I think there is a mixed answer there to this one. You will need...

I think there is a mixed answer there to this one. You will need seismic in general to properly image these reefs (fair enough that sometimes you can extrapolate from surface geology but most of those prospects are gone), and onshore seismic is certainly more expensive than normal offshore seismic. However, if you are talking about the structure partially sitting under any of that tidal flat out there, then we are talking about very expensive seismic using ocean bottom techniques. The tides there are nasty making it even more expensive than usual.

No serious explorer would drill without seismic these days except in very unusual circumstances.