Re: TRAP ROCK VOLUME IN PETREL
You can calculate the volume under a surface (structure) using the operations tab in the settings of that surface.
Go to the calculations category and there you can enter a contact level. The volume will be outputted to the message log.
You can also use the "area depth" method. In that case Petrel will output the area (and volume) for a set of contours and you can use Excel to calculate the voluem for different contact levels and for different top strucutre uncertainties. This is a common method used in exploration.
hope this helps.