Page 334 - Shale Shakers Drilling Fluid Systems

316 SHALE SHAKERS AND DRILLING FLUID SYSTEMS

Permeability A measure of the ability of a formation to allow passage of a fluid. Unit
of permeability is the darcy. See.- Darcy, Porosity.
Pf The phenolphthalein alkalinity of the filtrate is reported as the number
of milliliters of 0.02 normal sulfuric acid required per milliliter of filtrate
for the pH to reach the phenolphthalein end point, which is a pH of 8.3.

pH The negative lograrithm of the hydrogen ion concentration in gram ionic
weights per liter. The pH range is numbered from 0 to 14, with 7 being
neutral, and is an index of the acidity (below 7) or alkalinity (above 7)
of the fluid. At a temperature of 70°F a neutral pH is 7 or a hydrogen
7
ion concentration of 10~ . The neutral pH is a function of temperature.
At higher elevated temperatures the neutral pH is lower. The pH of a
solution offers valuable information as to the immediate acidity or alka-
linity, in contrast to the total acidity or alkalinity, which may be deter-
mined by titration.

Phosphate Certain complex phosphates, commonly sodium tetraphosphate (Na 6P 4O 13)
and sodium acid pyrophosphate (SAPP, Na 2H 2P 2O 4), used as either drill-
ing fluid thinners or for treatment of various forms of calcium and mag-
nesium contamination.
Piggy Back "Piggybacking" is the attachment of fine solids particles to the surface of
larger solids particles due to surface attraction, fluid consistency, and
particle concentration. This attachment phenomena causes fine solids to be
discharged from the screen that would normally pass through the screen.

Pill A small volume of a special fluid slurry pumped through the drill string
and normally placed in the annulus. See: Slug.

Pilot Testing A method of predicting behavior of drilling fluid systems by adding vari-
ous chemicals to a small quantity of drilling fluid (usually 350 cc) and
then examining the results. One gram of an additive in 350 cc is equiva-
lent to 1 Ib/bbl.

Plastic Flow See.- Plastic Fluid.
Plastic Fluid A complex, non-Newtonian fluid in which shear force is not proportional
to shear rate. A definite pressure is required to start and maintain fluid
movement. Plug flow is the initial flow type and only occurs in plastic
fluids. Most drilling fluids are plastic fluids. The yield point, as determined
by a direct indicating viscometer, is in excess of zero. See.- Plastic Flow.

Plastic Viscosity A measure of the internal resistance to fluid flow attributable to the con-
centration, type, and size of solids present in a given fluid and the viscosity
of the continuous phase. This value, expressed in centipoise, is proportional
to the slope of the shear stress/shear rate curve determined in the re-
gion of laminar flow for materials whose properties are described by
Bingham's Law of Plastic Flow. When using the direct indicating viscom-
eter, plastic viscosity is determined by subtracting the 300 RPM reading
from the 600 RPM reading. See: Viscosity, Yield Point, API Bulletin RP 13B.
Plasticity The property possessed by some solids, particularly clays and clay slur-
ries, of changing shape or flowing under applied stress without develop-
ing shear planes or fractures (i.e., it deforms without breaking). Such bod-
ies 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 movement ceases when the stress is removed. See.- Fluid.