Page 231 - Handbook Of Multiphase Flow Assurance

230 10. Research methods in flow assurance

FIG. 10.7 Schematic of sI and sII hydrates formation.

12
12 4
Cubic structure (sII) hydrate is formed when 5 and 5 6 cavities arrange themselves in a
lattice. sII hydrate may be formed with molecules ranging in size from argon (0.38 nm diam-
eter) to isobutane (0.65 nm diameter).
Hexagonal structure hydrate (sH) was discovered recently (Ripmeester et al., 1987). This
12
3 6 3
12 8
hydrate is composed of the three types of cavities: 5 , 4 5 6 , and 5 6 , forming a lattice
shown in Fig. 10.10. Sizes of molecules which may participate in sH hydrate range from that
of argon (0.38 nm diameter) to hydrogen sulfide (0.46 nm) and from the size of cyclohexane
(0.75 nm) to that of methylcyclohexane (0.86 nm diameter).
Any molecule that is of the abovementioned size or smaller may be a simple or binary hy-
drate former. The exception to this statement are the molecules with a size smaller than argon.
These very small molecules can't form hydrate because they cannot stay in the cavity formed