Cuttings in the wellbore are not efficiently removed from the annulus because the drilling fluid does not sufficient carrying capacity and/or there is not enough flow rate to create good annular velocity. When pumps are off, cuttings fall down due to gravitational force and pack and annulus. Finally, it results in stuck pipe. Typically, the wells classified as vertical or near vertical wells have an inclination of less than 35 degrees.
Note: In order to clean annulus effectively, the annular velocity must be more than the cutting slip velocity in a dynamic condition. Moreover, mud properties must be able to carry cutting when pumps are on and suspend cutting when pumps are off.