Abstract: Reservoir pressure can be divided into normal pressure, abnormal high pressure and abnormal low pressure in terms of the ratio between formation pressure and hydrostatic pressure. These pressure phenomena are analyzed in this paper. Study shows that the pressure in non-confining beds normally belongs to the range of normal pressure; confining zones with invasion of external fluids could give rise to abnormal high pressure; provided that induced fractures occur in confining zones where are affeted by tectonic movement, leading to growth of pore volume, it tends to appear abnormal low pressure herein.

Key words: oil-gas reservoir, pressure factor, abnormal pressure, formation pressure