Microscopic distribution patterns of natural gas hydrates in sediments and the resistivity response

Resistivity is an important property of hydrate reservoirs for research. We conducted X-CT scanning and resistivity synchronous measurement experiments on hydrate formation process in marine sediments in combination of microscopic and macroscopic tests. Through the X-CT images scanned during the experiment and the measured resistivity data, the microscopic distribution of hydrates, changes in pore water, and resistivity response during hydrate formation were analyzed, and the impact factors on hydrates on pore water evolution and resistivity were explored. Results show that the distribution of microscopic morphology of hydrates is the direct manifestation of resistivity changes. The mechanism is that the distribution alters the spatial connectivity of pore water and reconstructs the conductive path. At low saturation levels, the hydrate distribution dominated by the suspension mode has no obvious effect on the connectivity of pore water and the resistivity change is small. As the suspension-type hydrates grow, the original large pore water spaces are divided into multiple smaller pore water spaces, the pore water network becomes more complex, and the electrical conductivity path becomes more tortuous, which consequently increases the resistivity. When hydrates meet sediment skeleton, the pore water connection is completely cut off, the electrical conductivity path becomes more tortuous, and thus the resistivity increases significantly. In the same sedimentary system, the resistivity under the cementation mode is higher than that under the suspension mode and the contact mode. The quantitative relationship between hydrate saturation and resistivity is positive and affected by the microscopic distribution of hydrates, and the correlation is positively related in different hydrate distribution modes with increase in the saturation.