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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 56 (1972)

Issue: 10. (October)

First Page: 2068

Last Page: 2071

Title: Aquathermal Pressuring--Role of Temperature in Development of Abnormal-Previous HitPressureNext Hit Zones: GEOLOGICAL NOTES

Author(s): Colin Barker (2)

Abstract:

Zones of abnormal subsurface pressures, both above and below hydrostatic, have been described in many areas. The very abrupt changes in pressures and salinities, together with the undercompacted nature of the high-Previous HitpressureNext Hit zones, indicate that they are effectively isolated from their surroundings. If this isolation occurred at a shallower depth than the present one, the isolated volume would have been subjected to increasing temperatures as it moved downward. The P-T-density diagram for water shows that, for any geothermal gradient greater than about 15°C/km, the Previous HitpressureNext Hit in an isolated volume increases with increasing temperature more rapidly than that in the surrounding fluids. This mechanism for producing excess pressures will operate in addition to most of the ot er processes that have been suggested, but the overall influence in any given area will depend on how well the system remains isolated. If a normally pressured system becomes isolated and is then subjected to a decrease in temperature (for example, if erosion removes considerable quantities of overburden) the Previous HitpressureNext Hit in the system will fall below the external hydrostatic Previous HitpressureTop. This may have happened in some areas which now have abnormally low pressures.

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