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Zhdanov M.S.,University of Utah | Cuma M.,University of Utah | Wilson G.A.,Technolmaging
72nd European Association of Geoscientists and Engineers Conference and Exhibition 2010: A New Spring for Geoscience. Incorporating SPE EUROPEC 2010 | Year: 2010

We present our implementation of an iterative migration algorithm for marine controlled-source electromagnetic (MCSEM) data based on the 3D integral equation method with inhomogeneous background conductivity and focusing regularization with a priori terms. The use of focusing stabilizers makes it possible to recover subsurface models with sharper geoelectric contrasts and boundaries than can be obtained using traditional smooth stabilizers. The method is implemented in a fully parallelized code which makes it practical to run large-scale 3D iterative migration within a day on multi-component, multiline MCSEM surveys for models with millions of cells. We present a suite of interpretations obtained from different iterative migration scenarios for a synthetic 3D MCSEM survey computed from a very detailed model of stacked anticline structures and reservoir units of the Shtokman gas field in the Russian sector of the Barents Sea. © 2010, European Association of Geoscientists and Engineers.

Zhdanov M.,Technolmaging | Endo M.,Technolmaging | Mattsson J.,PGS
Proceedings of the Annual Offshore Technology Conference | Year: 2015

The towed streamer EM system makes it possible to collect EM data with a high production rate and over very large survey areas. At the same time, 3D inversion of the towed streamer EM data remains a very challenging problem because of the huge number of transmitter positions of the moving towed streamer EM system, and, correspondingly, the huge number of forward and inverse problems needed to be solved for every transmitter position over the large areas of the survey. We overcome this problem by exploiting the fact that a towed streamer EM system's sensitivity domain is significantly smaller than the area of the towed streamer EM survey. We apply the concept of moving sensitivity domain, originally developed for airborne EM surveys, to the interpretation of marine EM survey data. This makes it possible to invert the entire towed streamer EM surveys with no approximations into high-resolution 3D geoelectrical sea- bottom models. Our implementation is based on the 3D integral equation (IE) method for computing the responses and Frechet derivatives for 3D anisotropic geoelectrical models. In the framework of the concept of the moving sensitivity domain, for a given transmitter-receiver pair, the EM responses and Frechet derivatives are computed from a 3D Earth model that encapsulates the towed EM system's sensitivity domain. The Frechet matrix for the entire 3D Earth model is then constructed as the superposition of Frechet derivatives from all transmitter-receiver pairs over the entire 3D earth model. This makes large-scale 3D inversion a tractable problem with moderate cluster resources. We present case studies of 3D anisotropic inversion of towed streamer EM data from the Troll West Oil Province and Mariner field in the North Sea. Copyright © (2015) by the Offshore Technology Conference All rights reserved.

Hobbs B.A.,PGS | Zhdanov M.S.,Technolmaging | Gribenko A.,Technolmaging | Paterson A.,PGS | And 2 more authors.
72nd European Association of Geoscientists and Engineers Conference and Exhibition 2010: A New Spring for Geoscience. Incorporating SPE EUROPEC 2010 | Year: 2010

We present a case study leading to the 3D inversion of transient electromagnetic (EM) data for delineating reservoir extent at the Alvheim field in the Norwegian sector of the North Sea. The survey was conducted in July and August 2008 using one method of marine EM surveying, namely a two ship operation and ocean bottom cables. One ship laid a receiver cable with 30 receivers on the sea floor, and the second ship placed a source cable on the sea floor which was used to generate a coded transient signal. The configuration of the source and receiver spread was analogous to 2D seismic acquisition, as the system was rolled along to obtain multi-fold coverage of the subsurface. The survey spanned 20 km, resulting in measurements of 1270 source-receiver locations. The measured electric field for each source-receiver pair was deconvolved for the measured source current to determine the impulse response function. Preliminary inversions were made for each source-receiver pair using a 1D model, and the results were stitched to a 2D image. Having defined a background model, all data were then simultaneously inverted in 3D with focusing regularization. This revealed high resistivity volumes corresponding to the known hydrocarbon-bearing reservoirs of the Alvheim field. © 2010, European Association of Geoscientists and Engineers.

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