Exploration for Gas Hydrate with Audio-magnetotelluric Data in the Juhugeng Mine of Qilian Mountain Permafrost, China

Gas hydrate in onshore permafrost area of China only occurs in the Juhugeng mine of Qilian Mountain until now. However, its subsurface distribution remains unclear. Electrical resistivity logs reveal the resistivity of zones containing gas hydrate is high than that of surrounding zones, which makes the electromagnetic (EM) methods available to detect the gas hydrate deposits. We deployed a natural-source audio-magnetotelluric (AMT) survey at the Juhugeng mine. AMT data were collected at 176 sites along five profiles and the resistivity models were derived from two-dimensional (2D) inversions after detailed data analysis. The resistivity model from profile 1 yielded good agreements with the gas hydrate inferred from the drill holes information. We found that the permafrost near surface with high-resistivity and high-thickness is also essential to the existence of underlying gas hydrate besides gas source, migration pathways, and reservoir rocks. The decrease in the resistivity and/or thickness of the permafrost caused by climate warming may lead to the gas hydrate dissociation. The other four AMT transects without logging data suggest three gas hydrate prospects, and one of them correlates well with previous geochemical observations. Our study can also provide useful reference for AMT exploration on gas hydrate in other potential regions.