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