As per our documentation page - Connecting JIRA to Oracle. The database-type property in dbconfig.xml should be configured as "oracle11g". see below:

 ....
  <delegator-name>default</delegator-name>
  <database-type>oracle11g</database-type>
  <jdbc-datasource>
  ....

Which apparently not recognize by JIRA:

java.lang.IllegalStateException: Could not find a field-type definition with name "oracle11g"

Workaround:

1. Change the database-type property to "oracle10g" instead.

    ....
     <delegator-name>default</delegator-name>
     <database-type>oracle10g</database-type>
     <jdbc-datasource>
     ....
   

2. Restart JIRA