Methods for predicting dynamic sag using viscometer/rheometer data

摘要

A method for quantitatively determining dynamic barite sag in drilling fluids includes measuring rheological properties with viscometers and/or rheometers, and introducing the parameters into an equation to obtain the sag rate.

主权项

1. A method comprising:
measuring rheological data for a plurality of fluids having particulates suspended therein, wherein the rheological data is selected from the group consisting of: a shear stress, a yield stress, a viscosity, a shear-thinning index, and any combination thereof; applying a pseudo-plastic model and a visco-plastic model to the rheological data to produce characteristic parameters for each of the plurality of fluids; applying the characteristic parameters for each of the plurality of fluids to an equation to predict a dynamic sag rate for each of the plurality of fluids, wherein the equation is: (4/3)*π*ai3*(ρs−ρf)*g=6*π*ai*Ui*(μ+k*(T0HB)1/n). wherein ai, is a radius of the particulates, ρs is a density of the particulates, ρf is a density of the fluid surrounding the particulates, g is acceleration due to gravity, Ui is the dynamic sag rate of particulates of size ai, μ is a viscosity of the fluid, γ is a shear rate, k is an empirical constant that ranges from 0.01 to 10, T0HB is a yield stress, and n is a shear thinning index; and formulating a drilling fluid based on the dynamic sag rate for each of the plurality of fluids so as to minimize sag in the drilling fluid.