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Tuesday
May212013

## Proceedings of an unsession

Two weeks ago today Evan and I hosted a different kind of session at the Canada GeoConvention. It was an experiment in collaboration and integration, and I'm happy to say it exceeded our expectations. We will definitely be doing it again, so if you were there, or even if you weren't, any and all feedback will help ensure the dial goes to 11.

One of the things we wanted from the session was evidence. Evidence of conversation, innovation, and creative thinking. We took home a great roll of paper and sticky notes, and have now captured it all in SubSurfWiki, along with notes from the event. You are invited to read and edit. Be bold! And please share the link...

ageo.co/unsession

The video from the morning is in the editing suite right now: watch for that too.

We have started a write-up of the morning. If you came to the session, please consider yourself a co-author: your input and comments are welcome. You might be unaccustomed to editing a community document, but don't be shy — that's what it's there for.

We want to share two aspects of the event on the blog. First, the planning and logistics of the session — a cheatsheet for when we (or you!) would like to repeat the experience. Second, the outcomes and insights from it — the actual content. Next time: planning an unsession.

Thursday
May162013

## Fitting a model to data

In studying the earth, we can't afford to take enough observations, and they will never be free of noise. So if you say you do geoscience, I hereby challenge you to formulate your work as a mathematical inverse problem. Inversion is a question: given the data, the physical equations, and details of the experiment, what is the distribution of physical properties? To answer this question we must address three more fundamental ones (Scales, Smith, and Treitel, 2001):

• How accurate is the data? Or what does fit mean?
• How accurately can we model the response of the system? Have we included all the physics that can contribute signifcantly to the data?
• What is known about the system independent of the data? There must be a systematic procedure for rejecting unreasonable models that fit the data as well.

Setting up an inverse problem means coming up with the equations that contain the physics and geometry of the system under study. The method for solving it depends on the nature of the system of equations. The simplest is the minimum norm solution, and you've heard of it before, but perhaps under a different name.

### To fit is to optimize a system of equations

For problems where the number of observations is greater than the number of unknowns, we want to find which unknowns fit the best. One case you're already familiar with is the method of least squares — you've used it fitting a line of through a set of points. A line is unambiguously described by only two parameters: slope a and y-axis intercept b. These are the unknowns in the problem, they are the model m that we wish to solve for. The problem of line-fitting through a set of points can be written out like this,

$\large \mathbf{d}=\begin{pmatrix}y_{1} \\ y_{2} \\ ... \\ y_{n} \end{pmatrix}, \mathbf{G}=\begin{pmatrix} x_{1} & 1\\ x_{2} & 1\\ ... & ...\\ x_{n} & 1 \end{pmatrix}, \mathbf{m}=\begin{pmatrix} a\\ b \end{pmatrix}$

As I described in a previous post, the system of the problem takes the form d = Gm, where each row links a data point to an equation of a line. The model vector m (M × 1), is smaller than the data d (N × 1) which makes it an over-determined problem, and G is a N × M matrix holding the equations of the system.

Why cast a system of equations in this matrix form? Well, it turns out that the the best-fit line is precisely,

$\large \mathbf{m}=(G^{T}G)^{-1}G^{T}\mathbf{d}$

which are trivial matrix operations, once you've written out G.  T means to take the transpose, and –1 means the inverse, the rest is matrix multiplication. Another name for this is the minimum norm solution, because it defines the model parameters (slope and intercept) for which the lengths (vector norm) between the data and the model are a minimum.

One benefit that comes from estimating a best-fit model is that you get the goodness-of-fit for free. Which is convenient because making sense of the earth doesn't just mean coming up with models, but also expressing their uncertainty, in terms of the errors with which they are linked.

I submit to you that every problem in geology can be formulated as a mathematical inverse problem. The benefit of doing so is not just to do math for math's sake, but it is only through quantitatively portraying ambiguous inferences and parameterizing non-uniqueness that we can do better than interpreting or guessing.

Scales, JA, Smith, ML, and Treitel, S (2001). Introductory Geophysical Inverse Theory. Golden, Colorado: Samizdat Press

Friday
May102013

## Laying it all out at the Core Conference

Bobbing in the wake of the talks, the Core Conference turned out to be more exemplary of this year's theme, Integration. Best of all were SAGD case studies, where multi-disciplinary experiments are the only way to make sense of the sticky stuff.

### Coring through steam

Travis Shackleton from Cenovus did a wonderful presentation showing the impact of bioturbation, facies boundaries, and sedimentary structures on steam chamber evolution in the McMurray Formation at the FCCL project. And because I had the chance to work on this project with ConocoPhillips a few years ago, but didn't, this work induced both jealousy and awe. Their experiment design is best framed as a series of questions:

• What if we drilled, logged, and instrumented two wells only 10 m apart? (Awesome.)
• What if we collected core in both of them? (Double awesome.)
• What if the wells were in the middle of a mature steam chamber? (Triple awesome.)
• What if we collected 3D seismic after injecting all this steam and compare with with a 3D from before? (Quadruple awesome.)

It is the first public display of SAGD-depleted oil sand, made available by an innovation of high-temperature core recovery. Travis pointed to a portion of core that had been rinsed by more than 5 years of steam circulating through it. It had a pale brown color and a residual oil saturation SO of 15% (bottom sample in the figure). Then he pointed to a segment of core above the top of the steam chamber. It too was depleted, by essentially the same amount. You'd never know just by looking. It was sticky and black and largely unscathed. My eyes were fooled, direct observation deceived.

