Abstract:
Consistent rheology water base drilling fluid, rarely reported presently, is a new working fluid used for deep water drilling. The rheological behavior and the consistent rheology mechanisms were studied by measuring the properties and analyzing the rheological model of the consistent rheology drilling fluid under certain temperature and pressure. It is demonstrated that in pressure range between 0.1 MPa and 35.4 MPa, when temperature was raised from 4℃ to 65℃, the φ6, φ3 readings, yield point and plastic viscosity changed only slightly, which were 10-13, 9-12, 13-18 Pa and 15-22 mPa·s, respectively, and the φ6 and φ3 readings showed "U" type pattern with temperature. At changing temperature/pressure combination, the correlation coefficients of the fitted empirical rheological equations are:Bingham model ≈ Casson model ≈ Herschel-Bulkley model ≈ Robertson-Stiff model, of which the bi-parametric Casson model has the highest correlation coefficient and simple expression and is therefore suitable for use in describing the consistent rheological properties of water base drilling fluid. Introduction of parameters into the Casson's model gave birth to a kinetic rheological equation f(T, P, γ) with high precision of prediction; the average relative error is 7.19% ±4.07%, and the maximum deviation appears at 100 (r/min)/65℃. In this paper, the molecular conformation, molecular structure and association with clay platelets of the key additives are analyzed, and the qualitative structure-activity relationship assumption based on molecular conformation is presented to reveal the essence of the consistent rheology of water base drilling fluids.
