Post #4 has a good point,
SPEX offer a good Wellhead Severance Package That will remove the wellhead and cut all the conductors below the sea bed in one operation
Are you planning on attempting to pull the 18 3/4" wellhead out of the 30" wellhead - or cutting together? The 18 3/4" HP wellhead housing may also be locked into the 30" LP wellhead
Garry has a good point about the template and removing the 30" subsea wellhead(s) during the structural decommissioning stage.
I remember from my past days of evaluating abrasive water cutting technology to cut out 30" wellheads away from a template in order to leave just the template down, recover all conductors and / or or wellheads and bury the template with a derogation process.