Abstract: Within the North Tian Shan piedmont structural belt along the southern fringe of the Junggar basin, plastic claystone formations below the high geo-stress area have posed many difficulties on drilling and cementing operation. In order to achieve successful completion under such complex geologic conditions,the authors put forward six criteria in regard to the design of
casing strength (including wellbore preparation and running casing) and slurry system. Operation record and logging examination indicate that, by using these design criteria and with primary cementing and plug flow displacement technology, the cement job at Well An-4 has been a success.

Key words: well drilling, well cementing, effective viscosity, rheology, plug flow displacement, Junggar basin