Lecture 18 - Oil and Gas

okay so we will we were talking about last time about about fossil fuels and we talked about coal and we started talking about oil but there's some more stuff about oil I want to show you and then I want to tell you a little bit about natural gas and then we'll sort of try you know across the boundary in this lecture into chapter 10 I think it is when we start talking about the climate impact of methane because natural gas is methane so it's kind of a natural segue there so oil a big question that always comes up about oil if you read about it in the newspapers or whatever is how long is it going to last and there's one way to sort of calculate how much how long it will last that sort of takes advantage of our newfound prowess at thinking about units at putting together a formula to calculate what we want just by letting the unit's sort of guide us and it looks like this the lifetime of the oil era is equal to reserves so how much oil there is in the ground and the units of that would be a Giga tons we could call it or you know kilograms or barrels or however you know whatever sort of unit you want and so the lifetime is we want something in years so reserves and then to convert Giga tons per year we'll use the production rate how fast we're consuming it and the production rate is in say Giga tons per year so in order to cancel out this gigatonnes on the top we need gigatonnes on the bottom so we will assemble our our formula this way one over production so now the units of this will be years on top and gigatonnes on the bottom instead of Giga tons per year one over it is years per Giga ton and so Giga tons cancel out and we got years on on both sides this is what they call a in the sort of petroleum industry the heart 2p ratio there's a figure in the textbook which I would have liked to have shown you today except I just stymied by this work of this cable have possibly gone it doesn't make sense but it should just vanish but it's I can't find it there's a plot of this R to P ratio as calculated by British Petroleum BP publishes these reports online every year this is these energy fact books that have lots of tables of numbers like how much oil there is in the ground and stuff and they've been calculating this r2p ratio over time so sort of from 50 years ago what they find is that the r2p ratio has been sort of steady throughout the years at about 40 years so it's saying that in 6 1960 or 1980 or something like that there was 40 years left and it's saying there's 40 years left today so that must mean that they're finding more you know to kind of keep up with how much they're taking out of the ground so that makes it sound like you know 40 years that's a long time kind of right I mean on a sort of political timescale that's a long that's a long time it's not something that's going to affect right away but there's another way to look at this which is called peak oil which is a also called Hubbert's peak after a geological survey petroleum geologist named Hubbard who originally came up with this idea he found that if you look at the production rate as a function of time for some oil field so he first did this for some Texas to some field in Texas and then and then applied it to the continental US as a whole and it worked both times that the production rate how much oil you get out of the ground per time goes as kind of a bell curve so there's an initial part where it kind of looks like exponential growth but it doesn't keep growing exponentially so the exponential growth part maybe is about you know building the infrastructure you know learning how to do it learning where the oil is it sort of tends to take off like that but then it sort of label levels out and plateaus at the top of a bell curve and then follows the curve back down again so where the where this really got famous was there were data from the continental US that sort of looked like it was still kind of in the exponential growth phase and it looked like you know the sky's the limit where we're golden forever at the time but he estimated how much oil is going to be in the earth in the continental US overall and then he fit a curve this bell curve so that it fit the data that already had you know happened the past and the total area under the curve is the total amount of oil so this is this is like barrels per year is the production rate sort of unit or you know could be Giga tons per year or whatever and then you know so this many barrels per year times this many years gives you just barrels and so the total inventory sort of constrains the total size of the curve the total inventory was was was twice as big you might have a curve that sort of looks like that or if it was half as big you might have to fit a smaller curve to the data but so in at about this part of the curve in I forget what year it was but but had a fairly sort of early part of the curve he said that the u.s. is going to reach the peak just a few years later and it seemed like a ridiculous prediction you know it's like those people that predict that you know the universe is going to the economy is going to collapse when you know such and such happens he's kind of like one of these sort of Looney theories but it turned out that he was exactly right and the real the real peak for the continental US came right when he predicted it would so you're going to be playing with a model one of the three for next week that's that's new to you that lets you kind of do this kind of curve fitting and and and see what the implication is for when peak oil will happen for the whole world so you'll put in you'll have data and and you'll get to fit a curve to the data and you have some estimate of the total amount of petroleum in the world and and then from that it'll give you when when the peak should come and then you can try to figure out how much kind of wiggle room there is in that now one fairly fundamental objection to Hubbert's peak is that it's not a theoretical sort of a thing it's not like blackbody radiation from quantum mechanics you can you can calculate exactly that curve and it's you know it you can trace it back to the fundamental you know physics of a blackbody and quantum mechanics and all that so that's real solid that's that's like you know the the gold standard in science is to go all the way back to the fundamental mechanisms but here the rate of oil extraction depends on all kinds of things like you know a extraction in iraq sort of plummeted when the war started extraction in venezuela depends on you know how chavez is feeling there's all kinds of sort of social and political things that go into it and so this curve is not a theoretically you know solid thing it's what they call empirical or sort of observed or just kind of the way things you know tend to be so it's perfectly possible that the the rate of extraction for the whole world oil may not follow this curve exactly Hubbert's peak can be wrong it's just kind of a way to guess or a way to bet if you had to make a bet on walk on it what it says is that well there's two sort of salient conclusions one is that the peak comes when when when the oil is half gone so this this r2p ratio that's essentially trying to estimate when the last drop of oil comes out of the ground and says forty years from now barring finding any more oil or changing the rate of extraction or whatever just keeping everything sort of as it is this is kind of a different thing the the peak extraction and shortage comes when the growth in demand demand is continuing to grow sort of exponentially and the if the bell curve sort of flattens out and lays ecla and lays over like that then the shortage is actually kind of around the time of the peak the time when the rates of extraction can't get any higher when they were sort of pumping it out as high as much as you can so if you talk to all company executives or somebody like that analysts Daniel Yergin the guy who wrote the prize is not a believer in peak oil theory he will say well the rate of extraction of oil today is entirely because you know they didn't invest in infrastructure the refineries and we could easily you know bring out more oil if we wanted to so he personally doesn't buy the empirical Hubbert's peak model but still it's a very interesting thing to watch what you find when you start to get to the peak and start to get shortages is that prices tend to get they go up for one thing because of supply and demand but they also get spiked year so you know the spikes in oil prices last year may have been kind of a harbinger of peak oil and if I could get my computer plugged in I would show you that uh the there was a there's a nifty figure of peak oil for a whale oil that I found on the internet and put in the textbook so the rate of extracting oil from whales which they used for lighting before they started using like me loyal as this amazing cupboard speak sort of a shape to it also so that's kind of the story of oil as far as as far as it goes and then the third kind of fossil fuel is natural gas which is mostly methane so the amount of natural gas in traditional sort of deposits we already talked about it's sort of a few hundred billion metric metric tons or Giga tons so it's comparable to oil and and less than coal by something like a factor of 50 so coal is the heavy hitter oil and natural gas by themselves wouldn't be enough carbon to just totally cook the planet really the big question you know I can't stress enough is is coal natural gas is kind of funny in a you know the the energy infrastructure in that it's difficult to transport because it's a gas so you can either have compressed natural gas in a like in a cylinder like a scuba tank and you know it's very high pressure in their 3000 psi or something like that pounds per square inch if you were to you know break it it would explode it's it takes a very heavy you know walls to hold in that much pressure or there's also liquid natural gas where they cool it down enough to make it into a liquid and you and then you you still have to sort of hold it under pressure and you don't want heat to getting there because you know at room temperature it doesn't want to be a liquid it wants to be a gas and so there's these are sort of the two ways of transporting natural gas around and they're both expensive so the price of natural gas depends very strongly on on where you are on earth and there are some places where natural gas is worth noting because the markets are so far away where you can sell it but to transport it from where it comes out of the earth like Siberia is a good example of this and so a lot of times if there's you know natural gas that is associated with with oil and it's not economical to capture and transport and then sell the natural gas they just burn it in place it's called flaring so price depends on location price I guess value and some places not really worth anything and so it's flared which is a burned to co2 and then just release to the atmosphere as co2 