Review: Communicating Rocks

Communicating Rocks by Peter Copeland
Pearson Education, July 2011, 160 pages

Visit Amazon.comI heard about this new book for geo-writers at the SEG Annual Meeting. I was there to teach a one-day course on technical writing for geoscientists, so naturally I ordered the book immediately. I've been leafing through it for about a month now and here's my verdict: I quite like it. Too wishy-washy? OK, I really like the contents. I really don't like the physical book. At all.

Why so bristly? Full disclosure: I love books. I know my recto from my verso, so to speak. Seeing a book typeset in Times and Arial makes me sad. Witnessing a publisher using the world's cheapest paper, flimsiest cardstock, and laughable page layout, I start to wonder if it's true what they say about the end of days for the medium. When they go on to charge $38 for such a book, I know it's true what they say about academic publishers gouging their customers.

None of this is author Peter Copeland's fault, and of course none of it really changes the message he wants to convey: writing matters. More particularly, your writing matters. Reading this short book, squarely aimed at and tailored for academic geoscientists, will make a difference to your writing. That's why it's on our recommended reading list.

I think it's fair to say that Copeland, a professor at the University of Houston, holds rather traditional views about writing. The first chapter, Communication equals thinking, is essentially a good-natured, 4000-word rant about the importance of writing well. He quotes the relatively tolerant George Orwell and the slightly-less-tolerant Lynne Truss, but gets quite worked up about the difference between forbid and prohibit, and sand and sandstone. I'm all for rigour and precision, but I do think there are contexts in which we can afford to write more comfortably, without feeling like we are programming a computer when we write. And I worry that would-be writers find it intimidating.

The second section of Copeland's book, Written communication, is the nub. After a look at types of writing, focusing pointedly on academic papers, there is a 65-page A-to-Z covering all sorts of topics from technical words to ordinary ones, and from points of English grammar to special geologic and scientific issues. One of the best passages is on accuracy, precision and repeatability; I will certainly refer to this section again. The section is rounded off with a useful collection of how-not-to examples, with clear and pertinent commentary—another dog-ear. 

Section three covers oral and poster presentations: more solid advice that, if taken, will lead the reader to be a fine presenter of observations, interpretations and ideas. But the advice is conventional and I do wonder if there's a missed opportunity to inspire, perhaps tacitly permit, the gifted communicator to take the risk of giving a remarkable presentation.

The final part of the book, aptly entitled Writing is hard, is another short piece about the graft of writing. Copeland celebrates the sheer hard work of planning to write, grinding out the first draft, and then writing the words all over again to make them the ones you really wanted. All excellent, practical, realistic advice for the grad student especially. 

Having accused Copeland of being a bit strict, I'll reveal myself to be a complete hypocrite by saying that I looked for several of my favourite peeves (i.e. and e.g., or the correct use of significant and begs the question) only to find them missing. And there is at least one slip: a billion is certainly no longer 10¹² in the UK. The 15 or so colour figures are generally quite weak, the math typesetting is poor, and the tables are grim. Stranger still, Copeland likes pie charts:

Pie charts are a fine way of displaying the relative amounts of several components.

Sacrilege! Or perhaps the very fact that all writing ranters have their own pet peeves means that they are nothing more than just peeves: silly predilections that don't really matter. 

H is for Horizon

Seismic interpretation is done by crafting, extracting, or digitally drawing horizons across data, but what is a horizon anyway? Coming up with a definition of horizon is hard. So I have narrowed it down to three.

Data-centric: a matrix of discrete samples in x,y,z that can be stored in a 3-column ASCII file. As such, a horizon is something that can be unambiguously drawn on a map, and treated like a raster image. Some software tools even call attribute maps horizons, blurring the definition further. The data-centric horizon is devoid of geology, and of geophysics; it is an artifact of software.

Geophysics-centric: an event, a reflection, in the seismic data; something you could pick with an automatic tracking tool. The quality is subject to the data itself. Change the data, or the processing, change the horizon. By this definition, a flat spot (a flattish reflection from a fluid contact) is a horizon, even though it's not stratigraphic. This type of horizon would be one of the inputs to instantaneous attribute analysis. The geophysics-centric horizon is still, in many ways, devoid of geology. It does not match your geological tops at the wells; it's not supposed to. 

Crossline 1241 (left), and geophysics-centric horizon (right) from the Penobscot 3D (Open Seismic Repository). Reds are highs and blues are lows.Geology-centric: a layer, a surface, an interface, in the earth, and its manifestation in the seismic data. It is the goal of seismic interpretation. In its purest form, it is unattainable: you can never know exactly where the horizon is in the subsurface. We do our best to construct it from wells, seismic, and imagination. Interestingly, because it is, to some degree, not consistent with the seismic reflections, it would not be possible to use the geology-centric horizon for instantaneous seismic attributes. It would match your well tops, if you could build it. But you can't. 

