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→Aquathermal effects
====Aquathermal effects====
====Aquathermal effects====
Aquathermal effects also cause overpressure. The temperature increases as sediment is buried, causing an increase in the volume of water. This in turn results in an increase in pressure if the sediment is sealed by an impermeable layer.<ref name=pt03r7>Barker, C., 1972, [http://archives.datapages.com/data/bulletns/1971-73/data/pg/0056/0010/2050/2068.htm Aquathermal pressuring—role of temperature in development of abnormal pressure zones]: AAPG Bulletin, v. 56, n. 10, p. 2068–2071.</ref>. For example, if a shale is totally sealed and there is no dilation to increase the pore volume, and if the geothermal gradient is [[temperature::25°C]] per [[depth::1000 m]], then the pressure increase is about 1.8 psi per ft. This is more than the increase in weight of the overburden. Consequently, this aquathermal pressuring will cause an increase of pressure up to the pressure at which the rocks [[fracture]] ([[:file:pressure-detection_fig2.png|Figure 2]]).
Aquathermal effects also cause overpressure. The temperature increases as sediment is buried, causing an increase in the volume of water. This in turn results in an increase in pressure if the sediment is sealed by an impermeable layer.<ref name=pt03r7>Barker, C., 1972, [http://archives.datapages.com/data/bulletns/1971-73/data/pg/0056/0010/2050/2068.htm Aquathermal pressuring—role of temperature in development of abnormal pressure zones]: AAPG Bulletin, v. 56, n. 10, p. 2068–2071.</ref>. For example, if a shale is totally sealed and there is no dilation to increase the pore volume, and if the [[geothermal gradient]] is [[temperature::25°C]] per [[depth::1000 m]], then the pressure increase is about 1.8 psi per ft. This is more than the increase in weight of the overburden. Consequently, this aquathermal pressuring will cause an increase of pressure up to the pressure at which the rocks [[fracture]] ([[:file:pressure-detection_fig2.png|Figure 2]]).
Pressure data from some U.S. Gulf coast wells suggest that the aquathermal effect is important.
Pressure data from some U.S. Gulf coast wells suggest that the aquathermal effect is important.