Connecting to Oracle using ODP.NET
You're using using blocks to dispose your disposables, which is excellent. However these blocks increase the nesting of your code; since there's nothing between using (var oracleConnection = new OracleConnection(ConnectionString)) and using (var oracleCommand = oracleConnection.CreateCommand()) you could drop the curly braces and "stack" them, like this:

    using (var oracleConnection = new OracleConnection(ConnectionString))
    using (var oracleCommand = oracleConnection.CreateCommand())
    {
        ...
    }


Within that scope, you're reassigning variable Id at each row that gets read; ultimately the value of Id will be that of the last row that was read. I doubt this is the intended behavior.

As for the string query, I agree it's "dangerous" - I prefer (by far) to use an object-relational mapper such as Entity Framework (which as @svick has mentioned has an Oracle provider), but never used it for anything other than SQL Server. I believe you could look into NHibernate as well, or shop around - something like ".net ORM for oracle" should find you some interesting links :)