The fractions having a limited range in particle size separated from a typical Texas Gulf Coast shale drilling mud have been recombined systematically into a regular series of mud systems for which the' viscosity, gel-strength, and waterloss have been obtained. The data have been studied and the effect of particle size on the physical properties of the mud systems has been ascertained to the end that the viscosity can be predicted for a given concentration of solids in a drilling mud system provided the distribution of particle size is known.
Les parties solides séparées d'une boue de forage caractéristique à base d'argile du Gulf Coast du Texas, et réparties suivant la grosseur des particules, ont été recombinées systématiquement de façon à constituer une série régulière de systèmes de boue, dont on a déterminé la viscosité, la résistance du gel et la perte d'eau. On a étudié ces données, ainsi que l'effet de la grosseur des particules sur les caracté- ristiques physiques des systèmes de boue; de façon à ce qu'on puisse prédire la viscosité d'une concentration donnée de corps solides dans un système de boue de forage pourvu que la distribution de la grosseur des particules soit connue. use of the Sharples super-centrifuge (2). The distribution of particle size for one of the muds, namely, the Curkeet mud (Figure I) has been studied further to ascertain its effect on some of the physical properties of drilling fluids which are of importance in the drilling of wells by the rotary method.
The Curkeet mud is a typical and normal Gulf Coast shale drilling mud, the solids of which were found by Fancher and Oliphant to be 30 per cent silica, 20 per cent calcite, and 50 per cent illite. Only about 7-8 per cent of the total solids in the mud as it came from the field were of colloidal dimensions.
In order to get at the problem, the numerous small fractions which had been obtained in the investigation (Table I) were recombined into five "major fractions" (Table 11) and these five major fractions were mixed systematically in various and different proportions into 170 composite systems of suspensions in water. The composition of the various mud systems so obtained is best portrayed by histograms (Figure 2). Similar systems of histograms can be prepared for any drilling fluid for which the distribution of particle size is known. The viscosity, gel-strength, and filtration rate (Standard API water loss) (I) of each of the various mud systems were measured at at least one, and, whenever possible, also at two or three concentrations, the concentrations employed being 28, 23, and 18 per cent solids, respectively.
The distribution of minerals, particle size and density for two shale drilling muds from the Hastings Effect of particle
