{HEAD ~ The injection} of hydrogen is carried out under {TAIL ~ a pressure} sufficient to cause the injected hydrogen to become absorbed within the matrix of the carbonaceous formation 
is carried out under
{ HEAD ~ The injection } of hydrogen is carried out under { TAIL ~ a pressure } sufficient to cause the injected hydrogen to become absorbed within the matrix of the carbonaceous formation
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH