I have 6+ years experience in SAP,
If anybody interested in SAP IS OIL,
I will train you on :
IOG100--> Primary & Secondary Distribution with SAP Oil & Gas
IOG150--> Oil & Gas Industry Supply Chain
IOG320--> Oil & Gas Excahnges Business
IOG330--> Bulk Transportation and Shipment Costing
IOG340--> Bulk Scheduling
IOG350--> Service Station Retailing
The above topics are certification related and I will go through them according to project, I will make sure you that you have completed project.
IS OIL is an industry specific, so basically you should be as function consultant (SD/MM/PP/APO) who is working in IS OIL project.
So, basic knowledge of sap core module is very important always.
To start, you have to stick for one core SAP module, I would recommend SD and then complete experience in IS OIL project.
It would help you to tell that you are SD consultant+ IS OIL, in future you can be settled either SD or IS OIL Domain.
I would say that it will take approximately 60 hours to learn, and you have to make sure that you know both core and domain modules.
I would recommend you to go through the below link, It is for downstream. we will cover all these topics but you also just go through that, it would help you more how is works? and then decide.
Let me know if you need any help/queries.