BAKER HUGHES - Drilling Fluids Reference Manual

Oil / Synthetic Fluids
Ions surrounded by clusters of water molecules are called hydrated ions, and the process itself,
hydration. Hydration is not limited to ions, but occurs with neutral (but polar) molecules as well.
Examples are sugar and alcohol.
Figure 5-4
Schematic Diagram of Hydrated Sodium and Chloride Ions
Figure 5-5 Sodium and Chloride Ions Surrounded by Water Molecule Dipoles
Hydration is a specific example of a more general phenomenon called solvation. Solvation must occur
when one substance, called a solute, dissolves in another substance, usually a liquid, called the solvent.
In order to dissolve, the molecules of the solute are surrounded by clusters of molecules of the solvent.
This process is called solvation and only occurs when the molecules of the solute are similar in ionic
strength to the molecule of the solvent. Examples are salt in water, sugar in water, fats in
hydrocarbons. “Like dissolves like” – therefore, molecules which are very dissimilar in charge will
not solvate and no solution occurs. Examples are salt in hydrocarbons and water in hydrocarbons.
Compounds which are solvated or hydrated by water, such as salt or sugar, are called hydrophilic,
meaning water-loving. Compounds which are solvated by oil, such as butter fat, are called lipophilic,
meaning oil-loving.
Baker Hughes Drilling Fluids
Reference Manual
5-10 Revised 2006