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"
