Re: seismic attribute to identify facies change at pay sand
I don't think there is a single attribute that has all the answers. it depends on your lithology, seismic resolutions, reservoir thickness, etc.
You can try sweetness as that combines frequency and energy. Then go through the frequency filters to see what you can pull out further.
Then maybe try extract RMS atributes to your top reservoir surface at different window offsets.
Do you have a far and near stack offset cubes? If so you can try AVO techniques...