This paper presents the study of electron mobility in intrinsic silicon nanowires using the Kubo-Greenwood approach. This architecture (now considered as a realistic technology [1,2]) is aimed for ultra-scaled devices up to technology nodes sub-11nm [3] with silicon films of some nanometers. At these dimensions, the transport regime is completely modified due to the multi-subband transport. However, the promising potentialities of nanowires for microelectronic applications are not still demonstrated at all simulation levels (from atomistic to circuit performances). That is why the electronic transport is here investigated numerically using the Kubo-Greenwood approach coupled to a self-consistent Schrodinger-Poisson solver. Then, to support compact modelling including ultimate physical phenomena, an analytical model of the electron mobility and backscattering coefficient is exposed. The geometry dependence is essentially pointed out on the backscattering coefficient for a wide range of channel lengths (up to 10nm) and diameters (3nm <= empty set <= 20nm).