BAKER HUGHES - Drilling Fluids Reference Manual

GLOSSARY OF TERMS
the initial type of flow and only occurs in plastic fluids. Most drilling fluids are plastic fluids. The
yield point as determined by direct-indicating viscometer is in excess of zero.
Plasticity - The property possessed by some solids, particularly clays and clay slurries, of changing
shape or flowing under applied stress without developing shear planes or fractures. Such bodies have
yield points, and stress must be applied before movement begins. Beyond the yield point, the rate of
movement is proportional to the stress applied, but ceases when the stress is removed. See Fluid.
Plastic Viscosity - The plastic viscosity is a measure of the internal resistance to fluid flow
attributable to the amount, type, and size of solids present in a given fluid. It is expressed as the
number of dynes per sq cm of tangential shearing force in excess of the Bingham yield value that will
induce a unit rate of shear. This value, expressed in centipoises is proportional to the slope of the
consistency curve determined in the region of laminar flow for materials obeying Bingham's Law of
Plastic Flow. When using the direct-indicating viscometer, the plastic viscosity is found by
subtracting the 300-rpm reading from the 600-rpm reading.
Plug Flow - The movement of a material as a unit without shearing within the mass. Plug flow is the
first type of flow exhibited by a plastic fluid after overcoming the initial force required to produce
flow.
P m - The phenolphthalein alkalinity of the fluid (mud) reported as the number of milliliters of 0.02
Normal (N/50) acid required per milliliter of fluid to reach the phenolphthalein end point.
Polyalkalene Glycol - A polymer or copolymer of an alkaline oxide, such as polyethylene glycol
(PEG), a polymer of ethylene oxide with general formula HO(CH 2 CH 2 O)nH, or polypropylene
glycol (PPG) which is a polymer of propylene oxide. PAGs are effective shale inhibitors and have
effectively replaced the earlier polyglycerols.
Polymer - A substance formed by the union of two or more molecules of the same kind linked end to
end into another compound having the same elements in the same proportion but a higher molecular
weight and different physical properties, e.g., paraformaldehyde. See Copolymer.
Pore Plugging Apparatus (PPA) – A device for the study of filter cake deposition. Drilling fluid
filter cake is deposited on a filter media and evaluated for potential differential pressure sticking
characteristics.
Pore Pressure Transmission (PPT) - The ability of a sedimentary rock of minimum porosity and
permeability, i.e. shale, to transmit fluid pressure across a given cross section, longitudinally as well
as horizontally.
Porosity - The amount of void space in a formation rock usually expressed as percent voids per bulk
volume. Absolute porosity refers to the total amount of pore space in a rock regardless of whether or
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 15-36