Rheological Properties of Hydrate Slurry in the Water-Based Drilling Fluid
Guilherme Mühlstedt, Jonathan Galdino, Diogo E. V. Andrade, Cezar Otaviano Ribeiro Negrão
Abstract
In deep-water drilling operations, gas hydrates may be formed when light compounds flow from the reservoir into the wellbore as a result of a kick. The crystalline structure must be broken so as to restart the drilling fluid circulation and consequently to remove the hydrate slurry from the wellbore. Although hydrate formation is an important industrial issue, there is still a lack of information about the rheological properties of hydrate slurries formed in drilling fluids. In the current work, hydrate formation was induced by adding tetrahydrofuran (THF) to the water-based drilling fluid, allowing hydrate crystallization at atmospheric pressure. The structure formed is the sII that is the structure of natural gas hydrates usually found in oil and gas fields. Rheometric tests that were conducted reveal that the hydrate slurry formed in the drilling fluid is a time-dependent elastoviscoplastic material in which the microstructure is irreversibly affected by shear. We investigated the influence of shear during the hydrate formation, and the results show that the elastic modulus and the yield stress of the statically (without shear) formed hydrate slurry are more than 1 order of magnitude larger than those dynamically formed (imposing shear). Finally, the hydrate slurry at the solid-like regime has a brittle structure as the linear-to-nonlinear transition limits are observed at very low oscillation strains (in the order of 10–3%). These findings can bring new perspectives for improving the techniques and procedures for flow startup of hydrate slurries in drilling fluid operations.