{HEAD ~ The deasphalting residue} is then added to {TAIL ~ a second portion} of heavy oil, such as a second portion of the same type of heavy oil that was used as feedstock in the solvent deasphalting 
{ HEAD ~ The deasphalting residue } is then added to { TAIL ~ a second portion } of heavy oil , such as a second portion of the same type of heavy oil that was used as feedstock in the solvent deasphalting
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH