There are a lot of areas of specialization in Oracle. For example, just under the category of "database"
Oracle Database 12c Administrator Certified Professional
Oracle Data Warehousing 11g Certified Implementation Specialist
Oracle Database 10g Managing Oracle on Linux Certified Expert
Oracle Spatial 11g Certified Implementation Specialist
Oracle Certified Master, Database Cloud Administrator
Oracle Enterprise Manager 12c Certified Implementation Specialist
Oracle PL/SQL Developer Certified Associate
Oracle Application Express (Oracle APEX)
Oracle Application Express Developer Certified Expert
Oracle Certified Professional, MySQL 5 Developer
And that's without getting into applications, Java, middleware, etc.
Your best bet is to go to
http://education.oracle.com
and take a look at the various certifications listed. In the far upper-right corner is a dropdown that will allow you to select your country. The information there will tell you about qualifications, training requirements, tests, etc.
None of this is cheap. You might be able to take some courses as self-study or from a third-party trainer who charges less than Oracle, but there will always be a few requirements that must be taken from Oracle itself.
In the plus side, Oracle will allow you to download software and manuals for free under a developer license for self-education. Start at http://oracle.com and look for "downloads" for both software and documentation.