so there's one last sort of point of comparison among the three different kinds of fossil fuel that I want to make and then we're going to talk about methane in the atmosphere as a greenhouse gas and that has to do with this sort of spectrum of oxidation states of carbon so co2 is oxidized the most oxidized form of carbon and in an oxygenated atmosphere like ours it's the stable form of carbon ch4 methane is the most reduced form of carbon so if you bond that carbon with all hydrogen's that's as you know that's that's giving it as many electrons as it can possibly take it's got four in its outer shell hydrogen's give it you know one more each four of them total so then it's got eight in its outer shell it doesn't want any more than that so you can't possibly make it any more reduce than that so this is sort of the spectrum and then in the middle of the spectrum we had biomass what gets produced by photosynthesis which is kind of at an intermediate oxidation state so let's see a minus two for each oxygen the carbon here has to be plus four here the carbon - for here the carbon is equal to zero the oxidation state of the carbon because you know it's losing two electrons to the oxygen but it's getting getting one each from the two two hydrogen's now coal is is mostly just elemental carbon so we just sort of write that as see a whole bunch of C together you know in some sort of a blob kind of a you know amorphous random messy sort of structure diamond is also pure carbon or graphite but those are crystals and ordered and and a little different but they're all sort of carbon so coal kind of has an oxidation state of about zero and then oil is long chains of carbon and the ones in the middle which is most of them are catch-22 carbons and also each one to two hydrogen's so oil is probably so the average carbon and oil is something like let's see where I put it right here oil the average carbon in a chain of oil is sort of ch2 so the oxidation state of this carbon right here for example is a it is it is a minus two because it's getting one hydrogen one electron from each of the two hydrogen's but it's not really doing anything with with the carbons that it's bonded to so that's there's no base sort of share equally the two carbons the electrons there's no contribution to the oxidation state there so we have this sort of spectrum of oxidation states of the fossil fuels where coal is here and then oil is here and then natural gas is there and the more reduced it is the more energy you get by by oxidizing it back to co2 so less energy burning the coal and more energy burning the natural gas so one way to think of it is the number of electrons that go to the carbon another way to think of it which is equivalent is that if you burn just coal you get energy because you're making co2 whereas if you burn natural gas you make co2 plus the hydrogen's there get get a get get made into water and you get energy from that too so I don't know if you ever made hydrogen and like you know science class by electrolysis and then you then you stick a a stick in there that's got a flaming em but I've got a hot ember on it and it makes the hydrogen explode it was a real formative experience for me in like middle school because you make explosions in science class so making hydrogen making water out of hydrogen gives you energy so making water as well as co2 is more energy it turns out that you get about twice as much energy per carbon molecule carbon atom by burning gas than by burning coal so there's sort of they talk about methane gas natural gas as being a cleaner fossil fuel than coal and it is in several ways one coal when you burn it releases all these sulfate aerosols that affect the climate and then become acid rain as always mercury coal mining is intrinsically an ugly process you know especially when they do these like mountaintop removal things natural gas you get more less carbon for the amount of energy that you produce and it's also you know it doesn't have as much sort of other baggage like the sulfur and the mercury and stuff with it yes a mercury likes to form a sulfide there's there's a whole suite of elements that if there's no oxygen and the sulfur is turning into sulfide sulfide hydrogen sulfide is is some of the stinkiest stuff in the world you can smell better hydrogen sulfide than any detector can tell because it's very poisonous and it sort of comes up in our in our environment you know that we evolved in so in a place where you're preserving coal there's no oxygen air that's why the organic carbon from the the photosynthesis gets preserved and that also tends to make sulfide and that tends to trap elements like mercury and cadmium and lead and others like that so it's n tends to travel it tends to concentrate in those sort of dark smelly anaerobic places where the where we get the fuels from okay so natural gas is cleaner than coal for energy but natural gas is still a source of carbon and in fact the methane itself is a greenhouse gas so just to kind of review what we learned when you're talking about greenhouse gases it is something like 30 times more powerful than co2 sort of comparing one molecule of methane to one molecule of co2 and that's because there's much more co2 in the air so co2 is more band saturated than methane is so the methane the way it behaves when it's released to the atmosphere is it is a transient gas it gets released to the air and then it has a lifetime of about a decade in the atmosphere before it before it reacts to make co2 after about a decade the ch4 reacts to make co2 and when it does that it loses most of its the carbon atom loses most of its greenhouse power because it's now a co2 molecule instead of a methane molecule so so the source of methane to the atmosphere is is it's sort of like a driver and the the seat where the methane goes depends on the methane concentration so this should look sort of familiar to you actually this is this is yet another example of where we can apply our wonderful sink analogy so there's the faucet there's the sink you have sources of methane that are putting methane into the atmosphere and then the sink depends on how much methane is in the atmosphere because if you're the high concentration of methane that means you're reacting more molecules per second or whatever then if there's you know no methane in the atmosphere so the the the the water level in the sink represents here the methane concentration in the air and then the going down the drain that's a reaction in the atmosphere making co2 so let's say that we had the the methane concentration in the air as a function of time and let's say that we started out with sort of a steady concentration of methane in the atmosphere so it's not changing as a function of time and now we're going to at this time we're going to add some new sources of methane what happens is so say the source goes up like this and then the concentration will will sort of rise until it is enough to to make the the sink for methane let's see so we'll call this a methane rate and we'll put the methane concentration get another plot kind of up here so we suddenly increase the source and then you know at that point after you've increased the source the there's more going into the air than going out and so your your concentration is going to rise and as the concentration Rises the reaction rate of converting it to burning it essentially to co2 Rises until it sort of balances the source rate and the time scale for this is about the 10-year life time of methane in the atmosphere so just like in the sink analogy two ways of changing the the water level in the sink one is with the faucet the sources that's what we just heared here the other is with with the sink if you change the chemistry of the atmosphere in some way and it turns out that most of the discussion about the methane concentration in the air and how it has changed involved new sources sources of methane there are natural ones there are human caused ones and there's also the possibility of sort of climate feedback sources so the biggest natural source of methane is swamps methane is called swamp gas so if you step in some really muddy yucky gross swamp or you know shallow water lake mud sediment or something a lot of times you'll see all these bubbles coming out and that's methane methane Catching Fire in swamps is you know that's the explanation you always hear for UFO sightings it's just swamp gas and so it burns because it's methane there are other sort of natural sources that are much smaller termites and and ruminant animals like natural ones deer moose or something like that as part of their digestive strategy they they they Harbor a consortium of bacteria that can digest cellulose which is something that we can't I mean we can't eat wood and and and and the digestive even though there's energy in that wood that you know you've burned wood in a campfire and get energy from it but you can't eat it because we don't have the enzymes to digest that so or grass for examples the way that cows eat grass is they have bacteria that they that they host that have the enzymes and they sort of do some of the digestion for them as part of that process it releases methane so under human one of the one of the sources are our livestock so it's not strictly speaking cow farts I told people for a long time the cow farts were this source and this was a question that nobody ever ever ever missed on the exam it was just the astonishing thing so once you've heard that it's in your mind forever there's nothing you can do about it but it's actually not true because where the methane comes out in a cow is is an exhale you know from the front end rather than the back end as it turns out so you know the one fact that I was very successful at conveying was wrong I just have to live with that truth there's an that human sort of analog to swamps which is a rice farming it turns out that rice doesn't you know require living in a swamp but if it tolerates standing water better than a lot of the weeds that that can confound rice agriculture so a lot of times rice is grown in sort of standing water and this makes a big source of methane to the to the atmosphere there's also methane released from fossil fuel industry like we talked about a flaring natural gas well maybe they don't always you know get around to burning it maybe something's just released you walk down 57th street there's this apartment building called the muse and they've got these very fancy gas lights out on the by the sidewalk these little Mantle's and they glow and sometimes a little mantle which is a little bag of string breaks in that case the fire goes out and you can smell as you walk down the street this natural gas coming out and it just really irritates me that they would that they would just cavalierly put methane in the atmosphere but we would call that I guess fossil fuel fossil fuel source and then there's a potential for climate to change things in ways that may add methane