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API RP 13D-2006 pdf free download

API RP 13D-2006 pdf free download.Rheology and Hydraulics of Oil-well Drilling Fluids.
4.9 Rheological models 4.9.1 Rheological models are intended to provide assistance in characterizing fluid flow. No single, commonly-used model completely describes rheological characteristics of drilling fluids over their entire shear-rate range. Knowledge of rheological models combined with practical experience is necessary to fully understand fluid performance. A plot of shear stress versus shear rate ( rheogram ) is often used to graphically depict a rheological model. 4.9.2 Bingham Plastic Model : This model describes fluids in which the shear stress/shear rate ratio is linear once a specific shear stress has been exceeded. Two parameters, plastic viscosity and yield point , are used to describe this model. Because these parameters are determined from shear rates of 51 1 s -1 and 1 022 s -1 , this model characterizes fluids in the higher shear-rate range. A rheogram of the Bingham plastic model on rectilinear coordinates is a straight line that intersects the zero shear-rate axis at a shear stress greater than zero ( yield point ). 4.9.3 Power Law : The Power Law is used to describe the flow of shear thinning or pseudoplastic drilling fluids. This model describes fluids in which the rheogram is a straight line when plotted on a log-log graph. Such a line has no intercept, so a true power law fluid does not exhibit a yield stress. The two required power law constants, n and K , from this model are typically determined from data taken at shear rates of 51 1 s -1 and 1 022 s -1 . However, the generalized power law applies if several shear-rate pairs are defined along the shear-rate range of interest. This approach has been used in the recent versions of API RP 1 3D. 4.9.4 Herschel-Bulkley Model : Also called the “modified” power law and yield-psuedoplastic model, the Herschel- Bulkley model is used to describe the flow of pseudoplastic drilling fluids which require a yield stress to initiate flow.4.9.5 The rheological parameters recorded in an API Drilling Fluid Report are plastic viscosity and yield point from the Bingham plastic model. These two terms can be used to calculate key parameters for other rheological models. 4.9.6 The mathematical treatment of Herschel-Bulkley, Bingham plastic and power law fluids is described in Clause 5. 4.9.7 The flow characteristics of a drilling fluid are controlled by: the viscosity of the base fluid (the continuous phase); and any solid particles, oil, or gases within the fluid (the discontinuous phases); the flow channel characteristics; and the volumetric flow rate. Any interactions among the continuous and discontinuous phases, either chemical or physical, have a marked effect on the rheological parameters of a drilling fluid. The parameters calculated by use of Bingham plastic, power law and other models are indicators that are commonly used to guide fluid conditioning to obtain the desired rheological properties. 5 Determination of drilling fluid rheological parameters 5.1 Measurement of rheological parameters The determination of drilling fluid rheological parameters is important in the calculation of circulating hydraulics, hole cleaning efficiency, and prediction of barite sag in oil wells. 5.1.1 Orifice viscometer—Marsh funnel a) Description
The Marsh funnel is widely used as a field measuring instrument. The measurement is referred to as the funnel viscosity and is a timed rate of flow, usually recorded in seconds per quart. It consists of a conical funnel that holds 1 .5 liters of drilling fluid with an orifice at the bottom of the cone. The instrument is designed so that by following standard procedures the outflow time of one quart of fresh water at 70 °F ± 5 °F (21 °C ± 2°C) is 26 s ± 0.5 s. b) Uses Funnel viscosity is a rapid, simple test that is made routinely on all liquid drilling fluid systems. It is most useful to alert personnel to changes in the drilling fluid properties or conditions. When a change in funnel viscosity is observed, rheological testing using a concentric-cylinder viscometer will identify the change in fluid properties. It is, however, a one-point measurement and therefore does not give any information as to why the viscosity may be high or low. No single funnel viscosity measurement can be taken to represent a consistent value for all drilling fluids of the same type or of the same density.

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