“I don’t always follow the mainstream.”

An interview with Gerhard Pratt

Coordinated by: Satinder Chopra | Photos courtesy: Penny Colton
Gerhard Pratt

Dr. Gerhard Pratt is a Professor of Geophysics at Queen’s University, where he joined in 1998, and is well-known for his work on seismic wave modeling and imaging. Early on in his career, after spending a few years as a Wireline Engineer at Schlumberger,Gerhard obtained his M.Sc. and Ph. D. degrees from Imperial College London (1986, 1989), under the supervision of Professor Michael Worthington. This stint got him interested in the powerful mathematical inverse methods of Albert Tarantola. He followed his Ph.D. with a two year postdoctoral fellowship at the University of Toronto, working with Professors Chris Chapman and Gordon West, developing methods for traveltime tomography in anisotropic media. From 1992-1997 Gerhard was the Elf Acquitaine Lecturer in Geophysics, in the Department of Geology at Imperial College, London.

A key development that Gerhard has been involved in lately has been the implementation of frequency-domain techniques that make possible large scale forward and inverse modeling of exploration seismic data, through numerical simulation of the full wave equation. Together with his students, he has been able to use these methods in imaging structures in a wide range of applications, from large scale wide-angle deep crustal profiling, to exploration scale imaging, to small scale site investigations. Most recently he has begun using these techniques for imaging breast cancers in medical ultrasound tomography . Gerhard is a well-published author and apart from teaching and research at Queens, he has been active as a geophysical consultant in a number of different fields. Since conducting the interview, Gerhard has accepted an offer to become the Chair of the Department of Earth Sciences at the University of Western Ontario, in London, ON. He is looking forward to joining this extremely active and productive department in September 2008.

Gerhard is the 2008 CSEG Distinguished Lecturer and has been visiting different Universities to deliver his talk,‘What else can the waveform tell us?’ Satinder Chopra sat down with him just before his CSEG Luncheon talk (March 31st, 2008), and they spoke on a range of topics. Following are excerpts from his interview.

Gerhard, let’s begin by asking you about your educational background and your work experience.

Okay, well I actually started my scientific life really as an Undergraduate at Queen’s so I am back where I started, although in 1980 I graduated in Engineering Physics. At the time I was all set to go and work as a nuclear design engineer. However, at the time the oil patch made me a better offer and I ended up working for Schlumberger as a wireline engineer for about five years, mostly on North Sea oil rigs. That’s where I got my first taste of seismics – I was running large walkaway VSP surveys and I became fascinated by them. I decided to look for a place to do more of that and I managed to get myself a place at the Imperial College of Science and Technology, in London, England where I got my Ph.D. I ended up working as an academic in the U.K. for about 10 years before returning to Queen’s as a Professor about 10 years ago.

So were you always interested in science, and in pursuing a career in science?

Yes, absolutely, I was, from a very young age. I loved science and reading about astronomy. Physics was a great interest of mine in High School, where I had some very good teachers. It was a bit of a surprise to the rest of my family, as there is not a scientist among them.

What kind of research did you do for your Doctorate?

My Ph.D. advisor was Michael Worthington at Imperial College. Michael was doing a lot of different projects in borehole geophysics and that fit in perfectly with my Schlumberger background. It was an exciting time because we were looking at some new mathematical methods that people had brought out that looked like they could be applied to borehole geophysics, but it wasn’t clear that they were going to work in practice. I focused on developing and applying waveform methods for crosswell seismics for my Ph.D.

What would you say about how your career has shaped up until now?

Well, I think the main thing is that I am doing something that I love doing and I get paid for it – I think for me that is a definition of success. You know, being an academic allows you a certain freedom to define your research program. Provided you can get bright students to help you, and provided you can get funding for them, then you have something that is really very, very valuable. Of course, academic life can be demanding – we don’t give ourselves many Friday afternoons off, and most of us work 6-7 days a week to keep up with the demands of the job. I have had a good run at two very good Universities and it has been challenging, and it has always been interesting.

Now let’s ask you about your personality – if I were to ask you to list three of your qualities what would they be?

That’s a bit of an odd question of course – I don’t usually do that much naval gazing! I have thought of myself as a little bit of a maverick, I tend to go a little bit off the beaten track and I don’t always follow the mainstream. I think I am a person driven by curiosity, and that requires a certain stubbornness perhaps, even a touch of obsession. But I am fortunate to be married to a woman who is an artist and she keeps me very well grounded and doesn’t let me get chasing off into my obsessions too far.

So that was the second or the third one?

I think that was three – being a maverick, curious, stubborn.