to the atmosphere and the most prominent source is a permafrost melts that has a with peat so there are peat deposits that are accumulating in the high latitudes today in Canada and Siberia and places like that and they're preserved by being frozen so you can put some you know leftover food or something in your freezer and it will preserve it they'll keep things keep bacteria from eating it so I've even heard about somebody finding an intact woolly mammoth that's been frozen for 20,000 years up in the high you know somewhere and it was thawing out and they they they they actually ate a stake of this and it was kind of gross but you know it was still perfectly edible it was still preserved freezing sort of preserves organic carbon so these permafrost soils have been preserving organic carbon for thousands of years and now if they start melting it may decompose and start releasing methane to the atmosphere and then there's also on very long time frames these hydrates that we mentioned last time so these are these ice deposits and ocean sediments and to to melt these and release carbon or methane it would take sort of thousands of years so those are the sources of methane the sink is this chemical reaction it's very interesting chemistry because it's it's a it all has to do with these radical compounds so ch4 gets attacked by this radical which is called HS if it's Oh H so oxygen really wants to be h2o it doesn't it's not happy being Oh H that's a very unstable it's a radical compound it's only found where there's sunlight that sort of blows molecules apart and it has a lifetime of you know microseconds or something like that before it finds some way to steal another hydrogen and go back to being water and one of the things it can steal hydrogen from is is methane so so now the oxygen there and that hydrogen are happy because they've made water you know a nice sort of little family there a nice stable molecule and now this one the ch3 is a radical so someone asked the other day if you can have three bonds to carbon instead of four you can but it's a very unstable compound it's a radical and so once this ch3 is formed it then attacks somebody else and it very very very quickly through a series of reactions gets oxidized to two co2 but this is sort of the first step and then after it happens you know the rest of it is all just is all just very quickly now the thing about this chemical reaction is that this Oh H radical has the potential to be affected by all kinds of other changes that have happened in the atmosphere so OAH is produced from ozone which you know there's more ozone in the sort of lower atmosphere especially in sort of smoggy urban environments there are these ozone alert days in the summer they tell us not to go outside running because it's worse for you than sitting there watching television I guess because there's this ozone in the atmosphere and it messes up your lungs so ozone is changing it's also produced by these nitrogen compounds called NO X so this is a family of N oh and no.2 which come from car exhausts and it's one of the components of urban smog so you get this nitrogen compounds coming out of tailpipes and then you shine Sun on it and it makes this sort of brew of nasty chemicals in the atmosphere and make ozone and another thing that affects OAH is carbon monoxide which comes from things like fires so there are you know more fires in the world than there would be naturally because people cut down trees and burn them in order to to do agriculture so all of these things seem like they ought to be changing the concentration of Oh H which should be changing the lifespan the lifetime of methane in the atmosphere and so that would be like messing around with the the drain of the sink analogy but it doesn't seem like like there have been any big changes in the lifetime of methane in the air and I you know it just it seems like there's there's all these sort of factor of two changes in these drivers for methane that seem to sort of cancel each other out by by sort of coincidence so what the methane has actually done in the air is a it has sort of doubled from the pre-industrial value of from-from the year 1750 but it it it sort of stopped rising actually in about the year 1993 so it was going up and it looked like it was going to keep going up and then it sort of defied all expectations and kind of leveled off and it's not clear why it did that one theory is that this was around the time of cleaning up the the the former Eastern Bloc leaky oil or gas pipelines and inefficient industry and things like that decreasing the source another theory is that the planet has been sort of drier since then so maybe there's less of a source from from swamps but at any rate it's kind of a mystery and it's not clear it looks like it's actually started going back up again just in the last since about 2007 but it's not clear what you know it is this sort of a loose cannon in the whole climate system it's not clear why it stopped going up or why it started again so we'll leave it at that you you

Channel: The University of Chicago

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Keywords: climate change class, global, university, climate change, uchicago, lecture, chicago, global warming, science, global warming class, david archer uchicago, warming, rigorous inquiry, university of chicago, chicago university, david archer climate change, class, climate

Id: FnM-eH2COoY

Length: 43min 38sec (2618 seconds)

Published: Tue Apr 06 2010