Create a oil material, set domain and blend modes as: deferral decal, translucent
Make a oil shape image in photoshop, export it as a texture in ue
Connect the mtl of the texture with its alpha channel to opacity
Add water normal texture to fresnel node and connect as:
Add Paner node lets the object spin/rotates (set speed X as 0.1, Speed Y optional)
Add Color multiplier
To get rid of the reflection, connect Flattennormal node to Normal:
Set multiply value from 2 to 0.2, if want less detail pattern: