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.
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