Exploration of permafrost with audiomagnetotelluric data for gas hydrates in the Juhugeng Mine of the Qilian Mountains, China

Abstract

In China, gas hydrates in onshore permafrost areas have so far only been found in the Juhugeng Mine of the Qilian Mountains. However, their subsurface distribution remains unclear. Electrical resistivity logs have revealed that zones containing gas hydrates have higher resistivity than surrounding zones, which makes electromagnetic methods viable for detecting gas-hydrate deposits. We have deployed a natural-source audio-magnetotelluric (AMT) survey at the Juhugeng Mine. AMT data were collected at 176 sites along five profiles, and resistivity models were derived from 2D inversions after detailed data analysis. After the available geologic and geophysical observations were combined, the inversion results from profile 1 suggested that permafrost near the surface with high resistivity and thickness is essential for underlying gas hydrates to be present. The decrease in resistivity and/or thickness of permafrost due to climate change may lead to gas-hydrate dissociation. The other four AMT transects suggested three prospective gas-hydrate sites. Our results indicate that the AMT survey technique is suitable for exploring gas hydrates in permafrost areas and analyzing the impact of permafrost characteristics on gas-hydrate occurrence.

Three-dimensional magnetotelluric modeling in the spherical and Cartesian coordinate systems: A comparative study

“…Indeed, magnetotelluric studies to date have been concerned with sufficiently small spatial scales such that this assumption is easily justified. From radio and audio magnetotelluric applications (Yang B et al, 2019) concerned with regions of a few meters to a few kilometers (Han Q et al, 2021), to wideband and long-period magnetotelluric data intended to probe areas up to a few thousand kilometers in diameter (Xu S et al, 2019), these applications were clearly well within the range of applicability of the Cartesian approximation. The forward methods generally used in the Cartesian magnetotelluric modeling mainly include the integral equation method (Wannamaker, 1991), the finite difference (FD) method (Mackie et al, 1994;Kelbert et al, 2014), the finite volume method (Haber and Ascher, 2001;Jahandari and Farquharson, 2014), and the finite element method (Ren ZY et al, 2013;Cai HZ et al, 2021).…”

A Review of Subsurface Electrical Conductivity Anomalies in Magnetotelluric Imaging

“…Benefiting from these technical improvements, MT has been widely used in various fields, such as geothermal prospecting [ 18 , 19 , 20 ], mineral exploration [ 21 , 22 , 23 ], volcano studies [ 24 , 25 , 26 ], earthquake generation studies [ 27 , 28 , 29 ], studies of structures and processes in the continental crust and mantle [ 30 , 31 , 32 , 33 , 34 ]) and marine surveys [ 35 , 36 , 37 ]. With the development of the new MT instrument [ 38 ], MT probably would be used to probe the interiors of other worlds.…”