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