The reserve pit is where drilling fluids (mud) is held. On most modern rigs, the reserve pit receives annular returns from the solids control equipment (shale shaker). Only clean mud and some cuttings should be making it into the reserve pit. The reserve pit must have both a large volume of mud and a large spare capacity for mud due to well control considerations.



On an older (SCR) rig there may be an intermediate pond between the mud returns and the reserve pit. The intermediate pond acts as a holding area so that contaminants in the mud can separate before the mud is pumped into the reserve pit. Newer generation rigs with modern mud cleaning equipment will not have an intermediate pit.


Ponds may be dug to contain other fluids as needed during the drilling process. A water-based mud system can use a freshwater pond to take and retain mud quality water. Similarly, a waste pond can be used to hold drilling wastes that are removed from the circulation system. If a freshwater pond becomes contaminated, then it must be treated as a waste pond-it must be converted so that the pollution is not allowed to enter the circulation system and the proper remediation is undertaken after operations have ceased.


The rig itself will have smaller metal pits to perform more intensive mud mixing and conditioning. Tanks are also used if the drilling rig needs large quantities of specialty fluids. A completions and workover unit will commonly use tanks to contain well control fluids while the well is open.

Recommended Training: Rig Pass Orientation with SafeLand

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