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Influence des cristaux d'hydrates de gaz ou de glace sur la perméabilité d'un milieu poreux

Abstract : The first part is a bibliographic study. We study the conditions for thermodynamic equilibrium of the hydrates as a bulk medium and the composition of the liquid and solid phases. We then describe the basics of fluid dynamics in a porous medium. Eventually, we merge the two approaches and study the influence of the porous medium on the hydrate stability. An off-shore hydrate field (Blake Ridge) and an on-shore field (Mallik) are precisely described. The latter will be used as a reference case for subsequent numerical simulations.

The second part is devoted to the experiments. Their goal is to measure the permeability of a sediment containing crystals. To get closer to natural geologic conditions, crystals are synthesized in absence of free gas. It turns out that hydrates form in a very heterogeneous way in the porous medium, which makes the measurements non representative. We believe that this result has a general character and that, at the laboratory time-scale, it is difficult, to say the least to achieve a uniform distribution of gas hydrates grown from dissolved gas. To circumvene this difficulty, we show, with a theoretical approach, that ice crystals behave much the same way as the hydrate crystals, concerning the Van der Waals forces that govern the agglomeration. This allows us to calculate the Hamaker constant of the hydrates. The second serie of experiments focuses on the permeability of a non consolidated porous medium under mechanical stress, where the pores are filled with ice crystals. Two silica beads populations are used to form a porous medium : 3 mm and 0.2 mm. With the large grains, results show two thresholds : for saturations below the lower threshold, the presence of crystals does not modify the permeability. For saturations above the upper threshold, the permeability vanishes almost completely (percolation phenomenon). Between these two limits, the permeability decreases exponentially with the saturation. With the fine grains, the permeability decreases with the same rate.

The last part concerns the numerical study of the Mallik field. We write the equations describing the heat and mass transfers as a function of space and time. Then, we study a one-dimensional limiting case. This allows us to evaluate the influence of the experimentally obtained 'Permeability = f(saturation)' curve on the amount of produced gas. The proposed code gives a way to assess different production scenario, as the pressure reduction enhanced by ice formation.
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Contributor : Olivier Bonnefoy <>
Submitted on : Monday, July 4, 2005 - 11:00:43 AM
Last modification on : Wednesday, June 24, 2020 - 4:18:31 PM
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  • HAL Id : tel-00009658, version 1


Olivier Bonnefoy. Influence des cristaux d'hydrates de gaz ou de glace sur la perméabilité d'un milieu poreux. Energie électrique. Ecole Nationale Supérieure des Mines de Saint-Etienne, 2005. Français. ⟨tel-00009658⟩



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