The 2nd RPI for October-November 2015: Leon Thomsen

Research Professor of Geophysics at University of Houston
Chief Scientist at Delta Geophysics

About the influencer 

Leon’s undergraduate degree was earned in 1964 at the California Institute of Technology, then and now a pre-eminent center of excellence in geophysics. In those days, the real excitement was in plate tectonics, planetary exploration, and the constitution of the earth’s deep interior, not in hydrocarbon exploration (oil cost just $4/BBL, pre-OPEC). So, Leon followed those ideas to Columbia University in New York City. His Ph.D. thesis, in 1969, dealt with seismic rock properties, and represented a new way to physically interpret seismic data for clues to the composition and crystal structure of the deepest interior of the earth.

In a post-doc position at the Centre Nationale de la Recherche Scientifique in Paris, another back at Caltech, and a faculty position at the State University of New York at Binghamton, he used relativistic quantum mechanics to improve and refine this physical interpretation. These particular tools of mathematics and physics might seem to be an inappropriate foundation for the task of finding oil and gas. Nevertheless, in 1980, during a period of high oil prices and rapid oil industry staff expansion, Leon left a tenured professorship at SUNY, and joined Amoco’s Research Center in Tulsa.

Within a month of his arrival, he discovered that the mathematical tools and physical insights which he had acquired in his previous academic career uniquely equipped him to recognize, in exploration seismic data, the effects of azimuthal anisotropy, to interpret it, and to deal with it. His foundational paper (1986) on weak polar anisotropy was intended as an introduction to the more general forms of anisotropy, but is now the most frequently cited paper in the history of GEOPHYSICS. It was motivated by the simple rock-physics observation that most formations are anisotropic, and the idea that ignoring an elementary fact like that is poor business strategy.

At the 1986 SEG Annual Meeting, the shear-wave implications of this work were revealed publicly, at the famous “Amoco Anisotrophy Technical Session”.  For eight more years, Amoco advanced the art and science of shear-wave exploration; the recognition of the critical importance of anisotropy to the propagation of these vector waves was crucial to our success. And, of course we deepened our understanding of the anisotropic effects in P-waves.

In 1994, Leon joined Amoco’s Worldwide Exploration department in Houston in order to help apply, in exploration, the ideas that he had helped to create, in research.  About this time, Ocean Bottom Seismics became feasible, and so we established many of the fundamental concepts of converted-wave exploration: registration, moveout gamma, effective gamma, diodic velocity, etc.

Following the 1999 acquisition of Amoco by BP, this work continued and expanded, until Leon’s retirement in 2008. At that time, he joined the University of Houston as Research Professor, and also founded a consultancy (cf.

Leon was given the Fessenden Award in 1994 by the SEG, and served as its Distinguished Lecturer in 1997, and as Distinguished Instructor in 2002. He is an Honorary Member of the EAGE and the GSH. He is a Foreign Member of the Russian Academy of Natural Sciences, and holder of their Kapitsa Medal. He served SEG as Vice President, as President-Elect, and as President (2006-07).

The secret of your success in being a well known name in the rock physics community

The secret of success is to be lucky. (If I had not, by pure chance, been assigned (upon my arrival at Amoco) to analyse that particular dataset, I might have never discovered anisotropy. If I had not, by pure chance, met a particular lady on campus, then she would have eventually married someone else, and I would probably be a bitter old bachelor, alone and unknown.) But, the secret to being lucky is to be prepared. I had a good educational foundation, at least in physics and mathematics, and that preparation enabled me to see things that others did not see.

Another part of the secret to success is to continually challenge the current paradigm of ideas. We should recognize that all our workflows are based on an interlocking network of assumptions, about the science and about the business. Giving ourselves the benefit of any doubt, let us stipulate that, when we make these assumptions, they are valid at the time.

But, as time passes, conditions change. For example, the cost of oil goes up (so that previous cost-benefit analyses become obsolete), or computers get bigger and faster (so that better algorithms become feasible). Nevertheless, we all have a tendency to stick with our current workflows, long after the assumptions on which they are based have become invalid. Progress comes when somebody examines those assumptions, realizes that they are no longer true, and fashions a better workflow, based on current assumptions.

Challenges you see in moving rock physics to the next level

Over the past 30 years, seismic anisotropy has entered the mainstream of exploration geophysics. Most geophysicists are familiar with the basic ideas, and most seismic processing is now anisotropic. But, most rock physics is still isotropic, and this limits our ability to maximize the value extracted from the data.

As a trivial example, consider the analysis of the AVO phenomenon, which is almost exclusively conducted in isotropic terms. But (challenging the conventional paradigm), we should ask ourselves does it make any sense at all to analyse Amplitude Variation with Angle while ignoring Velocity Variation with Angle? The answer is, “No!”, and in fact the equations for anisotropic AVO analysis have been known for 30 years. For 30 years, we have known the anisotropic terms in the AVO gradient and curvature, and that they were plausibly as large as the isotropic terms, hence could not properly be neglected!

But, all this time, we neglected those terms anyway, since we did not know how to estimate them, from the data. Now we know a way (Lin and Thomsen, SEG 2013). But, the algorithm has its limitations, and we all should be thinking about finding other algorithms to accomplish the same estimation.

As another trivial example, consider the analysis of Fluid Substitution, also almost exclusively conducted in isotropic terms (bulk modulus [sic!]). Or the analysis of brittleness, also almost exclusively conducted in isotropic terms (Poisson’s ratio [sic!], Young’s modulus [sic!]). We rock physicists have a long way to go to catch up with our anisotropic seismological colleagues. This is especially true in the current era of exploitation of the shale resource.

Advice for early career scientists (rock physicists, geophysicists, etc.)

My own career has been so improbable that I never advise young people to try to emulate me. But, here is some good general advice: take the shale resource seriously. Don’t try to use the ideas which were developed over the past 80 years for exploration for conventional clastic and/or evaporitic reservoirs, to try to exploit the shale resource. Challenge that paradigm.

Most of the recent advances in conventional exploration addressed the problem of seismic imaging beneath complex overburdens (e.g. salt). But, the shale resource usually occurs in structurally simple settings, where primitive imaging algorithms are sufficient.

However, economic exploitation of the shale resource does require advanced subsurface physical characterization (estimating physical properties like fluid content, and brittleness). Seismic rock physics lies at the heart of this workflow. And, since the shales are anisotropic, the rock physics must also be anisotropic. Only in this way can we maximize the value extracted from the data.

We thank Leon for his continuous contributions to the rock physics community.