Mineral extraction industries, be it coal, gas, copper, whatever, all come with their own set of challenges.
Perhaps for those who aren't involved in the operations and daily processes of extraction related businesses, its easy to confuse those issues. Or maybe its easy to confuse other people by lumping them all together. Either way, challenges can't be "applied" across the board.
I had a moment of amazement yesterday reading a story from the Cornell University newspaper, in which the writer was talking about the possibilities of drilling coming to University property. But that wasn't the interesting part. The article quoted an anti-drilling activist in the last paragraph who insinuated that we may soon find out that hydrofracing leads to subsidence, ala coal mining.
It was one of those "not sure if I should laugh or cry" moments. Laugh beacuse of the absurdity and ignorance of the comment, or cry, beacuse someone out there will believe that, and a new gas drilling "urban legend" could well begin.
Lets explore the basics of the shale once more to see why this allegation just doesn't hold water - no pun intended. The Marcellus is between 5,000 and 8,000 ft below the surface. It is a tight shale -- using traditional drilling techniques to extract gas from it is not optimal, because the low porosity of the rock does not allow gas to easily flow to the well bore. Enter the combination of horizontal drilling and hydraulic fracturing.
We all know what those are. But let's consider their actual use. After a horizontal well is drilled, its is perforated with small charges to create a pathway to the shale for frac water through the casing. The frac water is forced into the well at high pressures. Sounds like that combination could create a large hole in the rock. Yet both the charges and the high pressure water create only fissures of various lengths (most not beyond 100 feet or so).
Sand is carried in with the frac water to "prop" the fissures open so gas can escape into the well. Think about that statement for a moment: Sand is used to prop open the fissures. Basic old play sand, for the most part. Not exactly the material one would use to prop open a large hole. The fissues created by high pressure fracing are quite thin -- they are not gaping holes in the rock formation.
Back in my environmental regulatory days, I used to respond to incidents of mine subsidence. Conisdering the extent of the coal mining in Southwestern Pennsylvania where I worked, you would have expected those instances to be more common than they are.
There was subsidence from the currently used longwall mining technique. That subsidence usually occurred in a few months of the longwaller undermining property. Longwallers shear coal in sheets from modern mines, leaving little or no support for the ground above. There is almost always subsidence and its almost always immediate.
Those living over older coal mines can experience subsidence as well. However, when that coal was extracted, the method used was called "room and pillar." In essence, miners worked by hand in large "rooms" to extract coal, leaving behind a series of "pillar" supports that held the ceiling -- some for longer periods of time than others. Some are still holding.
The hydraulic fracturing used to extract natural gas does not leave these kind of large voids underground. In fact, in most cases, beacuse of the pressure of 5,000 to 8,000 feet of soil and rock above them, fissures begin to close on their own, causing no subsidence on the surface.
Its scary to think of the ground giving way below your feet, or home, or business. But what maybe a reality of one extraction industry is not necessarily one of any other. This is one challenge that just doesn't apply to natural gas wells. Hydrofracing isn't going to cause subsidence events.
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