Mudlogger is basically towards the Mud Logging line. You start with sample catcher, then mud logger than Data eng. Field Specialist (FS) differs from Field Eng (FE) in the sense FS is for technician background while FE is for Engineering Degree graduate. But, I have seen some engineer graduate prefers to take up the FS post as they usually offer better daily rate. FS & FE can be applied to any scope (MWD, Completion, Fishing etc). To be DE, you can start from anywhere, as long as you can gain as much knowledge as you can, because DE is the lowest position of the career path structure. Some experience field hands who became DE might join as a senior DE or maybe start from a higher grade DE.