Having been in this same situation myself when trying to decide on a doctoral research topic, I would suggest the following pathways. First, where are you located globally? Is there oil & gas activity in your country or your local area (if you are in a very large country)? If so, research what the exploration and production targets are and what is the drilling method: conventional or unconventional, is it offshore or onshore? Secondly, look into the problems associated with this industrial effort. Are there exploration issues such as unusual geology, poor seismic quality, not utilizing gravity or magnetic surveys, is there an issue with random reservoir quality, etc. Are there problems with development wells? If production is underway, how could it be made more efficient? or more cost effective? If there is no oil & gas industry where you are working, then you might want to look at industry-wide issues in general, depending on what is your skill set: geologist, geophysicist, engineering, mathematics, or computer programming. Ask yourself "What could I do that would make a difference in success rates or cost effectiveness?" Trying to solve industry problems in your research efforts will get you noticed when you graduate. A word of caution is not to make your research too obscure, such that it has a limited application. Too many graduate students spend years on research that very few people care about or find useful, and then wonder why they can't find employment. Make that time and effort count!