Computing for hydrostatic pressure

Fluid statics plays a vital role in the practice of petroleum engineering. Oil, essentially a fluid, is still governed by the laws that generally affect fluids. Thus, even at the state of rest, petroleum engineers must be able to understand the principles that underlie its movement, or lack thereof. One of the most important concepts in fluid statics that all engineers must master is “hydrostatic pressure.”

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According to Gas Volume Requirements for Underbalanced Drilling: Deviated Holes by Ali Ghalambor, hydrostatic pressure is “the pressure of the weight of fluid.” In other words, it is the pressure exerted by a liquid at an equilibrium state due to gravitational force. Its value is considered to be directly proportional to the height of a liquid column of uniform density.

A liquid’s hydrostatic property remains variable because it is heavily influenced by two factors: local gravity and the liquid’s density. The interplay of these quantities results to a particular liquid’s hydrostatic pressure.

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In SI units, the hydrostatic pressure of a liquid column may be calculated as follows:

Height (in meters) x Density (in kg/m3) x Local Gravity (in m/s2) = Hydrostatic pressure (usually expressed in N/m2 or Pascal) 

Hydrostatic pressure, while hardly ever completely accurate, is a very expedient way to relate pressure to a height of liquid. Its practical uses in petroleum engineering include the “hydrostatic test,” a way to determine strengths and leaks in pressure vessels such as pipelines and fuel tanks.

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