API RP 13D:2006 pdf download
API RP 13D:2006 pdf download.Rheology and Hydraulics of Oil-well Drilling Fluids.
4.8.8 General statements regarding drilling fluids are usually subject to exceptions because of the extraordinary con)lexity of these fluids
4.9 Rheological models
4.9.1 Rheologecal models are intended to provide assistance In characterizing fluid flow. No single. commonly.used model completely describes theological characteristics of &ilIing fluids over their entire shear-rate range. Knowledge of rheological models combined with practical experience is necessary to lully understand fluid performance. A plot of si-lear stress versus shear rate (rheoglam) is often used to graphically depict a rtieological model.
4.9.2 Thngham Plastic MOdeL This model describes fluids in which the shear stressshear rate ratio is linear once a specific shear stress has been exceeded. Two parameters, plastic vscosify and yieJd poinL are used to describe this model, Because these parameters are determined from shear rates of 511 St and 1022 s’. this model characterizes fluids in the higher shear-rate range. A rheograni of the Bingham plastic model on rectilinear coordinates is a straight me that intersects the zero shear-rate axis at a shear stress greater than zero (ye.(dpoint).
4J.3 Power Law: The Power Law is used to descnbe the flow of shear thinning or pseudoplastic drilling fluids. This model describes fluids in which the theogram is a straight line when plotted on a log-log graph. Such a tine 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 511 8 and 1022 1 However, the generalized power law applies it several shear-rate pairs are defined along the shear-rate range of interGst. This approach has boon used in the recent versions of API RP 130.
4.9.4 Herschel-Budey ModeL Also called the rnodified power law and yiofd-psuodoptastic model, the Herschel• Bulldey model is used to describe the flow of pseudoplastic &ilbng fluids which require a yield stress to initiate flow. A rheogram of shear stress minus yield stress versus shear rate is a straight line on log-log coordinates. This model is widely used because it (a) describes the flow behavior of most drilling fluids. (b) includes a yield stress value inWorlant for several hydraulics issues, and (C) includes the Bingham plastic model and power law as special cases.
4.9.5 The theological parameters recorded ., 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 oases 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 theological 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 theological properties.
5 Determination of drilling fluid rheological parameters
5.1 Measurement of rheological parameters
The determination of drilling fluid theological 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) Descnption
The Marsh funnel Is widely used as a field measunng 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 hters of drilling fluid with an orifice at the bottom of the cone. The instrument is designed so that by following standard ocedures the outflow time of one quart of fresh water at 70 F t 5 F (21 C ± 2C) is 26 a ± 0.5 a.
b) Uses
Funnel viscosity is a rapid. simple test that is made routinely on all hquid drilling fluid systems. It is most useful to alert personnel to changes in the dnlling fluid properties or conditions. When a change In funnel viscosity is observed. theological tesbng usig 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 of the same density.
