FORDIMHYS Project

Experimental program and set-up

In the first part, a model for the dissociation of a sediment core partially saturated in methane hydrate was developed. Numerical simulation allow to follow pressure and temperature inside the core; the evolution of the border between hydrate zone and non hydrate zone is also given during the resolution.
This second part deals with the problem of validation for this model ; indeed the main objective is to compare numerical and experimental results in order to verify the veracity of it. This validation can be done exclusively by this mean.

Device
Like we need to compare experimental and numerical results, we must obtain through this experiment the evolution of temperature and pressure during the dissociation of a sediment core partially saturated in methane hydrate. The list of main objectives can be resumed :

In order to satisfy all these points it’s essential to have an experiment that we can dismantled quickly in order to be able to freeze and extract sediment (stop the dissociation and observe the hydrate evolution in the porous medium). The place where we find sediment must be decomposed in several zones (lengths are variable and oscillate between 20 cm and 1 m).

Fig. 1 : Schema of hydrate dissociation experiment.

The figure 1 gives a global idea of the experiment structure : different sediment zones can be distinguished on this figure. All these zones have an independent methane supply that we can control and regulate with valves.
We use Inox tubes of ¼ ’’ for the main part of the experiment and tube of 1’’ where the sediment is. Each section of sand (between 20 cm and 1 m) is cooled by a cryostat, independently of the others and can be isolated with a pair of valves. The solenoid valve, closed or opened according to reactor pressure, permit us to regulate the pressure during hydrate dissociation (P constant) and we recover dissociated gas in the ballasts , in which we control the temperature and we measure the pressure.

In connection with the cooling of the sediment figure 2 shows us system with a jacket around the 1’’ sediment tube in which an ethanol circulation takes place (ethanol is chosen in order to be able to cool until 250 K). At the end of each sediment zone a system was set up to prevent introduction of sand in the rest of the experiment and in particular inside valves ; on the figure 3 we can see the Teflon plug which supports the two different filters, the grain size of the sand is roughly equal to 250 µm : that’s why we have chosen a 120 µm (filter 1) and a 180 µm (filter 2) filters. By this mean we can be sure that sand will not entry inside valves and break them.

Fig. 2 : Thermo-regulation of sediment.

Fig. 3 : Sediment zone boundaries

The images 1, 2, 3 and 4 show the actual experiment where the sediment zone and the different probes can be identified.