# Annular Pressure Loss

on . Posted in Drilling Engineering

Annular pressure loss, abbreviated as AP, is the reduction in pressure that occurs when fluid flows through the annulus, the space between two concentric cylindrical objects, such as the drill string and the wellbore in oil and gas drilling operations.  This pressure loss happens due to friction between the moving fluid and the surfaces of the annulus, as well as the fluid's viscosity and flow rate.

### Annular Pressure Loss formula

$$AP \;=\; [ \;( 1.4327 \; 10^{-7} ) \; MW \; l \; AV^2 \;] \;/\; D_h - D_{pod}$$     (English)

$$AP \;=\; [ \;( 7.39 \; 10^{-6} ) \; MW \; l \; AV^2 \;] \;/\; D_h - D_{pod}$$     (Metric)

Symbol English Metric
$$AP$$ = annular pressure loss $$lbf \;/\; in^2$$ $$kPa$$
$$MW$$ = mud weight (ppg) $$lbm \;/\; gal$$ $$kg \;/\; m^3$$
$$l$$ = length of annular $$ft$$ $$m$$
$$AV$$ = annular velocity $$ft \;/\; min$$ $$m \;/\; min$$
$$D_h$$ = drill hole or casing ID $$in$$ $$mm$$
$$D_{pod}$$ = drill pipe of drill collor OD $$in$$ $$mm$$