Satinder and Gerhard

You have been and still are a consultant for many companies; what kind of help or guidance do these companies look for?

Well, my expertise is in seismic imaging and then it’s always in these areas where people ask for my help. But the fascinating thing is it has been in a very wide range of applications, from seismic imaging with gas hydrates, to work in nuclear waste disposal, mineral exploration and of course in a lot of work with the oil and gas industry. More recently I have even become involved in medical ultrasound imaging. So the applications have been very wide and varied, but we are all sort of trying to bring the same imaging expertise to all these different problems.

Very interesting. Looking back on your geophysical career will you share with us one or two of your most exciting success?

Yes, okay. Certainly my Ph.D. work was one of the most exhilarating times in my career partly because it was not certain whether the project was going to work out. It was fairly high risk and it did work out, so there was a tremendous sense of success in that project. But more recently, I think one of the things that has been highlighted was our contribution at the 2004 BP Velocity Bench Mark Test in Europe: our success with that Bench Mark Test kind of opened up people’s eyes regarding the methods that we are using. It has been quite gratifying to see several groups within the industry that are now trying to develop their own imaging methodology using the techniques that we were advocating in that workshop.

Would you elaborate a little more on this methodology that you are talking about?

Well, in 2004 BP decided they would like to do a blind test of velocity model building and they invited contractors, universities, other oil companies to participate in a test where they distributed a synthetic data set. This was a completely blind test – the participants were not shown the model until after the workshop. The synthetic data set was shot over a fairly complex model that captured some of their key imaging problems. They produced long offset data and we were the only group in the workshop to use the refracted component of the data to form an image. We did a pretty good job and so the potential of using refractions for high-resolution imaging is something that came out of that workshop result.

According to you what would be your most important contribution to geophysics?

Well, my students and I and other collaborators have been focusing on this waveform inversion project for a while. You may be aware that in the 1990s people were beginning to wonder about the waveform inversion methodology. There was a feeling that this was never really going to be of any production value to the Industry, that it was kind of an esoteric method that had a lot of difficulties with it. We persevered, and I always encouraged my students to waveform inversion from an engineering perspective (I have an engineering background myself). There are aspects of the methodology that can be made to work if you handle the data properly and if you handle the mathematics properly. So I think that has been the contribution that we have made: to make people aware that the formal approach of inverting seismic waveforms can indeed produce quite useful results.

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What personal and professional visions are you working towards?

It is often difficult in Academia to keep a perspective on a particular vision. We are often fighting hard to even stay standing up within the University system to keep our programs going and that’s quite a challenge. One of the visions I have is to just maintain our Undergraduate and Graduate program in geophysics at Queen’s. But in terms of research, I have a number of very bright young Graduate students and we are continuing to push forward on this waveform inversion problem and try to handle a variety of different data applications.

As you mentioned, your research efforts have focused on tomography, anisotropy, attenuation, inversion and hydrate research; could you tell us in a general sense about the different problems you have tackled in each of these different areas?

Yes, I think the key word here, in that list that you gave me just a moment ago is the word “inversion”. If you think about what earth scientists do in general, whether you are in Industry or an Academic: we are all trying to make sense of our data. We are all trying to use data to learn something new about the earth. So in a sense we are all doing inverse theory, we are all working on the inverse problem. But to formalize it in terms of inversion methodology sometimes can allow you to ask some very fundamental questions about your data – whether the data actually resolve the parameter that you are looking for, or whether that parameter might lie in the null space. So that is the power of the inverse methodology, to be able to approach this thoroughly, and as you apply this methodology to a variety of problems you are forced by the nature of the data to grapple with more and more rigorous parameterizations. For example in the cross-well problem it is very rare that we get a data set in which you can ignore anisotropy. Isotropy is just not an adequate model and so we have been using anisotropy in cross-well velocity tomography for quite a while now.

Another example would be if we start to look at gas hydrates. Sub- permafrost gas hydrates, apparently – and this was a surprise to us – apparently are very attenuative and so it was impossible really to make sense of the data without incorporating attenuation into the models as well. So in a general sense, the more data you look at the more you realize how inadequate your models are and the more parameters you need to incorporate to do it properly.

Would you also tell us now what is the state of the art in each of these areas, in say tomography, anisotropy...?

Well, those kinds of questions are difficult to answer in a general sense because I think every data set brings with it its own particular issues.

The question of anisotropy is perhaps better resolved for example in the cross-well geometry, as you often have significant coverage with a variety of different propagation angles and that gives you a much better idea what the anisotropy is. If you just had standard, near-normal incidence reflection data then the anisotropy parameters are much more elusive, and much harder to resolve. With surface data I think the addition of long off-set data and the addition of refraction events into the problem is a way of getting a little bit further with this whole question of anisotropy. So one of the things that we are working on is a project with Talisman Energy in the Alberta Foothills to actually design the experiment to acquire much longer offset data that might enable us to shed some light on that question.

