bound fluid

1. n. [Formation Evaluation]
Fluid in the pore space that does not flow under normal reservoir conditions. This fluid may include water, oil or gas, but most often refers just to bound water. Bound fluid does not flow on primary or secondary production, injection or invasion unless the rock wettability is altered. When used in connection with a nuclear magnetic resonance measurement, the term refers to the signal that occurs below a certain cutoff, typically 33 ms in sandstones and 100 ms in carbonates. The source of this signal is bound water, but may also include oil with a viscosity above about 60 cp in sandstones or 30 cp in carbonates. Note that, contrary to the sense of "bound," this oil may or may not be moveable under normal reservoir conditions.