N ARSLOW,
A significant number of Shell's Aviation Advisors came from within the ranks of Bristow. Leopoards find it hard to change their spots and I would assume Shell being a very large corporation, changes start at the top and not from the bottom. Thus, major changes seldom occur. Combine that with varying degrees of safety standards as applied within the same oil company worldwide and one has an uphill fight improving the applied standard.
One example, Texaco got taken over by Chevron in Nigeria. Immediately upon that happening, the Texaco twin engine only rule went away and Jetrangers replaced 355's as the minimum aircraft.