考虑海底地形的三维频率域可控源电磁响应有限体积法模拟

为了提高海洋可控源电磁的地形响应模拟精度,探讨了三维交错网格剖分有限体积法求解频率域电磁场解的数值方法.在似稳场近似条件下,推导了有限差分法和有限体积法低频电磁场控制方程的离散表达式.通过对离散表达式的分析比较表明,有限体积法较之有限差分具有更高的计算精度,同时也具有与有限差分相当的计算效率.对含地形界面网格单元电导率采用加权平均处理,通过与二维有限元程序的计算结果对比,验证了该方法可以有效提高有限体积法对地形变化的模拟精度.应用有限体积法计算了一个三维带地形储层模型的可控源电磁响应,分析表明地形变化对电场分量影响明显,磁场分量对地形变化不敏感.

3D frequency-domain modeling of marine controlled source electromagnetic responses with topography using finite volume method

We present an algorithm for modeling the 3D frequency-domain marine controlled-source electromagnetic(CSEM) response by using the finite volume method.In this paper,the formulae of the discrete form of the governing equation have been deduced in details.Comparison of the discrete formulae of the finite volume method(FVM) with the finite difference method(FDM) shows that FVM is more accurate,while it is as efficient as FDM.The weighted mean conductivity of the seawater and the sediment,which is calculated by using two volumes divided by the interface as the weightings,are set to be the conductivities of the cells on the terrain interface.Our numerical modeling shows that the weighting processes of the terrain interface can improve the accuracy of the terrain effects of CSEM.An oil reservoir with bathymetry variation has been simulated by our code.The modeling result demonstrates that the electric field is influenced by the terrain,however,the magnetic field is insensitive to the bathymetry.