focus on salary,so which engineering is good?

This is pretty dicey to answer. Where is the guarantee that one or the other will get a higher salary? It will depend upon the placement - the company, the job profile, the B.Tech scores of the student. Both the streams are good. I would suggest you see which syllabus is comprehensive and what it covers. Check the job profiles of petroleum engineers and petrochemical engineers and the salaries offered. Make your decision.