Re: regular grid and strtural surface
A regular grid has grid cells with the same dementions. So all cells for a regular latice of squares (they an have a different x and y length though).
A structured grid has irregular grid cells and is usually extracted from a 3D pillar grid. Strucutred surfaces can have triangular cells to generate sharp fault cuts, but can not be read by all software packages.
Regular grids are easy to transfer to software other than Petrel