It is estimated that about 20% of subsurface gas is of biogenic origin.
In a talk at the forthcoming NCS Exploration conference Recent Advances in Exploration Technology at Fornebu, Oslo (May 21-22), Gugliotti Luigi of Vår Energi will enlighten the audience about the principal factors influencing the generation of biogenic gas, like organic matter availability, temperature and heating rate.
The speaker will also introduce what is termed the Biogenic Efficiency Conditions (BEC). The BEC is computed starting from temperature and heating rate maps at selected horizons as output of the 3D temperature and pressure model.
In this talk, the authors will also demonstrate the validity of this approach for the estimation and calibration of biogenic gas discoveries in different sedimentary basins on a regional scale.
Estimated quantities were calibrated with respect to known giant biogenic gas discoveries. The computed volumes of the biogenic gas are comparable with the amount of the biogenic gas discovered in the area.
How Biogenic Gases are Formed
Natural gas, which is produced by methanogenic organisms, is called biogenic gas.
Methanogens are tiny methane producing mechanisms that chemically break down organic matter to produce methane. They are found in marshes, bog, landfills and shallow sediments.
Formation of methane through biogenic process takes place closer to the earth’s surface with the majority of it getting lost in the atmosphere; however, some of them can be trapped underground.
Methanogenic archaea is responsible for all biological forms of methane. As these methanogens live and grow, methane accumulates in their underground habitat.
This biogenic natural gas is composed almost purely of methane and can be found in bodies of fine-grained sediment at depths of 10-300 feet underground.
Methane hydrates are ice-like structures in which molecules of methane are trapped. The chief constituent of methane hydrates is natural gas. They are found either in the ocean floor or in the Arctic permafrost.
Methane that forms the hydrate can be of biogenic origin from the biological activity of sediments in the ocean floor or of thermogenic origin caused by geological activity deep within the earth. Some estimates put the reserves of energy found in methane hydrates exceeding that of all other fossil fuels put together. However, their development and commercial exploitation are still in the nascent stage due to environmental considerations.