Most of these Saudi projects are completly nuts but this one really isnt that bad. Saudi Arabia want to build a cruise market, "Cruise Saudi" probably just bought a pretty decent ship for it, the World Dream. For cruises to work they need destinations. All the major cruise lines have built their own private resorts on islands in the Caribbean. Royal Caribbean even built their own massive waterpark on their Island.
I think this oil rig is just a larger version of one of these islands. Meant to provide cruise passengers and yachters with yet another incentive to cruise and visit Saudi Arabia. Quite a smart idea in my opinion. Unlike most other projects I think this one can be financially justified and even become profitable. Something that Six Flags park maybe wont ever be.