Tuesday, January 31, 2012

Calculating Biot characteristic frequency

In the theory of poro-elastic wave propagation, Biot (1956) defined a characteristic frequency (fc) given by this equation

For the fact-checkers out there, this relationship can be found by combining Biot (1956) equations 7.4, 6.8 and 3.7. A PDF of the paper can be found here.

At frequencies below fc, the Biot slow wave is not really a wave at all, but a highly attenuated diffusion phenomena. Above fc, the slow wave propagates with less attenuation and therefore would be more easily observable in lab experiments and has more influence on the reflection process.

The units used in poro-elasticity can be tricky. For example, the brine sandstone parameters of Dutta and Ode (1983) are pore fluid viscosity (0.01 poise), porosity (0.3), permeability (1 darcy), and in-situ pore fluid density (1 g/cc). You can imagine it is a rather horrific exercise to convert all this to MKS units for calculation of fc. However, we can navigate this very nicely using using wolfram|Alpha. The answer in this case if fc = 48379 Hz. Click the link in the previous sentence to do the calculation yourself. From there, you can put in other numbers and find fc in any case of interest.

To be sure you are on the right track, Dutta and Ode (1983) give a gas sand example with the same porosity and permeability as the previous calculation, but pore fluid viscosity is 0.00015 poise and density is 0.1 g/cc. From this you should find a characteristic frequency of 7257 Hz.

Biot, M. A., 1956a, Theory of propagation of elastic waves in a fluid-saturated porous solid, I: Low frequency range: Journal of the Acoustical Society of America, 28, no. 2, 168–178, doi:10.1121/1.1908239.

Dutta, N. C., and H. Ode, 1983, Seismic reflections from a gas-water contact: Geophysics, 48, 148–162, doi:10.1190/1.1441454.

Monday, January 30, 2012

DISC 0.1 U Houston (27 January)

A DISC dress-rehersal was held on the University of Houston campus last Saturday (Jan 28). This was unofficial, but we still had 57 students. Food and drink were sponsored by Apache (thanks to Tad Smith) and all arrangements were made by the SEG student section, the SEG Wavelets. In particular, great credit is due to Wavelets lecture coordinator Antonio Sierra, an excellent and energetic organizer.

This was the first time I had presented the entire course material. Although a day earlier, I gave a 1-hour overview in departmental seminar.

So how did it go? Well, we finished on time which was a relief. You never know with new material. I got a lot of good feedback from students and quite a few questions. It is a course that spans many, seemingly-disconnected, topics: vibroseis, thin beds, Biot waves, anisotropy, attenuation, wavelet transforms, etc. No one complained, but seems like I need to do a better job keeping all these topics in perspective, they are all pieces of the dispersion puzzle. Hey, maybe I could use a jigsaw puzzle slide.

(The official DISC book is still in production, but we managed to splice together PDF files from galley proofs and print a draft book for participants. I'm hoping SEG will recognize the important role this audience played by giving each attending student a real DISC book when they are ready. If not, are there any donors out there who would like to cover the book cost? Nice way to impress 60 potential employees. Or maybe the SEG Foundation?)

Some very good, specific suggestions were made. Since the slides contain every figure in the book (in order), but also other figures, it was sugessted I have an easily-recognizable symbol and number on slide figures that are in the book. This would help with book navigation. Similarly, it was suggested to add equation numbers in the slides that sync with the book. Luanxiao Zhao pointed out an error in my definition of the Biot characteristic frequency; many thanks for the bug report.

The dress-rehersal was, it turned out, badly needed. The slides had many spelling errors (spell checker had been turned off), and many annoying animations were present that need to be removed.

At the top of this post is a class picture. It is a bit blurry, but you get the idea. A high-res version will be uploaded when I get it from Antonio.

Thanks to all the UH students for a great class!!

Let's finish with a slide the audience seemed to enjoy. Ciao

Saturday, January 28, 2012

Tuesday, January 24, 2012

DISC Interview

Hi Chris,

We would like you to consider writing a pre-tour article (to tantalize geoscientists to attend your DISC) that will go on our “Feature Focus” on the home page of our website.

All the best,

Jenny Cole
Professional Development Administrator
Society of Exploration Geophysicists


1. Please tell us a little bit about yourself. (e.g. your education and work experience, why you became a geophysicist, etc.)

