Hydrate melting and related foundation problems

Abstract

In this research, the potential hazard to offshore foundations induced by gas hydrate melting has been investigated. An analytical solution was derived for the heat transfer phenomenon in marine soils rich in gas hydrates. A numerical analysis was also performed to evaluate the evolution of temperature distributions within the sediments in the vicinity of the platform foundations as time varies. A parametric study was conducted on relevant parameters such as the thermal porperties of the medium, geothermal gradients, cluster size and hydrate morphology. Their effect on heat transfer was determined. Soil thermal properties used in the F.E.M. model were selected from the literature or determined experimentally. A procedure was proposed when heat transfer is to be evaluated in sediments containing hydrates since parametric studies showed the impact of the medium thermal properties on the temperature distributions. The post melting behavior of gas hydrates was modeled in the TAMU geotechnical centrifuge to simulate the effect of large sediment and water depths. This centrifuge was calibrated, instrumented and modified to allow the performance of such experiments. Gas cavities were initiated at the bottom of soft soil specimens placed in cylindrical containers 0.30 m in diameter and 0.45 m in height. They were accelerated at various g - levels up to 100 g. Study of the failure mechanisms showed that both hydraulic fracturing and cavity expansion are possible failure mechanisms depending on the soil strength properties and the depth.