Hi Garrett, depends on the well design but they normally start...

Hi Garrett,
depends on the well design but they normally start with a larger hole size then work their way down depending on the casing (pipe) they run for each section. (ie 20-30" conductor, 17.5" top hole, 12.25" intermediate and 8.5" production hole and sometimes down to 6" if they need to). Most production hole sections tend to be 8.5" diameter around Australia with all manner of different sizes globally. Its all based on the formation pressure that needs to be contained and the integrity of the casing that is needed to prevent burst or collapse based on expected formation pressures when drilling.