One of the big, contentious questions about the fracking boom in the United States is whether all that new drilling can contaminate nearby drinking water with natural gas (methane) or other chemicals.
THE WATER CONTAMINATION WAS COMING FROM FAULTY WELLS — NOT FRACKING ITSELF
In recent years, as energy companies have used hydraulic fracturing to extract gas from shale rock in Pennsylvania and Texas, a number of homeowners have complained that their drinking water is getting contaminated. Since 2008, Pennsylvania has seen more than 20,000 new wells drilled and 243 reported cases of water contamination.
This week, a new study in the Proceedings of the National Academies of Sciences shed some light on what’s going on. It found that the fracking process itself — in which shale rock thousands of feet below the surface gets cracked open — didn’t appear to be polluting the water.
But there was a crucial caveat: The PNAS study also found that the vertical wells through which the gas is pumped up to the surface can sometimes leak, often due to faulty cementing. And those leaks appear to have caused some of the water contamination that people in Pennsylvania and Texas are reporting.
This may sound like a trivial distinction. After all, without fracking, many of those wells wouldn’t even exist in the first place. But the study’s authors noted that this was potentially encouraging news for the shale-gas industry, since faulty cementing is fixable, at least in theory.
But in another way, the news is worrisome. Just because the problems are fixable doesn’t mean they necessarily will get fixed. A number of oil and gas wells around the country are thought to be poorly cemented, and no one knows how many, exactly. What’s more, regulations around well construction can vary widely from state to state. So here’s a rundown of both the latest study and the larger controversy:
How fracking works — and how it might pollute the water
Let’s first take a closer look at how energy companies actually use hydraulic fracturing to extract natural gas from shale rock. Let’s take a sample operation in the Marcellus Shale in Pennslyvania:
1) First, a well needs to be drilled all the way down to the layer of gas-rich shale. This shale layer can sit more than 5,000 feet underground and drilling can take as long as a month. The well is typically lined with cement and a steel casing to prevent any leakage into groundwater near the surface.
THERE ARE SEVERAL STAGES WHERE DRILLING COULD, CONCEIVABLY, POLLUTE THE WATER
2) Once the drill reaches all the way down to the shale layer, it slowly turns and begins drilling horizontally, for a mile or more along the rock.
3) A “perforating gun” loaded with explosive charges is lowered to the bottom of the well and punctures tiny holes in the horizontal section of the casing that’s deep down in the shale layer.
4) Now comes the actual “fracking,” or “completion” stage: A mixture of water, sand, and chemicals is pumped into the well at extremely high pressures and goes through the tiny holes in the casing. The fluids crack open the shale rock. The sand holds those cracks open. And the chemicals help the natural gas seep out.
5) The “flowback” stage: The water and chemicals flow back out of the well and are taken for disposal or treatment.
6) Finally, natural gas begins flowing from the shale and up out of the well, where it’s eventually shipped to consumers via pipeline. A typical well can produce gas for 20 to 40 years, pumping out thousands of cubic feet of gas each day.
That’s a rough overview. Now, there are lots of different points during the above is process in which gas or chemicals could potentially leak into the water supply — as the chart below from the PNAS study shows:
Possible sources of water contamination from shale-gas operations: