Yes you can choose the GIS as a part of your Petrolium Engineering. The reason behind choosing this course is that with the use of Geo informatics, the petrolium layers can be identified and you can be a petroleum data manager too. One can use various software in order to get the data of petrolium products like ARCGIS can be used for this. So having the knowledge of Geoinformatics will help you in your Petroleum course and you can better use your knowledge with Geoinformatics.