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