Application of the perfectly matched layer in 3-D marine controlled-source electromagnetic modelling

Abstract

SUMMARYIn this study, the complex frequency-shifted perfectly matched layer (CFS-PML) in stretching Cartesian coordinates, is successfully applied to three-dimensional (3D) frequency-domain marine controlled-source electromagnetic (CSEM) field modelling.The Dirichlet boundary, which is usually used within the traditional framework of EM modeling algorithms, assumes the electric or magnetic field values are zero at the boundaries. This requires the boundaries be sufficiently far away from the sources in the area of interest. To mitigate the boundary artifacts, a large modelling area may be necessary even though cell sizes are allowed to grow toward the boundaries due to the diffusion of the electromagnetic wave propagation. Compared with the conventional Dirichlet boundary, the PML boundary is preferred as the modelling area of interest could be restricted to the target region and only a few absorbing layers surrounding can effectively depress the artificial boundary effect without losing the numerical accuracy. Furthermore, for joint inversion of seismic and marine CSEM data, if we used the PML for CSEM field simulation instead of the conventional Dirichlet, the modeling area for these two different geophysical data collected from the same survey area could the same, which is convenient for joint inversion grid Downloaded from https://academic.oup.com/gji/article-abstract/doi/10.1093/gji/ggx382/4157794/Application-of-the-perfectly-matched-layer-in-3D by GEOMAR Bibliothek Helmholtz-Zentrum fuer Ozeanforschung user on 22 September 2017 2 G. Li and B. Li matching. We apply the CFS-PML boundary to 3D marine CSEM modelling by using the staggered finite-difference (SFD) discretization. Numerical test indicates that the modeling algorithm using the CFS-PML also shows good accuracy compared to the Dirichlet. Furthermore, the modeling algorithm using the CFS-PML shows advantages in computational time and memory saving than that using the Dirichlet boundary. For the 3D example in this study, the memory saving using the PML is nearly 42 % and the time saving is around 48% compared to using the Dirichlet.

Improved Detectivity for Detecting Gas Hydrates Using the Weighted Differential Fields of the Marine Controlled-Source Electromagnetic Data

“…The marine electromagnetic (EM) method, especially the marine controlled-source EM (CSEM) technique, is widely used for investigating the gas hydrate [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]. The presence of methane or free gas increase the resistivity of the gas hydrate zone significantly [21,39,40], thus the EM method is useful for detecting the space distribution of hydrate in natural sediments, estimating its saturation [41][42][43][44] and monitoring the formation and dissociation of hydrates with the help of the borehole data [45][46][47][48].…”