Seismoelectric Exploration

Theory, Experiments, and Applications

Niels Grobbe, André Revil, Zhenya Zhu, Evert Slob, Niels Grobbe, André Revil, Zhenya Zhu, Evert Slob

• Publisher: American Geophysical Union
• Year: 2020
• ISBN:
  9781119127390
• Edition: 1
• Topic: Sciences physiques
• Subtopic: Géologie et sciences de la Terre

Seismoelectric coupling and its current and?potential future applications

The seismoelectric method—the naturally-occurring?coupling of seismic waves to electromagnetic fields—can provide insight into important properties of porous media. With a variety of potential environmental and engineering uses, as well as larger scale applications such as earthquake detection and oil and gas exploration, it offers a number of advantages over conventional geoEdit HTML Sourcephysical methods.

Seismoelectric Exploration: Theory, Experiments, and Applications explores the coupling between poroelastic and electromagnetic disturbances, discussing laboratory experiments, numerical?modeling techniques, recent theoretical developments, and field studies.?

Volume highlights include:

• Physics of the seismoelectric effect at the microscale
• Governing equations describing coupled seismo-electromagnetic fields
• Examples of successful seismoelectric field experiments in different geological settings
• Current and potential applications of seismoelectric coupling
• Noise removal techniques for seismoelectric field measurements

The American Geophysical Union promotes discovery in Earth and space science for the benefit of humanity. Its publications disseminate scientific knowledge and provide resources for researchers, students, and professionals.

FOREWORD 1

The topic of seismoelectric and electroseismic exploration that this book describes so completely is near and dear to my heart even if I have not been working in the area for some time now. Let me recall here some fondly‐remembered anecdotes from my early connection to this field of research.

In 1991, when I was a young post‐doc working for Professor Nafi Toksöz at MIT’s Earth Resources Laboratory, Nafi let me go to the annual Society of Exploration Geophysics meeting in Houston and I attended a talk given by Dr. Art Thompson of Exxon Mobil Research entitled “Electroseismic Prospecting”. Art described his beautifully‐conceived field experiments where his team had sent seismic waves into the Earth from a source on the surface and recorded electric fields as the voltage difference between metal rods inserted into the ground. The electric fields seemed to be contained within the seismic waves themselves but also created from dipoles that were generated whenever the spherical seismic wave passed through an interface at depth. I was fascinated. When I was in graduate school at Texas A&M, in a class taught by Professor Dale Morgan called “Rock Physics”, Dale (who is now at MIT) had described electrokinetic phenomena in porous media. It was intriguing to learn that fluid flow through the pores of a rock could drag along the extra cations of the nanoscale charge separation at the fluid‐solid interface to produce a macroscale and easily measurable electric field. As a term paper for that class, I worked out how the electric field generated by the pressure gradients in a seismic wave influences the relative fluid‐solid movement and the associated seismic attenuation. I later chose to make the theoretical understanding of seismic waves in porous media my PhD thesis topic. One of the chapters in the dissertation, and my first publication in 1991, focused on the electric fields generated within a seismic wave by electrokinetic effects.

So after attending Art’s pioneering talk at the 1991 SEG meeting, I reported to Nafi that I was in a position to quantitatively model the seismically‐generated electric fields that Art had recorded. Nafi told me to invite Art to come give his talk at MIT, which Art agreed to do. After Art’s presentation, Nafi introduced himself and, in classic Nafi style, immediately invited Art to come do a sabbatical at MIT, which led to Art spending a semester with us at the Earth Resources Laboratory in 1992. Nafi also said that I should write a seismoelectric research proposal to Basic Energy Sciences of the U.S. Department of Energy. So I typed up a proposal covering both theory and experiments and sent it into the program manager Bill Luth and to my surprise it was accepted for full funding a month or two later. Nafi let me work with one of his brilliant doctoral students Matthijs Haartsen and before long Matthijs had a numerical code simulating the electric fields generated by seismic waves propagating through layered porous media. Although my research focus across my career, both then and now, has been on more purely mechanical topics of porous‐media response, the year or so I spent at MIT developing the equations, theory and simulations of seismoelectric response will always be a highlight.

Let me share a final particularly fond memory from 1992 at the Earth Resources Laboratory. Art and I had been discussing various types of laboratory experiments to quantify seismic‐to‐electrical coupling and, as is Art’s style, some of the experiments he was conceiving of were quite sophisticated and all were quite expensive. One morning after getting funding, I was explaining to Zhenya Zhu, who is one of the editors of the present book, the basic idea of an electric field moving along with a compressional wave as part of the material response. Zhenya has been the Earth Resources Laboratory lead experimentalist over many decades. At that time, although he had created many types of ingenious lab‐scale seismic models, he had not done much in the way of electrical measurements. An hour or so after our discussion, I was walking by Zhenya’s lab and he had a huge slab of rock sitting on his bench top that he was hitting with a hammer. Two metal wires had been inserted into the rock and Zhenya was recording their voltage difference on an oscilloscope. Each time he hit the rock, the seismic pulse would appear on the screen of the oscilloscope; he was measuring the co‐seismic electric field we had just discussed! I went and got Art Thompson and we all had a good laugh with how quickly and simply (and at zero cost) Zhenya had begun to observe seismic‐to‐electric coupling in the lab.

