Oil is extracted from the oil recovery zone through an outlet opening at {HEAD ~ the intermediate level} of {TAIL ~ the oil stratum} in the zone 
of
Oil is extracted from the oil recovery zone through an outlet opening at { HEAD ~ the intermediate level } of { TAIL ~ the oil stratum } in the zone
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH