I heard a few days ago that Pennsylvania had recorded its first earthquakes caused by fracking. I’ve been hearing for a while that fracking causing earthquakes and all sorts of other mean, nasty stuff, but I didn’t know exactly how. I figured this was a good opportunity to read up on the matter and write a neat little science-explainer post.
Except it turns out fracking doesn’t cause most of the earthquakes we’ve been hearing about. Fracking is bad, don’t get me wrong, it’s just that the situation is more complex.
The story in Pennsylvania is that there were a series of very small earthquakes almost a year ago. They were too minor to even notice without the help of instruments and nobody would have cared except that they were centered right next to fracking operation. So, the authorities investigated and decided that yes, the fracking probably caused the shaking.
No, it didn’t, said the Daily Caller, a website about which I knew nothing and was frankly suspicious. I poked around on the site, and offhand, it looks to be a legitimate newspaper with a conservative, anti-environmental bias, but so far I haven’t seen anything too far off that wasn’t on the opinion page. More to the point, they’re almost right about fracking.
Fracking can cause earthquakes, but they are typically too small to feel, just as the quakes in Pennsylvania, were. The Daily Caller’s contention that the story is some kind of liberal media conspiracy seems off-base at best. But they are correct in noting that the US Geological Survey (USGS) says that fracking does not cause strong earthquakes.
As the USGS explains, induced earthquakes are caused by the injection of fluid into rock near faults capable of producing earthquakes, but how much fluid and when it is injected both matter a lot.
Fracking (or hydraulic fracturing) means using water and chemicals (mostly acids, lubricants, and poisons–the poisons are used to kill microbes that might otherwise damage the equipment. And yes, you can look up these chemicals) to break up deep rock layers so that oil or natural gas can flow more easily into the well. Once the fracture occurs, it doesn’t have to be done again, not for that well. Extraction commences, and most of the fracking fluid comes back up, along with the oil or gas. Because the injection operation is brief, involves relatively little fluid, and normally occurs in rocks that have already had some of their oil extracted by conventional means (thus freeing up some space) the resulting earthquakes are small.
What causes the big earthquakes is wastewater injection.
When oil or gas are pumped out of the ground, water comes, too. It may be a little water or a lot of water–usually, the proportion of water increases as the well starts to empty out. Wells are often abandoned, not because there isn’t any more hydrocarbon down there, but because there is to much water and separating it out gets too expensive. The water can come from a number of sources. Some of it was pumped into the well as part of the drilling process (either for fracking or for other forms of drilling), and then withdrawn again along with the oil. The water picks up substances from the rock in the process an becomes salty and toxic. Water can also leak into a well when the bore hole passes through an aquifer–though drilling companies try to prevent those leaks because the water causes various expensive complications for them. Sometimes when oil or gas are pumped out of the rock, water from nearby flows in to take up the newly emptied space. But oil and gas pockets generally contain their own water as well, because the organic ooze that became the hydrocarbon and the sediment that surrounded it were wet. Some of that water is salty because it’s seawater. Sometimes it’s fresh. For some reason I find the idea of underground pockets of ancient seawater charming.
But no matter how the water gets in there, it’s not safe to drink when it comes back out. Water is very good at dissolving things, and while it’s underground, it usually picks up several different toxins or radioactive substances. There are various ways to dispose of this stuff (some places spray it on roadways to control ice and dust, a practice of questionable wisdom). Injecting it back underground is not a new idea, and has obvious advantages–if it’s injected into the space that used to contain oil, the water can prevent subsidence. But if the wastewater is injected into rock that hasn’t had anything removed, it can cause earthquakes. Serious ones.
Wastewater disposal involves a lot more fluid than fracking does, and it continues as long as the oil pumping. Its impact on the rock is therefore much greater. And yet, even then, most wastewater injection wells don’t cause earthquakes. For the rock to move, there must be a pre-existing fault capable of causing earthquakes either near the injection site or somewhere the water can flow to from the injection site–sometimes the earthquake is up to ten miles away. So, the take-home message is that injection can’t cause an earthquake in a place where no earthquake could happen otherwise, but it can make those earthquakes much more likely. Like, hundreds of times more likely, as is happening in Oklahoma, and will likely continue happening for years after the injection stops.
The other take-home message is if someone ten miles away agrees to put an injection well on their land, the earthquake might happen under your house.
But there is a connection between fracking and strong induced earthquakes.
Scientists have known for decades that wastewater injection can cause earthquakes under some circumstances. They’ve known that there are some places where these wells just shouldn’t go. But in recent years, the economics of exploiting certain very wet carbon deposits has simply gotten too good to pass up–and fracking and horizontal drilling together have made it so. The result is more injection wells where they’re not supposed to be. So far, Pennsylvania has not had many injection wells, which is part of why it hasn’t had many induced earthquakes, but that could change.
As long as large volumes of wet hydrocarbons are being exploited, there will be large volumes of wastewater to be disposed of, somehow. It may be difficult to restrict disposal wells to those places that are not going to cause earthquakes. And as bad as injection is, all the other forms of disposal seem to be worse.
So it comes down to a societal choice–how much are we willing to pay to have oil and gas? Ad are the people making the decisions really the same people who end up paying the cost?