Although our various publications surrounding the theory and simulation of seismoelectric and electroseismic response did not come out until after I left MIT for the University of Paris (Institut de Physique du Globe), it was the nexus created by Nafi’s management style at the Earth Resources Laboratory, where Art Thompson, Matthijs Haartsen, Zhenya Zhu and I were given the freedom to overlap and interact, that allowed this field to develop rapidly and in different directions in the early 1990s. I also recall Andre Revil, another editor of the present book, regularly dropping by my office at the Institut de Physique du Globe de Paris in the mid 1990s. He was a graduate student at the University of Strasbourg at the time and very interested in seismoelectric and electrokinetic topics and we had many detailed discussions surrounding the various technical issues.

What makes the seismoelectric topic so fascinating is that the macroscopic response that is being recorded is generated from transport processes occurring within the electric double layer, which is typically a nanometer or less in width depending on the electrolyte salinity. Having response play out over so many orders of length scale and having the theoretical predictions be able to match the macroscale recordings (at least in some cases) represents everything that I find enjoyable about the study of multi‐scale Earth materials. The present volume is a needed opportunity to shine light on this interesting and still developing field that ultimately should find applications even beyond the Earth sciences. What makes this book special is its coverage of all aspects of seismic‐and‐electrical coupling. From its nanometer‐scale and fluid‐chemistry‐dependent origins associated with the electric double layer, to a derivation of the pertinent macroscale governing equations and the associated modeling of the seismic and electrical sources, to laboratory studies, numerical simulation procedures and field studies, this book covers the current state of the art of seismoelectric and electroseismic exploration and is the essential reference for anybody interested in the topic.

Steve Pride

University of California at Berkeley and Lawrence
Berkeley National Lab
Berkeley, CA, USA
30 July, 2019

FOREWORD 2

Seismoelectricity is a ubiquitous natural phenomenon in the Earth with great potential to be utilized for scientific studies and for geophysical exploration. Put in the simplest terms, seismoelectricity occurs because seismic waves propagating through a porous, permeable medium induce fluid motion in the pores. The fluid contains ions; the ions in the fluid separate. One group of charged ions adheres to mineral surfaces around the pore wall leaving an access of free ions in the fluid. Seismic waves that induce the motion of the fluid also move the free ions and produce electrical current. The seismically induced “streaming current” is the source of seismoelectricity.

The seismoelectric phenomenon is fascinating both for its scientific significance but also for its potential applications to the Earth. Fluids play an important role in Earth’s crust, especially for determining its electrical properties. Seismic waves are most sensitive to elastic properties but not sensitive to fluid properties in the rocks. Seismic and electrical measurements, made separately, as is done in general practice, provide good information but cannot be correlated with the desired spatial resolution. Seismoelectrical measurements that combine both of these together focus directly to the source of conversion.

Seismoelectricity is a very broad field of study and it extends over physical, mathematical and earth sciences. Seminal papers in this field have been published in a wide spectrum of journals. This book, “Seismoelectric exploration: Theory, experiments and applications,” is a major contribution to the field. It provides a comprehensive overview of the seismoelectric phenomena. It contains 28 carefully selected articles representing a tremendous amount of work done by more than 60 authors. The papers are presented in four sections that cover the physical and theoretical aspects of seismoelectricity, laboratory measurements, numerical models and field data examples from earth observations.

The first section is on the theory. It includes the microscale origin of seismoelectric effects, electrokinetics, and streaming potential and the governing set of coupled seismo‐electromagnetic equations. This section also includes the Green’s functions for earthquake sources.

The twelve papers in Section 2 represent an impressive number of laboratory studies on various aspects of seismoelectricity. They include measurement of streaming potentials, seismoelectric coupling coefficients, effects of porosity, permeability anisotropy on seismoelectric conversion. Laboratory measurements in scaled‐down borehole models are also included.

Section 3 is devoted to the modeling of seismoelectric signals due to various seismic sources including surface sources and earthquakes. Both point sources and finite rupture models are used for modeling. Seismoelectric conversion at interfaces and scattering at heterogeneities are also included.

The Section 4 “Field experiments and applications” is an important part of the book. It extends seismoelectricity from purely theoretical, numerical and laboratory domains into the real earth field applications. The papers in this section cover topics such as design of field instrumentation, noise removal and data processing. Field examples include measurements in unconsolidated sediments for shallow exploration, studies of ice sheets and glaciers, and seismoelectric signals related to earthquakes.

The editors have done an excellent job in their selection of the 28 papers in this book from a field of thousands of articles. Many of these papers are cited in the references. I would like to take the liberty of listing a few references that deserve special attention at the end of this Foreword.

The editors of “Seismoelectric Exploration: Theory, Experiments and Applications,” Niels Grobbe, André Revil, Zhenya Zhu and Evert Slob must be congratulated for producing such a comprehensive volume on this important subject. The book will be an excellent resource to faculty and graduate students and researchers in academia, industry and government agencies. The scope of electroseismicity is far broader than geophysics and earth sciences. It could be applicable in any field dealing with fluids in porous media that can be imaged with acoustic and electromagnetic waves. Such imaging is widely used in many fields including medicine.

M. Nafi Toksöz

Massachusetts Institute of Technology

Cambridge, MA, USA

12 August 2019

PREFACE

The aim of this book is to provide a wide overview of recent research activities on the coupling between poroelastic and electromagnetic disturbances, caused by charged particles in pore fluids. With this overview we hope to make the potential benefits of the phenomenon for several possible subsurface applications be...