The main idea of studying the geological properties of natural gas in China is that to start from basin analysis

take thermal effect as fundamental principle

and use the view-point of dynamic equilibrium.Based on the theory of the relationship between basin

ther-mality

hydrocarbon

centered on the formation environment and the resources distribution of natural gas

three kinds of interrelated classification such as thermal

structural and oil-gas resources proportional classfications of the basins were proposed in this paper.Natural gas in China is mainly come from sets of immature sequences

coal-bearing formations

carbonate rook series and lacustrine clastic rooks

and belongs to five genetic types named as biogenic gas

biogenic-thermal catalytic gas

sapropelic gas

humic gas and deep sourced gas.The geological conditions to form big-and medium-size gas fields are:1.certain gas-generating capacity;2.conventional reservoir of considerable thickness;3.late gas-generating stage and pool-forming stage;4.the development of paleo-uplift and paleo-traps;5.favourable regional caprocks;6.faults and unconformities as passage ways forgas migration.There are mainly four gas-bearing domains in China including humic gas

marine carbonate rock gas

lacustrine sapropelic gas and biogas.They are mainly distribut-ed in four major gas provinces which are arranged in the following order:offshore North-west China

Central China and East China oil and gas provinces.The general policy fornatural gas exploration in China is"to explore large-medinm-and small size gas fieldscontemporaneously and to give consideration to long

medium and short terms planning"