Crystal growth phenomena of CH4 + C3H8 + CO2 ternary gas hydrate systems

摘要

Gas hydrates are crystalline solids comprised of a three-dimensional network of water cages that can trap small hydrocarbon molecules at high pressure and low temperature. Formation of gas hydrates can lead to blockages in subsea oil and gas flowlines, where these conditions are readily achieved. As gas reserves mature over time, new CO2-rich reservoirs can be prolific hydrocarbon producers for markets willing to bear the additional production costs. However, there is a lack of understanding about the formation behavior and growth morphology of CO2-rich hydrates. In this work, hydrate growth rate and resistance-to-flow (torque) data for a ternary CO2-rich gas mixture were measured in a high-pressure sapphire autoclave apparatus and were compared with baseline data for a pure methane system. Images of hydrate growth and eventual plug formation were captured for methane hydrate and ternary gas systems, where early hydrate growth in the latter was dominated by an opaque film nucleating at the gas-water-wall interface and growing into both gas and water phases with time. Only 7 vol% methane hydrate was required to increase the motor torque above its baseline value, while at least 20 vol% hydrate was required when formed from the CO2-rich ternary gas. These new observations provide insight into the effect of guest species solubility on hydrate growth and resistance-to-flow in the resultant slurries, which are key parameters when assessing the risk of hydrate blockage in oil and gas pipelines. (C) 2016 Elsevier B.V. All rights reserved.