The CAA stuff is probably a good bet. In 1987, on behalf of the CAA, an independent research company studied "Helideck wind flow distortion and hot gas plume dispersal in relation to helicopter operational difficulties when operating to offshore oil/gas production facilities."
We didn't do actual flight testing, but did computer modelling and pilot experience studies, plus simulator examination of pilot reaction to taking off from and landing on offshore decks, with simulated turbulence from structures and gas plumes.
One of the documents we had hold of was a study undertaken by BP on the effects on gas turbine engines of flying through plumes. BP may still have a copy of that in their archives.