Typically {HEAD ~ six or more mud pits} of {TAIL ~ various sizes} are located at 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 the wellbore WB and returning to the surface S 
Typically { HEAD ~ six or more mud pits } of { TAIL ~ various sizes } are located at 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 the wellbore WB and returning to the surface S
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL 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 OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH