I don't think there's anything in country big enough to service an offshore contract that far out, and I'd guess that whatever does it will be based in Dar to save an extra fixed wing leg to Mtwara. If it's for Shell that would probably rule out an S76. That would probably mean an AW139 or even an S92 with current aircraft availability and prices in a depressed market. That would probably narrow it down to CHC or Bristow both of which will probably have aircraft crews available, some of whom would likely have previous experience in Tanzania and may even have Tanzanian licences