Abstract: According to the characters of wellbore flow in the extended reach well , wellbore pressure drop calculation model considering radial inflow through wall in the extended reach well with arbitrary dip angle was established by using the principle of mass conservation and momentum conservation. The calculation model about monophasic fluid pressure drop in the ordinary horizontal pipe and the Dikken’s pressure drop model are special
examples of the model set up in this paper. Under the conditionof laminar or turbulent flow in the wellbore , the wall friction actor considering inflow through wall was analyzed and discussed. As an applied example , the pressure distribution and pressure drop along the well bore of varying wellOlength and well production in the case of singleOphase flow in the wallbore was calculated. The result of calculation shows that the pressure
drop in the long well bore and high production can not be neglected.

Key words: extended reach well, radial inflow, wellborn pressure drop, friction factor