Offshore Technology Research Center

 

OTRC Project Summary

Project Title:

Hydrate Melting and Related Foundation Problems

Prinicipal Investigators:

Jean Louis Briaud

Sponsor:

National Science Foundation

Completion Date:

May, 1994

Final Report ID#

A57(Click to view final report abstract)

Due to economy and energy related reasons, offshore exploration has had to move to deeper depths where temperature and pressure values are favorable to the stability of gas hydrates.

Platforms are very likely to be anchored to ocean floors where hydrates exist.  However, these hydrates are at a marginal state of pressure and temperature.  Therefore, any variation in one of these parameters due to manmade processes may induce their dissociation.  Oil production causes the hot oil (say 100°C) to flow up through the conductor and consequently to transfer heat into the soil.  Gas bubbles will be released from the dissociated hydrates and will induce cavity expansion or/and hydraulic fracturing of the soil jeopardizing the stability of the platform.

The main objective of this research is to develop a realistic scenario for the melting process of hydrates, its influence on the surrounding soil mass and check experimentally its validity.  This study needs to specify the extent to which the heat is transferred from the oil conductor to the soil-hydrate medium.  To do so, the effect of thermal properties of the soil and the hydrates such as thermal conductivity, specific heat, latent heat for the hydrates exclusively and thermal diffusivity is to be evaluated.

These parametric studies will be performed for different soil-hydrate configurations that would imitate actual situations in the field and will provide an understanding of the potential hazard that melting hydrate might present for the safety of foundations.

The post melting behavior of hydrate-bearing sediments as foundation material will be carefully examined.  Simulations will be performed to identify the most realistic failure mechanism such as heave, cavity expansion or hydraulic fracturing and evaluate their impact on the engineering properties of such soils and the danger that it could represent to the stability of the foundations.

In other words, the aim of this research is to provide reasonable answers to the following questions:

  1. Will the temperature in the soil due to the heat generated by the hot conductor rise enough to melt the hydrates?
  2. If the hydrates melt, what would be the soil response to the gas generation process?

Related Publications: Chaouch, A. and Briaud, J.-L., “Post Melting Behaviors Gas Hydrates in Soft Ocean Sediments,” Proceedings, Offshore Technology Conference, 1997.

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