User:Fredwiegand/Pore pressure gradient

Pore pressure gradient is a dimensional petrophysical term used by drilling engineers during the design of drilling programs for drilling ( constructing ) oil and gas wells into the earth. It is the pressure gradient inside the pore space of the rock column from the surface of the ground down to Total Depth ( TD ).

Whereas in "pure math", the gradient of a scalar function expressed by the math notation grad(f) may not have physical units associated with it; in drilling engineering the pore pressure gradient is usually expressed in API-type International Association of Drilling Contractor (IADC ) physical units of measurement, namely "psi per foot".

In the well-known formula

p = .052 * Mud Weight * Total Vertical Depth

taught in almost all petroleum engineering courses world wide, the Mud Weight ( MW) is expressed in US pounds per US gallons, and the Total Vertical Depth is expressed in American feet ( of 12 American inches per foot, and .052 is a conversion constant that can be derived by dimensional analysis later.

Therefore, for fresh water of 8.33 pounds per gallon ( ppg ) standing still hydrostatically in a 41,000 foot vertical wellbore ( vertical hole ), the pressure gradient would be

grad (pore pres) = pore pressure gradient = .052 * 8.33 = 0.43316 psi/ ft

and the hydrostatic Bottom Hole Pressure ( BHP ) is then

BHP = grad pore pres * TVD = 0.43316 * 41,000 = 17,759.56 psi

These are the most important and basic math calcuations in almost all Well Control courses taught world wide, for the prevention of oil and gas well blowouts.