含断层煤层反射槽波数值模拟及响应特征研究

Study on numerical simulation and response characteristics of reflecting in-seam wave in coal seams with faults

槽波勘探是煤矿井下勘探的重要手段,其借助槽波在煤层中传播具有能量强,传播距离远等优点,实现采煤工作面断层或其他地质异常体的探测。透射槽波勘探研究较为成熟,已在煤矿生产中得到广泛应用。近年来,反射槽波逐渐得到关注,利用反射槽波预测断层落差是今后槽波勘探的研究方向,其理论依据研究并不充分。为了明确反射槽波能量特征与断层落差间的关系,建立6个不同落差的断层模型(断层落差分别为煤层厚度的1/8、1/4、1/2、3/4、1倍、2倍),设计反射槽波勘探观测系统,基于高阶交错网格有限差分算法进行数值模拟,通过提取6个不同模型的反射槽波振幅信息,分析反射槽波能量随偏移距以及断层落差的变化特征,并分析带通滤波对反射槽波能量分布的影响。分析结果表明:断层落差小于1倍煤厚,随着落差增加,反射槽波能量逐渐增加;断层落差继续增加,反射槽波能量逐渐降低;断层落差不同,其对应的反射槽波能量随偏移距的变化趋势一致,但断层落差大于3/4煤厚时,远近偏移距反射能量出现显著差异;100~150 Hz和150~200 Hz带通滤波分别对断层落差小于1/2煤厚和大于3/4倍煤厚的反射槽波能量影响显著。因此,基于反射槽波能量分布特征进行断层落差探测,理论依据充足,具有实际应用价值。

ISS(in-seam seismic)exploration is a significant method for underground coal mine exploration.It has the advantages of strong energy and long transmission distance through the transmission of waves in coal seams to detect the fault or other geologic anomalies.Research on transmitted ISS exploration is relatively mature,and it has been widely used in underground coal mine production.In recent years,reflected ISS exploration is getting more and more attention.Detection of fault drop by reflected ISS exploration is the future research direction,and its theoretical basis is not sufficient.In order to clarify the relationship between in-seam wave reflected energy and fault drop,six fault models with different fault drop are established.In those models,fault drop varies from 1/8 times coal thickness to 2 times coal thickness.Observation system is designed for those models and numerical simulation is performed by high order staggered grid finite difference algorithm.By extracting the reflection wave amplitude information of six different models,the reflection wave energy with offset and fault drop change characteristics were analyzed and the effect of band-pass filtering on the energy distribution of the reflected inseam wave were analyzed too.The analysis results indicate that:while fault drop is less than one time of the coal seam thickness,the reflection amplitude gradually increases with the increase of fault drop.When fault drop is larger than coal seam thickness,reflection amplitude decreases with increase of fault drop.In the situation of various fault drops,the trend of amplitude versus offset is consistent,but when fault drop is larger than 3/4 times of the coal seam thickness,the reflected energy of the near and far offset is significantly different.The 100~150 Hz and 150~200 Hz band-pass filters have significant effects on the energy of reflection in-seam waves with a fault drop less than 1/2 coal thickness and greater than 3/4 coal thickness,respectively.Therefore,the detection of fault drop based on the energy distribution characteristics of the reflected in-seam wave has sufficient theoretical basis and practical application value.