Changes

==Circulating system==

==Circulating system==

Circulation of [[drilling fluid]] (mud) serves several functions on a rig, including cooling the bit, providing hole stability, and aiding in formation evaluation. (For more information on drilling fluid, see [[Drilling fluid]], and for more on how the circulating system aids in formation evaluation, see [[Mudlogging: drill cuttings analysis]].)

Circulation of [[drilling fluid]] (mud) serves several functions on a rig, including cooling the bit, providing hole stability, and aiding in formation evaluation. (For more information on how the circulating system aids in formation evaluation, see [[Mudlogging: drill cuttings analysis]].)

[[Drilling fluid]] is circulated by the mud pumps. The volume of mud being pumped is measured by the stroke counters, and the rate of movement is recorded by the stand pipe pressure. The stand pipe connects the mud pumps to the kelly hose. The kelly hose is connected to the swivel on top of the kelly. Mud is pumped down the drill string through the bit and up the ''annulus'' or “back side” (the space between the drill pipe and the borehole). Returning mud flows down the flowline into a ''surge tank'' (possum belly) and across the shale shakers. ''Shale shakers'' are vibrating screening devices that are designed to shake so as to separate out the drill cuttings from the mud. The shale shakers are the first place that drill cuttings can be examined and where the gas is extracted from the mud ([[:file:land-rigs_fig2.png|Figure 2]]). After going through the shake shakers the mud passes through a series of tanks or pits where the finer solids are removed via desanders, desilters and centrifuges, and the mud properties are adjusted. Pits are named for their function (e.g., shale pit, settling pit, volume pit, mixing pit, and suction pit). The mud pumps are charged from the suction pit. Excess mud can also be diverted from the metal mud pits into a large, plastic lined reserve pit located to the side of the rig.

Drilling fluid is circulated by the mud pumps (34 in [[:file:Land rig example drawing.png|Figure 1]]). The volume of mud being pumped is measured by the [[stroke counter]]s, and the rate of movement is recorded by the [[stand pipe]] pressure. The stand pipe connects the mud pumps to the [[kelly hose]]. The kelly hose is connected to the swivel (6) on top of the kelly. Mud is pumped down the drill string through the bit and up the ''[[annulus]]'' or “back side” (the space between the drill pipe and the borehole). Returning mud flows down the flowline (24) into a ''[[surge tank]]'' ([[possum belly]]) and across the shale shakers (25). ''Shale shakers'' are vibrating screening devices that are designed to shake so as to separate out the drill cuttings from the mud. The shale shakers are the first place that drill cuttings can be examined and where the gas is extracted from the mud ([[:file:land-rigs_fig2.png|Figure 2]]). After going through the shake shakers the mud passes through a series of tanks or pits where the finer solids are removed via desanders, desilters and centrifuges, and the mud properties are adjusted. Pits are named for their function (e.g., shale pit, settling pit, volume pit, mixing pit, and suction pit). The mud pumps are charged from the suction pit. Excess mud can also be diverted from the metal mud pits into a large, plastic lined reserve pit located to the side of the rig.

==Control and measurement system==

==Control and measurement system==