More in-dept offshore/rig gameplay

Add helicopters and helipad for citizens working on rigs
Add Casing/drillpipes a item to produce to futher supply rigs
Add Rig Supply vessels
not quite sure about game balance though :P

Adding a Crude Oil terminals that could directly receive crude for Oil Rigs in stead of a Tanker would be nice. Laying Crude pipes from Oil Rig to the terminal jobs for the World map/Shipyard would be nice finishing touch.