Drill String Design For Inclined & Horizontal Wells
As was discussed in the previous sections (Drill String Design), the drill string in vertical wells is designed so that the mechanical weight on the bit is provided by the drill collars. The buckling neutral point should always be below the top of the drill collars to prevent any buckling to the DP and HWDP.

The drill pipe in vertical hole should always be in tension because drill pipe has very low resistance to buckling.
https://www.drillingmanual.com/drill-string-design-for-inclined/