What your dissertation focuses on depends on whether you are an engineer or a geoscientist. Engineers really like to get into minute details of how a measurement is taken, its repeatability, overall reliability, and significance of the values recorded in terms of borehole success. Geoscientists tend to be more interested in how a suite of well logs either confirm or contradict what they predicted before drilling. Pressure and temperature measurements are always necessary and usually vary considerably in reliability due to issues unrelated to the measurement tool. What are the latest logging tools and what do they do that hasn't been done before? A visit to a local logging contractor would be really helpful.