BAKER HUGHES - Drilling Fluids Reference Manual

Formation Mechanics
Figure 2-12
Photomicrograph of Platy Kaolinite Crystals
This photomicrograph is of a cluster of platy kaolinite crystals (k) that are filling a sandstone pore.
Although these clays do not swell, they can still be made to detach and migrate if a fluid of greatly
higher or lower salinity than the natural formation water is introduced.
If a fluid is introduced into a rock that contains many of these clays, they can detach, migrate, and plug
pores if the invading fluid is chemically different from the natural formation fluid. Knowledge of a
formation's water chemistry can be helpful in designing a non-damaging fluid. Another type of
chemical formation damage, not caused by clays, involves the precipitation of materials in the pore
spaces due to a reaction between formation water and the drilling fluid. For example, if a formation's
water contains abundant bicarbonate ions, it could react with a calcium-rich drilling fluid to form poreblocking
calcium carbonate.
Reference Manual
Baker Hughes Drilling Fluids
2-18 Revised 2006