In Ordos basin

abnormally low and low pressures are common

while high pressure is rare in Upper Paleozoic.Laterally

the Upper Paleozoic in Suligemiao area displays abnormally low and low pressures

while that in Mizhi area dispalys normal and high pressures

and the other areas mainly display normal pressure and low pressure.Vertically

pressure of acquifers basically distribute along the trend line of hydrostatic pressure;while that of gas-bearing acquifers and gas-bearing formations deviate from the trend line of hydrostatic pressure

the latter has larger extent of deviation than the former

and the pressure coefficient decreases with increasing depth.Both the test data of inclusions and the burial-denudation data of the basin indicate that the Upper Paeozoic gas pools with abnormally low pressure in Ordos basin would have been formed in two stages: gas charging and pressurizing from Late Jurassic to Early Cretaceous

and gas-dispersion

temperature lowering and depressurizing stage from the end of Early Cretaceous up to present time.The depressurization of gas pool would have mainly resulted from basin uplift

temperature lowering

gas dispersion and density contrast of gas and water.