A four well model can help us illustrate this nuance. Geological tops have been correlated across these wells, and used as input to a seismic model to study the changes in thickness of the Bakken Formation (green to blue) interval.

Four-well synthetic seismic model illustrating how a geological surface (green, blue) is not necessarily the same as a seismic reflection. From Hall & Trouillot (2004).

The synthetic model shows how the seismic character changes from well to well. Notice that a stratigraphic surface is not the same thing as a seismic event. The top Bakken (BKKN) pick is a peak-to-trough zero-crossing in the middle, and pinches out and tunes at either end. The top Torquay (TRQY), transitions from a trough, to a zero-crossing, and then to another trough.

This uncertainty is part of the integration gap. It is why building a predictive geologic model is so difficult to do. The word horizon can be a catch-all term; reckless to throw around. Instead, clearly communicate the definition of your horizon pick, it will prevent confusion for yourself and for other people who come in contact with it.

REFERENCE
Hall, M & E Trouillot (2004). Predicting stratigraphy with spectral decomposition. Canadian Society of Exploration Geophysicists annual conference, Calgary, May 2004.

News of the week

This news feature has settled down into a fortnightly groove. News of the week sounds good, though, so we'll keep the name. Filtered geoscience tech news, every other Friday. Got tips?

Is it hot in here?

Google's philanthropic arm, Google.org, sponsored a major study at Southern Methodist University into the geothermal potential of the United States, and the results are in. This was interesting to us, because we've just spent a couple of weeks working our first geothermal project. Characterizing hot rocks is a fascinating and fairly new application of seismic technology, so it's been as much research exercise as interpretation project. From the looks of this beautiful map—which you must see in Google Earth—seismic may see wide application in the future. 

And the possibilties in Google Earth, along with Google SketchUp, for presenting geospatial data shouldn't go unnoticed!

CLAS arrives in OpendTect

A log analysis plug-in for dGB Earth Science's open-source integrated interpretation tool OpendTect was announced at EAGE conference earlier this year, and now it's available. The tool was developed by Geoinfo, a small Argentinian geoscience tech shop, in partnership with dGB. So now you can compute all your seismic petrophysics right in OpendTect.

On a sort-of-related note, Bert Bril, one of dGB's founders, just launched his blog, I can't believe it's not SCRUM, about agile software development. He even posts about geophysics. Yay!

Agile* apps

We're still regularly updating our completely free apps for Android. If you have an Android phone or tablet, go ahead and give them a spin. Volume* (right) is on version 3.1 already, and now does gas volumetrics, including B_g computation, and can grab any of the major crude oil benchmark prices for a quick-look value. And AVO* is just about to get a boost in functionality with an LMR plot; watch this space. Don't hold back if you've got requests. 

This regular news feature is for information only. We aren't connected with any of these people or organizations, and don't necessarily endorse their products or services. Unless we say we think they're great.

Please, sir, may I have some seismic petrophysics?

Petrophysics is an indispensible but odd corner of subsurface geoscience. I find it a bit of a paradox. On the one hand, well logs fill a critical gap between core and seismic. On the other hand, most organizations I've worked in are short of petrophysicists, sometimes—no, usually—without even recognizing it.

When a petrophysicist is involved in a project, they usually identify with the geologists, perhaps even calling themselves one. There’s a lot of concern for a good porosity curve, and the interpretation of the volume of clay and other mineralogical constituents. There’s also a lot of time for the reservoir engineer, who wants a reliable estimate of the reservoir pressure, temperature and water saturation (about 20–40% of the pore space is filled with water in an oil or gas field; it’s important to know how much). This is all good; these are important reservoir properties.

Incomplete and spiky logs in the uphole section of the Tunalik 1 well from the western edge of the National Petroleum Reserve in Alaska [click for larger image]. Image: USGSBut where is the geophysicist? Often, she is in her office, editing her own sonic log (called DT, the sonic is P-wave slowness), or QCing her own bulk density curve. Why? Because bulk density ρ and P-wave velocity V_P together make the best estimate of acoustic impedance I :

Acoustic impedance is the simplest way to compute a model seismic trace. We can compare this model trace to the real seismic data, recorded from the surface, to make the all-important connection between rocks and wiggles. The acoustic impedance curve determines what this model trace looks like, but we also need to know where it goes in the vertical travel-time domain. The sonic log comes into play again: it gives the best first estimate of seismic travel time. Since each sample is a measure of the time taken for a sound wave to travel the unit distance, it can be integrated for the total travel time. Yeah, that’s mathematics. It works.

