Gas reservoirs in craton basins have experienced multicyclic tectonic movement during the long geologic history

resulting in varied diagenetic environments

complex diagenesis and long-term superimposition.Their pores have experienced several cycles of evolution and the present porosities of reservoirs are low.According to the structural location

trap type and reservoir nature

the gas reservoirs can be further subdivided into three types

including palaeohigh structural gas reservoirs

anticlinal gas reservoirs

and lithologic gas reservoirs.Their diagenetic sequences and pore evolutions are somewhat different.Gas reservoirs in the thrust belt and slope zone of foreland basin are characterized by their relatively short geologic histories

relatively less tectonic cycles

relatively rapid burial and relatively simple diagenetic sequence and pore evolution

so the present porosities are relatively small.While gas reservoirs in rift basin are characterized by their short geologic histories

less tectonic(cycles)

rapid burial and simple diagenetic sequence and pore evolution

so the reservoirs have relatively large(porosities.)