The effect of particle properties and solids concentration on the yield stress behaviour of drilling fluid filter cakes

Filter cakes made from model water-based drilling fluids were tested to determine cake properties such as porosity, thickness and yield stress. The effects of drilling fluid particle concentration, size distribution and shape on the properties of the resulting cakes were investigated. A hole punch tester was used to find the shear stress of the cakes, obtaining a yield stress from the measured peak force. The cake yield stress increased with increasing barite solids content in the fluid from 16.5 kPa at 3.1 vol% to 65.6 kPa at 24.8 vol%. A similar trend was observed for cakes made from calcium carbonate. Furthermore, the calcium carbonate cakes were thicker and stronger than the barite equivalents, with yield stresses increasing by between 29% and 56%. The addition of calcium carbonate particles to the existing barite network did not affect the cake thickness appreciably but gave cakes of lower porosity and higher yield stress.BP ICA