Preferably, {TAIL ~ hydrogen} is introduced into the formation through {HEAD ~ the same wells} in which nitrogen is injected and nitrogen and methane withdrawn 
Preferably , { TAIL ~ hydrogen } is introduced into the formation through { HEAD ~ the same wells } in which nitrogen is injected and nitrogen and methane withdrawn
OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH