The price of fuel has risen sharply in recent months, by as much as 50% in some parts of the world. It\u2019s being driven by the conflict in the Middle East, and growing uncertainty over global energy supply chains. This has a knock-on effect on all of us, because oil and gas lie upstream not just of transport, but manufacturing of materials as diverse as fertilisers, and therefore food production; and rising input costs are being passed straight on to the consumer. Many nations are trying to mitigate this by exploring alternatives to hydrocarbon energy sources, but there are, of course, limits to what we can do in the short term. The UK is no exception. There are calls from some quarters to renew drilling in the North Sea to tap into local reserves for instance. We\u2019ll explore that later on. But first, geologically speaking, how does oil and gas form in the first place? Here\u2019s Jonathan Redfern, a professor of petroleum geoscience at the University of Manchester, in conversation with Chris Smith…<\/p>\n
Jonathan – We need rocks that are rich in organic matter, and that organic matter is basically ancient life that was living in the seas, like algae, plankton, bacteria, but it could also be plant material, trees, leaves, woody material. So anything that’s got organic components in there, because that contains carbon and hydrogen, and they are the building blocks for oil and gas. We call those rocks source rocks because they’re the source of the oil. So we’re looking for conditions on the Earth going back millions of years where we can generate those carbon-rich rocks. We’re looking for an environment where we have lots of algae and plankton, typically warm waters. Now, when they die, they will land on the seabed and then can start to be buried. So over millions of years, those rocks will slowly get buried deeper and deeper and deeper, and as you go deeper into the Earth, the temperature increases and the pressure increases. On average, if you go down one kilometre, the temperature increases by roughly about 30 degrees Celsius. So when we go down, say, two, three, four kilometres, then we’re at temperatures of typically 60, 80 degrees Celsius, and we also increase the pressure because of the weight of the overlying rock on the top. At that pressure and temperature, that organic matter will start to break down, and as it breaks down, it releases hydrocarbons.<\/p>\n
Chris – Presumably, this is a bit like Goldilocks then, isn’t it? It’s got to be just right in the sense that we need the right sorts of organic matter at the right concentrations, falling in the right sorts of geology, so that it gets buried to the right extent with the right pressure at the right temperature for the right amount of time, and when all those conditions are ideal, then it cooks up into what we call crude oil.<\/p>\n
Jonathan – Exactly. Geologists who are looking for hydrocarbons spend their time trying to identify where on Earth we may have had these unique conditions that give us these very rich source rocks, and where they’ve been buried to the right depths to be able to generate oil and gas, and reach the right temperatures. And then we also have to think about where it goes as well, because in most cases, we’re not looking for the oil and gas in the source rocks; the oil and gas is leaving the source rock because when it’s released as bubbles of gas or oil, it’s then buoyant. It then really wants to make its way up to the surface. It’s moving slowly over millions of years up to the surface, and probably most of the world’s oil leaks out. Over time, it’s just leaked to the surface and evaporated or got eaten by bacteria or something. But some of it is trapped in the subsurface. It gets to a point where it can’t get to the surface. So there are rocks that do not allow the fluid to flow. We call them seals, impermeable rocks. The obvious one is salt. Nothing can flow through salt. So if you have a big unit of salt, then underneath that, any oil is going to be trapped, and we’re looking for that oil trapped in the subsurface, and not trapped in small amounts, of course. We need to find it in millions and millions of barrels is what we’re looking for, so very large amounts.<\/p>\n
Chris – One question that often comes into us here at The Naked Scientists, especially at the moment because of what’s going on, people say, well, what’s it like underground? Is there a huge, great bubble down there of oil? So when we then pull it out, do we leave behind this enormous hole in the ground? Or is it that it’s almost like coral or bone marrow down there, lots of little holes and voids, and then they’re stuffed full of oil and gas bubbles with the rock around them. What does it look like?<\/p>\n
Jonathan – Most oil and gas is found in sedimentary rocks, so the two main types of rocks would be sandstones and limestones. Sandstones comprise sand grains, which are cemented together, but in between the grains, there are holes. A sandstone is porous. So it’s a bit like a sponge, and typically the rocks we’re looking at have got anything from 10 to 20 to maybe 30% of the rock is pore space, and the oil is trapped inside those pores. But the pores are connected, so that the oil can move through from one pore to the next to the next. So when we drill into a sandstone, we drill from the surface, and then the oil will flow from the rock into the borehole and up to the surface, and it will flow under its own pressure.<\/p>\n
Chris – Why is it, though, that we’ve got some places where there’s enormous amounts of gas and a relative paucity of oil, and others that there’s absolutely loads of oil? If these processes just produce equal amounts or they’re the same, why do you end up with some places dominated by gas and some dominated by oil? I’m thinking Qatar, for example, produces huge amounts of liquid natural gas, which supplies half the world, from what I can make out. Why is that a hotspot?<\/p>\n
Jonathan – There’s two ways to produce the differences. One is that we have different types of source rock. So typically, we think that source rocks that are generated mostly from algae and plankton are more likely to produce oil because they’re very rich in carbon and hydrogen, quite a high amount of hydrogen in the rock. Whereas other types of rock, for instance, coals generally, they’ve got less hydrogen in the organic matter. So they tend to want to produce, when they get buried, to produce more gas than oil. But the other thing is that with all source rocks, when you bury them, if they get beyond a certain temperature, then all source rocks will start to generate gas. Because at high temperature, the long-chain molecules that make up oil start to break down and they break down into the smallest molecule, which is methane. So it could be one of two things. It could be the original source rock that’s more prone to generate gas than oil because of the organic matter in it. Or the second thing, it could be that it’s been buried deeper and hotter, in which case all basins in the world, when any source rock gets buried really deep, it starts to generate gas.<\/p>\n
Chris – And is that the same reason that people say that different oils from different geographies often have different, I don’t want to use the word flavours, but characteristics? We talk about them being sweet and light or heavy. Is that why? Is that a reflection on the geology and the processes that have occurred during the formation of that hydrocarbon deposit?<\/p>\n
Jonathan – Yes, exactly. It’s the two things. So it could be related to the type of source rock originally. So, for instance, some oils are heavy, some oils are light. The light oils, we call them sweet oils because they’re very easy to refine, and other oils, we call them heavy or sour. And also another thing with oils as well, sometimes they’re associated with sulphur as well. Not a huge amount, typically a few per cent of sulphur, but that sulphur would have to be removed. So that’s not so good for the refining, and that also reflects the geology where the source rock was.<\/p>\n","protected":false},"excerpt":{"rendered":"The price of fuel has risen sharply in recent months, by as much as 50% in some parts…\n","protected":false},"author":2,"featured_media":607802,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[64,63,294665,11053,10588,19136,128,295659,295658],"class_list":{"0":"post-607801","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-science","8":"tag-au","9":"tag-australia","10":"tag-formation","11":"tag-gas","12":"tag-geology","13":"tag-oil","14":"tag-science","15":"tag-sedimentary-rock","16":"tag-source-rock"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/posts\/607801","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/comments?post=607801"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/posts\/607801\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/media\/607802"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/media?parent=607801"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/categories?post=607801"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/tags?post=607801"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}