PURPOSE: To improve the dissolving power and dissolving rate when an asphaltene residue present in an oil well is to be dissolved by preparing a hydrocarbon blend having a compsn. selected from a specified region in a ternary chart of satd. compds., alkylbenzenes and polyaromatic compds.

CONSTITUTION: As for this hydrocarbon blend used to dissolve an asphaltene residue present in an oil well, a compd. selected from a specified triangular region in the ternary chart with the vertex A representing 100% of polyaromatic compds. with z<-6, vertex B representing 100% of polyaromatic compds., and the vertex C representing 100% of a alkylbenzene with z=-6. The specified region is defined by lines connecting the vertex A, the point representing 77% of aromatic compds. with z<-6 and 23% of satd. compds. on the side AB, and the point representing 55% of polyaromatic compds. on the side AC. The compsn. having ≥150°C initial boiling point is used. Or, the compsn. is selected from the region defined by lines connecting the vertex A representing 100% of polyaromatic compds. with z<-6, the point representing 80% of aromatic compds. on the side AB and the point representing 42% of alkylbenzene on the side AC.