Check with helicopter companies in Galliano and Houma, Louisiana. They transport personnel to oil rigs, have been on them many times. Many oil rigs and oil spill response vessels (pollution control) vessels also have the aviation frequency painted on their landing pad. There are also itinerant frequencies in VHF/UHF and AM/FM used for the oil industry. However, many of the companies have transitioned to Trbo in some cases, with Basic Privacy enabled. Helicopters use the aviation frequencies for the airports they fly into and out of, along with the specific frequencies for the company landing pads. Scanning the aviation bands (VHF and UHF) should yield some results on what is being used in your area.