Shattering shale

In shale gas exploration, one of the most slippery attributes we are interested in is fracability. The problem is that the rocks we study have different compositions and burial histories, so it's hard to pin down the relative roles of intrinsic rock properties and extrinsic stress states. Glass could be considered an end member for brittleness, and it has fairly uniform elastic parameters and bulk composition (it's amorphous silica). Perhaps we can learn something about the role of stresses by looking more closely at how glass fractures. 

The mechanics of glass can be characterized by two aspects: how it's made, and how it breaks.

Annealed glass is made by pouring molten glass onto a thin sheet of tin. Upon contact, the tin melts allowing for two perfectly smooth and parallel surfaces. The glass is cooled slowly so that stress irregularities dissipate evenly throughout, reducing local weak points. This is ordinary glass, as you might find in a mirror.

Tempered glass is made by heating annealed glass to near its softening point, about 720˚C, and then quickly cooling it by quenching with air jets. The exterior surface shrinks, freezing it into compression, while the soft interior of the glass gets pulled out by tensional forces as it freezes (diagram). 

How glass is made is directly linked to how it breaks. Annealed glass is weaker, and breaks into sparse splinters. The surface of tempered glass is stronger, and when it breaks, it breaks catastrophically; the interior tensional energy releases cracks from the inside out.

A piece of tempered glass is 4-6 times stronger than a piece of annealed glass with the same elastic properties, composition, density and dimensions. This means it looks almost identical but requires much more stress to break. Visually and empirically, it is not easy to tell the difference between annealed and tempered glass. But when you break it, the difference is obvious. So here, for two very brittle materials, with all else being equal, the stress state plays the dominant role in determining the mode of failure.

Because natural permeability is so low in fine grained rocks, production companies induce artificial fractures to connect flow pathways to the wellbore. The more surface area exposed, the more methane will be liberated.

If we are trying to fracture-stimulate shale to get at the molecules trapped inside, we would clearly prefer shale that shatters like tempered glass. The big question is: how do we explore for shale like this?

One approach is to isolate parameters such as natural fractures, anisotropy, pore pressure, composition, and organic content and study their independent effects. In upcoming posts, we'll explore the tools and techniques for measuring these parameters across scale space for characterizing fracability. 

Update on 2011-04-19 15:59 by Matt Hall

You might also like some of our other recent posts about shale gas:

• What is shale?, a look at how to define shale
• Shale vs tight, a comparison with tight gas plays
• What is unconventional?, a look at how to define unconventional resources

News of the week

The AAPG Annual Convention and Exhibition was this week in Houston. Several companies took the opportunity to announce news. Here's a quick round-up.

Real time well-site mineralogy

Fugro Robertson, a UK-based subsidiary of Dutch company Fugro, introduced RoqSCAN™, a new well-site tool for real-time mineralogical analysis of cuttings. It seems to be a field-portable version of the same technology as their well-received QEMSCAN® lab-based product. Both systems are based on scanning electron microscope analysis. Exciting to see more quantitative tools for geologists. 

More gear for 3D imaging

Ingrain, the exciting 'digital rock physics lab', have bought another Carl Zeiss microscope. But not just any microscope, the AURIGA Crossbeam FIB/SEM, or focused ion beam and scanning electron microscope. Ion beams are useful because, since ions are relatively massive, they can be used to shave extremely thin layers from a rock. The SEM can build up a 3D image of the rock, as it is progressively ablated in this way. If you have never seen Ingrain's 3D images, check out their website for papers like this one (1MB PDF). Amazing.

New plug-ins for viz tool

TerraSpark Geosciences, Geoff Dorn's spin-off from the University of Colorado at Boulder, make a nice-looking piece of software called Insight Earth®. Based on ARCO/BP-funded technology, it's an integrated seismic interpretation tool that seems to have some interesting functionality (we've never seen it in action though). The news is that the company has signed an agreement with visualization gurus INT to develop plug-ins for Insight Earth. Very cool, but we can't help thinking (dreaming?) as we look around these sites: Why isn't any of this open source? 

LMKR go announcement crazy!

The Dubai-based consulting and software firm pwned AAPG, at least if your yardstick is press releases or social media presence (follow @LMKRNews). They are clearly growing aggressively, having taken on marketing and support of Landmark's very nice GeoGraphix software last fall. Watch out for them! Here's what they had to offer:

• They are hooking up with Object Reservoir, physicist and Landmark co-founder John Mouton's new company, to deliver new shale gas services 
• They have acquired Cambridge Petroleum Software's Velocity Manager software, for depth conversion functionality.
• They are adding Scrybe's weirdly-named Convofy to GeoGraphix. What does that mean? We think this may be the most momentous announcement of the year: they have added social media functionality to an integrated interpretation suite. The platform is fully mobile and supports, among other things, microblogging, document sharing, and commenting. 

