1. n. 
Water that is mobile, available to flow, and not bound to surfaces of grains or minerals in rock.
2. n. 
In cementing, any water in the slurry that is in excess of what is required to fully hydrate the Portland cement and other additives. Free water can physically separate as a cement slurry sets. This separation tendency, especially in the presence of a high-pressure gas-bearing formation, can impair zonal isolation, the primary job of the cement. For that reason, the well designer usually specifies a maximum free-water content for the slurry.
3. n. 
The aqueous phase that separates from a slurry or mixture of fluids. In cementing operations, free water is undesirable since channels tend to form through the set cement, providing potential gas migration paths. When processing reservoir fluids, the water that separates easily under gravity separation is known as free water. In some cases, additional water may be locked in an emulsion, contributing to the aqueous phase but not available as free water.
See: gas migration
4. n. 
Water in the pore space that can flow under normal reservoir conditions. When used in connection with nuclear magnetic resonance (NMR) measurements, free water is all the water that is not clay bound, capillary bound or in mineral hydrates. The latter is in any case excluded as it relaxes too fast to be measured by NMR. When used in connection with the dual-water model, the term means the far water.
Alternate Form: far water