Correlation between the gel-liquid transition stress and the storage modulus of an oil-based drilling fluid

The rheological characterization of drilling fluids is crucial to ensure an adequate performance of drilling operations. These materials show elastoviscoplastic and thixotropic behaviors simultaneously so that its gel strength is highly affected by the aging time to which the sample is subjected. This work presents experimental evidences of a correlation between the stress overshoot observed in flow start-up rheometric experiments after different aging times and the storage modulus, G′, monitored during a low amplitude oscillatory sweep over the aging time. A comparison of the correlation with the measured data at five different shear rates show that results lie within error bands of 10%. The results also suggest that the stress overshoot for different aging times can be estimated by using only two rheometric tests: an oscillatory sweep and a controlled shear rate experiment.