Institute of Petroleum Engineering

Centre for Gas Hydrate Research Publications

Abstract 018
Measurement and Prediction of the Amount of Gas Hydrates
Avlonitis, D., Danesh, A., and Todd, A. C.
BHR Group Conference - Multiphase 95, Cannes, France, 7-9 June (1995).
Low oil prices and the highly competitive nature of the world-wide oil and gas industry demand more efficient and cost effective design and operation in the offshore and subsea sectors. The use of extended gathering networks and transportation of unprocessed wellstreams are two attractive options which may have major impact on the development of many marginal oil and gas fields in the North Sea. These subsea pipelines carry a number of potential mixtures of fluids such as oil/gas with formation water and gas with condensed water. A major concern with these pipelines is the possibility of their blockage due to hydrate formation which can lead to serious operational and safety problems. These problems can be avoided by either preventing hydrate formation or allowing the formation of hydrate, but preventing their aggregation and transporting hydrates as a slurry. In the latter case, which is receiving considerable attention recently, information on the amount of hydrate to be transferred is very valuable in the design and operation of transfer-lines. In this paper, novel equipment and numerical models recently developed for measuring and predicting the amount and composition of equilibrium phases in the presence of gas hydrate are presented. Two different design hydrate rigs have been employed in generating dissociation and compositional data. Synthetic and real reservoir fluids, including a dry gas and a gas condensate, in different production scenarios, such as in the presence of condensed water, methanol, or formation water, have been investigated. All fluid phases, including the water-rich phase, have been modelled by the Valderrama modification of the Patel and Teja (VPT) equation of state (EoS) with a non density dependent mixing rule. In order to take into account the effect of salt(s), the Debye-Hückel activity model was combined with the EoS with only one adjustable parameter. Solid solution theory has been used for hydrate phases. The model predictions are compared with the experimental data and good agreement is demonstrated.

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