wellhead to facilitate injection of the tubing 142 in the wellbore 90 installation procedures to move the bottom hole assembly 130 into the wellbore 90 is described in u s pat no 5 738 173 commonly assigned with this application the primary purpose of the injector 182 is to move the tubing 142 to the injector 190 and to provide desired tension to the tubing 142 if a subsea injector is used then the primary purpose of the surface injector 190 is to move the tubing 142 between the reel 180 and the subsea injector if no subsea injector is used then the injector 190 is used to serve the purpose of the subsea injector for the purpose of this invention any suitable tubing injection system may be utilized to drill the wellbore 90 a drilling fluid 20 from a surface mud system 22 see fig2 for details is pumped under pressure down the tubing 142 the fluid 20 operates a mud motor in the bha 130 which in turn rotates the drill bit the drill bit disintegrates the formation rock into cuttings the drilling fluid 20 leaving the drill bit travels uphole through the annulus between the drill string and the wellbore carrying the drill cuttings a return line 132 coupled to a suitable location at the wellhead 125 carries the fluid returning from the wellbore 90 to the sea level as shown in fig2 the returning fluid discharges into a separator or shaker 24 which separates the.