A STUDY ON THE IMPROVEMENT OF HOLE STRAIGHTNESS IN GUNDRILLING OF INCONEL-718

Abstract

Deep hole gundrilling has been used in oil and gas industries to produce high aspect ratio holes on downhole equipment, which are normally made of Nickel-Chromium based superalloys, such as Inconel-718 to withstand the stern downhole environment. However, gundrilling of Inconel-718 has been plagued by the undesired hole straightness deviation as drilling depth increases. To improve the hole straightness deviation, a thorough study is presented in this thesis. Firstly, the fundamental study on the multispan gundrill shaft’s static and dynamic behavior was carried out. Subsequently, novel methods of improving the rigidity of gundrill shaft were performed by using support-inside-chipbox and stabilizer. Lastly, a dynamic model for a rotating multispan gundrill shaft considering mainly the thrust force, and coolant pressure was developed using energy method. This study helps to lay the foundation in developing greater drilling aspect ratio in gundrilling of Inconel-718 using the understanding of gundrill shaft behavior.