SPWLA Glossary

An expression which has been used commonly to refer to low pressure found in some formations, subnormal pressure. Technically, it should be said that underpressure is that amount of pressure by which normal pore pressure exceeds the pore pressure of an underpressured formation. Pore pressure lower than normal pore pressure can occur in a bed of interest when the water solution filling the pores of the body are in communication with an outcrop at an elevation lower than the water table at the well site. More commonly, underpressure results from prior production from a zone.