(under subclass 256) A process in which plural, naturally distinct, vertically related zones of earth are involved.
(1) Note. The distinct zones are usually identified by the fluid they contain, such as oil or water. But where it appears that different fluids are in a single zone having the same physical characteristics throughout, the zone is considered to be a single entity.
(2) Note. It is common to produce a fluid from a formation located between two or more other formations. Patents are classified in this subclass only when the existence of plural distinct zones or formation is a significant factor in the claimed process. A reference in a claim to the top or bottom of a zone is not enough for classification under this definition.
