薄煤层中垂直裂缝地震响应特征模拟分析

通过定义一个简单的薄煤层模型,在不断增加煤层中垂直裂缝数量的条件下,利用基于分裂节点的有限元数值方法模拟了含有不同条数裂隙煤层的地震反射波场;通过与不含裂缝、各向同性薄煤层反射的多波波场对比分析发现:裂缝的存在会对煤层的反射产生影响,但裂缝密度低时影响微弱,裂缝密度增加到一定程度后会出现类似调谐作用的反射能量干涉加强;裂缝密度进一步升高,对煤层反射的影响主要反映在高频成分的增加,对振幅影响较弱,说明煤层的反射强度主要受薄层的干涉作用影响较大;从理论地震波场分析的角度证明了薄煤层含裂缝的不可忽视性及反演的可能性。

Simulation Analysis of Seismic Response Characteristics of Vertical Cracks in Thin Coal Seam

Defines a single model of a thin coal seam, and sets cracked coal seam by adding vertical cracks in the middle layer constantly. The seismic reflected wave fields of cracked coal seams are researched by utilizing the finite element methods based on node splitting. Comparison with seismic multi-wave fields of isotropic thin coal seams without crack shows that: the existing of cracks influences seismic response of a thin coal seam, while the effect is very weak for low crack densities.When the crack densities increase to a certain extent, there is a similar interference enhance of reflected energy to the effect of thin-bed tuning. Beyond the crack density, the crack effect on seismic responses of coal seams is mainly reflected in the increase in high frequency information, while has a weak influence in amplitude, which shows that the reflected energy of coal seams is mainly determined by thin-bed interference. From the perspective of theoretical analysis on seismic wave fields, shows that the effect of cracks on seismic responses of a thin coal seam can not be ignored and seismic inversion of cracks in a thin coal seam is possible.