Clathrate hydrates are solid compounds containing small organic molecules (e.g., methane, ethane, or cyclopentane) that form at high pressure and low temperature conditions, such as the conditions typically found inside oil/gas flowlines. Thus, gas hydrates can form and plug oil and gas flowlines causing major safety, environmental and economic concerns. Current research has focused on advanced strategies to prevent hydrate plug formation in flowlines. Particularly critical is a better understanding of the rheological properties of gas hydrate slurries. An increase in the viscosity of a hydrate slurry can increase the pressure drop in the flowlines and can thus provide an early warning sign of hydrate plugging. Several researchers have conducted research to understand the rheological properties of gas hydrate slurries using high or ambient pressure rheometers, as well as large scale flowloops. Our recent investigations of gas hydrate slurries have been conducted using a high pressure rheometer. These measurements were conducted at various temperatures, pressures and water contents. While challenging, high pressure measurements are beneficial as they are a closer representation of the actual condition in oil/gas flowlines. A common challenge in high pressure measurements is the difficult in attributing any trend in viscosity profiles to physical phenomena such as bedding/settling and wall growth. Another challenge is the difficulty in quantifying agglomeration phenomenon that affects the hydrate particle size distribution. In our recent work, we developed a new visual ambient pressure rheometer cell. The new visual rheometer cell has a similar geometry to that of our high pressure rheometer cell, and allows observation of the flow patterns of hydrate slurries that are being measured. As such, changes in viscosity profiles can be associated with physical phenomena. In this work, we used model (sII) hydrates formed from cyclopentane. The benefit of cyclopentane hydrate is that it forms at ambient pressure and low temperature. Hydrate slurries formed from both non-emulsified and emulsified model systems were investigated. Hydrate slurry development in the non-emulsified systems exhibited several stages including initial formation, wall growth and sloughing, which led to sharp fluctuations in the viscosity profiles. In contrast, the hydrate slurries from the emulsified systems were well dispersed with minimal wall growth, resulting in smooth viscosity profiles.

Visualization of hydrate slurries coupled with slurry viscosity measurements

2019 Fall National Meeting

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