Document Type: Original Article
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 investigated 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 experiment results showed that base mud compounded 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/cm3), and low clay content contributed to control drilling fluid rheology. The sequence of rheological parameters in 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 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 high salinity and the “three high” water-based drilling fluid system was built 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 anti-pollution property reached to 1% CaCl2, 10% poor clay. It also had excellent reservoir protection and plugging performance.