Institute of Petroleum Engineering

Centre for Gas Hydrate Research Publications

Abstract 055
Hydrate Equilibrium Data of Multi-Component Systems in the Presence of Structure-II and Structure-H Heavy Hydrate Formers
Østergaard, K.K., Tohidi, B., Burgass, R.W., Danesh, A., and Todd, A.C.
Journal of Chemical and Engineering Data, 46(3), 703-708 (2001).

The effect of six newly discovered heavy hydrate forming compounds on the hydrate phase boundary of a gas mixture, a natural gas, and a model oil has been measured. The study, which is a continuation of a previous work(1), investigates the effect of cyclopentane, cyclohexane, neopentane, isopentane, methylcyclopentane, and methylcyclohexane at various concentrations. The first three compounds form structure-II hydrates, while the last three compounds are known to promote structure-H hydrates. The experimental hydrate dissociation data have been successfully predicted by the use of a thermodynamic model. The results show that structure-II is the stable hydrate structure for the systems investigated at various heavy hydrate formers concentrations (from 0.27 mol% to 59.66 mol%). Also, the structure-II heavy hydrate formers promoted structure-II hydrate formation whereas the structure-H heavy hydrate formers (at concentrations used) did not change the stable hydrate structure to structure-H, and hence inhibited hydrate formation in the above fluid systems. Based on the above study, it was concluded that the inclusion of structure-II heavy hydrate formers in the thermodynamic modelling would improve the reliability of hydrate free zone predictions in real reservoir fluids.

(1) Tohidi, B., Danesh, A., Burgass, R. W., and Todd, A. C., "Effect of Heavy Hydrate Formers on the Hydrate Free Zone of Real Reservoir Fluids (SPE 35568)", The European Production Operations Conference and Exhibition, Stavanger, Norway, 16-17 April, 257-261 (1996).

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