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Has the lifetime of deep GeoThermal wells been studied at all? Unlike oil/natural gas drilling, a deep geothermal well should provide energy indefinitely barrin

by lumost 10y ago

Has the lifetime of deep GeoThermal wells been studied at all? Unlike oil/natural gas drilling, a deep geothermal well should provide energy indefinitely barring collapse or obstruction of the well. I'd venture the cost of shutdown and clearing obstructions is fairly low relative to the initial CapEx of the well.

chris_va 10y ago
Yes, most wells are productive for about 30 years, and then you have to wait a bit (another 30) to let the rock heat back up. The NPV past 60 years is pretty tiny, so it is hard to amortize capex that far out. Worst case, you run them continuously at half capacity, but then your cost per kWh is about 2x.
- xoa 10y ago
  >Yes, most wells are productive for about 30 years Wait, I haven't looked at geothermal in a long time so I'm not at all up to speed on the current state of the at. But previously you wrote: >and so geothermal plants are generally only built in areas that require shallow (1km) wells That sounds like your "30 years" number there is for shallow wells. Intuitively it doesn't seem like this logic would necessarily be identical for deeper wells: obviously at some depth the rock is always extremely hot (or, in fact, molten). The article seems to indicate that they expect a deeper well to produce higher temperatures and pressures, in turn allowing more energy production, and that seems like it'd make sense. Maybe 1km vs 5km makes no difference in lifetime beyond that, but does your analysis include deep wells already in an equivalent area? Otherwise it doesn't seem reasonable to extrapolate past lifetimes of shallow wells to future lifetimes of deep wells, even ignoring that they say they'll be able to achieve far higher energy generation per well.
  - BurningFrog 10y ago
    > obviously at some depth the rock is always extremely hot Not if you keep pumping in water to run a steam turbine. I assume that's how geothermal energy works, and I'm not going to double check.
    - xoa 10y ago
      >Not if you keep pumping in water to run a steam turbine. Are you being serious? In terms of known capabilities the Kola borehole shows that even with older tech we can drill down to over 12km in depth, and there have been decades [1,2,3] of efforts drill all the way through the Mohorovičić discontinuity into the mantle (20+km minimum from a continental starting point, 5-10+km from ocean). Lithosphere/mantle boundary tends to be defined by temperature, in that around 1800°F is when the weakest common mineral (olivine) begins to exhibit viscosity. Well before that it'd reach the point where the amount of pressurized water we could pump through it wouldn't be able to keep up with new thermal load. So yeah, at some depth the rock is always extremely hot. In terms of economics though of course there is some set of balance points for a given level of tech and economics between cost of drilling to a given depth, gains in lifetime/power density, maintenance costs, costs/losses of actually moving working fluid from heat point to generator, reliability advantages, etc etc. Presumably experts go through and consider all of this, it should be tractable within some set of risk bars. If an experienced power company is actually putting down millions on doing a project after evaluation, I see no reason to doubt that they've done the math to their/their investors' satisfaction to a level sufficient for a pilot project. 1. http://www.smithsonianmag.com/science-nature/decades-long-quest-drill-earths-mantle-may-soon-hit-pay-dirt-180957908/ http://www.smithsonianmag.com/science-nature/decades-long-qu... 2. https://en.wikipedia.org/wiki/Chiky%C5%AB https://en.wikipedia.org/wiki/Chiky%C5%AB 3. https://www.extremetech.com/extreme/247370-drill-baby-drill-japanese-scientists-hope-reach-earths-mantle-massive-drilling-project https://www.extremetech.com/extreme/247370-drill-baby-drill-...
      - BurningFrog 10y ago
        I'm just making the simple point that however hot the rock is, it will cool down when you pour enough water on it. I don't know what the Mohorovičić discontinuity is, but I'm sure it doesn't change this physics fact.
        mmmpop 10y ago
        The rock will radiate heat sufficient enough to boil the water before it can even come close to coming in contact, so no, basic thermodynamics would like a word with your physics fact....
  - chris_va 10y ago
    Yes, you have a point, though the reality is even more complicated. There are physical limits to the heat capacity of the rock, and the heat flux into the region. Deeper wells are not necessarily hotter. Going hotter adds other costs (drilling mud, water=>co2, casement, etc), so its a big multivariate optimization.
DougN7 10y ago
Dumb question and I'm not trying to be pendantic: if the whole world got their power from geothermal, which must (I assume) extract heat and thus cool the core, at what point is there some effect (on magnetic poles? rotation of earth? tides??)? I wonder similar things about solar - what effect is there on global weather patterns when enough solar energy to make a difference is extracted from the environment? Like, what would happen globally if the entire state of Arizona was in the shadow of solar arrays?
- adekok 10y ago
  Think of it this way... the Earth is a rock ~4K miles in radius. Essentially all of it is molten rock. When people try hard we can melt rocks to make metals. But we need special-built furnaces, machines, etc. And these furnaces are maybe 50 feet across. So the Earth has a heat stored which is (4K miles / 50 feet)^3 times larger than a blast furnace. i.e. about 7x10^16 times larger. If everyone on Earth had their own personal blast furnace, we'd be controlling 10 million times less energy than what's in the core of the Earth. Similar calculations apply to other calculations. A Physics 101 calculation I did (years ago) was how much a tidal plant would slow down the rotation of the Earth. The answer was by less than a second a day, after 100 years of running. > ke, what would happen globally if the entire state of Arizona was in the shadow of solar arrays? The plants wouldn't grow. :) But seriously, the energy has to go somewhere. If it's hitting solar panels instead of the ground, the net effect to the world is essentially zero. Maybe locally the ground would be cooler because it's in the shade. But that's about it.
  - xtreme 10y ago
    Less than a second a day in 100 years is a huge change in earth scale. I'm curious, what kind of tidal plant would even come close? Is it assuming we extract 100% energy from the tidal waves and entirely stop the tides, somehow?
    - simonh 10y ago
      Doesn't it depend on how much less than a second it is?

