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→Height above the free water level
===Height above the free water level===
===Height above the free water level===
[[File:charles-l-vavra-john-g-kaldi-robert-m-sneider_capillary-pressure_5.jpg|thumb|{{figure_number|5}}Effect of capillary pressure (left) on water saturation (right). At any given height above the free water level, water saturations vary widely among rock types (A-E) due to diffferences in capillarity. For example, at 50 ft above free water level, water saturations vary from 18% (rock type A) to 95% (rock type E). A well drilled into an interbedded sequence of these rock types would show multiple oil-water contacts and a highly irregular vertical saturation profile. Note also the wide transition zone in rock type B caused by poor sorting of the pore throats.]]
Having converted the capillary pressure data to the hydrocarbon-brine system of the reservoir and knowing the hydrocarbon and brine densities from laboratory analysis, we can now calculate the amount of hydrocarbon column required (height above the free water level or level where ''P''<sub>c</sub> = 0) to attain a pressure of interest:
Having converted the capillary pressure data to the hydrocarbon-brine system of the reservoir and knowing the hydrocarbon and brine densities from laboratory analysis, we can now calculate the amount of hydrocarbon column required (height above the free water level or level where ''P''<sub>c</sub> = 0) to attain a pressure of interest:
* 0.433 = the gradient of pure water at ambient conditions
* 0.433 = the gradient of pure water at ambient conditions
This information can be used to compare expected fluid saturations of different rock types at given levels in the reservoir (Figure 5). (For information on the application of capillary pressure data to evaluating [[fluid contacts]], see the chapter on [[Fluid contacts]] in Part 6.)
This information can be used to compare expected fluid saturations of different rock types at given levels in the reservoir ([[:File:charles-l-vavra-john-g-kaldi-robert-m-sneider_capillary-pressure_5.jpg|Figure 5]]). (For information on the application of capillary pressure data to evaluating [[fluid contacts]], see [[Fluid contacts]].)
===Evaluating seal capacity===
===Evaluating seal capacity===