Definition - What does Geostatic Pressure mean?
Geostatic Pressure is the stress or pressure exerted by the overlying rock or sediments above a depth or formation of interest. It is usually considered to be about 1.0 psi per feet although the value can vary depending on the specific area. Hence this value can be considered for approximations. Geostatic pressure is not related to fluids therefore instead of the word "pressure" in geostatic pressure, the word "stress" is more appropriate. This is why sometimes geostatic pressure is also called geostatic stress.
Geostatic pressure is also known as overburden pressure or overburden stress or lithostatic pressure.
Petropedia explains Geostatic Pressure
Geostatic pressure is commonly referred as overburden pressure. In order to estimate the overburden pressure at any point, it is important to first determine the material density, i.e., the density of rocks and fluids at that point. The equation for estimating the overburden pressure at depth z is given by:
p(z) = density of overlying rock at depth z
g = acceleration due to gravity
po = datum pressureThere are certain assumptions made while deriving the above equation, such as the acceleration due to gravity is considered to be constant at depth z which is why it is kept outside the integral. However, in actual scenario, acceleration due to gravity will not be constant and changes very little when moved deeper into the earth. The reason for keeping “g” outside the integral part is to practice most near surface applications which need the determination of lithostatic pressure.