Even if you are skeptical about social media, please staunch your inner cynic just for a moment and please watch this video. Think about where this last innovation could lead our notions of teamwork, especially in distributed teams. We are excited!

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. 

What is your competitive advantage?

What gave you an advantage once may no longer be helping you. Fortresses just aren't relevant today. Surami Fortress, Georgia.I've been thinking a lot about openness recently. Open-source software, open publishing, and open data are important themes in science today, but not really in business. I think this is going to change in the coming decade, as open-minded young professionals with openness in their blood infiltrate management. I hope Agile* is part of this shift. 

Years ago, oil companies were closed systems. They had secrets. They had large research divisions, rivalling universities in size and scope. They developed their own technology, wrote their own software. The people who worked in these companies were trained in-house, and had long careers. These companies competed with each other on an every-man-for-himself basis, with little regulatory intervention, and little more than admiration and awe from the general public, just glad for its precious petroleum.

Today's industry, however, does not look like this. The typical medium to large oil company...

• has a small research division, if it has one at all;
• lets service companies and universities do its innovation, usually as part of a consortium;
• does little in-house training, relying instead on universities and external trainers;
• buys dated, off-the-shelf software;
• has staff attrition and loyalty problems, with most people staying only a few years;
• is under substantial regulatory and public scrutiny;
• has customers who don't want or like their product, but are simply addicted to it.

In this environment the research is shared with competitors, the technology is the same as everyone else's, the employees switch companies regularly, and everything is done under the public's disapproving gaze. It is clear that competitive advantage ain't what it used to be. Yet oil companies are stuck in yesterday's mindset, hiding all their data, software, technology, and ideas, even (especially?) the ones that are generic, or useless, or just wrong. What a waste of energy.

So what is your competitive advantage? In the next post, I'll take a look at what I think sets companies apart, and what I think we can safely share. In the mean time, let us know what you think. 

Update on 2012-02-09 16:34 by Matt Hall

The follow-up post came two weeks later...

Scales of sea-level change

Click to read about sea level on Wikipedia. Image prepared by Robert Rohde and licensed for public use under CC-BY-SA.Sea level changes. It changes all the time, and always has (right). It's well known, and obvious, that levels of glaciation, especially at the polar ice-caps, are important controls on the rate and magnitude of changes in global sea level. Less intuitively, lots of other effects can play a part: changes in mid-ocean ridge spreading rates, the changing shape of the geoid, and local tectonics.

A recent paper in Science by Petersen et al (2010) showed evidence for mantle plumes driving the cyclicity of sedimentary sequences. This would be a fairly local effect, on the order of tens to hundreds of kilometres. This is important because some geologists believe in the global correlatability of these sequences. A fanciful belief in my view—but that's another story.

The paper reminded me of an attempt I once made to catalog the controls on sea level, from long-term global effects like greenhouse–icehouse periods, to short-term local effects like fault movement. I made the table below. I think most of the data, perhaps all of it, were from Emery and Aubrey (1991). It's hard to admit, because I don't feel that old, but this is a rather dated publication now; I think it's solid enough for the sort of high-level overview I am interested in. 

After last week's doodling, the table inspired me to try another scale-space cartoon. I put amplitude on the y-axis, rate on the x-axis. Effects with global reach are in bold, those that are dominantly local are not. The rather lurid colours represent different domains: magmatic, climatic, isostatic, and (in green) 'other'. The categories and the data correspond to the table.
It is interesting how many processes are competing for that top right-hand corner: rapid, high-amplitude sea level change. Clearly, those are the processes we care about most as sequence stratigraphers, but also as a society struggling with the consequences of our energy addiction.

References
Emery, K & D Aubrey (1991). Sea-levels, land levels and tide gauges. Springer-Verlag, New York, 237p.
Petersen, K, S Nielsen, O Clausen, R Stephenson & T Gerya (2010). Small-scale mantle convection produces stratigraphic sequences in sedimentary basins. Science 329 (5993) p 827–830, August 2010. DOI: 10.1126/science.1190115

News of the week

AAPG conference starts on Sunday 

The community of petroleum geoscientists will convene in Houston in a few days for the AAPG 2011 Annual Convention & Exhibition. If any geo-tweeps will be there, spare a thought for those that aren't and update us on the events and happenings with the hashtag #ACE2011. Follow @AAPG_Events or @AAPG on Twitter. Wish we were there!

DownUnder Geosolutions coming up over

Australian based DownUnder GeoSolutions (aka DUG, at DuGeo.com) have recently announced that they will be opening offices in Calgary in May. One of the young entrepreneurs helping build this emerging technology company's was recently featured in Petroleum Exploration Society of Australia's magazine. One to keep an eye on!

