ODT is not available yet for VS2013. The current latest release (ODT 12.1.0.1.0) only supports 2008, 2010 and 2012.
Source: http://www.oracle.com/technetwork/developer-tools/visual-studio/overview/index.html
"Integration with Visual Studio: Use Server Explorer with Visual Studio 2012 to browse your Oracle schema and launch one of the many integrated Oracle designers and wizards to create and alter schema objects. Use Microsoft Query Designer to visually design queries. Visual Studio 2010 and 2008 are also supported."