone exhibit the microseismic response characteristics of “high frequency, low energy”, “high frequency, high energy”, and “high frequency, high energy”, respectively. The nuclear density distribution of microseismic energy frequency is consistent with it. After regional fracturing, the microseismic activity and clustering effect decrease, and the distribution of microseismic events shows a trend of migration and aggregation from the front of the work face to the back of the work face. ② The impact range of overlying rock mining is inversely proportional to the degree of regional fracturing. Regional fracturing can reduce the length of the cantilever, cut off the load transmission path, and thus reduce the impact range of advanced and inclined mining. Compared with the non-fractured zone, the impact range of advanced mining is reduced by 20.6% and 14.7%, respectively, while the impact range of inclined mining is reduced by 21.5% and 10%. ③ Regional fracturing can effectively alleviate the intensity of mining pressure manifestation. Regional fracturing weakens the overall integrity and strength of thick and hard rock layers, reducing the number of fractured blocks in the overlying strata and enabling them to collapse in an orderly and timely manner. Compared with the unfractured zone, the cyclic pressure pattern is unclear, and the pressure intensity is low. The continuous pressure time is shortened, the interval between pressure periods is increased, and the number of pressure cycles is reduced. ④ Based on the characteristics of overburden mining response in different extraction areas, when conducting regional fracturing construction in horizontal wells targeting thick and hard roofs, it is necessary to ensure that the regional fracturing network effectively covers the working face and the coal pillar areas on both sides of the roadway, and to avoid forming unfractured areas on the working face.

     

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