From what I understand the .gri file is from the Petrosys system.
Hi @Ryan Long,
A grd or gri file can't be directly read by ArcGIS, but can be copied to an ASCII file by simply changing the extension. This is not guaranteed to work but it's worth a shot. To use the ASCII to Raster tool, a header containing information about the number of rows/columns as well as other information needs to be added to the ASCII. Additionally, the cell values need to be delimited by spaces. Once these changes are made to an ASCII, then the ASCII to Raster tool can be run.