Usually done to open a grid in Petrel 2011 so you can export to CMG without errors.
Before exporting, make sure your porosity and permeability values are all non-zero. Use the calculator to replace zeros with a very small value such as 0.0001.
Right-click grid in model pane, export, rescue.
Model pane, right-click, import
Select rescue format
Right-click model, export