Figure 1. Schematic of the circulating system: The drill bit, drill collar, annulus, drill pipe, kelly and swivel are depicted in the upper right. Drilling mud flows through the mud return line (center) upon its return to the surface from the hole to the shale shaker (upper left), then to the adjacent desander, desilter and degasser back to the mud tank (upper left). Mud passes through the suction line, and the mud pump (center) circulates the mud through the discharge line (above), the stand pipe (upper right) through the rotary hose (right) and the swivel (lower right), back to the kelly and into the drill pipe.