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