In short, the logs are critical for doing any geophysics at all.

But they always need attention. Before we can use these logs, they must be quality checked and often edited. There is often a need to splice data form various logging runs together. The uphole sections are usually bad (there may be measurements in cased intervals, for example). Both of the logs are sensitive to hole condition. 

So the logs are critical, and always need fine-tuning. But I have yet to work on a project where a clean, top-to-tail DT and RHOB log are seen as a priority. Usually, they are not even on the List Of Things To Do. 

Result: the geophysicist gets on with it, and edits the logs. Now there's a DT_EDIT curve in the project. Oh, that name's been taken. And DT_Final and DT_edit2. I wonder who made those? DT_Matt then... but will anyone know what that is? No, and no-one will care either, because the madness will never end. 

There is even the risk of a greater tragedy: no geophysical logs at all. A missing or incomplete sonic because the tool was never run, or it failed and was not repeated, or it was just forgotten. No shear-wave sonic when you really just need a shear-wave sonic. No checkshots anywhere in the entire field, or the unedited data have been loaded in some horrible way. No VSPs anywhere, or no-one knows where the data are. Probably rotting on a 9-track tape somewhere in a salt cavern in Louisiana. 

Here's are some things to ask your friendly petrophysicist for:

• A single, lightly edited, RHOB, DT, and DTS (if available) curve, from the top of the reliable data to the bottom.
• If they're available, a set of checkshots with time and depth measured from the seismic datum (they are almost never recorded this way so have to be corrected).
• Help understanding the controls on sonic and density with depth; for example, can we ascribe some portion of the trends to compaction, and some to diagenesis?
• Help understanding the relationship between lithology and acoustic impedance. Filter the data to see how the impedance of sands and shales vary with depth.
• If there are several wells with complete sets of logs and there's to be an attempt to model missing or incomplete logs, then the petrophysicist should be involved.

What have I missed? Is there more? Or maybe you think this is too much?

Last thing: when the petrophysicist is making his beautiful composite displays of the well data, ask him to include acoustic impedance, the reflection coefficients, the synthetic seismogram, and even the seismic traces from the well location. This will surprise people. In a good way.

Thin-bed vowels and heterolithic consonants

Seismologists see the world differently. Or, rather, they hear the world differently. Sounds become time series, musical notes become Fourier components. The notes we make with our vocal chords come from the so-called sonorants, especially the vowel sounds, and they look like this:

Consontants aren't as pretty, consisting of various obstruents like plosives and fricatives—these depend on turbulence, and don't involve the vocal chords. They look very different:

Geophysicists will recognize these two time series as being signal-dominated and noise-dominated, respectively. The signal in the vowel sound is highly periodic: a small segment about 12 ms long is repeated four times in this plot. There is no repeating signal in the consonant sound: it is more or less white noise.

When quantitative people hear the word periodic, their first thought is usually Fourier transform. Like a prism, the Fourier transform unpacks mixed signals into monotones, making them easier to examine and explain. For instance, the Fourier transform of a set of limestone beds might reveal the Milankovitch cycles of which I am so fond. What about S and E?

The spectrum of the consonant S is not very organized and close to being random. But the E sound has an interesting shape. It's quite smooth and has obvious repetitive notches. Any geophysicist who has worked with spectral decomposition—a technique for investigating thin beds—will recognize these. For example, compare the spectrums for a random set of reflection coefficients (what we might call background geology) and a single thin bed, 10 ms thick:

Notches! The beauty of this, from an interpreter's point of view, is that one can deduce the thickness of the thin-bed giving rise to this notchy spectrum. The thickness is simply 1/n, where n is the notch spacing, 100 Hz in this case. So the thickness is 1/100 = 0.01 s = 10 ms. We can easily compute the spectrum of seismic data, so this is potentially powerful.

While obvious here, in a complicated spectrum the notches might be hard to detect and thus measure. But the notches are periodic. And what do we use to find periodic signals? The Fourier transform! So what happens if we take the spectrum of the spectrum of my voice signal—where we saw a 12 ms repeating pattern?

There's the 12 ms periodic signal from the time series! 

The spectrum of the spectrum is called the cepstrum (pronounced, and sometimes spelled, kepstrum). We have been transported from the frequency domain to a new universe: the quefrency domain. We are back with units of time, but there are other features of the cepstral world that make it quite different from the time domain. I'll discuss those in a future post. 

Based on a poster paper I presented at the 2005 EAGE Conference & Exhibition in Madrid, Spain, and on a follow-up article Hall, M (2006), Predicting bed thickness with cepstral decomposition, The Leading Edge, February 2006, doi:10.1190/1.2172313. 

News of the week

Help us stay on top of the latest and greatest: if you hear about something that might make geophysics even awesomer for all of us, drop us a line! In the meantime, here's some news that caught our attention...

Free software goodness

Innovative Australian software shop DownUnder GeoSolutions, aka DUG, is now offering DUG Insight to students for free! As if one amazing free (as in beer) seismic visualization and interpretation tool wasn't enough—you do have OpendTect, right?—now there's another. Just email them a copy of your student ID, and they'll get you started. 

NEWSFLASH  Hard-up students might also like this: Nature Geoscience for $10 a year! 

S-ray vision

OK, it doesn't sound quite as cool as X-ray vision, but S-band microwaves really can see through walls. Sort of. Boffins at MIT demonstrate their claims in this video... it's not geophysics, but another hard inverse imaging problem.

Petrophysics for Dummies

Occasionally while wandering lost in the interweb you stumble on gold. This is gold. Graham Davies was a geoscientist at Enterprise Oil, the plucky British independent exploration company I did my first internship at. He's been recording petrophysics tutorials, and they're 100% brilliant. "Even if you've never heard of petrophysics before," claims Davis.

What the heck is the geoblogosphere?

Not really a geotechnical story, but some readers might be interested to know more about geoscience blogs. A recent research paper, Geißler et al 2011, is a good place to start. The authors, who include übergeoblogger Callan Bentley of the structural geology blog Mountain Beltway, do a terrific job of exploraing the reasons for blogging, the perceptions of employers and supervisors, and every other angle you can think of. 

NEWSFLASH The 315th Where on (Google) Earth geomorphological puzzle went unsolved for 11 days, but was finally solved this morning. Congratulations to Ron Schott, the next episode is yours to host.

This regular news feature is for information only. We aren't connected with any of these people or organizations, and don't necessarily endorse their products or services. 

McKelvey's reserves and resources

Vincent McKelvey (right) was chief geologist at the US Geological Survey, and then its director from 1971 until 1977. Rather like Sherman Kent at the CIA, who I wrote about last week, one of his battles was against ambiguity in communication. But rather than worrying about the threat posed by the Soviet Union or North Korea, his concern was the reporting of natural resources in the subsurface of the earth. Today McKelvey's name is associated with a simple device for visualizing levels of uncertainty and risk associated with mineral resources: the McKelvey box.

Here (left) is a modernized version. It helps unravel some oft-heard jargon. The basic idea is that only discovered, commercially-viable deposits get to be called Reserves. Discovered but sub-commercial (with today's technology and pricing) are contingent resources. Potentially producible and viable deposits that we've not yet found are called prospective resources. These are important distinctions, especially if you are a public company or a government.

Over time, this device has been reorganized and subdivided with ever more subtle distinctions and definitions. I was uninspired by the slightly fuzzy graphics in the ongoing multi-part review of reserve reporting in the CSPG Reservoir magazine (Yeo and Derochie, 2011, Reserves and resources series, CSPG Reservoir, starting August 2011). So I decided to draw my own version. To reflect the possiblity that there may yet be undreamt-of plays out there, I added a category for Unimagined resources. One for the dreamers.

You can find the Scalable Vector Graphics file for this figure in SubSurfWiki. If you have ideas about other jargon to add, or ways to represent the uncertainty, please have a go at editing the wiki page, the figure, or drop us a line!

Are you a poet or a mathematician?

Many geologists can sometimes be rather prone to a little woolliness in their language. Perhaps because you cannot prove anything in geology (prove me wrong), or because everything we do is doused in interpretation, opinion and even bias, we like to beat about the bush. A lot.

Sometimes this doesn't matter much. We're just sparing our future self from a guilty binge of word-eating, and everyone understands what we mean—no harm done. But there are occasions when a measure of unambiguous precision is called for. When we might want to be careful about the technical meanings of words like approximately, significant, and certain.

Sherman Kent was a CIA analyst in the Cold War, and he tasked himself with bringing quantitative rigour to the language of intelligence reports. He struggled (and eventually failed), meeting what he called aesthetic opposition:

What slowed me up in the first instance was the firm and reasoned resistance of some of my colleagues. Quite figuratively I am going to call them the poets—as opposed to the mathematicians—in my circle of associates, and if the term conveys a modicum of disapprobation on my part, that is what I want it to do. Their attitude toward the problem of communication seems to be fundamentally defeatist. They appear to believe the most a writer can achieve when working in a speculative area of human affairs is communication in only the broadest general sense. If he gets the wrong message across or no message at all—well, that is life.

Sherman Kent, Words of Estimative Probability, CIA Studies in Intelligence, Fall 1964

Kent proposed using some specific words to convey specific levels of certainty (right). We have used these words in our mobile app Risk*. The only modification I made was setting P = 0.99 for Certain, and P = 0.01 for Impossible (see my remark about proving things in geology).

There are other schemes. Most petroleum geologists know Peter Rose's work. A common language, with some quantitative meaning, can dull the pain of prospect risking sessions. Almost certainly. Probably.

Do you use systematic descriptions of uncertainty? Do you think they help? How can we balance our poetic side of geology with the mathematical?

Update on 2011-10-14 14:36 by Matt Hall

As I was adding to the SubSurfWiki page for WEPs, I came across a wonderful article by Bernie O'Brien (1989), a physician. He interviewed 56 doctors about twenty-three words and phrases, asking them to place them on a probability scale. He then used the interquartile range of the responses as an indication of ambiguity. Here's how his data plot:

This is very interesting: words used to express equivocality and fence-sitting are themselves ambiguous and uncertain. That makes intuitive sense, but it's a fascinating insight into the language of uncertainty.

O'Brien also compared the interquartile range to a 3-point rating of ambiguity, as given by the respondents. You can read more about it on the wiki page. 

Reference
O'Brien, B (1989), Words or numbers? The evaluation of probability expressions in general practice. Journal of the Royal College of General Practitioners 39, p 98–100, March 1989. Link to PDF.

Where on (Google) Earth #315

After a long break from this awesome game, I got WoGE #314 by simple recognition. I've never been to Florida, but have scoured the whole region looking for interesting modern analogs. So I have the honour of turning in the next edition; the time is 1100 ADT, 1400 GMT, or 44-07-07 ∇ 14:19:14 Lunar Standard Time. In case you're on the moon.

Where on (Google) Earth is the best way to tour the virtual globe since the mighty View-Master. If you are new to the game, fear not, it is easy to play. The winner is the first person to examine the picture below, find the location (name, link, or lat-long), and give a brief explanation of its geological interest. Please post your answer in the comments. And thanks to the Schott Rule, which I am invoking, newbies have a slight edge: previous winners must wait one earth hour for each win before playing—with a maximum of 48 (yes, some people are quite good at this game).

So: where and what the Dickens is this?

Update on 2011-10-15 19:32 by Matt Hall

It's been five days. Here's 100% more data, by way of a clue:

Update on 2011-10-17 12:50 by Matt Hall

This is off-topic; please refer to the comments to see why there is a picture of Paris here.

Image is ©Aerodata International Surveys, Digital Globe, GeoEye, IGN France, The GeoInformation Group. © Google

News of the week

Some news and views from the world of geoscience this last fortnight.

Open source GIS on a thumb drive

If you ever wanted to get into open source geospatial software but didn't know where to start, check this out. Last month OSGeo, the open source geospatial foundation, released version 5 of their OSGeo-Live project. This is a bootable disk image containing 47 pieces of free software, including several full GIS, world maps, and quick-start guides. Amazing!

Probability and panic

The L'Aquila earthquake of April 2009 killed 308 people. Six seismologists are now on trial for manslaughter, not so much because they failed to predict the quake, but because they allegedly downplayed the risk of a severe event. Most geoscientists believe that we cannot predict earthquakes today; these seismologists are effectively accused of trying to predict a non-earthquake. We don't know, but suspect their intent was misinterpreted—always a danger when specialists communicate with non-specialists. There is no daily coverage of the trial that we are aware of, but there are occasional reports in the press. In this short video, Giustino Parisse explains why he is one of the plaintiffs.

Magical geobloggery

If you're new to blogs—maybe you got a tablet recently and are discovering how easy it is to read the web these days—you might not be aware that there's a lot of geology in the blogosphere. Finding writers you want to read isn't easy though. You could scroll down this page and look for our BLOGROLL for some leads, or head over to Highly Allochthonous and read the latest Accretionary Wedge, a regular meta-post. This month: practical advice for the lifelong learner. 

Communicating rocks

We recently learned of this terrific new book from University of Houston professor Peter Copeland (thanks to his colleague, Rob Stewart, for the tip!). We haven't actually got our hands on it yet, but the Amazon preview has whet our appetites for geo-communication tips galore. The publisher, Prentice Hall, has kept the price to a reasonable amount, close to $35. Get your copy now!

This regular news feature is for information only. We aren't connected with any of these organizations, and don't necessarily endorse their products or services. Public domain map image from the USGS.