In Situ Formation and Evolution of Gas Hydrates in Water-in-Oil Emulsions Using Pressure Rheometry

Abstract

In oil and gas production and transportation a major concern is the formation of gas hydrates (crystaUine gas-water inclusion compounds that are stable at high pressures and low temperatures). Gas hydrates have a tenacious ability to plug pipelines, and may lead to unscheduled shut downs. The successful operation of pipeline transport with gas hydrates particles will depend on the ability to control gas hydrate agglomerations and depositions. Gas hydrates can be thermodynamically inhibited but this is proving cost ineffective and environmentally unfriendly. For this reason the oil/gas industry is moving to hydrate management rather than traditional methods of thermodynamic inhibition. One intriguing possibility would be to convert the water in the pipelines to non-agglomerating gas hydrates and then flow the slurry. However, this cannot be reliably achieved until basic understanding of hydrate slurry rheology is gained.To develop this fundamental understanding, in situ pressurized gas hydrate formation and rheological measurements from a water-in-oil emulsion have been conducted. In this work, small amplitude oscillatory and steady shear techniques have been used to characterize the rheological properties of these systems. The results demonstrate that hydrate formation can be detected in steady shear and oscillatory measurements, where a large viscosity (and elastic modulus) increase coincides with hydrate formation. Since temperature and pressure affect the thermodynamic stability of hydrates these are particular key variables that need to be tuned for this system.

Effect of the fluid shear rate on the induction time of CO2‐THF hydrate formation

“…Similar behaviour has been observed in previous studies characterizing the rheological properties of hydrate slurries. Hydrate formation experiments have been performed using an aqueous liquid phase initially free of hydrates and an experimental setup similar to the one used in the present study . As in these studies, we assumed that the peak in the temperature of the solution and the rapid increase in its apparent viscosity are two macroscopic indications of the end of the gas hydrate formation induction period and that the time at which they occur can be used as a measure of the induction time.…”

“…Furthermore, the exact flow characteristics generated at different agitation intensities in the mixing system and their effect on the gas‐liquid mass transfer coefficient, which affects the time required to achieve a given level of supersaturation in the liquid phase solution, can be deduced from the results of two other studies, in which these aspects were investigated using an almost identical mixing system . Rotational rheometers have been used in past studies to investigate the evolution with time of the rheological properties of hydrate suspensions formed from different systems and the performance of gas hydrate kinetics inhibitors . To the best of our knowledge, this is the first study that exploits such a device to examine the influence of the flow conditions in the liquid phase from which hydrates are formed on the induction time of gas hydrate formation.…”

Analysis of CO2 Hydrates in Crude Oils from a Rheological Point of View

“…Although several researchers have used rheometers to analyze the rheology of hydrates, in the majority of the cases, they use chemical substances, such as cyclopentane and tetrahydrofuran, to have measurements at atmospheric conditions, avoiding the inconvenience of working with high-pressure levels. − Other works have been carried out in flow loops. − In the specific case of pressure cells, only a limited number of investigations have been published and most of them used methane as the guest molecule. − In this study, the tests were performed in a pressure cell, with carbon dioxide as the guest molecule, because high concentrations of this gas have been reported in the Brazilian presalt oil wells, with large potential to form hydrates.…”

Rheological evaluation of kinetic hydrate inhibitors in NaCl/n‐heptane solutions

“…The solid hydrate particles may aggregate with time and can then block the flow . Because gas hydrates are formed in pipelines, rheological properties would change and slurry viscosity increases . Hence, measurement of slurry viscosity either directly by using rheometers or by measuring pressure drops during hydrate formation can represent the growth and aggregation of hydrate crystals and particles.…”