Natural gas has multi-origin compared with oil

which can be expressed as multiple genetic types

multiple gas genetic models and multiple occurrences of gas-generating material.Multiple genetic types include organic origin and inorganic origin

single origin and multiple origins

as well as the multistage and continuous gas-generating and evolutional processes from organic matter.Multiple gas genetic models

including mainly various gas-generating mechanisms(such as biochemistry

decarboxylation

polycondensation

pyrolysis

cracking

mechanical chemistry

catalysis and hydrogenation

as well as other chemical reactions) would play different roles in different stages of gas generation

due to the differences in source rock's kerogen and physico-chemical conditions.Multiple occurrences of gas-generating material include the dispersed and accumulative

dissoluble and insoluble organic matters

as well as the water-soluble organic matters that can be used by organisms

CO

2

and the previously formed organic matter.In superimposed basins

accompanying the resubsidence and resedimentation

the better catalytic condition of dispersed and dissoluble organic matter or asphaltene would lower the activation energy for cracking which would be favorable for cracking of kerogen into gaseous hydrocarbons.