Counting on … day 70

20th March 2024

The geological history of oil and gas. 

“The formation of oil takes a significant amount of time with oil beginning to form millions of years ago. 70% of oil deposits existing today were formed in the Mesozoic age (252 to 66 million years ago), 20% were formed in the Cenozoic age (65 million years ago), and only 10% were formed in the Paleozoic age (541 to 252 million years ago). This is likely because the Mesozoic age was marked by a tropical climate, with large amounts of plankton in the ocean.

“The formation of oil begins in warm, shallow oceans that were present on the Earth millions of years ago. In these oceans, extremely small dead organic matter – classified as plankton – falls to the floor of the ocean. This plankton consists of animals, called zooplankton, or plants, called phytoplankton. This material then lands on the ocean floor and mixes with inorganic material that enters the ocean by rivers. It is this sediment on the ocean floor that then forms oil over many years”.

1. The dead plankton, plus algae and bacteria form an organic rich mud.
2. If the mud remains in an anoxic environment  – lacking in oxygen such as stagnant water – it does not decompose and so retains its carbon content. 
3. This anoxic environment becomes embedded by subsequent layers of mud, compressing the carbon rich  layer into an organic shale. 
4. Overtime the shale sinks as more layers are added. At a depth of 2 to 4km the temperatures from the earth’s core plus the increased pressure converts the organic shale to oil shale.
5. If the temperatures at this depth are between 90 and 160C this oil shale is transformed into oil and natural gas. This will either seep upwards being lighter than water, or maybe sealed in by subsequent layers of impervious rock.

(https://energyeducation.ca/encyclopedia/Oil_formation)

Again it is mind blowing to reflect that these oil and gas deposits that took millions of years in the making, are now being burnt at an annual rate of 6.6 billion tonnes, such that we have 47 years of reserves remaining – should we be foolish enough to want to burn them.(https://www.worldometers.info/oil/) 

We should keep in mind that the IEA warns that a cannot risk developing and burning new oil and gas reserves without exceeding the 1.5C global warming limit.