Resistivity in Formation and Decomposition of Natural Gas Hydrate in Porous Medium

Abstract

A new one-dimensional system for resistivity measurement for natural gas hydrate (NGH) exploitation is designed, which is used to study the formation and decomposition processes of NGH. The experimental results verify the feasibility of the measurement method, especially in monitoring the nucleation and growth of the NGH. Isovolumetric formation experiment of NGH is performed at 2 °C and 7.8 MPa. Before the NGH formation, the initial resistivity is measured to be 4–7 Ω·m, which declines to the minimum value of 2–3 Ω·m when NGH begins to nucleate after the pressure is reduced to 3.3 MPa. As the NGH grows, the resistivity increases to a great extent, and finally it keeps at 11–13 Ω·m, indicating the completion of the formation process. The NGH decomposition experiment is then performed. When the outlet pressure decreases, NGH begins to decompose, accordingly, the resistivity declines gradually, and is at 5–9 Ω·m when the decomposition process ends, which is slightly higher than the resistivity value before the formation of NGH. The occurrence and distribution uniformity of NGH are determined by the distribution and magnitude of the resistivity measured on an one-dimensional sand-packed model. This study tackles the accurate estimation for the distribution of NGH in porous medium, and provides an experimental basis for further study on NGH exploitation in the future.