Study on Rheological Property Control Method of “Three High” Water Based Drilling Fluid

The rheological regulation of the “three high” (high temperature, high density and high salinity) water-based drilling fluid is a worldwide problem due to the combined influence of temperature, solid content and salinity. this paper investigates the factors and regulation methods about rheological property of “three high” water based drilling fluid, and the effects of clay, salinity and weighting materials on the drilling fluid rheology. the experimental results show that base mud compound bentonite with attapulgite had good salt resistance and temperature resistance. the clay content should be kept close to 2% in high density mud (ρ=2.0g/cm^3), to control drilling fluid rheology. the sequence of rheological parameters of the “three high” water-based drilling fluid with same density was: manganese oxide> micronized barite> barite> ilmenite powder. when barite compounded with ilmenite powder or micronized barite in the ratio of 1:1 to weight drilling fluid respectively, the rheology and filtration of the “three high” water-based drilling fluid performed well. based on the optimization of a series of mud additives including fluid loss additive, thinner, anti-collapse filtration reducing agent, lubricant with salt and calcium resistance, a formula of the “three high”water-based drilling fluid system was prepared which had excellent rheology, filtration and sedimentation stability property with the density of 2.2g/cm3 (180℃). the expansion rate of the drilling fluid was 1.84%, shale recovery rate was 85.73%, lubrication coefficient was 0.122, and resistanced to pollution of 1% cacl2 and 10% poor clay. it also had excellent reservoir protection and plugging performance.