Methanol as a hydrate inhibitor and hydrate activator

Abstract

During their transport to processing plants, produced hydrocarbon streams are always accompanied by water appearing as a separate phase in contact with the hydrocarbons. Dramatic temperature and pressure changes during processing can lead to condensation of water and possibly hazardous formation of ice and hydrates. Historically, methanol has been the dominating chemical agent added to prevent the formation of solid water phases. In this work, the technique of molecular dynamics simulation has been utilized to investigate and illustrate the impact of methanol as a surfactant in a water-methane system. We have found that adding 5% of methanol boosted the diffusion of methane through the interface by more than 40% compared to the reference system. The amount of methane accumulated in the aqueous phase was also significantly higher. This effect will likely also result in a significant increase in homogeneous and heterogeneous hydrate formation in these regions in the case of the methanol-stimulated system, and thus necessitate the application of classical nucleation theory. In particular, our analysis emphasised the fact that several different hydrates may form in this scenario. In case of the homogeneous hydrate formation, there will theoretically exist an infinite number of hydrate phases corresponding to concentrations spanning the range between methane's solubility and its hydrate stability limit.

Stages in the Dynamics of Hydrate Formation and Consequences for Design of Experiments for Hydrate Formation in Sediments

“…The models for extending thermodynamic properties of water and fluid phases are discussed in detail elsewhere [19][20][21] and will not be repeated here due to space limitations. keep in mind that the parameters for free energies of inclusion have been calculated from MD simulations with the procedures described in Kvamme and Tanaka [12] for temperatures up to 280 K for CH4.…”

“…For the small cavities in structure I there is not statistical justification to distinguish between the effect of surround gas or liquid CO2. The models for extending thermodynamic properties of water and fluid phases are discussed in detail elsewhere [19][20][21] and will not be repeated here due to space limitations. Two aspects regarding Figure 2a,b are worth mentioning.…”

“…where J 0 is the mass transport flux supplying the hydrate growth. The phase transition in Equation 1it will be the supply of CH 4 or CO 2 across an interface of gradually more structured water towards the hydrate core, as discussed in Kvamme et al [19][20][21]. The units of J 0 will be moles/m 2 s for heterogeneous hydrate formation on the growing surface area of the hydrate crystal.…”

“…This rate is expected to be slightly higher than regular diffusion through a block of hydrate without dynamics of couplings to heat transport and dynamic situations of partial local dissociation and reformation. See Kvamme et al [21] for a brief summary of reported diffusivities of hydrate-formers through hydrate. In summary the diffusivities range from 10 −15 m 2 /s to 10 −17 m 2 /s.…”

“…Nevertheless, more detailed studies are needed to verify these observations in a scientifically satisfactory manner. For our purpose in the context of this work we The concentration profiles for CH 4 as a function of distance from the liquid side of the interface (z = 0 Å) to the hydrate side of the interface (z = 12 Å) is available from Kvamme [19,20] and Kvamme et al [21]. The diffusivity coefficient profile for CH 4 is assumed to be the same as for CO 2 since the diffusion of CH 4 and CO 2 through the liquid/water interface is dominated by the gradually increased structure of water towards the hydrate side of the interface.…”