In a comment on another blog post, Ed asked what I thought about the earthquakes in Oklahoma.
Before I give my opinion about whether I think there is a relationship between fracking and the recent earthquakes, I should give a little background. Except for a petroleum engineering class I took in college, I don't have any education or direct experience working in the oil and gas industry.
On the farm, there are pipelines running everywhere (in the recent boom, two new ones were built across a couple of pastures), back in the boom of the '70's a well was drilled on almost every 80 acres, and my grandparents, aunts, and parents own a portion of the mineral rights under the farm.
From what I know, the wells drilled in the '20's were shallow (1000 feet deep?), the wells in the '70's were deeper (around 5000 feet deep), and the recent wells were almost all directional (going down about 5000 feet, then running horizontal for about a mile). Because the oil is in shale formations, all the wells were hydraulically fractured after drilling, and all the wells produced salt water that was disposed of in disposal wells. If I had to guess, I'd guess that there was as much or even more drilling activity and production in the seventies as there was in the recent boom.
The recent earthquakes in Oklahoma started back in 2006 before the oil boom and started happening in my local area (where I live) about two years ago. There isn't as much drilling activity or as many disposal wells around the area where I live, but there was about a month or two when the earthquakes came all the time. The biggest was probably around a 4.0, but most of them were small 2.0 type of earthquakes. The small ones feel sort of like the way the house shakes when there's a close thunder clap or if a large truck drove by the house. The larger ones feel like you'd think an earthquake would feel with the ground slightly "rolling", but it wasn't big enough to be alarming.
According to the geological websites I looked at, most of those earthquakes typically originated from 30,000 feet deep.
I never saw a good explanation for how injecting water into a disposal well that was around 5000 feet deep could cause an earthquake to originate from a faultline that was 30,000 feet deep. From what little I know about hydrology, the water would tend to go upward towards the surface of the earth after being disposed of in the well.
To make a long story short, oil wells have been drilled in almost the same basic way since the oil fields opened up in Oklahoma, earthquakes have happened in the past in Oklahoma, the people blaming the oil/gas industry for earthquakes have a long history of blaming the oil/gas industry for anything and everything, and I don't see how anything that happens at 5000 feet underground can have an effect at the 30,000 feet deep mark.
So based on those thoughts, I'm not convinced that fracking or disposal wells caused the recent earthquakes, but I could be wrong, and I know that a ton of people will disagree with me.