Hydrostatic Pressure
Also known as Hydrostatic Head, Hydrostatic Pressure is defined as vertical pressure exerted by the weight of fluid. While planning a well, specific gravity of the drilling fluid (mud) is selected to ensure that the hydrostatic pressure exerted by the column of mud is more than pore pressure at any point in the well. This acts as a primary barrier for well control by ensuring that the formation fluid is held back from flowing into the well at any point of the time.