CGGV have a new processing centre in Oman

The new CGG Veritas office will focus on onshore seismic acquisition and imaging services for the petroleum industry. The centre will also be hosting a university training facility in partnership with the national energy ministry and other industrial partners. In this regard, CCGV is hoping to help develop highly qualified Omani professionals.

Geoscientists without borders

The April issue of SEG's The Leading Edge features stories of the geoscience community solving global humanitarian problems. The International Symposium on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP) has been formed to tackle everything from natural hazards and environmental awarness issues, to finding scarce freshwater resources in impoverished regions. Read more about how geoscientists are making a positive impact and empowering people through education and technology. Great to see this kind of out-reach.

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. 

The scales of geoscience

Helicopter at Mount St Helens in 2007. Image: USGS.Geoscientists' brains are necessarily helicoptery. They can quickly climb and descend, hover or fly. This ability to zoom in and out, changing scale and range, develops with experience. Thinking and talking about scales, especially those outside your usual realm of thought, are good ways to develop your aptitude and intuition. Intuition especially is bound to the realms of your experience: millimetres to kilometres, seconds to decades. 

Being helicoptery is important because processes can manifest themselves in different ways at different scales. Currents, for example, can result in sorting and rounding of grains, but you can often only see this with a hand-lens (unless the grains are automobiles). The same environment might produce ripples at the centimetre scale, dunes at the decametre scale, channels at the kilometre scale, and an entire fluvial basin at another couple of orders of magnitude beyond that. In moments of true clarity, a geologist might think across 10 or 15 orders of magnitude in one thought, perhaps even more.

A couple of years ago, the brilliant web comic artist xkcd drew a couple of beautiful infographics depicting scale. Entitled height and depth (left), they showed the entire universe in a logarithmic scale space. More recently, a couple of amazing visualizations have offered different visions of the same theme: the wonderful Scale of the Universe, which looks at spatial scale, and the utterly magic ChronoZoom, which does a similar thing with geologic time. Wonderful.

These creations inspired me to try to map geological disciplines onto scale space. You can see how I did below. I do like the idea but I am not very keen on my execution. I think I will add a time dimension and have another go, but I thought I'd share it at this stage. I might even try drawing the next one freehand, but I ain't no Randall Munroe.

I'd be very happy to receive any feedback about improving this, or please post your own attempts!

Update on 2011-04-13 03:12 by Matt Hall

I have just finished a new version of this graphic, incorporating some comments from readers. I replaced the one in the original post, so please grab it from there if you want to see what I did. 

If you like this post, you might also like the more recent one on the scales of relative sea-level change, and also this older one on the scales of various experiments in oil & gas geoscience. 

News of the week

Paradigm showcases new geophysical software

Paradigm will preview its latest exploration and development software technologies and workflows at the AAPG convention 9–13 April 2011. Their agenda covers workflows for multi-disciplinary subsurface teams, next generation geologic software, and a Windows 7 interpretation platform. Paradigm is one of the sponsors of the 2011 AAPG Imperial Barrel Award student propsect competition. Follow them on Twitter: @ParadigmLtd.

Ikon Science releases RockDoc 5.5

Ikon Science has teamed up with the experts at Statoil and immersed rock physics modeling templates into the software interface, allowing users do rock physics all in one place. And with a new extension, External Interface, users can add their own C and MATLAB code to RockDoc. As a MATLAB users, we find this is a very appealing step. Click here to read more.

Third beta release for OpendTect 4.2.0

dGB Earth Sciences, creators of OpendTect, the purveyors of the Open Seismic Repository, have announced their third Beta release of OpendTect 4.2.0. The roll-out of the official version 4.2.0 is due in mid-April. If you aren't using OpendTect, why not download it, and start using this software today. And while you're at it, grab some data from the Open Seismic Repository. 

PetroChina drills first horizontal shale gas well

China sprang into the embryonic stages of shale gas exploration and development this week when PetroChina completed the drilling of its first horizontal shale gas well in Sichuan Province. It will be exciting to watch the results China strives to access its massive shale gas resources, which up until now have been beyond its technological reach. Click here to read more.

University of Aberdeen opens seisLAB

Thanks to industry sponsors BP, Chevron, BG Group, Halliburton, and Schlumberger, the University of Aberdeen will soon be decked-out with state-of-the-art geoscience software and infrastructure. seisLAB will accelerate training, research, and teaching in one of Europe's energy capitals, pushing innovation and collaboration in the field. Click here to read more.

