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[Vehudur]

But if the geothermal plant is causing the quakes, why the hell would you leave it on?  Doesn't matter how weak you think they are, 3.6s all the damn time, directly caused by the plant, are going to piss A LOT of people off.

They'll be a whole lot more pissed off if you don't do a thing to it for a hundred years and it slips as an 8.0 -- oh wait, they'll be long dead and just have left it for their grandchildren, so they don't care.

It is far, far better to release that energy over a long period of time then to release it at once.  Truthfully, we should be doing this along major fault likes to intentionally lubricate them.  It's simple, because the energy released now will be less than the energy released later, it's far better in the long run.

[Gearheart]

Now I can just see a town on the edge of one of these plants, which is constantly vibrating due to seismic activity.

Some guy waking up in the morning and his bed has moved into the kitchen because of the constant vibration. Then he can't pour any coffee because all of the mugs and glasses have shattered. He then realises that his car has disassembled itself, and his entire house has moved about 4 feet to the left.

Just another day in Quaketopia, Switzerland.

... I would live there.

[Dwarf]

Dude, you'd have to be aware there is an earthquake to notice 3.6. And since that energy is released, it's not said that there would be such quakes all the time.

[Hyndis]

Generally if its below a 4.0 you don't even notice it. A 5.0 can start to cause some minor damage, and you start to get significant damage at 6.0+.

But for small earthquakes the shaking is literally so tiny that if you live next to a major road a regular car driving by will produce more of an event than something like a 2.0 or 3.0. A truck might be a 4.0.

[Vehudur]

I used to live next to rail tracks (like 30 feet from them - and it was double tracks), and those heavy coal trains rolling past at 70mph is like a several minute long earthquake.  It could knock things off shelves and everything.

Even strong shakeing hasn't bothered me for years.  I wonder why.

[Brewster]

I don't know about magma, but I hate using the & sign at work now.

[MarcAFK]

The problem isn't really just because of the tiny earthquakes but with the way these modern geothermal systems work, rather than taking steam that's already coming out of the ground they pump water into a underground hotspot then collect the steam that pours out.
But, the ground is cracked, filled with faults and areas of different density and porosity so the steam generated can go practically anywhere, if a plant like that is left on for a long time the steam may cut it's way through a seam of weak material into a nearby mine or lake or whatever leading to more unpredictable results. You might get a random steam eruption under somebodys house...
Hell in basel they did it in the middle of a city that's just insane.
Worst case scenario you might end up with your steam cutting large scale channels into the hot underlying rock then accidentally releasing an unknown aquifer or lake of oil or something into it causing a massive explosion...
You do not want the epicenter of that in the middle of a city.
From what i remember the most violent volcanic eruptions are caused mostly by the pressure caused by dissolved gasses and steam building up past the point where the weight of rock above can contain it, any weakening of the above material by earthquake or whatever causes violent eruption.
Letting your steam erode the ground unprodictably could trigger unknown volcanos, or even create new ones. But it kinda depends on the scale of the plant. Theres far less danger if you just keep your hole sealed, but the amount of energy you can get that way is terrible.

[Xenos]

or keep the steam contained within a pipe system which is heated by the surrounding rock.  (not as much power generated, but much safer and easier to control)

[MarcAFK]

Also on a partially related note those deep boreholes in germany and russia found 5-10 kilometers down massively thick layers of throughly fractured rock saturated with fresh water. And large quantities of hydrogen gas.
You might end up with hydrogen eruptions coming randomnly out of the ground near your geothermal plant which could be fun.
And the virtually infinate quantities of water which exist down there could be fun if it finds an easy path down to the hotter parts of the crust a few kilometers further down. Which could be caused by the destructive influence of your hot steam on a large scale.
It's probably fairly unlikely but the possibility of massive accidents is there.