What is the direction in which we are going with attenuation determination of some sort?

Well I can tell you what we are thinking. Attenuation is something that affects seismic amplitudes, and it affects seismic bandwidth. But so too does velocity structure. To unravel the contribution of velocity structure from the contribution of seismic attenuation requires you to be very, very rigorous in how you approach the problem. So, if you cannot handle all of the variety of things that velocity structure can do to the amplitudes then you just can’t hope to look at attenuation. For example you can actually do some really interesting synthetic modeling experiments in which you can generate data sets through the use of attenuation, and you then find you can simulate those data sets without even using attenuation at all – just by introducing velocity structure. So it’s a very elusive parameter. On the other hand, from a rock-physics perspective it may tell you some very, very interesting properties of the reservoir that may be quite critical. It may be related to permeability and fluid flow, so it’s a problem that has a very high payoff, but it’s also a very high risk research project as well because of the subtlety of the problem.

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Apart from these areas that we have mentioned, are there any other areas in geophysics that fascinate you but you haven’t had the time to put your hands on it?

Well, I certainly read the published literature as widely as I can, right through from solid earth, whole earth geophysics through to exploration, and through to the very small scales. One thing that I have been doing with students at Queen’s as part of their 4th year projects work is a lot of environmental geophysics. At Queen’s we have the sort of basic equipment that you need to do that: ground penetrating radar, EM systems, IT resistivity, etc. Some of these projects have been quite valuable in learning about things like the hydro-geological controls on a landfill site, or adding geophysics to archeological investigations and so forth. That’s the kind of thing that we are doing at the moment just on a project basis with students that I find really fascinating. I think the value of geophysics is something that environmental engineering firms are learning more and more about. As a result we teach all our geological engineers in our program at least two full courses in geophysics as part of their Undergraduate Degree.

Now we know that 3D seismic has been a revolutionary technology; what is the direction in which R&D is going that might bring us another revolutionary technology in the future?

Yes, I think that is a really interesting and provocative question. From my perspective the time when I had a lot of involvement with Industry was in late 1980s early 1990s, when there were still a number of large research groups at some of the majors. The reality is that there are not a lot of industry labs left that have the really open-ended, blue skies research approach. This has largely disappeared and there is a lot of “short-termism” that is preventing us from looking at the really big questions I think. Fortunately this has not entirely disappeared, and some of the recent work in wide azimuth data acquisition in the Gulf of Mexico by BP has come out of a research group that is not afraid to ask these big, big questions. But I do think there has been a shift in the culture of Research and Development over the last 10 or 20 years.

I would like to think to some extent these waveform inversion methods may play a more significant role in the future, in that if we could rigorously predict, and account for, and make use of every wiggle in the seismic database and if we could come up with models that accounted for all of those wiggles, then we might learn a lot more about our reservoirs than we can presently. Our models might be a lot more quantitative and reflect the inner structures of the reservoirs perhaps that much better if we could make progress in that field.

So will you give us a glimpse of that in your talk today?

Oh, I will try to give you a glimpse of where we are with that in any case.

That’s the title, “How much can you get out of the Waveform”?

“What else can the waveform tell us?” The key is to try to extract as much information as possible from the data, and to use aspects of the data that might not be fully utilized in standard approaches.

Gerhard, you have written and published quite a few research papers as I saw on your CV; have you ever thought of writing a book or could you share with us your thoughts about your writing experiences?

Yes, that’s a little bit of a sore point, because I have had an outline on a book on waveform tomography sitting on my computer for a number of years and I have been desperately trying to get a sabbatical leave to write that book. So yes, I am definitely thinking that book should be written.

So would you look at it as sharing of knowledge?

Yes, absolutely, I enjoy writing and I try to instill that in my graduate students and sometimes I am successful and sometimes I am not. Not all scientists enjoy writing but I think communicating our discoveries is one of our functions as scientists. If you can’t structure your publications in such a way that they are accessible and that they are readable as well as being scientifically correct, I think you are losing out, so I am a great believer in the skill of writing properly.

What is your impression about the current state of the Canadian Universities in general and then with the respect to Geophysics in particular? How do they compare with other North American and European Universities. You might also want to include in terms of funding, problem- oriented research, dearth or abundance of students?

