Monday, August 11, 2014

The Problem with Fracking: Part 1

The problem with fracking is that fracking itself is fairly benign. It's really the associated wastewater disposal that presents the most serious environmental challenge.

Almost every day, I see anti-fracking posts on Facebook. About once a month, I get handed anti-fracking leaflets on the street. All of these tell me that fracking is bad because of, amongst other things, the risk of contamination of drinking water aquifers with fracking fluid and hydrocarbons from the completion, as depicted in this graphic that I found via Google Image Search:

“Gasland” Fracking Graphic

The problem with this is that it's a lie. In this first instalment of The Problem with Fracking series of blog posts, I'll explain why.

Aquifers used for drinking water and irrigation are usually shallow, something like a few hundred feet down. Anything over 500 feet down is considered a “deep bedrock aquifer”. There are a couple of reasons why shallow aquifers are preferred: economics and water quality. As a general rule, the deeper you go, the worse the water. The reason for this is that temperature and pressure rise as you go down, with a corresponding increase in the proportion of dissolved salts in the water. Geothermal plants, where the water comes from deep underground at high temperature, regularly measure salinities as high as 20% (sea water is about 3.5%).

Most shale gas plays occur at depths of around 10,000 feet. The famous Marcellus shale is often chosen to exemplify the problems with fracking because it is well-known, vast, and unusually shallow in places, but still about 5,000 feet to the top of the formation, with an average well depth of 6,300 feet.

Marcellus Shale

I've said that the graphic above is a lie, so it's reasonable to ask what happens if we correct it? I took the number of pixels from the “surface” to the bottom of the water well on the right, dramatically shown with a big yellow flame on top, and found it to be 90 pixels. The average depth of a domestic water well in Pennsylvania is 200 feet, or 4.4 feet per pixel. At this vertical scale, the picture becomes:

So as not to be accused of hypocrisy, here's what it looks like if we correct the aquifer depth and fracture tops to their worst-case values (1,000 feet and 4,500 feet, respectively):

So, now we have something a little more honest, but there's also the issue of the composition of the rock. With its choice of color, the graphic implies that the gas play and the aquifer are part of the same rock formation. I have little doubt that the color is chosen to be suggestive of sandstone, which is typical of the permeable rock found in both aquifers and oil reservoirs, but these aren't called shale gas plays for nothing, and, in this case, it isn't called the Marcellus shale for nothing, so let's add somewhat plausible Pennsylvania stratigraphy (I've changed the color of the gas shale from black to light bluish gray to retain easy visibility of other features, such as the completion; other colors are unchanged):

This final diagram couldn't honestly be described as “representative”, because it stretches the facts to within a hair's breadth of breaking-point, yet it still leaves an impermeable barrier totalling over a kilometer of rock in three facies between the worst-case fractures and the worst-case aquifer. At least this diagram bears some passing resemblance to the truth, but the original is outright

It is possible for groundwater contamination to occur at the surface, but fear of aquifer contamination from the completion, as depicted in the original graphic, is about as reasonable as the premise of Black Sheep.

The next installment of this series will demonstrate why another hobby-horse of anti-fracking hysteria — the composition of fracking fluid — holds no water (pun intended).

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