Thursday, February 16, 2012


Probably the hottest geologic topic right now is called "fracking", which is short for "hydrofracking", which is short for using water (hydro) pumped down wells at enormously high pressures to fracture (frack) so-called gas-rich "tight" rocks. The idea is that a huge formation found all over the north central and northeastern US, called the Marcellus Shale, is... well, shale. Shale is a rock formed from deeply rich, usually black muds at the bottom of swamps. These muds are loaded with carbon, because they are mostly organic in composition (e.g., "stinking swamp muck"), and carbon usually "matures" under heat and compression to a number of different forms ranging from coal through liquid hydrocarbons to different forms of carbon-based gas. A major component in the Marcellus is methane, a.k.a. natural gas. But shale itself looks typically like a dark gray to black, raggedy-edged yard stepping stone. It's just a gassy version of stepping stone.

This particular shale formation is widespread, extending from New York state (whose town of Marcellus is the type-locality) throughout much of Appalachia. It is OLD: around 400 million years old (Devonian age). It is also "tight", which oil drillers coined to refer to a rock that didn't let gas or fluid pass through it very easily. However, if you can break up the formation - fill it with fractures - then just the pressure of the overlying rock could potentially force trillions of cubic feet (the standard measurement of natural gas) out of your well. And guess what? The Marcellus is located strategically close to where it would be needed most: the northeastern US.

Fracking, however, means more than just water being injected. It also involves proprietary (e.g., secret) mixes  of solvents and lubricants and sand. Yes sand: after the hydraulic pressure is released, the particles of sand will keep those new fractures open so the natural gas trapped in the shale can get out. And the lubricants and solvents are designed to keep the fluids flowing - keep everything slick, not gooey. The theory, of course is that the top kilometer or so of the frack well is cased (lined with steel tubing) and that tubing is cemented into the hole to stop any potential leaks. This in most cases will extend beyond the groundwater being used by overlying communities and keep the fracking fluids and your drinking water separate.

The idea is that the solvents will sort of, you know, be nice, stay where you put them, and behave themselves. Here's a clue for you to think about however: the secret nature of those mixes. Why keep those chemicals secret unless you are trying to hide something? Another thing to think about: no underground system is "closed" - sealed off for eternity from everything else around it. Groundwater specialists know that there is always movement of groundwater through the sands and rock that it saturates. That movement can be as low as a few tens of centimeters per year, but is often far higher than that. So anything underground is not going to stay where it is - unless it's solid. Maybe you can see where this might lead to by now. There are whole communities in Appalachia, Colorado, South Carolina... and for that matter all over the world where the groundwater is poisoned for one reason or another. It could be mine waste leaching into the ground in West Virginia or Colorado. It could be a leaky tank beneath a service station in Illinois. It could be an abandoned landfill from a World War II Army base in Arkansas. It could be a plutonium-loaded and corroding tank on the Hanford nuclear facility near Pasco, Washington... leaking into the adjacent Columbia River that runs through Portland, Oregon. I kayak in that river, so it gets personal.

And "stuff" always moves.

I'm in the middle of a PhD in economics right now at University of _, and right now I'm working on possible dissertation projects. One project I've been thinking about is looking at gas drilling (specifically fracking), and looking at the economics of drilling. For example, I'm thinking of looking at the economic impact of drilling in the Marcellus Shale formation in Pennsylvania, where there's been a recent expansion of fracking.
I have a geological question for you that I haven't been able to figure out. Is there a way to determine a map that gives both (1) the depth of the top of the Marcellus formation and the (2) depth of the bottom of the Marcellus formation? When I look at standard geological maps, there doesn't seem to be a way to convey that information well in a 2D map, since the information I'm trying to figure out is 3D. I don't know how well this information is known. I imagine that mapping it would be tough, since it is expensive to take deep-earth samples.
Eric L.

You have certainly picked a relevant (and highly politicized) subject - and one that will remain relevant for many, many years. Look forward to full employment for a long time! What you are searching for is an Isopach map - a map contouring the thickness of a particular sedimentary unit - of the Marcellus Shale. You can be absolutely certain that the Oil & Gas companies have these. These are what they base their drillstring-whipping efforts on: where to guide the drill (first downwards, then they "whip" it horizontally to follow a particular stratigraphic horizon). It's a 100% bet that if they DIDN'T have this information, their efforts would be a hugely expensive bust: it's not economic if a million-dollar drill-stem can't be contained within the producing horizon. The stratigraphic unit of interest can be quite thin, but spread over a large area - that's where the dollar value starts clocking in. The strata are almost never horizontal and rarely stay at the same depth over any significant distance, either, so you need to know where the top is and where the bottom is.

This inherently 3D information is generally obtained using 3D reflection seismic surveys... very expensive, but current technology has the capability of resolving layers as little as 5 meters thick when buried more than 2,000 meters down. It's really amazing where brains and (nearly) unlimited resources can bring technology these days.

One reason that this is not found much in modern geologic maps is that the graphic systems used to display and evaluate the unit(s) of interest are also 3D - the top and bottom of the Marcellus is inherently three dimensional so must be viewed that way to be meaningful. The display technology is handled using workstations costing $20,000 or more, with software that is far more costly still. Generally the people working with these data - and planning the drilling programs - are using 3D glasses and working off of multiple 50" plasma screens.

The problem facing YOU (and also the US Geological Survey) is that this information is highly proprietary: one oil company has very strong incentives to keep the information secret from competitors... AND from government entities that might want to tax and/or regulate them. I know some people in the Energy Program of the USGS these days... but their programs are more oriented towards doing large-scale resource estimates. THESE things are available in the public domain: If you want more detailed information on the Marcellus Shale, my first recommendation is to get in touch with one of the "Minors" - smaller Oil & Gas companies working the Marcellus right now - and see if you can meet with one of their geologists. Explain what you are trying to do, and see if they might be willing to talk with you and share some of their data (perhaps even show their 3D data to you, after you sign a non-disclosure agreement).


No comments:

Post a Comment