I went to college at The University of Arkansas in my recently-adopted home town of Fayetteville.  Preceding me at the UofA where my older brothers Jeff (to whom my DISC book is dedicated) and Robert, both of whom majored in geology. We were really the first generation of our family to attend college, although my mother had taken some college classes.  After a dead-end majoring in entomology, it seemed natural to consider geology as a major. My first meeting was with Dr. Walter Manger -- paleontologist, stratigrapher, tireless promoter of geology -- who looked over my transcript, discussed my interests, and declared: "You are a geophysicist!" Manger became a life-long mentor, role model and friend. The UofA did not offer a geophysics degree, so I took a degree in geology with geophysics option. That meant taking advanced math and hard-core physics classes, as well as a full geology curriculum. I think this mix is geology/math/physics has shaped my interests and success ever since. In today's university, it is all too easy to specialize early and become an uber-expert in one narrow topic. I have known geophysicists with a top-school PhD who are lost in conversations about unconformities, soft-sediment deformation, or stratigraphy.

After completing my BS degree at Arkansas, I earned a Masters under Dr. Stan Laster at the U of Tulsa. Stan was a great advisor and from him I began to absorb the lore of geophysics at the highest level: MIT and the GAG group, imaging and what was going on with Jon Claerbout at Stanford, a love of wave propagation, a deep respect for great geophysicists and great papers. Through his contact with Ken Larner (then at Western Geophysical), Stan got me an interview that turned into a research job in London. I defended my MS on Aug 15 and got on the plane the next day.

AFter working in London for a year, I joined Conoco in Oklahoma City as an exploration geophysicist. My geology/geophysics background was a perfect match to the job. Somewhere along the line I began asking myself this question: "Would you rather retire with 40 years experience and an MS degree, or 36 years and a PhD?" The answer lead me to the Colorado School of Mines in 1986. Whatever plans I had were instantly reset when I had lunch the first day with Norm Bleistein and Jack Cohen. They were applied mathematicians working on deep seismic problems, exactly the kind of thing Stan Laster had talked about. Bleistein and Cohen were also kind, understanding, brilliant, and patient. They would need all of that to get a reformed geologist through a PhD at CSM. I recall Norm telling me after the PhD qualifying exam that lengthy discussion by the committee was cut short by his comment: "Come on, the guy was a geologist last week." Jack kept a slide rule duck-taped on the wall over his computer monitor with the label: Emergency Use Only. It was also Jack who stopped cold one day while deriving an expression on the hallway chalkboard, then turned to me and said "You know, mathematics for me is a social science, because it lets me spend time with people I like."

On the subject of mathematics, I should mention that in my early undergraduate days I was weak and struggling at math. This was a hangover from high school when football and social life trumped academics. As a freshman, I failed to pass the first module of Calculus I. The way it worked back then, the professor and students who passed a module moved up together; a sort of conveyor belt of math professors. If, like me, you did not pass the module, it was retaken with the next prof in line. For me this meant I retook the module with Dr. Dennis Brewer. As if by magic, I understood what he was saying, what the math was about. I got an A in the module and followed Dr. Brewer through all of Calc I, II and III, honors differential equations, and Applied Math I. This showed me the power of one good teacher.

So, as you can see, my career was propelled by strong, benevolent, brilliant personalities. If they all think you are worth the effort, then working your butt off to accomplish something seems the least you can do.

2. Would you like to mention anything about your personal attributes that helped you achieve the professional status you enjoy today; was it self-belief, hard work, a mentor, or something else?

I have already covered the important topic of mentors. My family always gave me unending support and a refuge when times were hard. I don't think of myself as working harder than anyone else, but I get a lot done by organizing, prioritizing, and staying focused. I did have a range of early jobs that required very hard work. Jobs like frame carpenter and shoveler on an asphalt crew. That kind of job in the summer made college look pretty good, but it also taught me to respect and understand guys who work for a living. Perhaps because of those early experiences, one of my favorite quotes is by Voltaire, "Keeping busy is a poor substitute for accomplishment."

They may not be personal attributes, but I believe two things really helped me be successful.

First, as a teen I was a voracious reader of science fiction, following the example of my older brothers. So many of those great books had a professor-type who got called off somewhere in the world (or beyond) to give advice or solve a problem. I wanted to be that guy, and now 40 years later I suppose I am. The DISC, for example, has me going around the world to share my thoughts with thousands of SEG members, many of whom are great friends.

