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Davydycheva S.,3DEM Consulting | Frenkel M.A.,EMGS Americas
PIERS 2010 Cambridge - Progress in Electromagnetics Research Symposium, Proceedings | Year: 2010

The 3D electromagnetic (EM) modeling and inversion techniques for the geological formation evaluation have been experiencing significant progress since the early 90s. There are three main 3D EM numerical techniques: finite-difference (FD), finite element (FE), and integral equation (IE). They have been used for simulating arbitrary 3D media as well as for development of 3D inversion-based interpretation of well log data acquired by the conventional and new-generation logging tools. We present a brief review of these three techniques as to their ability to simulate and interpret the new-generation of triaxial tensor wireline and logging-while- drilling (LWD) measurements. The new EM tools provide full triaxial tensor measurement, in addition to the conventional axial measurement, when the formation is excited by an axial z- directed magnetic dipole transmitter, and the response of axial receivers is analyzed. Due to full 3D sensitivities, the new tools allow significantly enhanced formation resistivity interpretation. We present synthetic logs for four different new-generation tools: both triaxial induction and directional propagation resistivity LWD tools. We also consider new features in the new tool responses and discuss various post-acquisition processing techniques. These approaches allow to better visualize tool responses and enable efficient application of fast stable inversion schemes for resistivity interpretation.

Ridyard D.,EMGS Americas | Hesthammer J.,Rocksource
World Oil | Year: 2011

Several oil companies such as ExxonMobil, Statoil and Shell, have been adopting electromagnetic (EM) imaging technology to reduce exploration risk in marine environments. EM data have been shown to be highly accurate in identifying subsurface resistivity variations with the commercial exploration drilling success rate of 50-70% for exploration wells drilled on prospects with a significant EM anomaly, compared to 5-14% for wells drilled on prospects without a significant EM anomaly. EM technology offers several benefits such as it avoids drilling dry wells and another benefit is to drill discoveries on prospects with an EM anomaly. EM surveys can provide useful quantitative information to delineate the reservoir and improve the estimation of fluid type and saturation. The additional value may be created by more accurate knowledge of the value of reserves obtained through integrated analysis of the EM data.

Kanhalangsy C.,EMGS Americas | Golubev N.,EMGS Americas | Zach J.J.,EMGS Americas | Baltar D.,EMGS Americas
SEG Technical Program Expanded Abstracts | Year: 2011

We present anisotropic 2.5D inversion examples illustrating the possibility to image a resistor beneath gas hydrates with marine CSEM. The inversion examples are from a large CSEM survey conducted in 2008 in Alaminos Canyon, covering part of the Perdido fold belt. The focus of our study is on a part of the survey which is co-located with a recent partially published well, AC818-#1 "Tiger", and was acquired with very dense receiver spacing 0.5 km and a source waveform with main frequencies of 0.5 Hz and higher. We show anisotropic CSEM inversion results for different background models. The resulting resistivity sections accurately recover the two most prominent features from the well independent of the assumed background model: shallow hydrates at the top of the Oligocene Frio sand as well as a high resistivity anomaly discovered in the Eocene Wilcox formation at the crest of the anticline. Both in terms of depth and structure, the CSEM, seismic and well log results agree well, even when the CSEM inversion is not constrained by a priori information in the form of seismic horizons. © 2011 Society of Exploration Geophysicists.

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