Influence of Petroleum Acids on Gas Hydrate Wettability

Abstract

Previous work has demonstrated that petroleum acids in some cases are able to convert systems with an initially high risk of hydrate plugging into easily flowable hydrate dispersions with low or no risk of plugging. In this work, we aim to identify the specific properties of the petroleum acids that make such a conversion possible. Petroleum acids are extracted from crude oils with anti-agglomerating hydrate behavior and fractionated into subfractions of different polarity by the use of solid-phase extraction. The separate effect of these subfractions on hydrate wettability is compared to the effect of the acid fraction as a whole, as studied by means of phase inversion in crude oil/brine emulsions. The results show that some acid subfractions display equal or even higher hydrate surface activity compared to the bulk acid matrix from which they are isolated. One of the subfractions displays an exceptionally high effect at low concentrations. Intermolecular effects may be of importance for the degree of effectiveness of the hydrate surface-active components. The acid fractions impose no or insignificant effects on lowering the interfacial tension between oil and water, implying that they are active at the hydrate−oil interface rather than the water−oil interface.

The effect of surfactants on hydrate particle agglomeration in liquid hydrocarbon continuous systems: a molecular dynamics simulation study

“…9 It should be noted that there are natural (as well as commercial) AAs, i.e., some oils contain naturally occurring surfactants that can prevent hydrate particles from agglomerating, such as surfactants in asphaltene or acid fractions of the oil. 10,11 The polyaromatic carboxylic acid surfactant molecules used in this study could be considered model molecules for these natural surfactants, 12,13 although it should be noted that the complexity of natural oils make it difficult to isolate the molecular structure of the active components.…”

A Multiscale Approach for Gas Hydrates Considering Structure, Agglomeration, and Transportability under Multiphase Flow Conditions: I. Phenomenological Model

“…In this sense, this study introduces new insights on the phenomena description (that is, a topological model) of how gas hydrates form, grow, and agglomerate in a much smaller scale than the ones presented so far in literature for gas–oil–water systems (the focus is liquid-dominant systems). This paper is theoretical and based on the following observations given in the literature: (A) water is never entirely converted into hydrates, but gas consumption presents an asymptote, proving that a phenomenon of kinetic limitation occurs, ,,, usually interpreted as a limitation due to the mass or heat transfer processes; (B) hydrates present a highly porous structure, visualized through a microscope; , (C) particles formed are visually much more voluminous than a perfect crystal should be in means of the amount of gas consumed; , (D) gas hydrates present a hydrophilic nature; ,, (E) when hydrates form, the oil–water emulsion can present a phase separation or inversion; ,,, (F) the water phase vanishes once hydrates form; (G) in the presence of surfactant additives, the hydrates structure can completely trap all liquid in the system (water and oil), called the dry-up phenomenon ; (H) higher driving forces can cause stable slurries for a longer time without the presence of surfactant additives (cold flow concept); (I) the use of additives can change the wetted angle of water–oil hydrates; and (J) a multiphase flow pattern can change all of the steps of gas hydrate formation and agglomeration, whereas the existence of hydrates can consequently change the flow patterns and structure characteristics. − …”

Methane hydrate formation behaviors in high water-cut oil-in-water systems with hydrate promoters

“…In the model, shells form rapidly rst, followed by a slow conversion of the internal, trapped water to hydrate, which is limited by mass transfer of the hydrate guest molecule through the shell. 7,8 Hoiland et al 9 have considered the interaction of hydrates and emulsions at high water cuts as they explored how the presence of hydrate particles can promote or delay the inversion of a water-crude oil emulsion (emulsion inversion describes the change in emulsion type from O/W to W/O or vice versa as discussed below). By comparing the water cut at inversion with hydrates to that without hydrates, Hoiland et al 9 predicted the relative wettability of the hydrate particles.…”

“…7,8 Hoiland et al 9 have considered the interaction of hydrates and emulsions at high water cuts as they explored how the presence of hydrate particles can promote or delay the inversion of a water-crude oil emulsion (emulsion inversion describes the change in emulsion type from O/W to W/O or vice versa as discussed below). By comparing the water cut at inversion with hydrates to that without hydrates, Hoiland et al 9 predicted the relative wettability of the hydrate particles. The results showed good correlation between the crude oil plugging behavior tested in a ow loop and the experimental wettability; crude oil, which formed oil-wet hydrates (through adsorption of natural components) showed no signs of plugging in the ow loop.…”