Abnormal pressure:
1.Pressure exceeding or falling below the normal pressure to be expected at a given depth.
Normal pressure increases approximately 0.465 psi per foot of depth (10.5kpa per meter of depth).
Thus, normal pressure at 10,000 feet is 4,650 psi; abnormal pressure at this depth would be higher or lower than 4,650 psi.
See pressure gradient.
2.
A subsurface condition in which the pore pressure of a geologic formation exceeds or is less than the expected, or normal, formation pressure.
When impermeable rocks such as shales are compacted rapidly, their pore fluids cannot always escape and must then support the total overlying rock column, leading to abnormally high formation pressures.
Excess pressure, called overpressure or geopressure, can cause a well to blow out or become uncontrollable during drilling.
Severe underpressure can cause the drillpipe to stick to the underpressured formation.
