Premelting-Induced Agglomeration of Hydrates: Theoretical Analysis and Modeling.

Ngoc N Nguyen,Hans-Jürgen Butt,Rüdiger Berger

doi:10.1021/acsami.0c00636

Abstract

Resolving the long-standing problem of hydrate plugging in oil and gas pipelines has driven an intense quest for mechanisms behind the plug formation. However, existing theories of hydrate agglomeration have critical shortcomings, for example, they cannot describe nanometer-range capillary forces at hydrate surfaces that were recently observed by experiments. Here, we present a new model for hydrate agglomeration which includes premelting of hydrate surfaces. We treat the premelting layer on hydrate surfaces such as a thin liquid film on a substrate and propose a soft-sphere model of hydrate interactions. The new model describes the premelting-induced capillary force between a hydrate surface and a pipe wall or another hydrate. The calculated adhesive force between a hydrate sphere (R = 300 μm) and a solid surface varies from 0.3 mN on a hydrophilic surface (contact angle, θ = 0°) to 0.008 mN on a superhydrophobic surface (θ = 160°). The initial contact area is 4 orders of magnitude smaller than the cross-sectional area of the hydrate sphere and can expand with increasing contact time because of the consolidation of hydrate particles on the solid surface. Our model agrees with the available experimental results and can serve as a conceptual guidance for developing a chemical-free environmentally friendly method for prevention of hydrate plugs via surface coating of pipe surfaces.

Highlights

Pipelines are used for transporting crude oils and natural gases from drilling sites to processing complexes
Intensive use of chemicals raises concerns about the costs of production and negative impacts on the environment.[39−41] Alternatively, hydrophobic coating of the pipe wall is emerging as a promising chemicalfree technique for preventing hydrate plug formation.[32−34] We have indicated that capillary forces, which act as attaching forces, between a hydrate particle and a pipe wall, decrease substantially when the contact angle θ of water on the pipe surface is increased (Figure 5b)
We have developed a new model of the interfacial interactions between a hydrate particle and a solid surface and between a hydrate particle and a hydrate surface

Summary

Introduction

Pipelines are used for transporting crude oils and natural gases from drilling sites to processing complexes. Crude oils contain certain fractions of water in the form of emulsified water droplets such as water-in-oil emulsions. Water can exist together with oils in geological pore structures and is extracted out from the pores concurrently with oils.[1] Water may be injected into the wells during extraction of oils to compensate the pressure drop in the wells. After multiple-stage separation at drilling sites, the mass fraction of water in crude oils is reduced to below 1% (ref 1), which is the fraction of water in crude oils in pipelines. Experiments indicated that the diameters of emulsified water droplets in crude oils are typically in the range between 1 and 300 μm.[2]

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Discussion

Conclusion