Formation Pressure

Formation pressure is the pressure exerted by the fluids in the pore spaces of a rock formation at a given depth. In many drilling calculations, it is estimated by multiplying the formation pressure gradient by the true vertical depth, because pressure increases roughly in proportion to depth when the gradient is treated as constant. This gives a quick way to estimate subsurface pore pressure for well planning, mud-weight selection, and kick prevention.

Use this when you need a first-pass estimate of pore pressure from a known or assumed gradient at a specific depth. It is common in drilling engineering, well control, and formation evaluation when comparing expected formation pressure to mud hydrostatic pressure.

• Using measured depth instead of true vertical depth when the well is deviated
• Mixing units, such as entering depth in meters while the gradient is in psi/ft
• Forgetting that this is an estimate and not a substitute for measured pressure data in abnormal formations