Fabric attributes

The catch-all term seismic interpretation, often used to refer to the labour of digitizing horizons and faults, is almost always spatially constrained. Picking seismic line-by-line means collapsing complex 3D patterns and volumes onto 2D maps and surfaces. It hurts me to think about what we are discarding. Take a second and imagine looking at a photograph one row of pixels at a time. So much is lost in the simplification.

Attributes, on the other hand, can either quantify the nature of a horizon, probe between horizons, or characterize an entire 3D space. Single-trace attributes can tell us about waveform shape and magnitude which allegedly responds to true physical impedance contrasts. Multi-trace attributes (coherency, curvature, etc.) pull information from neighbouring traces.

The fabric test model

In a spirited act of geeky indulgence, I went to my linen closest, grabbed some tea towels, pulled out my phone (obviously), and captured this scene. A set of four folded tea towels overlapping and spread across my counter top—reverse engineering what I thought to be a suitable analogy for training my seismic inutition. The left (blue) tea towel is a honeycomb texture, the second (green) is speckled like a wash cloth, the third is a high thread-count linen, and the fourth has a grid of alternating cross-hatches and plain print. Don't laugh! It turns out to be quite difficult to verbally describe the patterns in these fabrics. Certainly, you will describe them differently to me, and that is the problem. 

Perhaps image processing can transcend our linguistic limitations. In seismic, as in image processing in general, there are attributes that work on each sample (or trace) independently, and there are attributes that use an ensemble of neighbouring samples in their computation. See if you can think a seismic analogy in the for each of these image attributes.

• Spectral decomposition shows the component of the RGB color spectrum at each sample location. I subsequently clipped and enhanced the red panel to show curves, wrinkles and boundaries caused by the interplay of light, shadows, and morphology.
• Spectral filtering extracts or removes hues. In this instance, I have selected all the color triplets that make up the blue tea towel. You could also select a range to say, show where the shadows are.
• Edge detection, after smoothing, shows sharp edges in white and yellow, soft edges in purple and blue. The wrinkles and subtle folds on the right most fabric have also been detected. 

My question: can you manually draw the morphology, or the blues, or the edges and discontinuities? Manual interpretation is time consuming, prone to error, seldom reproducible, and that makes it flawed. Furthermore, none of these attributes actually tell us about the nature of the textures in the fabric. Indeed, we don't know if any of them are relevant at all. Colour happens to be one proxy for texture in this case, but it fails in delineating the two whitish fabrics.

Artistically and computationally speaking, I submit to you that seismic data are nothing but images. In the next post I will extend this fabric-photograph model to explore the utility of textural attributes. 

Theses images were made using the open source FIJI and the illustrations were done in Inkscape. The attributes were computed in MATLAB and FIJI.

Comments

[Mark]

This topic is relevant to the geology side as well. What is slabbed core if not an image? (Sometimes it is literally an image). Facies interpretation is nothing more than classification of patterns and textures in a rock fabric. Even wireline logs, for that matter, are interpreted simply as images. Interpretation of logs is impossible without consideration of the shapes and textures of a line. Great post Evan. I look forward to part 2.

[Chapman]

Taking a complex or confusing topic and making it easily digestable for people who aren't experts is incredibly difficult, and incredibly effective. Kudos to your ability to do this time and time again - looking forward to reading part two as well.

[evan]

@Mark:
I am delighted that you commented here. In fact, the use of the word "facies" is totally appropriate. I think you will see how I take this notion of an image to the next level in the next post. You are right, images are data (numbers are numbers).

Regarding well logs: "the texture of a line", what a wonderful way to put it. Computing Haralick statistics along a single column image (a line). Brilliant.

In the midst of my tea towel prototyping I have noticed that it is difficult to capture, say, two textures, if they are not at a similar scale. When the effective scale of the patterns occurs over a large range (as it does with rocks or slabbed core) it is difficult to capture the fine and coarse details simultaneous. This might require one to look at an adaptive or flexible kernel size. Texture at the grain (or pixel scale), texture at the bedding scale, texture at the hetereolithic scale. I suppose we could use the word fabric to describe texture at the highest resolution (smaller scale), and then use other words to describe texture at larger scales. This all might fall under a new buzzword, which I introduce just now: texture bandwidth.

But then again, maybe it is best not to use any words at all :)

Finally, did you see Doug Schmitt's core scanner at the CSEG convention this year? Genuis that device. I want one.

Consider the seismic example I give in the next post and see if you can assemble 4 or 5 core photos to do the same thing? Could be amazing :)

[Evan Bianco]

@Chapman,
I appreciate your comment, and I feel like the ability to do so in any field demonstrates mastery of the subject. Oh and there are so many subjects! *sigh*

I suppose my approach has evolved as follows: when I encounter something that is new or interesting, I try to understand it well enough to do a blog post about it. If it is not a blog post that I would want to share, pass on to a colleague, or a client, or a teacher, or a fellow geo-enthusiast, then I probably haven't learned the new subject well enough. So I must say, the benefits for me (and Matt as well; I will speak on his behalf), are really underestimated, even by ourselves. This act of learning in public, iterating, and being responsive is a true joy. It is also a rare skill and mindset that we are practicing. It is so much fun, it is a hobby and it is art. The next post, took about 4 drafts, and I recreated the figures too many times to count. It took more time than I would have liked, but I have the final post the way I like it.

Thanks for reading.