Inversion of inline and broadside marine controlled‐source electromagnetic data with constraints derived from seismic data

Abstract

We present a structural smoothing regularization scheme in the context of inversion of marine controlled‐source electromagnetic data. The regularizing hypothesis is that the electrical parameters have a structure similar to that of the elastic parameters observed from seismic data. The regularization is split into three steps. First, we ensure that our inversion grid conforms with the geometry derived from seismic. Second, we use a seismic stratigraphic attribute to define a spatially varying regularization strength. Third, we use an indexing strategy on the inversion grid to define smoothing along the seismic geometry. Enforcing such regularization in the inversion will encourage an inversion result that is more intuitive for the interpreter to deal with. However, the interpreter should also be aware of the bias introduced by using seismic data for regularization. We illustrate the method using one synthetic example and one field data example. The results show how the regularization works and that it clearly enforces the structure derived from seismic data. From the field data example we find that the inversion result improves when the structural smoothing regularization is employed. Including the broadside data improves the inversion results even more, due to a better balancing between the sensitivities for the horizontal and vertical resistivities.

Two‐dimensional magnetotelluric inversion using reflection seismic data as constraints and application in the COSC project

“…Furthermore, we use two sets of weights for the horizontal and vertical directions (which depend directly on the model mesh) while Zhou et al [] used four (obviously linearly dependent) directions which may have caused the imperfect structure in their synthetic model with a normal fault. Wiik et al's [] method is more similar to ours with two sets of weights for 2‐D models and usage of seismic reflectivity, but the weights β to the regularization are based on the local seismic structural consistency. Structural consistency considers faults and fractures as structural discontinuities, whereas internal layering of a structure is not considered a discontinuity, making this approach very well suited for sedimentary terrains.…”

“…Zhou et al's [] inversion processes a guiding seismic image and determines its discontinuities and coherent regions to assign small and large smoothness weights, respectively, across the associated cell boundaries. Wiik et al [] add a spatially varying function β to the regularization based on the local structural consistency (stratigraphic attribute) in the seismic image.…”

“…Wiik et al [2015] add a spatially varying function β to the regularization based on the local structural consistency (stratigraphic attribute) in the seismic image.…”

Integration of geoscientific uncertainty into geophysical inversion by means of local gradient regularization

“…For instance, gravity data, which have poor horizontal resolution, can be integrated with seismic inversion to mitigate the poor lateral resolution of seismic inversion (Lelièvre et al, 2012). Likewise, geological modelling and geophysical inversions are routinely performed in the same area to obtain a subsurface model consistent with geological and geophysical measurements (Guillen et al, 2008;Lelièvre and Farquharson, 2016;Pears et al, 2017;Williams, 2008). When sufficient prior information is available, petrophysical constraints can be used in inversion (Lelièvre et al, 2012;Paasche and Tronicke, 2007) and integrated with geological modelling to derive local constraints (Giraud et al, 2017).…”

Controlled-source electromagnetic and seismic delineation of subseafloor fluid flow structures in a gas hydrate province, offshore Norway

“…To improve the unconstrained inversion results for line 1 and line 2, we constrained them with seismic information. In a seismically constrained CSEM inversion, the structural smoothing regularization enables any seismically derived stratigraphic attribute to constrain the EM data, thus yielding a refined and geologically realistic final model (Wiik et al 2015). In our seismically constrained inversions, the regularization is relaxed across seismically defined interfaces, thus enabling a discontinuity to appear if one is favoured by the data.…”