Well, there are a lot of different topics in that question. The Canadian University System, the Public University System that we have in this country is a very, very valuable asset and I think we have been getting support for this, Government support for this project that has been going for many, many decades in this country. But I have to say, it is getting increasing difficult for those of us who are committed to the Academic life to see it continuing, and there are tremendous pressures on the system.

It is interesting to compare the differences in Ontario to those in Alberta. One of the major differences is that, I believe Resource Sector Exploration is far less valued in Ontario than it is here in Alberta. And so within Ontario Universities, Earth Science programs are finding it hard to keep their heads above water. With the limited resources we are finding it difficult to keep our programs on the radar screens of the Deans and University administrators. So at Queen’s for example the tendency is to look at public policy, and students often come to Queen’s to study humanities and political science and sociology. Unfortunately there are very, very few high school graduates in Ontario that actually come to University in order to do Earth Science. That I think is quite different in Alberta, as the perception or the profile of Earth Science in Alberta is somewhat higher. So it is a particular problem in Ontario perhaps.

Well perhaps, you have answered the next question that I was going to ask; what sets Queen’s University apart from other Universities in Canada?

Oh, what I was answering was in terms of the pressures but there is another way to answer that question and that is with respect to the sort of education that Queen’s students receive. My home department is known as the Department of Geological Sciences and Geological Engineering. One of the strengths of our program is that we provide students with a very thorough background in the geological sciences no matter what their field of specialization is. Thus a geophysics graduate fro m Queen’s comes out of the program knowing a great deal of geology and I think that stands them well. It is a result of a very sort of holistic approach at the faculty level. My colleagues are mineral explorationists, sedimentologists, carbonate sedimentologists, structural geologists but we work very, very closely together and you know there is a lot of interdisciplinarity in what we do. So that I think is something that Queen’s is very good at: providing students with a view of earth sciences that is very interdisciplinary.

How many faculty members do you have in this geological sciences and geological engineering department?

Right now we are about, depending on how you count them, but in the order of 17 or 18 professors. There are bigger departments but we are not the smallest either.

Tell us about your experiences as 2007-2008 CSEG Distinguished Lecturer.

That has been an absolute highlight of my career, Satinder. It has been just a fascinating experience. I am nearly at the end of it and I wish it could go on. This talk that I am giving this afternoon I believe is going to be my 16th, and I have visited Universities right across the country. Next week I am going to Newfoundland to visit Memorial University, and that will be my first trip to Newfoundland. Every University I go to I meet keen, young (and old) geophysics professors who have really interesting ideas and good students. Wherever I go I try to pass on as much information as I can about the activities of the CSEG, but for me personally, it has been very, very rewarding.

I am very happy to hear that. Well you have been invited by many universities, companies and professional societies to give presentations. Are such requests always look for presentations on particular topics or are they more for you to participate. What sort of requests do you get?

Well, it’s usually the case as an academic that your talks are based on current research results. So the intent is usually to essentially present recent research results and to generate as much interest as possible in those results.

So basically on the topic that you have been working on —

To be somewhat esoteric, I managed to get myself involved in a medical imaging project quite recently and so I attended my first medical imaging conference in San Diego about a year ago, so that has opened up a whole new aspect of waveform inversion for me.

What other interests do you have apart from the science that you practice?

Well, I guess the thing I would point to if I am not actually doing geophysics or sort of enjoying family life in Kingston, is I am a great believer in popular scientific writing. Right at the moment I happen to be reading “The Trouble with Physics” by Lee Smolin, a book about a String Theory in physics. The author has some very damning conclusions about the inability of University Physics Departments to be imaginative in their research, and he has some very interesting things to say about how those problems should be fixed. I also am a great admirer of Richard Dawkins and one of his most recent books, “The Ancestor’s Tale” is something that anybody who is interested in evolution should read. Another favorite author is Oliver Sacks, the neuro-scientist. So I keep a fairly well stocked bookshelf, and reading about the wider scientific world keeps me well occupied.

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So are you an indoor person or an outdoor person or what?

Oh well, you know a lot of my time is indoors but actually a couple of years ago I started getting interested in triathlon training and competitions, so I do spend a certain amount of time running and cycling outdoors.

One last question that I have is what would your message be for a young geophysicist who is entering our profession?

Oh it is certainly one of optimism. If I could get more people to come in to our own particular Undergraduate Program in Geophysics I think that they would have an absolutely thrilling time and they’d come out of the program with all sorts of job prospects in the oil and gas industry, or the mining industry, or in Academia that would just open up their lives. So it is a message of tremendous optimism at the moment.

Gerhard, in these questions that I asked you was there anything that you expected me to ask you and I lost track of it somewhere?

No, I think you pretty well covered it.

Thank you very much for giving us this opportunity to sit and chat with you.


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