After water and a significant amount of methane is recovered from the coal bed, {HEAD ~ an inert gas} such as nitrogen is injected into {TAIL ~ the coal bed formation} 
is injected into
After water and a significant amount of methane is recovered from the coal bed , { HEAD ~ an inert gas } such as nitrogen is injected into { TAIL ~ the coal bed formation }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL