Development of an Empirical Model for Settling of Solids in Gelled Foams

Abstract

The underbalanced drilling fluid plays a vital role in the field of exploration of coal bed methane and tight gas reservoirs. It is used to minimize the formation damage and other drilling associated problems. Foam is considered as a popular alternative over the air in underbalanced drilling operations. Development of stable and uniform foam and prediction of its rheological behaviour under dynamic borehole conditions are real challenges in the successful drilling operations. If not designed properly, drilling fluid will fail to transport the cuttings to the surface efficiently. The present study focuses on the development of an empirical correlation for settling velocity of solid cuttings through gelled foams. A number of solids such as coal, sand and shale with variable particle sizes were selected for the present study. Foam fluids prepared with different compositions were characterized. Effects of various parameters such as foam density, composition, viscosity, gel strength, stability and quality, which control the hydrodynamic behaviour during drilling, were studied in detail. The settling velocities of cuttings were experimentally determined for foams with variable compositions. An empirical model has been developed for settling velocity of solid cuttings through gelled foams. This correlation is validated using different solid–fluid experimental data. The model is found to satisfactorily trace the experimental data. This model can be used in designing and characterizing the gelled foam better than the existing models.