BAKER HUGHES - Drilling Fluids Reference Manual

Hydraulics
Shale Inhibition (Wafer Test)
The shale wafer test measures the disintegrative properties of particular shale in contact with a drilling
fluid or liquid composition over a measured period of time. Knowledge of shale disintegration
tendencies is important because of their effects on drilling fluid properties in actual field use.
Incorporation of unwanted drill solids into the fluid negatively impacts the rheological properties of
the system, reduces rates of penetration, produces poor filter cake quality, increases dilution rates and
potential pore throat plugging that cannot be cleaned up.
Shale disintegration, as defined in this test procedure, is measured and recorded in four ways:
3. Weight recovery in weight percent
4. Shale hydration in weight percent
5. Change in shale wafer hardness
6. Increase or decrease in shale wafer volume
This test compares results of one fluid to another. It is one of several tests providing information on
the interaction of a fluid in contact with a given shale. This testing is important for the design of
reservoir drilling fluids that will ensure well bore stability and maximum fluid stability.
Density (API Standard Practice 13B-1, June 1990)
This test procedure determines the weight of a given volume of liquid. Fluid weight may be
expressed as pounds per gallon (lb m /gal), pounds per cubic foot (lb m /ft 3 ), kilograms per cubic meter
(kg/m 3 ), or specific gravity. Density is designed to meet well bore pressure requirements.
Fluid Viscosity
A viscometer is a mechanical device used to measure viscosity at varying shear rates. Viscosity and
gel strength measurements relate to the flow properties of fluid. From the viscometer readings
rheological parameters may be determined. Rheology is the study of deformation and flow of matter.
Hole size, hole angle, and formation type determine optimal rheological properties.
Water, Oil and Solids
The retort instrument provides a means for separating and measuring the volumes of water, oil, and
solids contained in a sample of fluid. In the retort, a known volume of a whole mud sample is heated
to vaporize the liquid components which are then condensed and collected in a graduated receiver.
Total volume of solids (suspended and dissolved) is obtained by subtracting the liquid volume from
the total sample volume. Calculations are necessary to determine the volume of suspended solids
since any dissolved solids will be retained in the retort. The relative volumes of low-gravity solids
and weighting material can also be calculated. Knowledge of the solids concentration and
composition is considered basic to viscosity and filtration control in reservoir drill-in and drilling
fluids.
Reference Manual
Baker Hughes Drilling Fluids
1-38 Revised 2006