[krenshala]

The problem isn't really just because of the tiny earthquakes but with the way these modern geothermal systems work, rather than taking steam that's already coming out of the ground they pump water into a underground hotspot then collect the steam that pours out.
But, the ground is cracked, filled with faults and areas of different density and porosity so the steam generated can go practically anywhere, if a plant like that is left on for a long time the steam may cut it's way through a seam of weak material into a nearby mine or lake or whatever leading to more unpredictable results. You might get a random steam eruption under somebodys house...
Hell in basel they did it in the middle of a city that's just insane.
Worst case scenario you might end up with your steam cutting large scale channels into the hot underlying rock then accidentally releasing an unknown aquifer or lake of oil or something into it causing a massive explosion...
You do not want the epicenter of that in the middle of a city.
From what i remember the most violent volcanic eruptions are caused mostly by the pressure caused by dissolved gasses and steam building up past the point where the weight of rock above can contain it, any weakening of the above material by earthquake or whatever causes violent eruption.

Actually, its the gases trapped in the magma getting released as the magma moves towards the surface and the subsequent pressure drop is what causes it to explode.  Think of an unopened soda can that gets shaken up.  The CO2 is still in the soda before you open it because the pressure in the can keeps it in place.  But if you open the can, all that CO2 suddenly has a place to expand into and your soda erupts out of the opening, potentially spraying everyone over a relatively large area.

Letting your steam erode the ground unprodictably could trigger unknown volcanos, or even create new ones. But it kinda depends on the scale of the plant. Theres far less danger if you just keep your hole sealed, but the amount of energy you can get that way is terrible.

The steam most likely won't cause volcanoes, but it definitely could undercut rock structures and cause caveins or other similar problems.  Think sinkhole.

[Vehudur]

The problem isn't really just because of the tiny earthquakes but with the way these modern geothermal systems work, rather than taking steam that's already coming out of the ground they pump water into a underground hotspot then collect the steam that pours out.
But, the ground is cracked, filled with faults and areas of different density and porosity so the steam generated can go practically anywhere, if a plant like that is left on for a long time the steam may cut it's way through a seam of weak material into a nearby mine or lake or whatever leading to more unpredictable results. You might get a random steam eruption under somebodys house...
Hell in basel they did it in the middle of a city that's just insane.
Worst case scenario you might end up with your steam cutting large scale channels into the hot underlying rock then accidentally releasing an unknown aquifer or lake of oil or something into it causing a massive explosion...
You do not want the epicenter of that in the middle of a city.
From what i remember the most violent volcanic eruptions are caused mostly by the pressure caused by dissolved gasses and steam building up past the point where the weight of rock above can contain it, any weakening of the above material by earthquake or whatever causes violent eruption.
Letting your steam erode the ground unprodictably could trigger unknown volcanos, or even create new ones. But it kinda depends on the scale of the plant. Theres far less danger if you just keep your hole sealed, but the amount of energy you can get that way is terrible.

No no no no.  This is just wrong in so many ways it's disgusting.

So you hit an aquifer.  No big deal; either it's already got ways out (and being in that environment will already be hot), or you've drilled through impermeable rock, in which case it's actually a benefit by having a bigger geothermal battery to draw from.  These arn't just holes we keep full of water; we're actively forcing more down.  The most it being pressurized could possibly do is make it harder to pump.

You're also forgetting one important thing about steam:  It's hot.  If it's not hot, then it's water.  That means, if it starts escaping to the surface, it's going to turn back into water when it starts hitting cold rocks.  The volumes of water involved here, while moderately large with a large plant, are nowhere near enough to punch through cold rock and create a geyser or thermal spring of their own.  Especially when you take into account that we're not just pumping water down, we're pumping steam out nearby too.  It is common knowledge that things under high pressure will go to places of lower pressure.  This means that the vast majority of the water that goes down is coming right back up that other tube, leaving very little left for your doomsday scenario.

If you hit a lake of oil, that would also be no big deal - except for the fact that oil doesn't exist in lakes, but rather fills the pores of certain types of rock just like an aquifer.  There are no open spaces deep underground - they're quickly crushed.  A lake of oil would only be a big deal because it'd be the first of its kind anywhere.  It couldn't burn, even if it was above those temperatures, unless you pumped oxygen down.  In which case, it would burn just like a coal seam fire - slowly, and fairly uneventfully, besides increasing the local thermal gradient - a gradient that, in this case, is already very high.