by lumost 10y ago

chris_va 10y ago

Yes, most wells are productive for about 30 years, and then you have to wait a bit (another 30) to let the rock heat back up. The NPV past 60 years is pretty tiny, so it is hard to amortize capex that far out. Worst case, you run them continuously at half capacity, but then your cost per kWh is about 2x.

xoa 10y ago
>Yes, most wells are productive for about 30 years Wait, I haven't looked at geothermal in a long time so I'm not at all up to speed on the current state of the at. But previously you wrote: >and so geothermal plants are generally only built in areas that require shallow (1km) wells That sounds like your "30 years" number there is for shallow wells. Intuitively it doesn't seem like this logic would necessarily be identical for deeper wells: obviously at some depth the rock is always extremely hot (or, in fact, molten). The article seems to indicate that they expect a deeper well to produce higher temperatures and pressures, in turn allowing more energy production, and that seems like it'd make sense. Maybe 1km vs 5km makes no difference in lifetime beyond that, but does your analysis include deep wells already in an equivalent area? Otherwise it doesn't seem reasonable to extrapolate past lifetimes of shallow wells to future lifetimes of deep wells, even ignoring that they say they'll be able to achieve far higher energy generation per well.
- BurningFrog 10y ago
  > obviously at some depth the rock is always extremely hot Not if you keep pumping in water to run a steam turbine. I assume that's how geothermal energy works, and I'm not going to double check.
  - xoa 10y ago
    >Not if you keep pumping in water to run a steam turbine. Are you being serious? In terms of known capabilities the Kola borehole shows that even with older tech we can drill down to over 12km in depth, and there have been decades [1,2,3] of efforts drill all the way through the Mohorovičić discontinuity into the mantle (20+km minimum from a continental starting point, 5-10+km from ocean). Lithosphere/mantle boundary tends to be defined by temperature, in that around 1800°F is when the weakest common mineral (olivine) begins to exhibit viscosity. Well before that it'd reach the point where the amount of pressurized water we could pump through it wouldn't be able to keep up with new thermal load. So yeah, at some depth the rock is always extremely hot. In terms of economics though of course there is some set of balance points for a given level of tech and economics between cost of drilling to a given depth, gains in lifetime/power density, maintenance costs, costs/losses of actually moving working fluid from heat point to generator, reliability advantages, etc etc. Presumably experts go through and consider all of this, it should be tractable within some set of risk bars. If an experienced power company is actually putting down millions on doing a project after evaluation, I see no reason to doubt that they've done the math to their/their investors' satisfaction to a level sufficient for a pilot project. 1. http://www.smithsonianmag.com/science-nature/decades-long-quest-drill-earths-mantle-may-soon-hit-pay-dirt-180957908/ http://www.smithsonianmag.com/science-nature/decades-long-qu... 2. https://en.wikipedia.org/wiki/Chiky%C5%AB https://en.wikipedia.org/wiki/Chiky%C5%AB 3. https://www.extremetech.com/extreme/247370-drill-baby-drill-japanese-scientists-hope-reach-earths-mantle-massive-drilling-project https://www.extremetech.com/extreme/247370-drill-baby-drill-...
    - BurningFrog 10y ago
      I'm just making the simple point that however hot the rock is, it will cool down when you pour enough water on it. I don't know what the Mohorovičić discontinuity is, but I'm sure it doesn't change this physics fact.
      - mmmpop 10y ago
        The rock will radiate heat sufficient enough to boil the water before it can even come close to coming in contact, so no, basic thermodynamics would like a word with your physics fact....
- chris_va 10y ago
  Yes, you have a point, though the reality is even more complicated. There are physical limits to the heat capacity of the rock, and the heat flux into the region. Deeper wells are not necessarily hotter. Going hotter adds other costs (drilling mud, water=>co2, casement, etc), so its a big multivariate optimization.

DougN7 10y ago

Dumb question and I'm not trying to be pendantic: if the whole world got their power from geothermal, which must (I assume) extract heat and thus cool the core, at what point is there some effect (on magnetic poles? rotation of earth? tides??)? I wonder similar things about solar - what effect is there on global weather patterns when enough solar energy to make a difference is extracted from the environment? Like, what would happen globally if the entire state of Arizona was in the shadow of solar arrays?

adekok 10y ago
Think of it this way... the Earth is a rock ~4K miles in radius. Essentially all of it is molten rock. When people try hard we can melt rocks to make metals. But we need special-built furnaces, machines, etc. And these furnaces are maybe 50 feet across. So the Earth has a heat stored which is (4K miles / 50 feet)^3 times larger than a blast furnace. i.e. about 7x10^16 times larger. If everyone on Earth had their own personal blast furnace, we'd be controlling 10 million times less energy than what's in the core of the Earth. Similar calculations apply to other calculations. A Physics 101 calculation I did (years ago) was how much a tidal plant would slow down the rotation of the Earth. The answer was by less than a second a day, after 100 years of running. > ke, what would happen globally if the entire state of Arizona was in the shadow of solar arrays? The plants wouldn't grow. :) But seriously, the energy has to go somewhere. If it's hitting solar panels instead of the ground, the net effect to the world is essentially zero. Maybe locally the ground would be cooler because it's in the shade. But that's about it.
- xtreme 10y ago
  Less than a second a day in 100 years is a huge change in earth scale. I'm curious, what kind of tidal plant would even come close? Is it assuming we extract 100% energy from the tidal waves and entirely stop the tides, somehow?
  - simonh 10y ago
    Doesn't it depend on how much less than a second it is?