1. n. [Drilling]

The complete, circuitous path that the drilling fluid travels. Starting at the main rig pumps, major components include surface piping, the standpipe, the kelly hose (rotary), the kelly, the drillpipe, drill collars, bit nozzles, the various annular geometries of the openhole and casing strings, the bell nipple, the flowline, the mud-cleaning equipment, the mud tanks, the centrifugal precharge pumps, and, finally, the positive displacement main rig pumps.

See related terms: bit nozzle,  casing string,  centrifugal pump,  drill collar,  kelly,  positive displacement pump,  surface pipe