The Origins of Petroleum
A Look at the Inorganic Abiotic and Organic Fossil Fuels Theories
The debate over oil’s origin has been going on since the 19th century. With advances in geophysics and geochemistry in the mid 20th century, the vast majority of scientists lined up on the side of the organic (biotic) fossil fuels theory. However, a small group of mostly Russian scientists—but including a tiny handful of Western scientists, held the view for an inorganic (abiotic) origin of petroleum.
Fossil Fuels Theory
In 1757, Mikhail Lomonossov originated an organic theory based on fossils that later became known as the “Rock Oil” theory. Points of interest are:
- Fuel originates from bodies of animals and ancient forest material buried in the sediments
- Material lays under the influence of increased temperature and pressure acting during an unimaginably long period of time
- Finally, fossil material under these conditions is transformed into “rock oil”
More recent arguments point to living organisms as small as plankton may have been the origin of the fossil fuel.
According to Wikipedia, the Peak Oil hypothesis was proposed by Hubbert in 1956. It follows on from the organic theory, which inherently implies:
- Reserves lie at relatively low depths and are finite in extent
- Reserves will be used up at the current rate of extraction
Hubbert argued that oil wells produce according to the shape of a bell curve. Once their production “peak” is hit, inevitable decline follows (Fig. 2). He predicted that the United States oil production would peak in 1970.
Abiotic Theory
Abiotic theory aims to establish the provenance of modern petroleum science and is based on fundamentals of physics, particularly thermodynamics, and chemistry.
High pressure and temperature experiments confirmed the theory when a “suite” of petroleum fluids (methane, ethane, propane, etc.) was observed to evolve from inorganic constituents. These experimental conditions correspond to oil genesis occurring at 100 km or greater beneath the earth.
Proponents of the abiotic theory argue that hydrocarbons are naturally produced on a continual basis throughout the solar system, including deep within the mantle of the earth. Some main points are:
- Methane is a common molecule found in huge concentrations and at great depth in the Earth
- At the mantle-crust interface, located between 7km to 30km, rising methane-based gasses hit pockets of high temperature causing condensation of heavier hydrocarbons, giving rise to crude oil formation
- In the relatively cooler and more geologically stable regions around the globe, crude oil pools into reservoirs (Fig 1)
Observations have been made around the globe of several oil reservoirs refilling themselves. For example, the Eugene Island reservoir is filling from the bottom up and not from the sides as may have been expected.
Duplex Theory
In a Nature article (No. 199, pp113-4, 1966), Sir Robert Robinson argued that both petroleum origin theories, organic and inorganic, are correct and that petroleum has a duplex origin.
Conclusions
The established fossil fuels theory is a finite theory of relatively shallow reserves, leading to scarcity as expounded by the peak oil hypothesis. On the other hand, abiotic theory is a theory of plenty - relatively deep reserves require that oil be searched according to this new paradigm.
The abiotic theory is not yet widely accepted and has been criticised as deficient. For example Geoffrey P. Glasby ("Abiogenic Origin of Hydrocarbons: An Historical Perspective", Resource Geology, vol. 56, no. 1, 85-98, 2006) put forward a range of objections - from the mechanistic model to its practical method of application. On the other hand, scientists from the abiotic camp vehemently reject the fossil fuels theory of petroleum.
