Dear Rzger Abdulkarim Abdula,

Congratulation, Your work is good one. And gave inspiration to answer something to the question… As I have learn at the university as a student: The lighter oils in majorities cases are younger than thicker oil… And in the next I will responding onto base of my own oil formation explanation,  Mr Rzger Abdulkarim Abdula will be able to verify it onto his experience:

Another think the Thick oil are closest to the their source rock than the lighter Oil…

Best Regards,

Laszlo

Also you can try the basic one is Halpern (1995) parameters, especially on "oil corelation star diagram" which you use C7 molecules in.

Halpern, H.I., 1995, Development and applications of light hydrocarbon-based star diagrams. American Association of Petroleum Geologists Bulletin 79, 801–815.

I think you can correlate light oil- light oil as long as the correlated data which covers oil properties, pressure and temperature is almost alike. Moreover, and from the geochemistry side, the unique character of each light oil needs to be evident from their n-alkane series and associated biomarker signature, hence differences in biomarkers suggest difference in the existed light oil, taking into account of thermal maturity where temperature decreases the usefulness of biomarker compounds. Light oil-light oil correlation have proven very useful in routine-gasoline analysis in some potential hydrocarbon basins like the intracractonic Williston Basin of N. America and Ghadames Basin of NW Africa.