Which is better PLC, DCS or SCADA to go for Control Automation after 12 years experience?

Dear friends

Advise me course suitable and scope in future for below profile of mine.

Working as Electrical and Instruemntation inspector in oil/gas for 12 years.
I would like to move control instrumentation engineer for they here they are asking depth knowledge of PLC DCS and SCADA.. for that which course is suitable for me.
More important if i do this course after 12+ yrs in E&I QC experience.. is it possible to pickup and get job in Control Automation ???????