Naked Science Forum
Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: neilep on 11/09/2007 14:19:15
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Fossil Fuels are great.
Amazing when ewe really think abut how life on the planet before becomes fuel for the future/present !
Do we know (guestimations ?) how much fossil fuel there is ?
How much there is left and how long we have before it's all gone ?
One we've dug it up/welled it up/syphoned it up what do we replace it with ?
Ahhhh..I've just realise my last question about ' replacing it' could be deemed ambiguous and I don't want to start giving myself a reputation as someone who might be called Mr Ambiguous !!
I meant...what do we replace in the cavities left by the extraction of the fuels !!
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Move it Neil, give the geologists something to do. Did you notice we now have two geologists named JimBob? Double the trouble........
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Move it Neil, give the geologists something to do. Did you notice we now have two geologists named JimBob? Double the trouble........
Done !!..moved !
Two geologists called Jimbob ?....uh oh !!! [;)]
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Yeah I noticed that too the other day! LOL!
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how much fossil fuels are left? that is a very difficult question. We're finding new reserves all the time and as technology gets better, this means that we can go back to old fields and suck out some more. Also there is a lot of hydrocarbons in something called oilsands. But as you can imagine from the name, there is a lot of sand in it too. Many oil companies are hoping that they can improve extraction methods to get oil from oil sands. If they do this, then there is estimated to be the same (if not more) amount of hydrocarbons in oils sands as we've found in conventional hydrocarbon reserves up to now.
How long have we got? well, that depends. If we find no more reserves and use oil at the same rate as today then we've got about 50-75 years, but like I said, we're finding more hydrocarbon reserves all the time and efficiency is use is improving constantly so I'd guess we've got a bit longer than that. (If we sort out the oil sands, then we'll have nearer to 150-200 years of reserves left. But that is bluesky speculation.
What replaces the oil? the stuff we're sucking out of the ground is under pressure, as we suck out stuff, the remainder expands 'cos the pressure is less and fills up the space. But also water can get in and fill up the gaps. But there is also some evidence that the ground subsides or there is fault movement/seismic activity. This is a bit controversial. I haven't seen any papers which say there is a definite link (perhaps because oil companies are sponsoring the research?) but I'd say that extracting hydrocarbons from near the surface couldn't help but cause subsidence.
Pete
inthehills
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Wunderbar!
Ein anderen geologin!
Hadn't noticed - (just blew my whole Gernman vocabulary on that message!)
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What replaces the oil? ...(snip)... But there is also some evidence that the ground subsides or there is fault movement/seismic activity. This is a bit controversial.
Pete
inthehills
No it isn't controversial. Ground subsidence has been proven over several salt domes in Louisiana as well as over some oil fields in Louisiana and California. Subsidence is highly noticeable in marsh areas where small changes in elevation can put 100's of acres underwater.
In areas such as the Rocky Mountains subsidence is probably more debatable since there is less overall water in the rock in the mountains. The sediments have been pressed together much more forcefully than in an area where deposition is still going on.
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To reinforce JimBob's comments: subsidence as a consequence of production is well established. A classic example is to be found in the Norwegian sector of the North Sea on the Ekofisk field. This was the first oilfield to be developed in the North Sea, following discovery in 1969.
Seabed subsidence on Ekofisk was first observed in 1984. Reservoir pressure had halved as a result of oil and gas production, allowing three kilometres of overlying sediments to compress the weak formation rocks. This was not the first time that such compression and associated surface subsidence had been caused by petroleum production or coal mining.
The unique feature on Ekofisk was that its installations stood 67 metres above the seabed, but had subsided by three metres in relation to the sea surface in 13 years. Phillips found a temporary solution by jacking up six of the installations and building a breakwater around the Ekofisk tank. But this was not enough.
The seabed continued to subside by up to 50 centimetres per year, and the operator resolved in 1994 - under pressure from the authorities - to redevelop the field. Designed to cope with 20 metres of subsidence, this Ekofisk II project came on stream in 1998. The seabed has so far subsided by 8.5 metres and the process is continuing - but only by about 10 centimetres per year.
Source: http://www.npd.no/English/Emner/Ressursforvaltning/Utbygging_og_drift/norsk_sokkel_2_2004_ekofisk.htm
Pete, I think your figures on available oil are unduly optimistic. Although you note that you base these on consumption continuing at the present level, you don't mention that this is very unlikely to be the case: consumption is growing steadily. Secondly, from an economics stanpoint it is not important when the oil runs out, but when we reach peak production. There are those who believe we are already at that levle and that from here on production levels can only decline. I think that is unduly pessimistic, but we certainly do not have the many decades your own brief summary suggests.
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# Kasmarek, M.C., Reece, B.D., and Houston, N.A., 2005, Evaluation of ground-water flow and land-surface subsidence caused by hypothetical withdrawals in the northern part of the Gulf Coast aquifer system, Texas: U.S. Geological Survey Scientific Investigations Report 2005–5024, 70 p.
http://pubs.water.usgs.gov/sir2005-5024/
Happened across this as I was working - pertinent data
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Has there not been efforts to inject water back into the wells, and would this not help limit subsidence (similarly if in future CO2 is injected in)?
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Has there not been efforts to inject water back into the wells, and would this not help limit subsidence (similarly if in future CO2 is injected in)?
We do inject water back in to the reservoirs, but not to help with subsidence, but to push more hydrocarbons out of the reservoirs.
I think some oil companies are looking are re-injecting CO2, but I'm not that up to date on the science.
As for how long our oil can last, I've got another 20-30 years of working left, so if it could just last that long, that'd be good. It can run out after I've left the oil industry.
pete
inthehills