From Phytoplankton to Jet FuelAs you may know, petroleum forms from dead plants and animals which we

From Phytoplankton to Jet FuelAs you may know, petroleum forms from dead plants and animals which were buried millions of years ago under water. What most of us don’t know is exactly how and why this process works.Petroleum formation is actually a lot like cooking. You start with the ingredients, turn up the heat and set the timer. The basic required elements are: organic matter (ingredients), a source rock (oven) and time. Firstly an oil- or gas-prone source rock must be formed; this is our oven. Under normal marine conditions, where the organisms which die are scavenged, very little organic matter remains to be buried on the sea floor and therefore little to turn into petroleum. So where do the ingredients come from? There are two main ways to disrupt this cycle: (1) periods of high biological activity at the surface such as an algal bloom, and (2) the development of anoxic (oxygen poor) conditions at depth which greatly reduce the number of scavengers. Once the organic matter is actually buried, we’ve got our ingredients.As the organic matter is buried under more and more layers of sediment, the temperature and pressure increase. The pressure increase is due to the weight of the overlying sediment whilst the temperature naturally increases with depth below the surface of the Earth; this is known as the geothermal gradient. After the first kilometer or so, the organic matter changes into kerogen. Kerogen is the most abundant organic component on Earth and can be used to describe the collection of complex organic compounds depended on the original source organism.  These increases in temperature and pressure continue, ‘cooking’ the kerogen. At a depth of around 3-4km/100°C, the chemical bonds in the kerogen begin to break in a process known as catagenesis. Here the kerogen is within the ‘oil window’; the conditions where kerogen is converted to oil. With further depth the temperature will increase moving the kerogen into the ‘gas window’, where it is instead converted to methane a.k.a. natural gas. Whether the kerogen will produce oil or gas is dependent on several factors principally kerogen type and depth of burial. It’s just like cooking; you get out what you put in, it’s all about how you cook it, and all good things come to those who wait.-LOPhoto courtesy of Ian West, University of Southampton -- source link

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