OS: Windows Win 7 -64 bit
I installed 32 bit client with Oracle Developer Tool, then I installed 64 bit driver.
1. Migrate EF5 to EF6 in Nuget.
2. Add Oracle.DataAccess and Oracle.DataAccess.EntityFramework.
3. Add provider to app.config both in application assembly and EF object assembly
<provider invariantName="Oracle.DataAccess.Client" type="Oracle.DataAccess.EntityFramework.EFOracleProviderServices,
Oracle.DataAccess.EntityFramework,Version=6.121.2.0,
Culture=neutral, PublicKeyToken=89b483f429c47342" />
4. Compiled project successfully and application runs well(I don't know whether it implements EF6 successfully or not).
5. Add new table to existing model and save edmx file, issues says:

No EF provider found for the provider with invariant name 'Oracle.DataAccess.Client'. Make sure provider is registered in the 'entityFramework' section of application config file.
I double checked config file, it's there:
<configSections>
\<!-- For more information on Entity Framework configuration, visit [http://go.microsoft.com/fwlink/?LinkID=237468](http://go.microsoft.com/fwlink/?LinkID=237468) -->
\<section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
</configSections>
<connectionStrings>
\<add name="HRCMContext" connectionString="metadata=res://\*/HRCMModel.csdl|res://\*/HRCMModel.ssdl|res://\*/HRCMModel.msl;Provider=Oracle.DataAccess.Client;provider connection string="Persist Security Info=False;User ID=HRM\_TRUNK;Password=hrm\_trunk;Data Source=DEV11"" providerName="System.Data.Entity.Core.EntityClient" />
</connectionStrings>
<oracle.unmanageddataaccess.client>
\<version number="\*">
\<edmMappings>
\<edmNumberMapping>
\<add NETType="decimal" MinPrecision="1" MaxPrecision="19" DBType="Number" />
\</edmNumberMapping>
\</edmMappings>
\</version>
</oracle.unmanageddataaccess.client>
<entityFramework>
\<providers>
\<provider invariantName="Oracle.DataAccess.Client" type="Oracle.DataAccess.EntityFramework.EFOracleProviderServices,
Oracle.DataAccess.EntityFramework,Version=6.121.2.0,
Culture=neutral, PublicKeyToken=89b483f429c47342" />
\</providers>
\<defaultConnectionFactory type="System.Data.Entity.Infrastructure.SqlConnectionFactory, EntityFramework" />
</entityFramework>