Plastic Flow Properties of Drilling Fluids - Measurement and Application

The application of Bingham's law to the behavior of drilling fluids in arotational viscometer permits the expression of viscometric data in terms ofplastic viscosity and yield value, the flow properties of a plastic fluid. Acommercially available rotational viscometer is described, and when modified toa multispeed type viscometer, is shown to provide a simple and convenientinstrument for the measurement of these properties both in the laboratory andin the field. The data obtained are shown to be useful in defining andunderstanding mud control problems relating to chemical treatment and to thehydrodynamic behavior of muds. Introduction The highly complex drilling fluids which are required for deep drillingoften give rise to new and unusual mud control problems. Rapid and economicsolutions to these problems may require, on the one hand, better understandingof the changes which contaminants and chemical treating agents produce in thecolloidal and inert solids of the mud, or, on the other hand, closer control ofthe hydrodynamic behavior of the mud. The latter objective obviously can beachieved only if a correct rheological analysis of the flow behavior ofdrilling muds is available and if this is accompanied by the appropriaterheological measurements. The purpose of this paper is to describe suchmeasurements in the field, and to show how the resulting data can be of valuein solving difficult mud control problems. It is now generally recognized that Bingham's law of plastic flow can beutilized in describing the hydrodynamic behavior of drilling fluids in thenon-turbulent flow range. Beck, Nuss, and Dunn have recently applied this lawto the flow of mud in small pipes, and Rogers has reviewed the rather extensiveliterature on this subject. So far, however, the use of Bingham's law has beenrestricted to the analysis of mud flow in pipes or capillary tubes, and it hasnot been directly applied to the flow in rotational viscometers. In the work tobe reported, the Reiner-Riwlin equation for the flow of a plastic fluid in arotational viscometer has been utilized to permit the expression of multispeedviscometric data in terms of plastic viscosity and yield value, the twoabsolute flow properties of a plastic fluid. T.P. 3061