| Summary: | Based on numerous laboratory studies, an environment friendly drilling fluid system is developed. The formula is 4% bentonite+0.3%IND-30+1.5%NAT-20+3%FXJS+2%NFT-25. By adopting environment friendly additives, the system has good temperature resistance (up to 150 °C) and excellent contamination resistance (30% saturated salt tolerance and 8% bentonite tolerance). It can also effectively protect reservoir and achieve more than 81.5% of permeability recovery. When spreading on land surface with thickness of 0-20 cm, all the indexes of the soil environmental quality are above the second degree of the national standard. Meanwhile, it can improve the water content and fertility of sandy land. And this drilling fluid system was successfully used in 15 wells of the Tarim Oilfield, Karamay Oilfield and Jiangsu Oilfield and got satisfactory results in environmental protection and reservoir protection. After this environment friendly drilling fluid is abandoned, the contents of organic matter, active nitrogen, active phosphorus and active potassium in the soil around wells are increased. 40.87×104 Yuan of comprehensive cost per well was saved and the total saved cost of the 15 wells was 613.05×104 Yuan. Key words: environment friendly drilling fluid system, biodegradation, temperature resistance, reservoir protection effect, environment protection performance
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