BAKER HUGHES - Drilling Fluids Reference Manual

HYDRAULICS
where:
V p
= -----------
90L s
t
L s = stand length, ft
t = time from slips to slips, sec
2. Measurement of the time required for the middle joint of a three-joint stand to pass through the
rotary table divided into the joint length.
where:
V p
=
Flow Regime
60L
---------- j
t
L j = joint length, ft
t = time through rotary table, sec
The possibility of turbulent flow in the annulus must be considered in surge and swab calculations.
The equivalent fluid velocity may be compared to the critical flow rate for the annular section of
interest previously calculated if the fluid properties or pipe diameters have not changed. If changes
have occurred, calculate a new critical flow rate by following the steps outlined earlier.
Surge or Swab Pressure
The appropriate Fanning Friction Factor for annular flow and Friction-Loss Pressure Gradient are
used to obtain the surge or swab pressure loss in each interval.
Equivalent Fluid Weight
In order to be meaningful, the surge or swab pressure and resulting equivalent fluid weight must be
compared to some fracture gradient or pore pressure. The pressure drops in each annular interval
are summed together, very similar to the steps used to obtain the Equivalent Circulating Density.
When running pipe in the hole, the equivalent fluid weight due to the surge pressure is:
EMW =ρ +
∑ P
( 0.052)( TVD)
a
When pulling pipe out of the hole, the equivalent fluid weight due to the swab pressure is,
EMW =ρ −
∑ P
( 0.052)( TVD)
a
where:
EMW = equivalent fluid weight, lb m /gal
ρ = fluid density, lb m /gal
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 9-22