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As a former exploration geologist on the petroleum side and marine geophysicist on the academic side - No, this data isn't very useful for petroleum exploration

by jofer 9y ago

As a former exploration geologist on the petroleum side and marine geophysicist on the academic side - No, this data isn't very useful for petroleum exploration at all. Most of the deep ocean basins have absolutely zero oil. To create thermogenic hydrocarbons, you need thick sediments. You can make methane biogenically without significant sediment cover, and that's important sometimes, but you cannot make oil that way. Oil is what drives exploration far away from population centers. The abyssal plain you're seeing in that data is mostly exposed oceanic crust. There's almost no sediment cover. No sediments --> no exploration potential. There's one narrow continental fragment that could have significant sediment cover. However, it's highly unlikely that that's prospective. (If you're curious, I'm happy to elaborate, but it will take a bit of explanation.) There is one way this data will be used for petroleum exploration. It aids our understanding of the tectonic evolution of the area, which in turn aids petroleum exploration. However, if you're going to take a moral stance against that, you also need to a moral stance against every scientific advance in every field. They all aid the oil industry indirectly. (Ditto for software.)

stochastician 9y ago
Yes please elaborate, this is fascinating! Can you recommend any good undergraduate textbooks on the subject, especially for someone with a quantitative background (PhD in ML-adjacent field)?
- jofer 9y ago
  If you're interested specifically in the petroleum side, I've heard "Introduction to Petroleum Exploration for Non-geologists" by Robert Stonely is good. There are probably more up-to-date books out there, though. For the more general geology portion, if you're wanting something that's a bit more detailed, but still very approachable, "Evolution of the Earth" by Prothero and Dott is absolutely fantastic. You can probably find a slightly older paperback edition quite cheaply, as well. If you're really okay with a quantitative approach, Turcotte & Schubert's "Geodynamics" walks through an impressive amount of basic tectonics in a "let's do the back of the envelope calculations" manner. It's the most dog-eared book on my shelf. It's incredibly useful. However, it's a graduate level textbook, and it assumes you have at least a basic understanding of geological processes and terminology. It would be a very tough way to dive in.
mikeash 9y ago
Great comment, thanks for the information. I suspected that the deep ocean wouldn't be good for oil, but only because it would be logistically difficult. Why isn't there sediment cover in these areas? I would naively think that you'd get some raining down as plants and animals die in the shallower depths. Clearly that must not be the case, but why not?
- jofer 9y ago
  In a nutshell, you're a long way from a sediment source. Most sediments by volume come from erosion of the continents or other landmasses. There's a much higher rate of deposition if you're near a continent (e.g. river deltas). Additionally, oceanic crust is always very young geologically. It's continually formed and destroyed (subducted). The ocean basins haven't had much time to fill up with sediment, because oceanic crust is essentially a conveyor belt. ----- So the short answer is: You're depositing things very slowly on something that doesn't have much time for sediments to build up. ----- In a bit more detail, the sediments you get in the middle of the ocean are either the initial volcanic-related sediments that were deposited as the oceanic crust formed, or they're limited to "pelagic rain" (things near the surface dying and very fine particles of clay) and some chemical sediments (things that precipitate directly out of water). Not only that, but a lot of the things that die and sink will dissolve below about 2 Km water depth (see Carbonate Compensation Depth). Therefore, deepwater depositional rates are very, very slow. There's a very important exception, though -- Carbonates. If you start in shallow water (say, due to a small sliver of continental crust), organisms in the photosynthetic zone can produce huge amounts of carbonate sediments just from their shells (e.g. coral reefs). Under the right conditions, carbonates can keep growing and keep pace with the subsiding crust. A good example of this is the Bahamas. You have several kilometers of sediment made of nothing but what grew there and died. There are some very significant oil fields in these sorts of "isolated platforms". However, you need fairly unique conditions to get oil in the sort of isolate carbonate platforms that develop far away from land. In most cases you'd find out in the ocean basins, you won't have a source rock capable of generating hydrocarbons beneath the pile of sediments that the carbonates produce. Instead, the source rock is conveniently sitting out there in the deep water where it's not buried deep enough to produce oil. There's one other exception, and that's when you're near a volcano. Volcanoes will happily produce lots of volcanic-related sediments. However, volcaniclastic sediments almost never make good reservoirs (there are exceptions) or seals, so even if you did generate oil in a narrow band around a seamount, it would either leak out (no seal) or be trapped in something that you can't get it out of (bad reservoir). And there's the longer answer :)

