Numerical examples of Ziolkowski, A., and E. Slob, 2019, Introduction to Controlled-Source Electromagnetic Methods: Cambridge University Press; ISBN: 9781107058620.
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README.md

Numerical Examples of Ziolkowski and Slob (2019)

DOI

The notebooks in this repository reproduce the numerical examples given in Chapter 5 of the following book:


Introduction to Controlled-Source Electromagnetic Methods: Detecting Subsurface Fluids

Anton Ziolkowski and Evert Slob, 2019, Cambridge University Press, ISBN: 9781107058620.

Abstract

This volume describes how controlled-source electromagnetic methods are used to determine the electrical conductivity and hydrocarbon content of the upper few kilometres of the earth, on land and at sea. The authors show how the signal-to-noise ratio of the measured data may be maximised via suitable choice of acquisition and processing parameters and selection of subsequent data analysis procedures. Complete impulse responses for every electric and magnetic source and receiver configuration are derived, providing a guide to the expected response for real data. One-, two- and three-dimensional modelling and inversion procedures for recovery of earth conductivity are presented, emphasising the importance of updating model parameters using complementary geophysical data and rock physics relations. Requiring no specialist prior knowledge of electromagnetic theory, and providing a step-by-step guide through the necessary mathematics, this book provides an accessible introduction for advanced students, researchers and industry practitioners in exploration geoscience and petroleum engineering.


The original figures in the book were created by Evert Slob in Matlab, using the formulae as given in the book. The figures presented here are reproductions using the Python modeller empymod (Werthmüller, 2017), which uses the derivations as given in Hunziker et al. (2015) and Slob et al. (2010). Both solutions are exact in the wavenumber-frequency domain, and for the diffusive half-space solution also in the space-frequency and space-time domains, so the results have to be the same up to numerical precision and differences in the Hankel- and Fourier-transforms. We compared the results from the Matlab scripts and the Python code to ensure that they agree. This is particularly valuable as the formulation of the book and the formulation on which empymod is based upon are not exactly the same. Whilst the numerical results are the same, their appearance might slightly differ due to the use of different plotting libraries (Matlab vs. Matplotlib).

Exceptions occur in examples that have added random noise and also in examples which show the relative error, where tiny differences can blow up quite significantly in the relative error when the responses go to zero.

Installation & requirements

The notebooks require at least empymod v1.7.1. The version included in the zip-archive of CUP is empymod v1.8.1.

Requirements

Python 3.5+ and recent versions of NumPy, SciPy, matplotlib, IPython, and Jupyter.

If you are new to Python I recommend using a Python distribution, which will ensure that all dependencies are met, specifically properly compiled versions of NumPy and SciPy; my preferred option is the Anaconda distribution.

Using the zip-archive provided by CUP

The zip-file is available as an Online Resource to the book at cambridge.org/csem.

Make sure your installation of Python meets the requirements. Then simply extract the archive and open the notebooks with your installation of Jupyter. The source code of empymod is located in the same folder, so Python will find it automatically.

Using the newest versions of the notebooks and empymod

Make sure your installation of Python meets the requirements. Follow the instructions on empymod.github.io to install the newest version of empymod using conda or pip. The maintained versions of the notebooks are available at github.com/empymod/csem-ziolkowski-and-slob.

References

Hunziker, J., J. Thorbecke, and E. Slob, 2015, The electromagnetic response in a layered vertical transverse isotropic medium: A new look at an old problem: Geophysics, 80(1), F1-F18; DOI: 10.1190/geo2013-0411.1.

Slob, E., J. Hunziker, and W. A. Mulder, 2010, Green's tensors for the diffusive electric field in a VTI half-space: PIER, 107, 1-20: DOI: 10.2528/PIER10052807.

Werthmüller, D., 2017, An open-source full 3D electromagnetic modeler for 1D VTI media in Python: empymod: Geophysics, 82(6), WB9-WB19; DOI: 10.1190/geo2016-0626.1.

Ziolkowski, A., and E. Slob, 2019, Introduction to Controlled-Source Electromagnetic Methods: Cambridge University Press; ISBN: 9781107058620.

License

Copyright 2018 Dieter Werthmüller

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.