裂缝参数对纵波各向异性影响的数值模拟

Numerical simulation to the influence of fracture parameters on P-wave anisotropy

利用地震资料研究天然裂缝的纵波方位各向异性,目前还缺乏纵波属性对裂缝的敏感性系统分析。为此,基于数字图像处理技术,通过设置裂缝参数,采用邻点融合方法建立非均匀性的随机裂缝介质;基于声波波动理论,对随机离散裂缝模型的声波波场进行数值模拟,通过计算不同测线方位的声波速度和衰减系数,分析声学参数与裂缝分布、走向、密度及流体间的关系,可较准确地判定裂缝方向。对随机离散裂缝模型的声波波场的数值模拟结果表明:裂缝参数变化对声波衰减系数的影响远远大于对声波速度的影响,采用声波衰减系数最小值对应的测线方位可较准确地判定裂缝走向;随着裂缝密度增加,衰减系数相对变化量减小;随着含水饱和度增加,速度和衰减系数的相对变化量均先增大后减小。

In the study of P-wave azimuthal anisotropy of natural fractures using seismic data,systematic sensitivity of P-wave attributes to fractures is not carried out.A non-uniform random fracture medium is produced through adjacent point fusion after setting fracture parameters based on digital image processing technology.Based on the acoustic wave theory,the acoustic wave field of the random discrete fracture model is numerically simulated.After calculating the acoustic velocity and attenuation coefficient of the azimuth of a survey line,the relationship between acoustic parameters and fracture distribution,orientation and density and fluid is analyzed to determine fracture orientation more accurately.Numerical simulation to the acoustic wave field of the random discrete fracture model shows that the influence of fracture parameters on acoustic attenuation coefficient is far greater than that on acoustic velocity,and the azimuth of the survey line corresponding to the minimum acoustic attenuation coefficient can be used to accurately determine fracture orientation.With the increase of fracture density,the relative change of attenuation coefficient decreases.With the increase of water saturation,the relative changes of acoustic velocity and attenuation coefficient increase first and then decrease.