1. n. [Drilling]

The flow of fluid across the bottom of the bit after it exits the bit nozzles, strikes the bottom or sides of the hole and turns upwards to the annulus. Modern, well-designed bits maximize crossflow using an asymmetric nozzle arrangement.

See: bit nozzle

2. n. [Drilling]

The flow of reservoir fluids from one zone to another. Crossflow can occur when a lost returns event is followed by a well control event. The higher pressured reservoir fluid flows out of the formation, travels along the wellbore to a lower pressured formation, and then flows into the lower pressure formation.

See: annulus,  backflow,  bit nozzle,  lost returns,  well control

3. n. [Well Completions]

A condition that exists when two production zones with dissimilar pressure characteristics are allowed to communicate during production. Reservoir fluid from the high-pressure zone will flow preferentially to the low-pressure zone rather than up the production conduit unless the production parameters are closely controlled.