Yield-power law model more accurately predicts mud rheology
ABSTRACT The yield-power law rheological model can calculate yield point much more accurately than that calculated by the Bingham plastic model. The yield-power law (Herschel-Bulkley) model offers many advantages over the Bingham plastic and power law models because it more accurately characterizes mud behavior across the entire shear rate range. The yield-power law model has not found widespread use in the oil field because of the lack of simple analytical solutions for viscometric and hydraulics calculations. These concerns are no longer pertinent, however, because of the rapid spread of personal computers in the field and recent developments in using this model. The paper describes yield stress, the Bingham plastic model, the power law model, the yield-power law model, calculation method, model comparison, mixed metal hydroxide drilling fluids, mud hydraulics, and results from applying the model to these drilling muds.
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ABSTRACT: The rheological properties of a drilling fluid directly affect flow characteristics and hydraulic performance. Drilling fluids containing bentonite mixtures exhibit non-Newtonian rheological behavior which can be described with a high degree of accuracy by the three-parameter Herschel-Bulkley (HB) model. To determine the HB parameters, standard statistical techniques, such as the non-linear regression (NL) method are routinely used. However, sometimes they provide non physically acceptable solutions which could produce wrong values of the significant hydraulic parameters which affect drilling operations. To obtain more accurate results, the Golden Section (GS) method was subsequently developed by Kelessidis et al. (2006). In this work a different technique was developed using the Genetic Algorithms (GAs) to provide an easy-to-use tool in order to determine the three parameters of the Herschel-Bulkley model more accurately. To evaluate the accuracy of the GAs method, experimental viscometric data sets of drilling fluids were taken from the literature and the results were compared with the ones obtained by using the NL and GS techniques. The results show that the GAs and the GS methods provide similar results with very high correlation coefficients and small sum of square errors for most of the samples exhibiting negative yield stress values by the NL technique, while giving similar to the NL technique for the samples that were predicted with positive yield stress. However, in some cases, the GAs method gives better and more realistic results than the GS method.Korea-Australia rheology journal 09/2012; 24(3). · 0.63 Impact Factor
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ABSTRACT: Experimental data is presented for the flow of bentonite–water dispersions, modeled as Herschel–Bulkley fluids, for the pressure loss at different flow rates covering laminar, transitional and turbulent flow regimes, while flowing in concentric and fully eccentric annuli. The concentric experimental data has been compared with predictions from a recently-introduced model which covers the full flow regimes for concentric annulus, while corrections for eccentricity, previously suggested for non-Newtonian fluids, have also been used to compare with eccentric data. Laminar flow data not only from this work but also from work from the literature is very well predicted while transitional and turbulent flow data are predicted with less accuracy, requiring improvements on predicting transition points. The corrections for eccentricity work well and can be used to accurately correct concentric annulus data. Turbulent non-Newtonian flow data exhibit a power law exponent relationship between flow rate and pressure loss smaller than the Newtonian case pointing out directions for future research.Journal of Petroleum Science and Engineering 06/2011; 77(3):305-312. · 1.10 Impact Factor