With the pressures of steam we deal with in these plants, if the steam reaches magma and the rock is weak enough to be effected by the steam, then the magma is already on its way up - as it's under far more pressure, and puts the rock near it through far more abuse (melting) then steam (which will...  oxidize it, possibly).  Unless it's sandstone, it could erode sandstone.  Oh wait, sandstone in the environment we're talking about undergoes metamorphism into quartzite - maybe low grade quartzite, if it's on the cold end of a geothermal region, but still quartzite.  Low grade quartzite is just slightly less hard than one of the hardest stones on the planet.

Steam in these types of rock - some of the hardest, most durable rocks on the planet - isn't going to make much of a difference to it.  The only places you might actually find erodible spaces is fault breccias (the crushed material along a fault line that actually forms the boundary) and other breccias.  However, that's packed in so tightly while you may allow the pieces to move against each other, you're not actually going to move it anywhere - especially when you consider that it has nowhere to go.

Letting your steam erode the ground unprodictably could trigger unknown volcanos, or even create new ones. But it kinda depends on the scale of the plant. Theres far less danger if you just keep your hole sealed, but the amount of energy you can get that way is terrible.

The steam most likely won't cause volcanoes, but it definitely could undercut rock structures and cause caveins or other similar problems.  Think sinkhole.

The steam couldn't cause a volcano to erupt.  It's simply not possible, in any stretch of reality.  It's a very simple reason why too:  The magma is under vastly more pressure.  Besides, if they drill into magma (it's happened, actually, a few times), they just back the drill bit up a few thousand feet and bore a new hole to the side somewhere.  Do you know what happened when they struck magma?   Nothing.  They go "Oh, why'd the temperature suddenly spike?", pull the drill bit back up some, try to push it back down and realize the magma has chased them up the drill hole a few feet (usually around 6 feet up the hole) and formed a plug.

Despite what you see in the movies, lava and magma are not boiling kool-aid.  They are extremely thick, molten-glass like substances, with a viscosity ten thousand times that of water even in the thinnest cases.  The other side of that, is once it starts moving it actually gets thinner through a process called shear thinning.

Hydrogen or other gasses (Hint: Underground has gasses that you have to worry about a lot more than hydrogen, which makes a pretty flame but that's it.  Hydrogen also requires oxygen to burn or explode.)  coming up the borehole is no big deal either; in fact there are devices that are specifically designed to capture and filter the drilling mud of gasses.  They're either used for something useful, burned off or (if they can't burn and aren't useful) stored for disposal later, and in rare cases just allowed to disperse into the atmosphere if they're not harmful in any way.

[meto30]

I do remember those photos of the Gulf War in which the oil spikes in Kuwait ignited from stray weapon fire and burned through the oil reservoirs quickly with devastating results. It looked like those pictures of Hell from the middle age...

The explanation that came with the photos was that the oil spikes are like straws, and the pressurized oil down in the rocks spontaneously sprout out through them. With the top of the spikes on fire, the entire thing works like a flamethrower with oil constantly coming out, catching fire, and bursting in big orange fireballs because of the sudden decrease in pressure upon reaching the surface.

[Vehudur]

I do remember those photos of the Gulf War in which the oil spikes in Kuwait ignited from stray weapon fire and burned through the oil reservoirs quickly with devastating results. It looked like those pictures of Hell from the middle age...

The explanation that came with the photos was that the oil spikes are like straws, and the pressurized oil down in the rocks spontaneously sprout out through them. With the top of the spikes on fire, the entire thing works like a flamethrower with oil constantly coming out, catching fire, and bursting in big orange fireballs because of the sudden decrease in pressure upon reaching the surface.

Except, it wasn't stray gunfire - the wells were intentionally lit by the retreating iraqi army using scorched earth tactics.  It worked; there was nothing left but oil and fire.  It turned the skies of the middle east into eternal night for most of a year until they were put out.  But that was thousands of wells.

Obviously, if you drill a hole down to an oil reserve, it's pressurized from being underground.  It's going to blow out with some force then (this event is, creatively enough, called a blowout).  If you light it, you have a really big torch.  However, there are usually devices placed over the top of wells to prevent this; their failure is very rare - and their failure while they actually need to do their job is very rare indeed.  The wells in Kuwait were blown open with dynamite, and just about the only other way to blow open these wells is to physically blow open the top, or drop something really really heavy (hundreds of tons) on it.