Electrical resistivity change laws of natural gas hydrate bearing clayey-silty sediments

The existing research results indicate that the studies on the electrical resistivity properties of natural gas hydrate (hereinafter referred to as hydrate) bearing clayey-silty sediments are of great significance for the safe and efficient development of hydrate reservoirs. At present, however, the influences of particle squeeze type hydrates in fine grained sediments are less researched, and particularly the change laws of reservoir resistivity in the processes of sediment consolidation shrinkage, force deformation and shear failure have not been understood sufficiently. In this paper, hydrate bearing clayey-silty sediments with different hydrate saturations are prepared using three sample preparation methods, the change laws of sediment resistivity in the stages of cooling, hydrate formation, N2 gas displacement, water saturation, triaxial consolidation, and shear failure are investigated, and the sensitivity of different electrical resistivity factors in consolidation and shear stages are analyzed. And the following research results are obtained. First, the formation of hydrate can lead to the sharp increase of the sediment resistivity to above 1 kΩ·m, and the difference in the electrical resistivity of hydrate-bearing sediments with 20% and 40% hydrate saturation exceeds 350 Ω·m, while the process of water saturation promotes the electrical resistivity to decrease below 40 Ω·m. Second, when the effective confining pressure increses from 1.0 MPa to 1.5 MPa, the maximum electrical resistivity of the hydrate-bearing sediments with 20% hydrate saturation can decrease by 253 Ω·m under the gas-saturated state, and approximately 2 Ω·m under the water-saturated state. Third, sediment conductivity is significantly affected by the phase state change of porous media, whose primary mechanisms include hydrate blocking conductive pathways and water saturation enhancing current conduction, while decreased hydrate cementation capacity and residual pore gas weakening current conduction. In conclusion, porous medium and external pressure are two major factors influencing the electric resistivity change of clayey-silty sediments, and the following researches shall focus on the coupled analysis of these factors, so as to provide theoretical support for predicting the reservoir disturbance risks in the process of marine hydrate production. © 2024 Natural Gas Industry Journal Agency. All rights reserved.