Pumping Hydrate Slurries in the Arctic: A Different Perspective

摘要

The formation of hydrates in oil-dominated production systems is a hazard that may potentially lead to theplugging of pipelines in deepwater and Arctic environments. Anti-agglomeration additives have been usedin the field as a mitigation strategy to prevent hydrates from growing into plugs. Studies have dealt withthe ability of certain crudes to form stable water in oil emulsions. These stable emulsions have beenproposed to be made in-situ with or without chemical additives. In recent years, an emphasis has beenmade to understand the mechanism of formation of stable hydrates that can be transported in a slurry form.In order to achieve this in the field, extensive work has been done to mathematically model hydrateformation and agglomeration with the aim to understand transportation of hydrates as a slurry mixturewithout plugging. One critical aspect to the slurry mixture is the complex slurry rheology which isdependent on the volume concentration of solids, that can include both hydrates and precipitatedasphaltenes, but is further complicated by the crystallization of hydrates by contact with a water droplet,and the growth into hydrates aggregates by agglomeration.The mining industry has been able to transport complex mixtures and operate without plugging inpipelines covering over distances from a few kilometers to 1000 km. The viscosity for non-Newtonianlaminar flows is often dependant on the shear rate and volume concentration of solids. The yield stressfor a Bingham mixture is controlled by additives. In recent years, the oil sands industry has developedbetter knowledge of the pumping of oil, bitumen mixtures often called “oil sand froth”. Learnings haveincluded velocity induced lubrication of pipe walls by forming a water layer or “self-lubricated” pipe flow,achieving lower friction than predicted by traditional models of viscosity mixing between two liquids.While the mechanisms of hydrate formation and agglomeration are different from traditional miningslurry, there are numerous practices from mining that can be applied to the pumping of stable hydrates;such as control of additives, control of shear rate, transition from a laminar to a turbulent regime, andself-lubrication of water-oil mixtures. In this paper the authors review some of the issues of hydrateformation, explore some efforts by researchers to understand hydrate-based slurry mixtures and proposesome comparisons with the handling of mineral based slurry mixtures and nuclear waste slurry mixturesto formulate a concept of stable flow without plugging.