The Migrate Storage geoprocessing tool exceeds the Oracle default ‘open_cursors’ limit of 300 when a large number of feature classes are migrated at one time. This is caused by a cursor leak in ArcSDE for Oracle.
Increase the ‘open_cursor’ parameter to a larger values, for example 2000. To do so, connect as the Oracle system administrator and execute the following Oracle SQL statement: ALTER SYSTEM SET open_cursors = 2000 scope = both;.