BAKER HUGHES - Drilling Fluids Reference Manual

Hydraulics
Leak-Off Control Tests
Permeability Plugging Test Apparatus
Spurt and cumulative leak-off into a producing reservoir is a concern because of its effect on
permeability. Altering the chemistry and/or disturbing in-situ particles in a producing zone are the
most common formation damage mechanisms, and must be controlled. Control of filtrate loss into a
producing formation is an important factor to consider when designing a drill-in fluid.
The Permeability plugging test apparatus helps determine the bridging characteristics of the drill-in
fluid. A low initial spurt filtration and low final filtration are desirable.
Net Breakout Pressure Determination
Breakout Pressure
The ability to deposit a filter cake that is easily removed when the reservoir is produced is a major
attribute of drill-in fluids. Some drill-in fluids deposit filter cakes that are easily removed by flowing
the well, while other deposits require remedial treatments to remove skin damage. Net breakout is the
difference in pressure required for oil flow before fluid-off or “mud-off” (recorded while determining
initial permeability) and the pressure required to initiate flow after fluid-off. Determining the net
breakout pressure before and after acidizing is useful in selecting a drill-in fluid.
A fluid that requires little or no procedural clean-up after drill-in is superior to one involving a series
of specialized steps to remove the filter cake.
Return Permeability Tests
Hassler Cell Permeameter
This test procedure determines the effect a drill-in fluid has on reservoir permeability. The return
permeability set-up is designed to simulate flow through a core sample under downhole conditions.
The set-up allows flow through a core (or simulated core) from two opposite directions under
controlled temperature and pressure.
A high-percentage return permeability indicates minimum formation damage.
Sandpack Permeameter
This test procedure determines the effect of a drill-in fluid on an unconsolidated sand reservoir. The
return permeability set-up is designed to simulate flow through a core sample under down hole
conditions. The set-up allows flow through a core (or simulated core) from two opposite directions
under controlled temperature and pressure. A high-percentage return is desirable.
Reference Manual
Baker Hughes Drilling Fluids
1-36 Revised 2006