摘要
为适应多通道瞬变电磁法的特点,文章对Wang和Hohmann的经典时域算法进行了四点改进:第一,通过解一个三维直流电法正演问题获取准确的初始值,既避免了光滑波形近似带来的误差,又可适应浅表电阻率不均匀的模型;第二,利用阶跃响应和脉冲响应的导数关系对二者进行交错递推,可同时获得阶跃响应和脉冲响应而不增加计算量;第三,引入了Kirchhoff积分延拓公式,代替传统的基于静磁场假设的地空边界条件,提高了地空边界条件的精度.第四,通过褶积合成最终响应,可以适应任意发射电流波形.文中利用改进后的三维时域差分格式分别对均匀半空间模型、含油气薄层的层状模型和含油气薄层的盐丘模型进行了正演计算,并通过与伪随机码褶积合成了带波形的响应.计算结果表明:在合适的参数条件下,该差分格式是稳定的,且模拟结果是精确可靠的.含油气薄层的模型计算结果证明多通道瞬变电磁法对油气薄层有较好的勘探能力.
A new finite-difference scheme for the solution of 3D multi-channel transient electromagnetic field simulation is presented.The approximation of fast flapping PRBS source wave is avoided by modeling the impulse response of earth,which is obtained by advancing the step and impulse responses alternatively. The scheme employs a modified version of Dufort-Frankel method in conjunction with staggered grid.Accurate initial value is achieved by solving a 3Ddirect current modeling problem.A Kirchhoff upward continuation formula is introduced to replace traditional air-earth boundary condition based on static magnetic field assumption.After the impulse response having been obtained,its convolution with PRBS is performed to get the final response. The results from homogeneous half space shows that our method is reliable.Two examples for thin reservoir are then simulated.Both examples demonstrate that MTEM method is sensitive to thin reservoir.
出处
《地球物理学进展》
CSCD
北大核心
2015年第5期2225-2232,共8页
Progress in Geophysics
基金
国家重大科研装备研制项目"深部资源探测核心装备研发"(ZDYZ2012-1)05子项目"多通道大功率电法勘探仪"资助
