SPWLA Glossary

(1) The fraction or percentage of the pore volume occupied by a specific fluid (e.g., oil, gas, water, etc.). The fluids in the pore spaces may be wetting or nonwetting. In most reservoirs, water is the wetting phase, but a few reservoirs are known to be oil wet. The wetting phase exists as an adhesive film on the solid surfaces. At irreducible saturation of the wetting phase, the nonwetting phase is usually continuous and is producible under a pressure gradient to the well bore.

(2) The occupation of fluids in a pore may take different forms:

1. Funicular saturation. A form of saturation in which the nonwetting phase exists as a continuous web throughout the interstices. The nonwetting phase is mobile under the influence of a hydrodynamic pressure gradient. The wetting phase might or might not be at irreducible saturation. In the illustration, the oil in the “A” figure is funicular.
2. Pendular saturation. The wetting phase exists in a pendular form of saturation. An adhesive fluid film of the wetting phase coats solid surfaces, grain-to-grain contacts, and bridges fine interstices or pore throats. The wetting phase might or might not be at irreducible saturation. In the illustration, water in the “A” and “B” figures is pendular.
3. Insular saturation. A form of saturation in which the nonwetting phase exists as isolated insular globules within the continuous wetting phase. A drop in pressure might or might not cause the insular globules to collect into a continuous phase. In the illustration oil in the “B” and “C” figures is insular.