垂向裂隙各向异性煤层地震波响应

Seismic response of anisotropic coal beds with vertical cracks

煤层中存在的裂隙会导致介质表现为各向异性,本文以HTI型煤层为例,结合各向异性介质弹性矩阵和各向异性裂隙理论,推导出不同充填物的垂直裂隙中各向异性参数表达式,将其应用于地震波响应分析;通过改进的交错网格差分法和各向异性Christoffel方程波场分解法,得到地震波合成记录和分解后的P波和SV波记录;将Thomsen群速度与相速度公式,经过坐标轴旋转变换,得到HTI型煤层中不同各向异性参数的地震波速度响应表达式;建立不同类型煤层地质模型,分析了裂隙密度、裂隙充填物以及煤层厚度等参数变化时的地震波响应特征.研究结果为分析垂向裂隙各向异性薄煤层地震波传播规律提供工具,为选用相应地震数据进行地震波各向异性参数反演提供依据.

There are many kinds of cracks in coals beds,which induce anisotropy in seismic waves.In this paper,combining elastic matrix and fracture theory in anisotropic media,the expressions of anisotropic parameters in a HTI coal bed are derived when it is filled by different materials such as gas and water,which are used to analyze characteristics of seismic response.Seismic synthetic records and decomposed P-wave and SV-wave records are simulated by the revised staggered grid difference method and wave field decomposition method for anisotropic Christoffel equation.Seismic velocity variation with angle is indicated by rotating the coordinate axis in the Thomsen′s group and phase velocity equations.The geological models of different types of coal seams are established and the characteristics of seismic wave response with different parameters such as crack density,filling materials and thickness of coal seams are presented.The results provide tools for analyzing seismic wave propagation in anisotropic thin coal seams and a theoretical basis for choosing appropriate seismic data for inversion of anisotropic parameters.