It’ s planned to build more adjustment wells for more production and output at W oilfield of western south China sea, which is an important crude oil production base of CNOOC.In order to continually reduce cost and increase efficiency, ?508 mm size conductor riser shall be used instead of ?762mm size conductor riser to simplify the casing program of additional wells. It’ s necessary to make a research about conductor riser stability in order to overcome wellbore unstability after conductor riser minimized and lost circulation during surface drilling. Thus a conductor riser stability analysis idea combining transverse mechanics, vertical mechanics and hydraulics has been adopted. First, a ?508mm conductor riser with steel grade K55 and 14.3mm size thickness has been recommended by finite element analysis. Second, the driving depth of conductor riser has been optimized to 50 meters after analysis of the ultimate load bearing capacity and fracture pressure of shallow formation. The oilfield application shows that the riser pipe of additional adjustment wells in W oilfield always remain stable and no lost circulation happened, a safe and smooth operation ensured. Over two million RMB investment has been saved and nearly three days of operation time has been saved. The cost is decreased and efficiency increased markedly after conductor riser stability analysis used.