This is the process when drilling a gas well of fracturing the underlying rock in order to all the gas trapped inside the rock to flow freely to the well pipe.
A few years ago they were drilling gas wells near my home. I knew nothing about this process so it was quite interesting to watch. The wells being drilled were called "shallow" wells because they did not penetrate very far into the earth (about 3,500 feet).
Basically the crew flattened what I would guess to be about 1/2 of an acre of ground with bulldozers. Next they dug a shallow pond and lined it with plastic. Then they brought in the drilling equipment. In the case of shallow wells this is basically a semi-trailer with a large hydraulic drill, some diesel, and some drilling pipe.
The drill itself is just a big hydraulic system that spins the drill tip. The drill tip starts on a section of pipe (about 25 feet long). The pipe is spun by the drill into the ground using water from the pond as a lubricant. Once about 20 feet of the pipe is in the ground the next pipe section is attached. Each section is threaded so the drill stops turning the section in the ground. Then a new section of pipe is taken from a rotating set of available pipes, positioned over the pipe in the ground, and then spun on until it locks tight. The drill then continues until the new pip is mostly in the ground and another section is to be added.
(Actually three concentric holes are drilled - the actual well bore hole and two outer holes - one a few hundred feet and one fairly short. This are filled with concrete in order to stabilize the hole and keep ground water from leaking into the well.)
Drilling to 3,500 feet took about 5 days or so.
When the drilling stops you have a chunk of pipe sticking out of the ground 5 feet or so. The drilling pipe is thick and has hexagonal walls (I think so the drill has something to grab on to to spin the pipe).
But once the drilling stops no gas comes out...
Why not?
Well, for one thing the pipe is sealed - so no gas leaks into it. For another there may not even be gas because no one really knows what's below the ground that far. They can guess but they are not always right.
The next step was for the drilling company to send out a specialized rig with thousands of feet of heavy cable and a winch. At the end of the cable was some sort of radioactive box with some sensors. The idea is that the box is lowered into the pipe and the sensors are recorded. The composition of the bore hole surroundings tells the geologist running the device whether or not a given section of pipe spans a likely gas source. (Gas is often found in shale.)
Now what? There still isn't any gas...
So how do I get gas to flow into a pipe 3,500 feet away from where I am above ground?
Explosives.
The next step, once we know where the pipe spans the likely gas formations below ground, is to "open up" the pipe so gas can flow into it. A large shrapnel bomb is constructed with a core of high explosives and a wrapper of shrapnel. This is lowered into the pipe to the span were the gas is likely to be and then detonated. The shrapnel pierces the pipe so the gas can flow in.
But even after this only a small amount of gas comes out.
Now what?
Now its time to "frack". With gas trapped in shale its necessary to create cracks in the shale so the gas can flow to the well pipe. To do this water (and other chemicals) is pumped into the well hole at very high pressure. The water flows out the holes blown into the pipe and enters the shale. Because its under such high pressure the shale fractures (hence "frac'ing") leaving room for the gas to flow.
So why is this so controversial?
First off people are ignorant of geology and physics. The outer well casings are put in place so that between the steel bore pipe and the ground there is about 2-4 inches of concrete down several hundred feet. The exact depth of this being determined among other things by the depth of the local ground water.
For some reason people believe that gas would flow either A) through the sides of the well bore pipe and through the concrete casing or B) up from 3,500 feet below to contaminate "ground water". Neither of which is physically possible (unless something goes drastically wrong which can happen).
(For example, if the casing and pipe broke at the level of 100 feet down were there was groundwater then, if the well were capped, there would be gas being forced into the water table. However the pipes are 1/2 or thicker steel surrounded by concrete - so they are not likely to break unless something like an earthquake hits.)
The bottom line is that under any groundwater source (which tends to be between about 50 to 400 feet below ground) is shale containing gas - anywhere in the world. If the gas could flow up to the surface it would have to do it through the local ground water.
But it doesn't.
And between the lower end of where groundwater is and the gas shale is about 3,000 feet of mostly solid rock. Which is why there is no gas in the groundwater to begin with.
Secondly all the water and chemicals pumped into the bore hole are drawn back out after the fracking. Otherwise there would be no way for the gas to reach the surface save bubbling through all that water. The gas pressure is typically 75 psi or higher so have that much pressure under the fracking liquid will only do one thing - make a heck of a fountain.
(All the water used for drilling and all the waste water generated by the well itself are saved in trucks or the pond built at the start. Nothing spills over onto the ground.)
The bottom line is that there is always danger of something going wrong but its very unlikely a gas well will ruin a water supply. Fracking has been used for many decades without issue for tens of thousands of gas wells.
Gas well drillers have no right to drill on any property for which they do not have permission by the owner (of either the property, the mineral rights, or both). So if there is a concern don't give them the right to drill or write a contract that ensures fresh water even if they make a mistake. If the risk is too high then the well won't get drilled.
If you're "green" you have to follow this line of reasoning:
1) Coal is killing 10,000 people per year.
2) Gas from wells does not kill 10,000 people per year.
3) Gas from wells could replace coal.
4) Are the deaths of 10,000 people worth the very low risk of groundwater contamination from "fracking"?
Newer Marcellus shale wells are 7,500 feet deep - do they pose a threat?
Do they pose a bigger threat because they are deeper?
Do they pose a threat (even a financial one) if they are on your neighbors property but not yours?
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