Experimental Studies on the Evolvement of Electrical Resistivity during Methane Hydrate Formation in Sediments

An experimental setup was developed to in situ measure the evolvement of the electrical resistivity during hydrate formation process to aid the interpretation of the influence of hydrate saturation on the electrical properties of the sediment. Five hydrate samples under different initial brine saturations of 12, 20, 30, 40, and 50% were formed from free methane gas and brine with 3.35 wt % NaCl in the 60-80 mesh sandy sediment, during which the variations of electrical resistivity were in situ measured. It was observed that the resistivity of the hydrate-bearing sediment increases with the increase of hydrate saturation during the hydrate formation process and finally achieves a constant value for each group of hydrate sample. For hydrate samples at different initial brine saturations, the values of electrical resistivity are larger, even though hydrate saturation is lower if free methane gas exists in sediment pores. Based on the measured electrical resistivity of hydrate-bearing sediment before and after brine injection at different hydrate saturations, parameters in Archie equation were determined to describe the relationship between resistivity and hydrate saturation, which would be helpful for mapping the hydrate concentration in the sediment through resistivity logging data from hydrate deposits.