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In an example with a 400 m deep piezometer, with an elevation of 1000 m, and a depth to water of 100 m: z = 600 m, ψ = 300 m, and h = 900 m. The pressure head can be expressed as: = = where is the gauge pressure (Force per unit area, often Pa or psi),
Well X has a measured depth of 9,800 ft and a true vertical depth of 9,800 ft while well Y has measured depth of 10,380 ft while its true vertical depth is 9,800 ft. To calculate the hydrostatic pressure of the bottom hole, the true vertical depth is used because gravity acts (pulls) vertically down the hole.
Using the figures above, we can calculate the maximum pressure at various depths in an offshore oil well. Saltwater is 0.444 psi/ft (2.5% higher than fresh water but this not general and depends on salt concentration in water) Pore pressure in the rock could be as high as 1.0 psi/ft of depth (19.25 lb/gal)
Pressure head is a component of hydraulic head, in which it is combined with elevation head. When considering dynamic (flowing) systems, there is a third term needed: velocity head. Thus, the three terms of velocity head, elevation head, and pressure head appear in the head equation derived from the Bernoulli equation for incompressible fluids:
The outside water pressure increases with depth and so the stresses on the hull also increase with depth. Each 10 metres (33 ft) of depth puts another atmosphere (1 bar, 14.7 psi, 101 kPa) of pressure on the hull, so at 300 metres (1,000 ft), the hull is withstanding thirty standard atmospheres (30 bar; 440 psi; 3,000 kPa) of water pressure.
The formula simply divides the absolute partial pressure of oxygen which can be tolerated (expressed in atm or bar) by the fraction of oxygen in the breathing gas, to calculate the absolute pressure at which the mix can be breathed. (for example, 50% nitrox can be breathed at twice the pressure of 100% oxygen, so divide by 0.5, etc.).
The pressure a liquid exerts against the sides and bottom of a container depends on the density and the depth of the liquid. If atmospheric pressure is neglected, liquid pressure against the bottom is twice as great at twice the depth; at three times the depth, the liquid pressure is threefold; etc.
The pressure of seawater at a depth of 33 feet equals one atmosphere. The absolute pressure at 33 feet depth in sea water is the sum of atmospheric and hydrostatic pressure for that depth, and is 66 fsw, or two atmospheres absolute. For every additional 33 feet of depth, another atmosphere of pressure accumulates. [6]