A comparison between the Upper Paleozoic gas reservoirs in Ordos Basin and typical deep basin gas reservoirs was carried out through analysis of sandstone and shale compaction

pore evolution

pressure forming mechanism

gas and water distribution

gas migration and accumulation

pooling characteristics

as well as previous research results.These two kinds of gas reservoirs show some similarities in terms of basic pooling conditions and certain manifestations.However

dynamic data from gas development indicate that the Upper Paleozoic gas reservoirs are characterized by poor connectivity of gas layers

multiple pressure systems

no extensive inversion of gas-water contact

the existence of local edge water

and the control of structure location and favorable reservoir facies belts on gas-water distribution.A research on process

key conditions

and mechanisms of hydrocarbon pooling suggests that the Upper Paleozoic gas reservoirs belong to lithologic or structural-lithologic gas reservoirs featuring in near-source migration

accumulation

and pooling.It is therefore concluded that the Upper Paleozoic gas reservoirs distinguish themselves from deep basin gas reservoirs by poor connectivity of reservoirs and control of lithology and structure on traps.