BAKER HUGHES - Drilling Fluids Reference Manual

Baker Hughes Drilling Fluids
Drill-In Fluid Properties
Static Filtration
Test seeks to find the filtrate volume and the quality of the filtrate cake. Although evaluating filter
cake quality is generally limited to estimating the thickness of the cake, other properties such as
lubricity, erodibility, and texture must be considered.
Lubricity Testing
Lubricity testing evaluates the lubricating qualities of drilling fluids. The different test procedures
measure the coefficient of friction characteristics of a fluid. These tests can measure the coefficient of
friction between two metal surfaces, or between a metal surface and a piece of rock. Since drill-in
fluids can be used to drill horizontal or highly deviated well bores, the coefficient of friction can be a
critical issue when selecting an applicable fluid.
Particle Size Distribution
Effective bridging of a reservoir depends upon both the particle size distribution of materials
comprising the drill-in fluid and the pore throat diameters of the reservoir rock. A bridging material is
chosen by matching its size to the diameter of formation pore throats. The industry-accepted rules for
selecting size and concentration of bridging materials are based upon work carried out by A. Abrams,
“Mud Design to Minimize Rock Impairment Due to Particle Invasion”, SPE 5713, 1977, and include
the following:
The medium particle size of the bridging additive should be equal to or slightly greater than one-third
the medium pore size of the formation.
The concentration of the bridging solids must be at least 5% by volume of the solids in the final fluid
mix.
Once the mean pore diameter is known, the particle size distribution of the bridging solids must be
measured and adjusted to meet the required specifications and included in the drill-in fluid
formulation.
An alternative method of determining optimal particle size distribution is to use the ideal packing
theory. This theory determines a particle size distribution based on sealing the pore sizes over a total
range, including pore spaces created by bridging agents.
Baker Hughes Drilling Fluids
Reference Manual
Revised 2006 1-37