It has been long known that drilling fluid viscoelastic properties have a significant impact on various elements of drilling hydraulics design (e.g., assessment of frictional pressure loss, particle settling velocity, hole cleaning, etc.). However, efforts for considering the viscoelastic fluid properties in drilling hydraulics design are traditionally hindered by the fact that there was no practical methodology to measure these critical fluid properties in the field.

Previous studies have highlighted the advantages of using the concept of “energy dissipation” for the quantitative evaluation of fluid elasticity. Energy dissipation theory provides a more comprehensive description of the fluid elasticity by considering the two characteristics of the fluid simultaneously; stretchiness (oscillation strain % at the crossover point of G’ and G” curves) and the stress corresponding to crossover point (i.e., flow point). In a recent study, we have shown that the “energy dissipation” of viscoelastic fluids can be correlated to fluid physical properties such as apparent viscosity and funnel viscosity, which can be conveniently measured using standard field-testing equipment (i.e., Rotational Viscometer and Funnel viscometer). Based on these findings, a new methodology for the field assessment of drilling fluid viscoelasticity has been developed, opening new opportunities to develop improved hydraulics models.

In this paper, using the new methodology developed in a recent study, we present a new generalized model for the field assessment of the particle settling velocity in viscoelastic fluids. The main objectives of the study were to: 1) Develop a generalized model for the field assessment of particle settling velocity in shear-thinning viscoelastic fluids by using the energy dissipation concept as an indicator of the fluid viscoelasticity; 2) Investigate the significant factors that influence the particle settling velocity to help provide a solution to the potential problem encountered in field drilling operations.

We prepared ten different fluids, which were divided into two groups based on their shear viscosity values. In each group, five fluids were having similar shear viscosity and variable elasticity values. Nineteen different spherical particles were used to conduct particle settling experiments with a density range from 2700 kg/m3 to 6000kg/m3 and a diameter range from 1mm to 4mm. Rheological characterizations of the fluids have been conducted by using funnel viscometer, API Rotational viscometer, controlled shear rate, and amplitude sweep test measurements.

Based on the experimental results and theory of the particle settling in non-Newtonian fluids, we developed a new model that can be used for predicting particle settling velocity in viscoelastic fluids. The statistical analyses had shown that the root means square error and mean absolute percentage error of model predictions were 0.0032 m/s and 4.1 percent, respectively.

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