### A bitumen core full of fractures

Jen-Russel-Houston held up a half-tube of core of high-density fractures riddled throughout bitumen saturated rock. The behemoth oil sands that require thermal recovery assistance have an equally promising but lesser known carbonate cousin, still in its infancy. It is the bitumen saturated Grosmont Formation, located to the west of the more mature in-situ projects in sand. The reservoir is entirely dolomite, hosting its own unique structures affecting the spreading of steam and the reduction of bitumen's viscosity to a flowable level.

Jen and her team at OSUM hope their pilot will demonstrate that these fractures serve as transport channels for the steam, allowing it to creep around tight spots in the reservoir, which would otherwise be block the steam in its tracks. These are not the same troubling baffles and barriers caused by mud plugs or IHS, but permeability heterogeneities caused by the dolomitization process. A big question is the effective permeability at the length scales of production, which is phenomenologically different to measurements made from cut core. I overheard a spectator suggest to Jen that she try to freeze a sleeve of core, soak it with acid then rinse the dolomite out the bottom. After which only a frozen sculpture of the bitumen would remain. Crazy? Maybe. Intriguing? Indeed.

### Let's do more science with rocks!

Two impressive experiments, unabashedly and literally laid out for all to see, equipped with clever geologists, and enriched by supplementary technology. Both are thoughtful initiatives—real scientific experiments—that not only make the operating companies more profitable, but also profoundly improve our understanding of a precious resource for society. Two role models for how comprehensive experiments can serve more than just those who conduct them. Integration at its very best, centered on core.

What are the best examples of integrated geoscience that you've seen?

Wednesday
May082013

## Submitting assumptions for meaningful answers

The best talk of the conference was Ran Bachrach's on seismics for unconventionals. He enthusiastically described the physics to his spectators with conviction and duty, and explained why they should care. Isotropic, VTI, and orthorhombic media anisotropy models are used not because they are right, but because they are simple. If the assumptions you bring to the problem are reasonable, the answers can be considered meaningful. If you haven't considered and tested your assumptions, you haven't subscribed to reason. In a sense, you haven't held up your end of the bargain, and there will never be agreement. This talk should be mandatory viewing for anyone working seismic for unconventionals. Advocacy for reason. Too bad it wasn't recorded.

I am both privileged and obliged to celebrate such nuggets of awesomeness. That's a big reason why I blog. And on the contrary, we should call out crappy talks when we see them to raise the bar. Indeed, to quote Zen Faulkes, "...we should start creating more of an expectation that scientific talks will be reviewed and critiqued. And names will be named."

The talk from HEF Petrophysical entitled, Towards modelling three-dimensional oil sands permeability distribution using borehole image logs, drew me in. I was curious enough to show up. But as the talk unfolded, my curiosity was left unsatisfied. A potentially interesting workflow of transforming high-resolution resistivity measurements into flow permeability was obfuscated with a pointless upscaling step. The meat of anything like this is in the transform itself, but it was missing. It's also the most trivial bit; just cross-plot one property with another and show people. So I am guessing they didn't have any permeability data. If that was the case, how can you stand up and talk about permeability? It was a sandwich without the filling. The essential thing that defines a piece of work is the creativity. The thing you add that wasn't there before. I was disappointed. Disappointed that it was accepted, and that no one else piped up.

I will paraphrase a conversation I had with Ran at the coffee break: Some are not aware, some choose to ignore, and some forget that works of geoscience are problems of extreme complexity. In fact, the only way we can cope with complexity is to make certain assumptions that make our problem solvable. If all you do is say "here is my solution", you suck. But if instead you ask, "Have I convinced you that my assumptions are reasonable?", it entirely changes the conversation. It entirely changes the specialist's role. Only when you understand your assumptions can we talk about whether the results are reasonable.

Have you ever felt conflicted on whether or not you should say something?

Wednesday
May082013

## A really good conversation

Today was Day 2 of the Canada GeoConvention. But... all we had the energy for was the famous Unsolved Problems Unsession. So no real highlights today, just a report from the floor of Room 101.

Today was the day. We slept about as well as two 8-year-olds on Christmas Eve, having been up half the night obsessively micro-hacking our meeting design (right). The nervous anticipation was richly rewarded. About 50 of the most creative, inquisitive, daring geoscientists at the GeoConvention came to the Unsession — mostly on purpose. Together, the group surfaced over 100 pressing questions facing the upstream industry, then filtered this list to 4 wide-reaching problems of integration:

• making the industry more open
• coping with error and uncertainty
• improving seismic resolution
• improving the way our industry is perceived

We owe a massive debt of thanks to our heroic hosts: Greg Bennett, Tannis McCartney, Chris Chalcraft, Adrian Smith, Charlene Radons, Cale White, Jenson Tan, and Tooney Fink. Every one of them far exceeded their brief and brought 100× more clarity and continuity to the conversations than we could have had without them. Seriously awesome people.

This process of waking our industry up to new ways of collaborating is just beginning. We will, you can be certain, write more about the unsession after we've had a little time to parse and digest what happened.

If you're at the conference, tell us what we missed today!

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