Behaviour of Mud Under Borehole Conditions
Authors: de Lautrec J. 
Published: December 2007

This paper was prepared for the SPE-European Spring Meeting 1974 of the Society of Petroleum Engineers of AIME, held in Amsterdam, the Netherlands, May 29–30, 1974. 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 publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor 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 Netherland Section of the Society of Petroleum Engineers, P. O. Box 228, The Hague, the Netherlands. 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.

Abstract
Petroleum engineers know how important to be familiar with the precise characteristics of drilling and completion fluids under bore-hole conditions.
For this reason we have perfected a set of equipment by means of which drilling and completion fluids can be examined under the severest of conditions (pressure : 500 bars, temperature : 250 degrees C, circulation speed of the fluid : 4 m/s).
Tests carried out with this equipment make the following studies on the muds possible in terms of pressure, temperature and circulation speed :–Evolution of rheological and filtration characteristics–Determination of the limits of utilization, and more particularly of the stability of the emulsions–Defining of plugging action, taking into account the petrophysical characteristics of the reservoirs–Choice of the most suitable fluid for eliminating plugging caused by the mud–Estimation of the effect of the cakes of mud on the quality of the cementing.

Introduction
Rheological and filtration characteristics of drilling and completion fluids are generally determined at ambient pressure and temperature and, above all, in steady conditions. Until recently, these measurements enabled most of the "mud" problems so far encountered in practice to be problems so far encountered in practice to be solved, at least in part.
For some years now, owing to the development of deep drilling and, above all, of off-shore boring, it has no longer been possible to solve the technical problems encountered (in particular the effects of pressure and temperature in deep wells and the behaviour of side-walls in off-shore directional drillings) solely through the use of measurements made under surface conditions. Owing to the excessively high cost price of current boring operations, the rheological and filtration characteristics of the fluids used for drilling and completion of the wells must be accurately known if the technical difficulties arising are to be solved. In some cases, these characteristics differ sharply from those determined under normal conditions. For example, under surface conditions, the API static filtrate of a heavy FCL-LC mud is slight (less than 5 cm3).
On the other hand, under pressure (200 b) temperature (80 degrees C), and circulation (1 m/s), the dynamic filtrate obtained for a differential pressure of 7 kg/m exceeds 60 cm3 in 30 mn. pressure of 7 kg/m exceeds 60 cm3 in 30 mn. In an attempt to solve these problems, ELF RE has designed and constructed a set of equipment by means of which muds can be examined in bore-hole conditions.