THE FILTRATION PROPERTIES OF COMPRESSIBLE MUD FILTERCAKES

The permeability and compressibility of drilling fluid filtercakes are investigated, by experiment and by modelling, as a function of the ba rite content of the cake and of the filtration pressure. Filtration ex periments give the rate of fluid loss as a function of pressure, and t he porosity of the cake is determined at the end of each experiment. T hese data are then combined with models for cake growth to predict the rate of fluid loss in two cases: at a constant filtration pressure, a nd when there is a step increase in the filtration pressure during the course of the experiment. Good agreement with experiment is obtained. The model predicts that the cake porosity varies with distance from t he filter paper, as is observed experimentally. The model described he re is generally applicable to filtration of other fluids, e.g. polymer ic fracturing fluids. (C) 1997 Elsevier Science B.V.