If you have completed your MSc Geology, then doing Diploma will be of no use. You have done enough education to get into top companies. I would recommend you apply for the companies such as-

• AECOM
• RELIANCE INDUSTRIES
• SCHLUMBERGER
• ONGC (THROUGH GATE)
• WIPRO
• CAIRN ENERGY INDIA
• HINDUSTAN ZINC LIMITED
• VEDANTA RESOURCES
• ACCENTURE

For more information regarding Geology consider the link below:

https://www.careers360.com/courses/geology-course

I hope this helps. Wish you a great day!