by jofer 9y ago

stochastician 9y ago

Yes please elaborate, this is fascinating! Can you recommend any good undergraduate textbooks on the subject, especially for someone with a quantitative background (PhD in ML-adjacent field)?

jofer 9y ago
If you're interested specifically in the petroleum side, I've heard "Introduction to Petroleum Exploration for Non-geologists" by Robert Stonely is good. There are probably more up-to-date books out there, though. For the more general geology portion, if you're wanting something that's a bit more detailed, but still very approachable, "Evolution of the Earth" by Prothero and Dott is absolutely fantastic. You can probably find a slightly older paperback edition quite cheaply, as well. If you're really okay with a quantitative approach, Turcotte & Schubert's "Geodynamics" walks through an impressive amount of basic tectonics in a "let's do the back of the envelope calculations" manner. It's the most dog-eared book on my shelf. It's incredibly useful. However, it's a graduate level textbook, and it assumes you have at least a basic understanding of geological processes and terminology. It would be a very tough way to dive in.

mikeash 9y ago

Great comment, thanks for the information. I suspected that the deep ocean wouldn't be good for oil, but only because it would be logistically difficult. Why isn't there sediment cover in these areas? I would naively think that you'd get some raining down as plants and animals die in the shallower depths. Clearly that must not be the case, but why not?

jofer 9y ago
In a nutshell, you're a long way from a sediment source. Most sediments by volume come from erosion of the continents or other landmasses. There's a much higher rate of deposition if you're near a continent (e.g. river deltas). Additionally, oceanic crust is always very young geologically. It's continually formed and destroyed (subducted). The ocean basins haven't had much time to fill up with sediment, because oceanic crust is essentially a conveyor belt. ----- So the short answer is: You're depositing things very slowly on something that doesn't have much time for sediments to build up. ----- In a bit more detail, the sediments you get in the middle of the ocean are either the initial volcanic-related sediments that were deposited as the oceanic crust formed, or they're limited to "pelagic rain" (things near the surface dying and very fine particles of clay) and some chemical sediments (things that precipitate directly out of water). Not only that, but a lot of the things that die and sink will dissolve below about 2 Km water depth (see Carbonate Compensation Depth). Therefore, deepwater depositional rates are very, very slow. There's a very important exception, though -- Carbonates. If you start in shallow water (say, due to a small sliver of continental crust), organisms in the photosynthetic zone can produce huge amounts of carbonate sediments just from their shells (e.g. coral reefs). Under the right conditions, carbonates can keep growing and keep pace with the subsiding crust. A good example of this is the Bahamas. You have several kilometers of sediment made of nothing but what grew there and died. There are some very significant oil fields in these sorts of "isolated platforms". However, you need fairly unique conditions to get oil in the sort of isolate carbonate platforms that develop far away from land. In most cases you'd find out in the ocean basins, you won't have a source rock capable of generating hydrocarbons beneath the pile of sediments that the carbonates produce. Instead, the source rock is conveniently sitting out there in the deep water where it's not buried deep enough to produce oil. There's one other exception, and that's when you're near a volcano. Volcanoes will happily produce lots of volcanic-related sediments. However, volcaniclastic sediments almost never make good reservoirs (there are exceptions) or seals, so even if you did generate oil in a narrow band around a seamount, it would either leak out (no seal) or be trapped in something that you can't get it out of (bad reservoir). And there's the longer answer :)