Why don’t the oil and gas drillers want our sand?

Several feet beneath me (and you, too, if you live in Minneapolis or St. Paul) is a thick layer of sugar-like sand — about a hundred and fifty feet thick. Here’s a tiny slice of it:

Photo by Mark Ryan, Science Buzz blog, Science Museum of Minnesota

It’s the St. Peter Sandstone, and the sand grains are 99 percent quartz.

St. Peter Sandstone

The grains are also quite small, too small to be useful in society’s latest effort to pull every last molecule of oil and gas from the ground.

That effort is called fracking. The word comes from the term hydraulic fracturing. If you haven’t heard of it, well, it’s probably time.

All over the country, oil and gas companies are now cracking, or fracturing, rock that used to be considered too tight or compressed to release its trapped treasure. In the fracking process, drillers inject a stew of water, chemicals and sand into the rock, which fractures it and creates pathways for the oil or gas to reach the well. The role of the sand is to help hold those tiny cracks open. This video does a great job of showing you the whole process.

So, why doesn’t the energy industry want our sand?

We can thank — or blame, depending on your point of view — about four million years of Paleozoic wind-blowing and wave-crashing.

Here’s the story behind the St. Peter Sandstone:

Once upon a time (early Paleozoic, about 450 million years ago), it was warmer and wetter than it is today, and not only that, our continent straddled the equator. There was a lot of life in the sea, but not much on land, maybe some single-celled stuff, just peach-fuzz. It’s hard for me to imagine that part.

In this warm, wet climate the sea covered much of the mid-section of the United States, including southern Minnesota. The exposed part of the continent wore down over the years, as continents do, and the sediments washed into the shallow sea.

The sand-sized particles (the ones we’re interested in) came to rest along the edge of this massive sea and formed things like beaches and tidal flats. The sand was tossed around by the tides and waves and wind for a long, long time.

As a result, the quartz grains in our sand are well-rounded, well-worn, frosted, scuffed…in other words, beat up. With all this knocking around, the grains got smaller and smaller, a fraction of a millimeter across.

Micro-photograph by M. Dittes and J. F. Labuz, University of Minnesota

The oil and gas drillers like their sand grains bigger, all the better to keep those cracks in the rock wide open. That’s why they don’t like our sand.

Elsewhere in Minnesota and Wisconsin, things are different. Oil and gas companies are finding just the right sand deposits and are removing entire hills from the rolling hills of Wisconsin. The StarTribune has written about the relatively new phenomenon. Many others have written about fracking, too, including the New York Times and the Wall Street Journal.

Even if our sand were just right for fracking, we probably aren’t desperate enough for fossil fuels to agree to a massive sand quarry in the middle of Minneapolis.

Are we?

I, for one, am grateful that our sand grains are too fine for fracking. But the whole issue is a pesky reminder that we Midwesterners can’t look at distant oil spills and then hop in our cars and say, Whew! Somebody else’s problem!

Thanks to many people for help with this post: Tony Runkel, Richard Lively, John Mossler, and Robert Tipping — all with the Minnesota Geological Survey, and Chris Paola, University of Minnesota.

 

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