The present paper describes the running process in horizontal wells and studies the effect of some factors on running forces required to push pipes through curved holes with short to medium radii of curvatures. Estimation of the running forces was performed using a general-purpose finite element program called ANSYS. The effect of pipe bending stiffness, hole radius of curvature, and hole clearance are investigated Finite element results showed that the pipe bending stiffness becomes insignificant for medium curvatures (i.e., radius of curvature greater than 80 m). it was also found that the running force at the kick-off point (k.o.p) increases as the radius of curvature shortens (severe doglegs) and as the pipe stiffness increases. In addition, FE results revealed that the effect of hole clearance on the running force is negligible.