What is natural gas?
Natural gas was formed over a hundred million years ago from plant and animal remains. The story actually started a lot earlier – approximately three hundred million years ago – when the Netherlands was a low-lying swampy region close to the equator with an extremely hot and humid tropical climate. It had rich flora and fauna including giant insects, amphibians, and giant trees and ferns. When plants and trees died, they rotted in the swamplands.
This created a thick layer of peat that also preserved the remains of animals. Every so often, seal levels rose and dropped depositing layers of sand or clay on top of the peat. These periods of deposition and peat formation alternated continuously. The pressure exerted on peat layers increased, causing them to ultimately turn into coal and to become hotter. This process caused the release of natural gas. The clay strata initially formed a seal preventing the light natural gas from permeating away. Later, tectonic stresses caused the earth's crust to form cavities where gas then accumulated in pockets sealed by salt domes formed by seawater. Gas fields formed at locations where salt strata sealed in rising natural gas.
Natural gas consists of methane, short-chain hydrocarbons (ethane, propane and butane) and other substances such as carbon dioxide and nitrogen. Natural gas' composition varies from region to region. Groningen natural gas consists of approximately 81.3% methane and 3.5% longer-chained hydrocarbons, e.g. ethane, propane, etc. It also contains approximately 15.2% incombustible gases, primarily nitrogen and a little carbon dioxide. Natural gas from other reserves generally contains other percentages of methane, a higher percentage of hydrocarbons and less nitrogen.