Study on drilling fluid technology in unconsolidated sand with high clay content

Shahejie formation is the major oil-bearing series in Wangzhuang Oilfield of Shengli oil district.Loose sandstone and high clay content result in wellbore instability and permeability reducing.According to the formation characteristics and the requirement of logging,the new polyol drilling fluid was developed.The properties of the new drilling fluid system,including inhibition,mud filtrate control capacity,rheology,resistivity and formation protection ability were evaluated in laboraty. Cuttings roller recovery is more than 90%, return permeability is more than 80%, and resistivity is more than 1.5 Ω·m.Laboratory tests and in-situ application indicate that this kind of drilling fluid has the advantages of excellent inhibition, anti-sloughing, formation protection property, and reach the need of well logging.