1. Upstream

1.1 The origins of natural gas

On our planet, a multitude of organisms, belonging to the animal and plant kingdoms, are constantly living and dying, composed mainly of carbon, hydrogen, nitrogen and oxygen. They make up the biomass. When they die, a small part of this biomass is included in the global process of sedimentation of the mineral layers affecting the earth's surface. This slow, permanent process, which accumulates sediment at the bottom of oceans and lakes after erosion, transport and deposition, may have little effect on the scale of a human lifetime, but it is of vital importance on the scale of "geological" time: a few million to a few billion years.

All sediments formed, while mineral in appearance, contain a fraction of organic matter, averaging...