Effect of Temperature on the Flow Properties of Drilling Fluids
Authors: Bartlett L.E. 
Published: December 2007

American Institute of Mining, Metallurgical and Petroleum Engineers, Inc.
This paper was prepared for the 42nd Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Houston, Tex., Oct. 1–4, 1967. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made.
Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Introduction
It has been widely accepted by drilling people that the behavior of drilling muds is generally very close to that of a Bingham plastic. The flow behavior for a Bingham plastic is expressed by a linear equation of the form Y = mX + b. All of the most widely used tests and procedures for controlling mud systems and equations for designing drilling programs are based upon this premise. The results of this paper indicate that none of the present day drilling fluids follow the Bingham plastic flow model and, in reality, the flow equations expressing the relations of shear stress to shear rate vary from simple formulas having a few exponential terms to polynomials of any degree of complexity.
Recently, while experimenting with mud samples from a hot rolling oven, we noticed dramatic differences in viscosity at various temperatures. Since the Farm meter is not satisfactory for measuring flow properties at elevated temperatures, a simple pipe viscosimeter was devised to make a series of tentative investigations with temperatures ranging up to 140F. In these investigations it was found that mud properties at surface conditions are greatly different from those at conditions prevailing in the hole. For example, the viscosity of a particular lignosulfonate mud decreased by a factor of two when the temperature was increased from 80F to 140F. This decrease is much more than is commonly thought to occur with such a change in temperature.
These tentative investigations indicated the need to devise a more elaborate viscosimeter, described in Appendix 1, with which to conduct more extensive investigations and to attempt to develop a correlation of actual flow properties at elevated temperatures with measurements made using a Farm meter. However, because of the variations of behavior among muds, no method could be found to use data obtained at surface temperatures to predict flow behavior at down-hole temperatures. There seem to be two reasons for this difficulty:drilling muds do not act as Bingham plastics, even at room conditions, andflow characteristics seldom, if ever, follow any one pattern throughout the range of temperatures commonly encountered.
From these investigations, the following conclusions were developed.Present day drilling fluids do not behave as Bingham plastics.