reacting the oxidant and fuel in {HEAD ~ the oxidizers} to produce heat to heat a portion of {TAIL ~ the formation}; and 
reacting the oxidant and fuel in { HEAD ~ the oxidizers } to produce heat to heat a portion of { TAIL ~ the formation } ; and
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH