BAKER HUGHES - Drilling Fluids Reference Manual

Hydraulics
Figure 1-18
SEM Photomicrograph - Sized Salt System
Return Permeability vs. Breakout Pressure
The following example shows that fluids with similar leak off or fluid loss characteristics can exhibit
extremely different return permeabilities and net breakout pressures. This example relates the
importance of complete system analysis before utilization and possible reservoir impairment.
Return Permeability is a measure of that permeability that can be re-established after a core has been
damaged by the flowing of a fluid through it and then being reversed out. Net Breakout Pressure is
the maximum pressure required to initiate flow after mudoff. Mudoff is defined as the condition
where a mud filter cake has been deposited on the face of and a short distance into the formation.
Figure 1-19 describes the relationship that exists between return permeability and net breakout
pressure. Note that the lower the net breakout pressure, the higher the percent return permeability
value. This is indicative of a minimum of formation damage having occurred from the invasion of
mud solids.
100
80
60
40
20
% Return Permeability
Specification :
Net Breakout Pressure = < 8 psi
Net Breakout Pressure, psi
0
0 10 20 30 40 50 60 70 80 90 100
Figure 1-19
A Plot of Net Breakout Pressure vs. Return Permeability
Reference Manual
Baker Hughes Drilling Fluids
1-42 Revised 2006