三维随机断裂带的航空时域电磁响应数值模拟

传统的均匀分布异常体模型，不能准确描述地下介质的不规则性变化，采用随机介质进行替代，将使电导率这一物性参数更加接近于实际的电导率分布.本文结合地质结构中断裂带特征，采用Von Kármán函数建立三维随机介质模型，通过讨论Hurst指数与自相关长度对三维随机电导率模型建模产生的影响，进行参数优化建立所需的随机介质模型.利用一维傅里叶变换建立三维随机变化的条状断裂带异常体，三维傅里叶变换建立三维随机变化的背景围岩，准确地表征了油气藏断裂带特征.基于时域有限差分方法，实现了磁源激励下的三维随机介质航空时域电磁响应数值模拟.采用均匀半空间模型验证了数值模拟的正确性，分析了随机断裂带与均匀断裂带的电磁响应特征，结果表明随机断裂带可以准确描述地下介质的分布特征，而且与断裂带垂直方向的电磁响应特征清晰地描述了断裂带的倾向、走向与位置，为断裂带结构探测提供了理论依据和技术指导，三维随机断裂带模拟方法同样适用于其它三维随机介质的数值模拟.

FTEM modeling of 3D random fracture based on FDTD

Homogeneous abnormal body model could not accurately describe irregular change of conductivity underground. The replacement of abnormal body model by random medium makes the conductivity closer to the actual conductivity distribution. Considering the characteristics of fracture in the real geological structure, we used Von Kármán function to establish 3D random fracture model, and improved it through parameter optimization in the discussion of Hurst number and autocorrelation length. We modeled streak fracture by using 1D Fourier transform and background rock by 3D Fourier in order to describe the fracture characteristics of hydrocarbon reservoir. FTEM modeling with loop sources of 3D random fracture was realized based on FDTD. The numerical integration method was used for a homogeneous half-space to verify the validity of our algorithm on Fixed-wing Time-Domain Electromagnetic. We analyzed the electromagnetic response characteristics of random fracture and homogeneous fracture. The results showed that fracture model could precisely describe the distribution features of underground medium. Trend, inclination and position of fracture could be more clearly described by perpendicular electromagnetic response to fracture, which provided theoretical guidance for structure detection of random fracture. This method can be applied to other numerical simulation methods similarly.