You will probably need to create an 'Other' report and write your own stored procedure to return the data you need. The features reports don't have the worklog data, and the worklog reports don't have the feature custom fields, so you cannot use those report types.
If you write your own stored procedure you should be able to filter by that custom field. So you will need to join the Features table with the FeatureCustomFields table and the WorkLog table
Dan Suceava
http://www.axosoft.com