412,
Bristow operate 412's from Qua Ibo Terminal for Exxon/Mobil. These are 2 crew. They also operate a couple of 412s from Port Harcourt and Escravos for other customers. They also operate EC155s for Shell and a couple of 332Ls. The normal Bristow roster is 7/5, not 6/6. Pan African, which is also the same company operate Bell 412, Bell 206 and Bell 407 from Escravos. The 206 and 407s are flown single crew and I think they still do 4/4 touring roster, but get paid less (NEO can probably tell you this). Pay will depend on your experience and what seniority they give you when you join - expect somewhere around $80 - 100,000 a year, though you'd only know for sure if they make you an offer. Again NEO should be able to tell you more.
CHC operate 6/6 and have a fleet of S76C+ and SA365 helicopters with AW139 expected soon. They are based in Port Harcourt. With the types you have Bristow would be a better bet if you want to come to Nigeria, but CHC operate 212s and 412s in other countries