Drilling EngineeringDrilling Hydraulics
Equivalent Circulating Density Formula
Equivalent circulating density converts annular pressure loss into an effective mud-weight value at depth during circulation.
How engineers use this formula
Use it to compare circulating bottomhole pressure against pore-pressure and fracture-gradient limits while drilling.
Assumptions
- Annular pressure loss is known for the circulating rate and well geometry.
- The field-unit conversion uses psi, ft, and ppg.
- Depth is true vertical depth.
Limitations
- Does not calculate annular pressure loss from rheology or geometry.
- Does not model transient surge, swab, cuttings loading, or temperature effects.
Common mistakes
- Using standpipe pressure instead of annular pressure loss.
- Using measured depth instead of true vertical depth.
- Ignoring ECD margin at weak formations or casing shoes.
Default example
Using the default inputs, ECD equals 10.961538 ppg.
MWppg
10
dP_apsi
500
TVDft
10000
Inputs
MW
ppgMud Weight
dP_a
psiAnnulus Pressure Loss
TVD
ftTrue Vertical Depth
Outputs
ECD
ppg
Equivalent Circulating Density
MW
ppg
Mud Weight
dP_a
psi
Annulus Pressure Loss
TVD
ft
True Vertical Depth
Source and review
reviewedRobello, S.E. 2015. 501 Solved Problems and Calculations for Drilling Operations, Page 258.
Source