Determination of the CO2 gas consumption rate due to dissolution and hydrate formation in porous media

Abstract

For a long time gas hydrates were considered to be a hindrance for the natural gas and oil industry. However, since natural gas hydrates deposits were discovered in 1967 the conception of natural gas hydrates as an important energy resource is well accepted. Latest estimations indicate that the amount of natural gas stored in hydrate form is almost six times the volume of conventional natural gas. A relative new method to produce methane from natural gas hydrate deposits is the sequestration of CO2 in a water-bearing layer underneath a natural gas hydrate deposit. This process depends, among others, on the in-situ formation rate of CO2 hydrate in a porous medium, which depends on pressure, temperature, composition of the aqueous and gas phase and the geometry of the porous medium. Concerning the formation rate of CO2 there is no general accepted value that could be used in numerical models to predict the speed of CO2 gas hydrate formation in porous medium. Additionally, the experimental determination of the formation rate is difficult or even not possible. However, indirect determination of the formation rate based on gas consumption rate can be realized. This study represents gas consumption rate experiments in glass bead and Bentheimer sandstone cores determining gas consumption during CO2 dissolution at relatively low pressure of 1.6 MPa and determining gas consumption during hydrate formation in a Bentheimer sandstone core at a high pressure of 3.0 MPa. For the experiments in the glass-bead core, the pressures reached at the end of the dissolution experiments are in good agreement with the thermodynamic equilibrium values. For the experiments in the Bentheimer sandstone core, the experimental procedure had to be modified to obtain reproducible results: these results were in good agreement with thermodynamic equilibrium data. The modified procedure was applied in the high pressure experiments. The resulting initial gas consumption rates of these two experiments are 4.1x10-4 mole/(s.m3.kPa) and 105 mole/(s.m3.kPa). Additional experimental investigation is necessary to explain this discrepancy.