Pressure is defined as the force acting on a unit area. In the oil field, pressure is commonly measured in pounds per square inch (psi).
At the wellsite, we are typically concerned with the pressures throughout the circulating system. We may need to know the pressure at a particular point in the wellbore (such as the casing shoe or a lost circulation zone) or we may want to know the total pressure required to pump a certain mud volume at a given rate. Various types of pressures exist due to different mechanisms, and are classified as either hydrostatic, hydraulic, or imposed. All of these pressures result in a force acting on a unit area, even though their origins may differ.
Note: The pressure at any given point in the circulating system is the sum of the hydrostatic, hydraulic, and imposed pressures which exist at that point.
