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Circulating System

Mud circulates through many pieces of equipment, including the mud pump, the discharge line, the standpipe, the rotary hose, the swivel, the kelly (or the top drive), the drill pipe, the drill col­lars, the drill bit, the annulus, the return line, the shale shaker, the desilter, the desander, the mud pits, and the suction line.

The mud pump draws in mud through a suction line from the mud pits, or tanks, and sends it out a discharge line. From the discharge line, the mud goes into the standpipe. The standpipe runs vertically up one leg of the derrick. Mud exits the standpipe into a strong, flexible, and reinforced rubber hose called the rotary hose, or kelly hose. The rotary hose joins the swivel at the gooseneck. The mud then flows down the kelly (or through the top drive), drill pipe, and drill collars. It jets out of the bit nozzles and moves cuttings away from the bit. The mud and cuttings then head up the hole in the annulus. The annulus, or annular space, is the area between the drill string and the wall of the hole.

Fig. 8 Schematic of example rig circulating system

The mud leaves the annulus through a steel pipe called the mud return line. It falls over a vibrating screen, the shale shaker. The shaker screens out the larger cuttings and, in some cases, dump them into the reserve pit. Offshore and in environmentally sensitive areas, however, the shaker dumps the cuttings into a receptacle. Later, the contractor removes the receptacle, washes the cuttings if required, and properly disposes of them. In either case, the clean mud drains back into the mud tanks. The pump then recycles it back down the hole. The mud pump recirculates the mud over and over throughout the drilling of the well. From time to time, the derrickhand adds water, clay, and other materials to make up for downhole losses. This crew member also adjusts the mud's properties as the borehole encounters new and different formations.