(18b) Hydrate Blockage Formation in Gas-Dominant Systems

Gas hydrates are ice-like solids, where molecular cages of water surround light hydrocarbon species at high pressure and low temperature. In subsea oil and gas flowlines, hydrate growth may result in constriction of the flow channel, increasing the frictional pressure drop across the line. In severe cases, hydrate formation may result in a complete blockage to production, requiring expensive remediation. Much of the benchtop and flowloop work to date has focused on hydrate formation from emulsified water in the oil phase, but there is insufficient data to inform hydrate growth rate or blockage mechanisms in gas-continuous systems. In this presentation, we propose a new conceptual model for hydrate blockage formation in gas systems, informed by the largest gas-dominant flowloop dataset collected to date. The mechanism includes a novel contribution for hydrate growth from liquid water dispersed in the gas phase, which provides a basis for sloughing behaviour observed in end-stage hydrate deposits. The growth model was benchmarked using a transient multiphase flow simulator (OLGA), and was able to accurately predict the average increase in frictional pressure drop within 0.2 psi/ft for high-velocity experiments. The effects of partial deposition and sloughing, hydrate film porosity, heat transfer resistance and surface roughness were not captured in the model, which represent a critical path forward for future experiments.