Geophysics bliss

For the first time in over 20 years, the EAGE Conference and Exhibition is in Copenhagen, Denmark. Since it's one of my favourite cities, and since there is an open source software workshop on Friday, and since I was in Europe anyway, I decided to come along. It's my first EAGE since 2005 (Madrid).

Sunday and Monday saw ten workshops on a smörgåsbord of topics from broadband seismic to simulation and risk. The breadth of subject matter is a reminder that this is the largest integrated event in our business: geoscientists and engineers mingle in almost every session of the conference. I got here last night, having missed the first day of sessions. But I made up for it today, catching 14 out of the 208 talks on offer, and missing 100% of the posters. If I thought about it too long, this would make me a bit sad, but I saw some great presentations so I've no reason to be glum. Here are some highlights...

One talk this afternoon left an impression. Roberto Herrera of the BLind Identification of Seismic Signals (BLISS, what else?) project at the University of Alberta, provoked the audience with talk of Automated seismic-to-well ties. Skeptical glances were widely exchanged, but what followed was an elegant description of cross-correlation, and why it fails to correlate across changes in scale or varying time-shifts. The solution: Dynamic Time Warping, an innovation that computes the Euclidean distance between every possible pair of samples. This process results in a matrix of cross-correlations, the minimal cost path across this matrix is the optimal correlation. Because this path does not necessarily correlate time-equivalent samples, time is effectively warped. Brilliant. 

I always enjoy hearing about small, grass-roots efforts at the fringes. Johannes Amtmann of Joanneum Research Resources showed us the foundations of a new online resource for interpreters (Seismic attribute database for time-effective literature search). Though not yet online, seismic-attribute.info will soon allow anyone to search a hand-picked catalog of more than 750 papers on seismic attributes (29% of which are from The Leading Edge, 13% from Geophysics, 10% from First Break, and the rest from other journals and conferences). Tagged with 152 keywords, papers can be filtered for, say, papers on curvature attributes and channel interpretation. We love Mendeley for managing references, but this sounds like a terrific way to jump-start an interpretation project. If there's a way for the community at large to help curate the project, or even take it in new directions, it could be very exciting.

One of the most enticing titles was from Jan Bakke of Schlumberger: Seismic DNA — a novel seismic feature extraction method using non-local and multi-attribute sets. Jan explained that auto-tracking usually only uses data from the immediate vicinity of the current pick, but human interpreters look at the stacking pattern to decide where to pick. To try to emulate this, Jan's approach is to use the simple-but-effective approach of regular expression matching. This involves thresholding the data so that it can be represented by discrete classes (a, b, c, for example). The interpreter then builds regex rules, which Jan calls nucleotides, to determine what constitutes a good pick. The rules operate over a variable time window, thus the 'non-local' label. Many volumes can influence the outcome as concurrent expressions are combined with a logical AND. It would be interesting to compare the approach to ordinary trace correlation, which also accounts for wave shape in an interval.

SV reflectivity with offset. Notice the zero-crossing at about 24° and the multiple critical angles. The first talk of the day was a mind-bending (for me) exploration of the implications of Brewster's angle — a well-understood effect in optics — for seismic waves in elastic media. In Physical insight into the elastic Brewster's angle, Bob Tatham (University of Texas at Austin) had fun with shear wave ray paths for shear waves, applying some of Aki and Richards's equations to see what happens to reflectivity with offset. Just as light is polarized at Brewster's angle (hence Polaroid sunglasses, which exploit this effect), the reflectivity of SV waves drops to zero at relatively short offsets. Interestingly, the angle (the Tatham angle?) is relatively invariant with Vp/Vs ratio. Explore the effect yourself with the CREWES Zoeppritz Explorer.

That's it for highlights. I found most talks were relatively free from marketing. Most were on time, though sometimes left little time for questions. I'm looking forward to tomorrow.

If you were there today, I'd love to hear about talks you enjoyed. Use the comments to share.

Comments

[David Markus]

As far as "Seismic DNA", unfortunately the editors musn't be that well read, since this technique is neither novel or new.

Chroma Energy made a famous splash back in 1998-9 with an advanced version of the same.

It got good coverage even until 2001 in AAPG Explorer as well as Forbes Magazine, etc. Demonstrated in papers at up until 2007 in SEG, EAGE, Taner Symposium, etc. spawned a company called GeoPatterns,..

You can start reading here:

http://www.aapg.org/explorer/2001/03mar/pattern_dna.cfm

We've ourselves have been doing advanced methods of seismic dna-like waveform correlation ourselves for years, and have much more advanced methods of string cutting, string matching way more advanced than regular expression matching (including uncertainty analysis), and much more sophisticated ways of extracting feature profiles.

We've also done a lot of work with rock physics based models to extract patterns that help de-risk things like "non-unique AVO", and more. Perhaps it's time to submit abstracts of advanced work in these regards?

If anyone wants to find out more about the wealth of literature available on this topic they can contact me at the above address.

Cheers,

David

David Markus
Saddleback Geosolutions
LinkedIn Profile

[Matt Hall]

@David... Thanks a lot for your comment the other day. Indeed - there's really nothing new under the sun. The AAPG Explorer article you link to is intriguing, but unfortunately it's a piece of classic oil industry non-explanation of a black box - I find it impossible to tell what they are on about. The Seismic DNS guys at least do a decent job of explaining their algorithm.

Anyway, the background here is much appreciated... Your company looks very interesting. I hope Saddleback can bring a little scientific transparency to the area!