Preface


Te purpose of this book is to give an introduction to exploration geophysics. Geophysicists explore the earth by making physical


measurements at the surface. Tey use these measurements to map subsurface rocks and their fluids at all scales, and to describe the subsurface rocks in physical terms – velocity, density, electrical resistivity, magnetism, and so on. In this book we explain how geophysics is used to ‘look into’ the earth and how geophysical technologies help us to understand the solid subsurface beneath our feet. Te book is derived from articles in the column


‘Recent Advances in Technology’ in the interdisciplinary magazine GEO ExPro, which the authors have been writing since 2007. Each article is based on our research and experience, with help from internet sources as well as from several colleagues from industry and academia who have contributed as guest authors. Each technical subject has its own chapter, and can


be read independently of other chapters, but to make it easier to read, we have prepared an introductory chapter called ‘Looking into the Earth’, which outlines the scope of geophysical methods and gives an overview demonstrating how everything in petroleum geophysics is interrelated. We focus on basic principles and from there explain the recent advances within various exploration techniques, hopefully in an easy way with limited use of equations but with many examples. We acknowledge that the area of application of


geophysical methods is very wide, and much has had to be omitted. It is inevitable that our selection of topics has prejudice resulting from personal interest and experience, which has led to a bias towards descriptions and examples based on our extensive expertise in the marine seismic industry in north-west Europe.


The chapters are:


1. Looking into the Earth: an introduction to geophysics and geophysical exploration methods, including seismics, electromagnetics, gravimetry and magnetometry and use of satellite data, followed by illustrative data examples of how geophysics is used to look into the earth. We show how rock physics can translate geophysical observations into reservoir properties.


2. Elements of Seismic Surveying: a brief history of seismic and, in particular, seismic surveying in the North Sea. We introduce four-component ocean- bottom seismic surveying and imaging, as well as wide and full azimuth seismic surveying. In Codes and Ciphers we look at ways of decoding nature’s


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disorder, and use that to discuss simultaneous sources as one avenue to improving the way geophysicists deliver high-quality data while maintaining viability in a cost-focused market.


3. Marine Seismic Sources and Sounds in the Sea: we summarise salient points for geoscientists who need to sharpen their rusty skills in seismic source technology. We give you a feeling for decibels in air and water; discuss the effect seismic sources may have on marine life; and present sound and sound modelling in the sea.


4. Reservoir Monitoring Technology: a review of the use of time-lapse (4D) seismic for reservoir monitoring and an introduction to the noble art of analysing data. We discuss typical monitoring parameters: fluid saturation, reservoir pressure, and reservoir compaction. Rapid implementation of 4D technology has led to increased hydrocarbon production through infill drilling. It is also effective in the early detection of unwanted and unforeseen reservoir developments, such as gas breakthrough and sudden pressure increases. Finally, we present several field examples from Life of Field Seismic (LoFS) / Permanent Reservoir Monitoring (PRM) over Valhall, Ekofisk, Snorre and Grane.


5. Broadband Seismic Technology and Beyond: an introduction to what broadband seismic is, what this technology has to offer, and the various broadband technologies that have recently been commercialised; and we describe how seismic ghosts can be exorcised.


6. Gravity and Magnetics for Hydrocarbon Exploration: how unexplored sedimentary basins can be unravelled by gravity, and how gravity and magnetics are used in cross-disciplinary workflows for hydrocarbon exploration.


7. Supercomputers for Beginners: an introduction to supercomputers: how to design parallel software, what is GPU-accelerated processing, supercomputers and seismic imaging, and quantum computers.


8. Gas Hydrates: gas hydrates have been often mentioned as an important possible source of natural gas. We give simple explanations of what gas hydrates are, where they can be found on Earth and what their physical properties are. We also discuss the possibilities of gas hydrates on Mars and elsewhere in outer space.

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