Great geophysicists #3

Today is a historic day for greatness: Rene Descartes was born exactly 415 years ago, and Isaac Newton died 284 years ago. They both contributed to our understanding of physical phenomena and the natural world and, while not exactly geophysicists, they changed how scientists think about waves in general, and light in particular.

Unweaving the rainbow

Scientists of the day recognized two types of colour. Apparent colours were those seen in prisms and rainbows, where light itself was refracted into colours. Real colours, on the other hand, were a property of bodies, disclosed by light but not produced by that light. Descartes studied refraction in raindrops and helped propagate Snell’s law in his 1637 paper, Dioptrica. His work severed this apparent–real dichotomy: all colours are apparent, and the colour of an object depends on the light you shine on it.

Newton began to work seriously with crystalline prisms around 1666. He was the first to demonstrate that white light is a scrambled superposition of wavelengths; a visual cacophony of information. Not only does a ray bend in relation to the wave speed of the material it is entering (read the post on Snellius), but Newton made one more connection. The intrinsic wave speed of the material, in turn depends on the frequency of the wave. This phenomenon is known as dispersion; different frequency components are slowed by different amounts, angling onto different paths.

What does all this mean for seismic data?

Seismic pulses, which strut and fret through the earth, reflecting and transmitting through its myriad contrasts, make for a more complicated type of prism-dispersion experiment. Compared to visible light, the effects of dispersion are subtle, negligible even, in the seismic band 2–200 Hz. However, we may measure a rock to have a wave speed of 3000 m/s at 50 Hz, and 3500 m/s at 20 kHz (logging frequencies), and 4000 m/s at 10 MHz (core laboratory frequencies). On one hand, this should be incredibly disconcerting for subsurface scientists: it keeps us from bridging the integration gap empirically. It is also a reason why geophysicists get away with haphazardly stretching and squeezing travel time measurements taken at different scales to tie wells to seismic. Is dispersion the interpreters’ fudge-factor when our multi-scale data don’t corroborate?

Chris Liner, blogging at Seismos, points out

...so much of classical seismology and wave theory is nondispersive: basic theory of P and S waves, Rayleigh waves in a half-space, geometric spreading, reflection and transmission coefficients, head waves, etc. Yet when we look at real data, strong dispersion abounds. The development of spectral decomposition has served to highlight this fact.

We should think about studying dispersion more, not just as a nuisance for what is lost (as it has been traditionally viewed), but as a colourful, scale-dependant property of the earth whose stories we seek to hear.

More on brevity

Yesterday, I wrote about one of Orwell's essays, and about Watson and Crick's famous letter to Nature. The theme: short expositions win. Today, I continue the theme, with two more brief but brilliant must-reads for the aspiring writer. 

Albert Einstein

The first time Einstein's equation appeared in printLike the Watson and Crick letter, Einstein's 1905 paper Does the inertia of a body depend on its energy content? was profound and eternal. In it, he derived the expression m = E / c². Though the paper was arguably little more than an extension of others he published that year, it was very short: exactly three (small) pages long. His concluding remark couldn't be clearer or more succinct:

If the theory corresponds to the facts, radiation conveys inertia between the emitting and absorbing bodies.

Einstein's writing style was influenced by Ernst Mach's book, The Science of Mechanics (Minor, 1984). Mach adopted a pedagogic, step-by-step style that guided the reader through the scientist's reasoning. Asking the reader to imagine an analogous scenario or simplified example was, in my experience, common in physics books of the period. Richard Feynman used a similar straightforward style. I try to use it myself, but sometimes the desire to impress gets the better of me.

Kenneth Landes

Years of reviewing journal papers has convinced me: the abstract is one of the most abused and misunderstood animals of science. I regularly hand Landes' brilliant little plea to new writers, and it bears re-reading once every couple of years. Landes points out that the abstract should "concentrate in itself the essential information of a paper or article". Here is his superbly cheeky, information-free counterexample:

A partial biography of the writer is given. The inadequate abstract is discussed. What should be covered by an abstract is considered. The importance of the abstract is described. Dictionary definitions of 'abstract' are quoted. At the conclusion a revised abstract is presented. 

Read his short note for the improved version of this soggy squib of an abstract. 

What do we draw from these authors? I'll be brief: so should you.

References
Einstein, A (1905). Ist die Trägheit eines Körpers von seinem Energiegehalt abhängig?, in Annalen der Physik. 18:639, 1905. Published in English by Methuen, 1923.
Landes, K (1966). A scrutiny of the abstract II. American Association of Petroleum Geologists Bulletin 50 (9), p 1992.
Mach, E (1883). The science of mechanics. Later English translation here. 
Minor, D (1984). Albert Einstein on writing. J. Technical Writing and Communication 14 (1), p 13–18. [Requires subscription or purchase].