BAKER HUGHES - Drilling Fluids Reference Manual

HYDRAULICS
ρ = fluid density, lb m /gal
D = inside diameter of pipe, in.
Friction-loss gradient in annulus:
P
P a = ------ a
× A n nu l a r L e n g t h
L m
where:
P a
------
L m
=
2
( f a ) ( V a) ( ρ)
-------------------------------------
25.81( D 2 – D 1 )
P a
------ = pressure loss per measured depth, psi / ft
L m
and,
f a = friction factor (laminar, transitional, or turbulent)
V a = bulk velocity in annulus, ft/sec
ρ = fluid density, lb m /gal
D 2 = hole diameter, in.
D 1 = outside pipe diameter, in.
Equivalent Circulating Density
The pressure required to overcome the total friction losses in the annulus, when added to the
hydrostatic pressure of the fluid, gives the Equivalent Circulating Density (ECD) as follows.
where:
ECD
=
ΣP
-------------------------------- a
+ ρ
(.052)( TVD)
ECD = equivalent circulating density, lb m /gal
ΣP a = sum of the friction loss in all annular intervals, psi
TVD = true vertical depth, ft
ρ = fluid density, lb m /gal
Note: Temperature and pressure affect both the density of fluids and their rheological properties,
both of which affect the ECD.
BIT HYDRAULICS
Conventional bits incorporate a number of nozzles through which the drilling fluid is forced at high
velocity. This fluid velocity results in hydraulic forces that affect penetration rate, bit cleaning, and
other parameters. While it is desirable to have most, if not all, of these parameters at an optimum
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 9-16