Natural gas occur naturally. It's happened by the sedimentation of living things in the rock, soils and sea million years ago , While that time nature has changed cause from thermal and pressure of earth surface. Until the fossil become raw oil , natural gas and coal that we use it, so we called them as fossil fuel. In scientific , we usually knew that plant,animal,human contains of many small cells. Those cells contains mostly of hydrogen and carbon . When the fossil getting sedimentation and transform to be a raw oil , natural gas , or coal. That's why they are contains of hydrocarbon mostly, and after you take it to burn. It will give you the same energy as when you burn woods, but the fossil fuel such as natural oil or coal give more heat. Natural gas is a mixture of hydrocarbon and another contaminated things in gas phase. The hydrocarbon which found in the nature such as methane,ethane,propane,butane,pentane ,the others contaminated which found in natural gas are co2,hydrogensulfide,helium,nitrogen,and vapor. The natural gas known as the composition of hydrocarbon because it's the solution which consists of 2 atoms types , they are hydrogen and carbon mixing in the different ratio atom, by starting from hydrocarbon composition that have 1 atom carbon with 4 atoms hydrogen has specific name as methane.Coal is one type of sediment and it's fuel that flammable. Have brown color along to black color , also have both smooth and rough surface , light weight. Coals are contains of 4 important elements are carbon,hydrogen ,nitrogen and oxygen. Beyond that are a little contaminated of sulfur. The coal which have high ount of carbon and low of others elements, when you get it burn. It will give you a heat much more than other. Its will count as high quality coals. Carbon dioxide injection in coal seams is known to improve the methane production of the coal seam, while ensuring a safe and long-term carbon sequestration. This improvement is due to the preferential adsorption of CO2 in coal with respect to CH4: an injection of CO2 thus results in a desorption of CH4. Gas extraction proceeds by desorption from the coal material and by convective transport through a set of small natural fractures (cleats), which are typically spaced by a few centimeters. Most of the permeability of the coal reservoir comes from the cleat network, but the permeability of those cleats strongly depends on the underground stress.