Abstract: Based on the geographic climate condition of Changqing Oilfield,drilling fluid used in this oil and gas field should exhibit non-toxicity,easy degradation and good environmental acceptability.Thus,water-based environmental friendly membrane forming drilling fluid was created that is suitable for low-pressure,low-permeability and low-porosity reservoir.It was synthesizedby taking polysaccharide derivative G312 as main agent and by optimizing other additives. This drilling fluid achieved the stated objective of protecting reservoirs and the environment through the semi-permeable membrane effect of polysaccharide derivatives and a distinctive sloughing control of organic amine. Compared with traditional alkylglucoside drilling fluid,this drilling fluid possesses the advantage of having good anti-collapse performance,requiring less dosage of main treatment additives and having a strong temperature and salt resistance ability.Laboratory performance evaluation results showed that water-based environmental-friendly membrane forming drilling fluid had no biotoxicity and its heavy metal content and other indicators met the standard wastewater discharge requirements.Due to its semi-permeable membrane effect,it had strong inhibition.The linear expansion ratio of cuttings in this drilling fluid was 35.6% lower than that in clear water.The primary recovery of cuttings reached 94.80% and secondary recovery rate reached 89.34%.Moreover,this drilling fluid had good temperature resistance of 120℃ and excellent comprehensive properties.In the trial use of water-based environmental-friendly membrane forming drilling fluid while drilling well A of Sulige area in Changqing Oilfield,no downhole failure and the well diameter was regular.Electric logging and operations for running casing were successful on first run.Besides,environmental protection property indices of the drilling fluid satisfied wastewater discharge standard.Therefore,the study indicated that the environmental-friendly properties and other properties of water-based environmental-friendly membrane forming drilling fluid could meet all requirements of Changqing Oilfield.