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 skin layer formation is directly related to the surface quality of the plastic produced. However, in Rapid Heat Cycle Molding (RHCM), the formation and movement mechanism of the skin layer is different from that of traditional molding. Therefore, the study on skin layer is of great significance for enriching RHCM theory and obtaining high surface quality products. This article reports results of experiments conducted on RHCM, utilizes multipoints sampling in the simulation and experimental results, and comparatively studies the skin layer structure of a single point as well as the thickness and orientation of multipoints with their variations by SEM and XRD method. Experimental results show that the product skin layer has asymmetric structure on two sides. The thickness of both the upper and lower skin layer decreases when its distance from the filling gate increases. Furthermore, it has been observed that the skin layer is mainly formed by α- and β-crystal type, in which the percentage of the β crystal and skin layer orientation are affected by the mold temperature and distance from the pouring gate.Polymer-Plastics Technology and Engineering 03/2014; 53(5). DOI:10.1080/03602559.2013.845210 · 1.48 Impact Factor
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ABSTRACT: Surge and swab pressures can be generated in different stages of well construction including tripping operations and reciprocation of drillstring in the wellbore. Significant surge and swab pressures can lead to a number of costly drilling problems such as lost circulation, formation fracture, fluid influx, kicks, and blowouts. This phenomenon is of economic importance for the oil industry.Theoretical and field studies indicate that pressure surges strongly depend on drillpipe tripping speeds, wellbore geometry, flow regime, fluid rheology, and whether the pipe is open or closed. Although a large number of studies were conducted in the past to investigate surge and swab pressures, experiments under controlled laboratory conditions have never been reported. This paper presents results of an experimental study aimed at investigating the effects of pipe speed (i.e., tripping speed), fluid properties and borehole geometry on surge and swab pressures under laboratory conditions. Other phenomena such as fluid gelling and pipe eccentricity effects were also examined. Experiments were performed in a test setup that has the capability of varying the tripping speed and accurately measure the surge or swab pressures. The setup consists of fully transparent polycarbonate tubing and inner steel pipe, which moves axially using a speed-controlled hoisting system. Experiments were conducted using mineral oil and polymeric fluids.A new regression model has been developed to calculate surge and swab pressures under steady-state flow conditions. The model is based on the results of approximate numerical solutions obtained by considering the annulus as a narrow slot. Model predictions were compared with experimental measurements and predictions of existing models. A satisfactory agreement has been obtained. Experimental results and model predictions confirm that the trip speed, fluid rheology, annular clearance and pipe eccentricity significantly affect the surge and swab pressures.Journal of Petroleum Science and Engineering 01/2013; 101:12-20. DOI:10.1016/j.petrol.2012.10.001 · 1.10 Impact Factor
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ABSTRACT: Recent laboratory and field studies performed by oil and gas service companies indicate that fracturing polymer may exhibit yield stress after water leak-off. Its rheology may be described by Herschel-Bulkley model. It is reported in the literature that yield stress might be responsible for low fracturing fluid cleanup efficiency. In this paper, we derive an extended analytical Buckley-Leverett type model for the displacement of non-Newtonian Herschel-Bukley fluid (e.g. fracturing fluid) by Newtonian fluid (e.g. hydrocarbon/water). Using this model, we study the effect of yield stress and other rheological parameters on fracturing fluid displacement efficiency. Parametric analysis indicates that high values of yield stress t0, consistency index K' and flow behavior index n' lead to low displacement efficiency. It is found that, for a given set of relative permeabilities, if a pressure gradient is not enough to overcome a critical pressure gradient, non-Newtonian fracturing fluid will not flow and only Newtonian fluid will be produced. It is demonstrated that low displacement efficiency can be overcomed by increasing displacing rate. Introduction Non-Newtonian fluids are extensively used in oil field development. As a result, flow and displacement of non-Newtonian fluid in porous media play an important role in many aspects of petroleum engineering. Generally, oil, gas and water in subsurface reservoir are considered as Newtonian fluid. For heavy oil, an initial pressure gradient is needed to flow. It may be treated as Bingham plastic fluid . Polymer solutions used to enhance oil recovery may be treated as power-law fluids [2-3]. For foam, concentrated fracturing fluid, and some drilling mud, Herschel-Bulkley model may be appropriate to describe the rheological behavior [4-6]. Fig. 1 provides a schematic description of those rheological models. Literature search indicates that considerable work is done in single-phase non-Newtonian fluid flow [2-3] and multi-phase non-Newtonian flow [6-8] in porous media. Wu et al. [1,7] present analytical models for two-phase flow and displacement of Bingham and power-law non-Newtonian fluid in porous media. Numerical model for multi-phase power-law non-Newtonian fluid flow is presented by Wu et al.  and validated by available analytical solutions  and experimental data. Numerical model for multi-phase Herschel-Bulkley non-Newtonian fluid flow is introduced by May et al.  to study the cleanup of polymer after hydraulic fracturing. However, the technical performance of their model is not verified. To the author's knowledge, there is no analytical model available regarding two-phase flow and displacement of Herschel-Bulkley fluid in porous media. In this paper, an analytical model is provided to study the displacement of Herschel-Bulkley fluid by Newtonian fluid in porous media based on Wu et al. [1,7]'s work. The solution derived in this work can be used to verify numerical models, such as the one presented by May et al.  and to study the displacement mechanism of Herschel-Bulkley fluid.