Depends on the exact spud location but the blocks are 70KM wide so edge to edge 121 to 120 is 140 KM. Both blocks share the same geologic basin. Block 120 covers 8500 SQ KM in total.
Detailed geo map at
http://www.jetro.go.jp/jfile/report/07000429/vn_energy_map.pdf
Don't forget we have some of the best 3D data ever shot in this area. I believe this block has the stuff....we just need to but the pin on the right spot.