The second thing that has helped me is related to the first. Maybe it came from all that early reading, but I like to write. My son Dave (a geologist) once told me: "I think you are just like a lot of other geophysicists, but you are a good writer." I will pass on further comment and let the reader decide.

3. Why did you choose this lecture topic? Why is it important?

This is a tough question. This all started when Tad Smith, then chairman of the DISC committee, took one of my classes at UHouston. Little did I know he was also there to get a good look at my style as a possible DISC presenter. I was offered the DISC and then asked what topic I wanted to do. Now most DISC presenters are chosen to build the course around a lifetime of focussed work on a tight and well-known subject (anisotropy, AVO, etc.). My work has been all over the map -- wave propagation, attributes, near surface, reservoir characterization, deconvolution -- not something that fits into a neat category. But even before the DISC offer, it was dawning on me that there was one over-arching theme in my interests and published work. That is frequency-dependence, the broad and varied collection of seismic phenomena that vary with frequency. This has been central to my work since the mid-1990s thanks to former UTulsa PhD student Chun-Feng Li (now professor at Tongji University). He introduced me to wavelet transforms and time-frequency methods in general, and his doctoral work lead to the Spice attribute. The DISC, then, is my chance to bring many far-flung topics together under a single heading of Seismic Dispersion. To my knowledge, this is the first attempt to build a coherent narrative of the various aspects of dispersion in a general sense. The Greeks used to say that all things are imperfect at the first try, and so I suspect it will be with my DISC.

The topic is important because these phenomena exist in our data. I think of it like anisotropy before Leon Thomsen's landmark paper in 1986. From a hydrocarbon exploration point of view, if we ignore dispersive effects present in the data and someone else figures out how to use them to create better images or more detailed interpretations, then they get a competitive advantage.

4. Could you tell us in a few sentences what your course objectives are?

The idea is to build an appreciation and understanding of the many seismic characteristics that depend strongly on frequency.

For example, sound in water is generally understood to be about 1500 m/s for any frequency you car to test. True, so long as we are not doing the test in shallow water. In that case, the wave speed becomes a very complicated topic. The idea of phase and group velocity pops up, as well as the vexing question of how 'shallow' is shallow?

Another example is reflection itself. We are all familiar with the normal incidence reflection coefficient and Zoeppritz's equations for angular incidence. But these are reflection from an elastic interface, an idealization that ignores porosity, pore fluid motion, and permeability. Reflection from a poor-elastic contact leads to a frequency-dependent reflection coefficient. How does it behave? If the variation important? Can it be observed in real data? These are the really interesting questions.

So, briefly, the course objectives are to explore a broad group of frequency-dependent phenomena related to acquisition, processing and interpretation. As we come to understand them, it also becomes clear that many dispersive phenomena contain information of interest to us.

5. Are there any more specific areas that you want to emphasize?

It is my hope that working geophysicists and students will not be daunted by the apparently theoretical nature of this course. Just the terminology of dispersive phenomena is a barrier to understanding. But that is why we have a DISC program. The DISC participants and I will go methodically through selected topics, bringing in a bit of math where it illuminates the subject and always working to draw out useful conclusions and applications. As a professor of 20 years, I have a pretty good eye on the audience and will work at the pace that makes sense for the group at hand.

6. What do you hope people will have learned after they attend your lecture?

DISC attendees should go away with a general knowledge of time-frequency methods and an appreciation of frequency-dependent phenomena. I hope attendees will be more comfortable in a meeting when someone says "the harmonics are killing us" or "wish we knew the seafloor shear wave speed" or "should be run a full-wave sonic?"

7. You have quite a busy year ahead. Do you enjoy traveling? Will it be difficult to balance the tour with your work?

I do enjoy traveling, but you may want to ask me this question again in a year. As for balance with work, I taught an extra course in fall 2011 to clear out this semester, and as an advisor I have not accepted new graduate students since mid-2011 (but I still have 12). My DISC travel is scheduled around the fall 2012 semester, so it is back to work as usual. With planning, almost anything can be accommodated.

