Petroleum Engineering Equations & Formulas

Fluid Pressure

Assuming a normal pressure regime, at a given depth below ground level, a certain pressure must exist which just balances the overburden pressure (OBP) due to the weight of rock (which forms a matrix) and fluid (which fills the matrix) overlying this point. The overburden pressure is in fact balanced by a combination of the fluid pressure in the pore space (FP) and the sress between the rock grains of the matrix (σg).

Formula:

       OBP = FP + σg

Where:

σg: is the stress between the rock grains of the matrix

FP: is the fluid pressure in the pore space.



$$OBP = FP + \sigma_{g}$$

Where:

• $\sigma_{g}$  is the stress between the rock grains of the matrix.
• $FP$ is the fluid pressure in the pore space.