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 influence of pH between 7.5 and 10.5, for 5% and 6.42% aqueous Wyoming bentonite dispersions and of NaCl for 2%, 5% and 6.42% of Wyoming-bentonite in water for a range of salt concentrations up to 1.0 M has been investigated. The dispersions were prepared according to American Petroleum Institute procedures and rheological data were obtained with a Couette viscometer. Data were represented very well by the Herschel–Bulkley model for all experimental conditions.The effect of pH and electrolyte concentration is significant, affecting the type of association of the montmorillonite particles thus influencing the rheology, the three Herschel–Bulkley parameters and the apparent viscosity. There is a maximum of the yield stress, flow consistency index and apparent viscosity at the natural pH of the dispersions, while there is monotonous decrease of these parameters with increasing salt concentration. Various scenarios of particle associations are discussed and comparison with similar data from literature is also performed.Applied Clay Science. 01/2007;
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ABSTRACT: The effectiveness of lignite addition to prevent gelation of 6.42% w/w water–bentonite suspensions exposed to high temperatures has been studied, using twenty six lignites from various basins in Greece with variable organic and inorganic contents at concentrations of 0.5% and 3.0%. The lignite-free bentonite suspensions thickened considerably when heated at 177 °C for 16 h, as was indicated by a two-fold increase of the yield stress, when compared to samples hydrated only at room temperature. However plastic viscosity did not change appreciably. Full flow curves showed a Herschel–Bulkley behavior of all suspensions. Addition of lignite maintained the stability of the suspensions exposed to high temperatures (177 °C) by keeping the yield stress low and did not affect plastic viscosity. Some of the Greek lignites performed equally well with a commercial lignite product and improvements of 80 to 100% of the stability of the suspensions, compared to lignite-free suspensions, have been found. Lignite addition also lowered yield stresses for the hydrated samples. No specific trends have been identified between the effectiveness of lignites to stabilize bentonite suspensions and their humic and fulvic acids and humins content. However, those lignites with highest humic and fulvic acid contents have maximum stabilization capacity. Similarly, no specific trends have been observed between the stabilization capacity of lignites and their inorganic components such as oxygen and ash content and also with the cation exchange capacity. The effectiveness of the Greek lignites to stabilize bentonite suspensions is very high and the minor differences in the efficiency of the different lignites cannot be attributed solely to any specific component.Applied Clay Science. 01/2007;
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ABSTRACT: An integrated approach is presented for the flow of Herschel–Bulkley fluids in a concentric annulus, modelled as a slot, covering the full range of flow types, laminar, transitional, and turbulent flows. Prior analytical solutions for laminar flow are utilized. Turbulent flow solutions are developed using the Metzner–Reed Reynolds number after determining the local power law parameters as functions of flow geometry and the Herschel–Bulkley rheological parameters. The friction factor is estimated by modifying the pipe flow equation. Transitional flow is solved introducing transitional Reynolds numbers which are functions of the local power law index. Thus, an integrated, complete and consistent set, combining analytical, semi-analytical and empirical equations, is provided which describe fully the flow of Herschel–Bulkley fluids in concentric annuli, modelled as a slot. The comparison with experimental and simulator data from various sources shows very good agreement over the entire range of flow types.On présente une méthode intégrée pour l'écoulement des fluides d'Herschel–Bulkley dans un espace annulaire concentrique représenté par une fente, couvrant la gamme complète des types d'écoulement, à savoir laminaire, en transition et turbulent. Des solutions analytiques antérieures sont utilisées pour l'écoulement laminaire. Des solutions d'écoulement turbulent sont élaborées à l'aide du nombre de Reynolds de Metzner–Reed après avoir déterminé les paramètres de loi de puissance locaux en fonction de la géométrie de l'écoulement et des paramètres rhéologiques d'Herschel–Bulkley. Le facteur de friction est estimé en modifiant l'équation d'écoulement dans un tube. L'écoulement en transition est résolu en introduisant les nombres de Reynolds exprimés en fonction de l'indice de loi de puissance local. Ainsi, un ensemble intégré, complet et consistant, combinant des équations analytiques, semi-analytiques et empiriques, est fourni, qui décrit entièrement l'écoulement des fluides d'Herschel–Bulkley dans des espaces annulaires concentriques représentés par des fentes. La comparaison avec les données expérimentales et les données de simulateurs de diverses sources montre un très bon accord pour la gamme complète des types d'écoulement.The Canadian Journal of Chemical Engineering 07/2008; 86(4):676 - 683. · 1.00 Impact Factor