Pressure Loss

Published: August 23, 2021 | Last updated: July 5, 2023

What Does Pressure Loss Mean?

Pressure loss, in the context of turbulent flow in pipes, is the loss of pressure caused by friction, elevation or change in kinetic energy. The Bingham plastic model is used to estimate pressure loss in a turbulent flow.

Drilling fluid has three possible flow regimes: plug flow, laminar flow or turbulent flow. The flow regimes change in the transition phase between these flows:

  • Plug flow happens at a low shear rate in the gel stage.
  • Laminar flow occurs at low flow velocity.
  • Turbulent flow is subject to fluctuations that happen in the direction of flow and velocity.

Trenchlesspedia Explains Pressure Loss

Pressure loss acting in the opposite direction of fluid flow is frictional pressure. The mud pump creates the necessary power to move the drilling fluid from one point to the other and the frictional pressure is the amount of pressure required to transfer the fluid. If the pump pressure is 1,000 psi at the starting point and 0 psi at the end point, it means that 1,000 psi pressure is required to overcome the frictional pressure to move the fluid between the two points. This pressure difference created while moving the fluid between the two points is called the pressure loss.

For turbulent flow, the Reynolds number should be above 4,000, meaning the flow velocity is critical. To calculate the pressure drop, the following equation can be used:

Δp = λ x (L/D) x (ρ / 2) x ϖ2


Δp is pressure loss or drop (Pa or kg/m-s2)

λ is the pipe friction coefficient

L is the length of the pipe (m)

D is the pipe diameter (m)

ρ is the density of the fluid (kg/m3)

ϖ is the flow velocity (m/s)


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