Typically six or more mud pits of various sizes are located at {HEAD ~ the surface} of most wells, but at any one time all mud pits are not necessarily “active”, i.e., contributing volume to the closed loop system of the circulating mud going into {TAIL ~ the wellbore} WB and returning to the surface S 
Typically six or more mud pits of various sizes are located at { HEAD ~ the surface } of most wells , but at any one time all mud pits are not necessarily “ active ” , i.e. , contributing volume to the closed loop system of the circulating mud going into { TAIL ~ the wellbore } WB and returning to the surface S
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH