Tuesday, February 23, 2010

Shale Gas and Drinking Water

Life is full of unintended consequences, and the energy industry is currently dealing with a significant one related to the step-change in US natural gas reserves and production made possible by exploiting gas resources locked up in deposits of a sedimentary rock called shale. The very success of these efforts has placed a decades-old, widely-used drilling technique called "hydraulic fracturing" at the center of a major controversy. In fact, it's hard to find references to fracturing (often called "frac'ing" or "fracking") that don't describe it as a "controversial drilling practice." As best I can tell from delving into the technology involved, the controversy around fracking is largely an artificial one, though that hasn't deterred Congress from holding hearings on it or introducing legislation to regulate it further at the federal level, on top of the state level where it already appears currently well-regulated.

I should preface my comments on fracking by pointing out that I haven't had any direct experience with the practice, either during my time at Texaco or in my studies of chemical engineering, a field that overlaps petroleum engineering extensively, though not in the specifics of this subject. My analysis and conclusions are the result of some research and a lengthy conversation with a former mentor who knows more about fracking from first-hand experience than most of us ever will.

The main concerns about fracking today involve its potential risk to our supplies of drinking water and the adequacy of current regulations to address this. Understanding whether these concerns are justified requires knowing a bit about how fracking works, as well as where drinking water comes from. I could fill up several postings exploring each of those topics, but for the purposes of this discussion let's take a quick look at one of the shale regions at the heart of this controversy, the Marcellus Shale in the Appalachian region of New York, Pennsylvania and the Virginias. In the course of my research I ran across a handy document on groundwater from Penn State. Aside from surface water (lakes, rivers and streams), it identifies the various aquifers in Pennsylvania by type in Figure 4. The key fact from the perspective of fracking safety is that the deepest of these aquifers lies no more than about 500 ft. below the surface, and typically less than a couple of hundred feet down. By contrast, the Marcellus Shale is found thousands of feet down--in many areas more than a mile below-ground--with a thickness of 250 feet or less. In addition, the gas-bearing layers are sealed in by impermeable rock, or the gas would eventually have migrated somewhere else. In other words, the shale gas reservoirs are isolated by geology and depth from the shallower layers where our underground drinking water is found.

Now consider what happens during drilling. As illustrated in this video from the American Petroleum Institute, the drill must go through the layers that might connect to a drinking water source on its way to the gas-prone shale far below. However, before the deeper horizontal portions of the well are fractured to create fissures in the shale through which the gas can flow, the vertical well is cased in steel pipe and cemented to the rock. This, by the way, is already required by law, and it seals off any possible connection with a drinking-water aquifer before the first gallon of fracturing fluid is pumped into the well. That fluid is mainly water, plus a few chemicals, such as surfactants (detergent) and gel to carry the sand used to prop open the fractured fissures. Some of that water remains in the reservoir--isolated from drinking water--and most of it is returned to the surface where it is captured for treatment and either disposal or re-use in another fracking job. As long as the well was completed in accordance with standard practices, the primary risk to water supplies is from surface activities that are already thoroughly regulated and have been for years. Accidental contamination of surface or groundwater would be handled by the appropriate authorities, and a driller would be liable for any damages.

The more I learned about fracking, the more puzzled I became that it has attracted so much criticism recently. After all, the practice was developed in the late 1940s and has been used since then in hundreds of thousands of wells to produce literally billions of barrels of domestic oil and trillions of cubic feet of domestic natural gas. That wouldn't be the case if this were some new, risky practice. In fact, it is an entirely mainstream industry practice that has become so vital to the ongoing production of oil & gas from the highly-mature resources of the United States that a study by Global Insight suggested that restrictions on fracking could cut US gas production by anywhere from 10-50% within this decade, depending on their severity. Similar consequences for oil production would follow. The only thing new here is the clever application of fracking with state-of-the-art horizontal drilling to shale reservoirs that couldn't economically produce useful quantities of gas without them.

The fracking controversy also involves a surprising irony: While many of us recall the old cliché about oil and water not mixing, it turns out that oil, natural gas and water are often found together deep underground--and this is not drinking water I'm talking about. Water is also routinely injected into producing oil & gas wells, either as liquid or as steam, in order to enhance recovery, and many wells produce a lot more water than oil. As a result, the oil & gas industry handles staggering volumes of water every day. By comparison fracking, in which water is only used to prepare a well and is not part of the ongoing production process, accounts for just a tiny fraction of the industry's involvement with water--all already regulated, I might add.

So how do we explain the current ruckus over hydraulic fracturing? Perhaps one reason this old practice is attracting new scrutiny is because it's being applied in parts of the country that haven't seen a drilling rig in decades, where it provokes a similar reaction to the arrival of 300-ft. wind turbines, utility-scale solar arrays, and long-distance transmission lines. But rather than just writing this off as yet another manifestation of NIMBY, I'm truly sympathetic to concerns about the integrity of our drinking water. My family drinks water out of the tap, and I would be irate if I thought we were being exposed to something dangerous. When you examine the science behind fracking and see that, if anything, these wells are drilled and isolated with more care than many water wells (which I understand often aren't cased and cemented to protect the water source from contact with other sedimentary layers) it becomes clear that the biggest potential exposure occurs not underground but at the surface, where fracking is just one of many other regulated industrial water uses, and a fairly small one at that. Thus, whether intentionally or as a result of a basic misunderstanding of how this technology works, we are being presented with a false dichotomy concerning shale gas and fracking. The real choice here isn't between energy and drinking water, as critics imply, but between tapping an abundant source of lower-emission domestic energy and what looked like a perpetually-increasing reliance on imported natural gas just a few years ago.


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Geoffrey Styles said...

Naina Arora,
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