8. Would you share with us one or two of your most exciting successes?

I'm not sure 'exciting' is the right term, but I would say being Editor of Geophysics (1999-2001) was a remarkable honor and recognition. Being named 2012 DISC instructor is in the same category. Not sure, but I might be the only former-editor also to be DISC. Interesting.

9. How about a couple of disappointments?

Like everyone in the seismic business I have applied for a few schools and jobs that did not work out. But in reality, I think we land where we really ought to be. Looking back at my student days, I would rather be at a grad school that was a good fit than somehow squeeze into one a bit beyond my abilities. My attitude about grad school is 'follow the money' and go to the school that wants you enough to offer an assistantship, that is where you belong. In the work world, every company has a different culture. The ones I worked with -- Western Geophysical, Conoco, Amoco, Saudi Aramco -- were all great companies and a pleasure to be with.

10. What advice would you give to geophysics students and professionals just starting out in the industry?

While undergrad do a double major or a minor.

Learn geology; the kind of geophysics we do is aimed at imaging geology and pore fluids.

If you get the chance, work for a major oil company for 5 years. You get great training and will know where your career is heading with that company. If you like it, stay. If not, jump to another (likely smaller) company and head for the career you want.

Join several societies (SEG, AAPG, SPE, etc.) and volunteer. The people you get to know this way cut across company and discipline lines. Most likely, you will meet lifelong friends.

Friday, January 13, 2012

Milton B. Dobrin Memorial Lecture

3rd update ...... new sponsor
Sponsored by BP PGS

The University of Houston Department of Earth and Atmospheric Sciences is delighted to announce the 18th Milton B. Dobrin Memorial Lecture will be given by Prof. Roel Snieder on Feb 27, 2012. Prof. Snieder of the Colorado School of Mines is W.M. Keck Distinguished Professor of Basic Exploration Science, an honorary member of SEG, author of several books, and an outstanding researcher in fields as diverse as interferometry, seismic modeling, multiple suppression, microseismicity, and seismic noise. Prof. Snieder web page

Rethinking Carbon Capture and Sequestration as a tool to reduce global warming
Because of the increasing world population, mankind is more and more vulnerable to changes in climate. The man-made contribution to global warming is due to emission of CO2 and other greenhouse gasses. Capturing CO2 and injecting it in the subsurface thus seems a natural method to reduce man-made global warming. The following questions must be answered before this process can be used on a scale that actually makes a difference in managing climate change. (1) How can the cost of this process be reduced from its projected cost of 150 billion dollars per year? (2) How can the capture and injection be up-scaled with a factor 1000 beyond current capabilities? (3) How can we predict and monitor leakage? Many actions alternative to carbon capture and sequestration are likely to be much cheaper, reduce greenhouse gas emissions, save energy, and increase the energy independence of the United States.

This event will be hosted at the UH Hilton in association with student poster presentations. Prof. Snieder also plans a student-only seminar earlier in the day. The Department will advertise the Dobrin evening lecture through the Geophysical Society of Houston to draw a diverse audience from the industry. Anticipated attendance is 120-170.

We are seeking additional sponsors to support this important lecture and student seminar. In addition to the Hilton venue, cost items include advertising, speaker travel, catered food and cash bar, as well as lunch for the student seminar. Any surplus funds will provide student support for geophysics field camp. Sponsorship level of $3000 or over will receive prominent acknowledgement and logo display.

If you are able to help sponsor the 2012 Dobrin Lecture, please contact me by email or phone.

Best regards,

Prof. Christopher L. Liner, Associate Chairman
Department of Earth & Atmopheric Sciences
University of Houston
713.893.0711 cliner@uh.edu


Here is a complete list of previous speakers at the UH Dobrin Memorial Lecture.  Thanks to Fernando Enrique Ziegler for filling many gaps.  More thanks to Stuart Hall for the early years.

Friday, January 6, 2012

Figure of the day

This figure was generated using OpendTect and the F3-Demo data from the Dutch North Sea. The gray-scale image is a vertical slice through a 3D seismic volume, and the color surface is a tracked horizon representing approximate base of the Tertiary. Fault and channel networks are clearly observed. Colors represent seismic reflection amplitude that is influenced by various rock and pore fluid properties.

Interpretation was done on a Macintosh with dual 30-inch cinema displays. OpendTect is an excellent (free!) system for academic seismic interpreters, hats off to the developers.

update 1