Measuring filter-cake cohesive strength and flowability

Abstract

The filter-cake has a critical role in temporarily reducing the permeability of the wellbore to prevent issues such as lost circulation, formation damage, wellbore collapse and differential sticking. The filter-cake's ability to perform these functions may be impaired by its deterioration caused by the circulation of fluid, swabbing or mechanical interaction. Therefore, being able to measure the strength of the filter-cake, and hence its ability to withstand disturbances, is important to ensure optimal drilling fluid design.Two water-based reservoir drilling fluids were used to produce filter-cakes under high differential pressures. The filter-cakes were thereafter analysed using a rheometer with a specially designed cell for accurate powder shear rheology. This enabled measurement of the cohesive strength and flowability of the filter-cakes.It was found that filter-cakes composed of a conventional reservoir drilling fluid with CaCO3 and polymers, showed low cohesive strength and high flowability. The other fluid, which contained cellulose-based fibres in addition to CaCO3 and polymers, showed much higher cohesion and lower flowability.It was concluded that the test methodology could be very useful in relation to optimising drilling fluid design, particularly for wells were lost circulation, wellbore stability and differential sticking may be relevant problems. It was also concluded that the addition of cellulose-based fibres may significantly increase the filter-cake strength in a water-based drilling fluid.