Non-Dispersed Weighted Muds
Authors: Anderson Duane B. 
Published: December 2007

This paper was prepared for presentation at the 47th Annual Fall Meeting of the Society of Petroleum Engineers held in San Antonio, Tex., Oct. 8–11, 1972. 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 who the paper is presented. Publication elsewhere after publication in the JOURNAL 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. 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.

Abstract
Non-dispersed weighted muds with controlled clay solids have been formulated using bentonite, a dual-action polymer (or selective flocculant), barite, and a polyacrylate fluid loss reducer. Viscosity and fluid loss control are achieved by the action of the polymers on specific quanta ties of bentonite and the barite used for increasing density. Laboratory tests and field usage have shown this fluid to have excellent stability at elevated temperatures and pressures. Common drilling fluid contaminants such as cement, gyp, and carbon dioxide can be easily treated. Maintenance of this fluid is based on chemical and mechanical means of solids removal rather than treating the effect of solids. Field application has shown this system is easily maintained and provides a superior fluid for drilling.

Introduction
The history of drilling fluid treatment can be summarized as a development of chemicals and materials which can be added to a mud system to obtain certain properties. Bentonite was used to increase the viscosity and resulted in improved removal of bit cuttings from the well. As drilling continued, the viscosity would increase further and phosphates or quebracho (dispersants) had to be added to reduce the viscosity. Continued additions of dispersants to thin the mud further increased the tolerance of the mud to drilled solids, which in turn increased the viscosity. Thus, the effect was treatment so that the drilling mud would tolerate more solids rather than elimination of the cause.
In 1961 a low solids-low weight drilling fluid was described in a paper by Lummus et. al. Figure 1 shows the improvement in penetration rate and the decrease in the number of bits and rig days by reducing the solids content of a drilling fluid. Since that time, various papers have shown that drilling rate papers have shown that drilling rate increases with the use of low solids-low weight muds.
Lummus and Lanman and Willingham have shown how polymers function in the presence of bentonite and drilled solids in a low weight system. some papers have given field results obtained with weighted non-dispersed mud, but no formulation or laboratory tests on this type of system has been formally reported.
POLYMER REACTION WITH BENTONITE POLYMER REACTION WITH BENTONITE Before discussing the formulation of weighted non-dispersed drilling fluids, low weight muds of this type should be described. Various papers have given the ingredients used in the papers have given the ingredients used in the formulation of this mud and the results of using them. however, no description of the polymers involved and their reaction with polymers involved and their reaction with bentonite has been given.