Changes

==Predicting leakage in shallow accumulations==

==Predicting leakage in shallow accumulations==

Hydrofractured seals also leak in shallow accumulations of normal water pressure. At depths < 1000 ft, the absolute magnitude of the difference between water pressure and geostatic pressure is relatively small—on the order of several hundred pounds per square inch. Exceptionally thick (1000–2000 ft) columns of gas or oil have a capillary pressure equal to or greater than this difference, so hydrofracturing may occur.

Hydrofractured seals also leak in shallow accumulations of normal water pressure. At depths < 1000 ft, the absolute magnitude of the difference between water pressure and geostatic pressure is relatively small—on the order of several hundred pounds per square inch. Exceptionally thick (1000–2000 ft) columns of gas or oil have a [[capillary pressure]] equal to or greater than this difference, so hydrofracturing may occur.

The potential for shallow hydrofractured leakage is best evaluated from a pressure-depth diagram, where

The potential for shallow hydrofractured leakage is best evaluated from a pressure-depth diagram, where

* Water pressure gradient is estimated from water salinity.

* Water pressure gradient is estimated from water salinity.

* Geostatic pressure gradient is estimated from density logs or [[porosity]] trend.

* Geostatic pressure gradient is estimated from [[Basic_open_hole_tools#Density|density logs]] or [[porosity]] trend.

* Petroleum density is estimated from the gas-oil ratio (GOR), API gravity, temperature, and pressure.

* Petroleum density is estimated from the gas-oil ratio (GOR), API gravity, temperature, and pressure.