We moved our 11.2 Local DB to 12c last month in preparation for out TR 9.2 upgrade. For the most part it was pretty smooth, provided you meet the required MTR's the only thing which is different is the use of a non-admin oracle user while installing the E1Local and Oracle client. You then need an admin account while installing the package otherwise your Local specs DB will not import (because the non-admin oracle user cannot write the logs to the folders). One of the ways of resolving that could be to add the oracle user to the Admin group before installing the package.
Secondly, while the documents listed above are helpful and will get the job done, if you check the "Manually Installing Oracle 12c as the Local Database (E1Local)" there are a lot of steps to be followed. I fund an easier way to get the E1Local DB install without going through the Manual steps. (And it's fun!)
Here is how you can install the E1Local.
1. Download the Disk4, Disk5 and Disk6 of the 9.2 Deployment server from e-delivery.
2. Disk5 and Disk6 would have the E1Local12c CAB files under ORACLE directory. Copy them over to the ORACLE directory under your OneWorldClient Install folder. I would essentially rename the existing Oracle directory create a new folder with these new CAB files(Disk4 has an important role to play too..I will come to that later)
3. Now edit the installManager.htm file and replace the OEESetup.exe to OEE12Setup.exe. This is to pick the new install exe file that you just copied.
4. Now go ahead and install the E1Local, like you do using the OUI Installer.
5. Like I said before, while installing it would ask you what oracle user it needs to use, either have it create a new user or give an existing user.
6. Once the E1Local install is done and the 12c client is installed; extract the disk4 and copy the bin32 folder from under System to your FAT client.
7. Launch ReConfigureDB.exe and change the E1Local password from Enhanced encryption to Legacy Encryption. I am sure you know the reason for this one.
And that's it your E1Local is ready for your 9.1.x tools release.