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| Forward simulation and feasibility study of applying the low frequency ground penetrating radar to detecting gas hydrate in permafrost area |
| BAI Da-Wei1, 2, 3, DU Bing-Rui1, 2, 3, FANG Hui1, 2, 3, ZHANG Peng-Hui1, 2, 3, QIU Gen-Gen1, 2, 3, PEI Fa-Gen1, 2, 3, HE Mei-Xing1, 2, 3 |
1.Key Laboratory of Geophysical electromagnetic Exploration of Ministry of Land and Resources,Langfang 065000,China;
2.National Modern Geological Exploration Technology Research Center,Langfang 065000,China;
3.Institute of Geophysical and Geochemical Exploration,CAGS, Langfang 065000,China |
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Abstract In order to study the feasibility and key parameters of applying low frequency ground penetrating radar (GPR) to detecting gas hydrate in permafrost area,the authors used forward modeling of detection depth,resolution and reflection feature analysis of the low frequency ground penetrating radar in Tibetan Plateau permafrost environment modeling.Firstly,the relationship between the maximum detection depth of theoretical ground penetrating radar and the transmitting frequency,the resistivity of the underground medium and the dielectric constant of the GPR is determined by the radar range equation and,according to the theory of electromagnetic wave reflection,the system gain required for detecting the depth of gas hydrate in permafrost zone was calculated;Secondly,the resolution of low frequency GPR at large scale (200 meters) is determined by resolution calculation and simulation;Finally,two dimensional forward modeling experiments are carried out by time domain finite difference (FDTD) method,and the reflection characteristics of GPR signals at the bottom of the permafrost and the top and bottom boundaries of gas hydrate are obtained,which provide useful information for the processing and interpretation of field data.The results show that the low frequency GPR with a center frequency of less than or equal to 15 MHz and a system gain of more than 165 dB can meet the requirements of the detection of gas hydrate reservoirs in the permafrost areas with high surface resistivity.The resolution calculation and simulation results show that the low frequency ground penetrating radar can reach the generalized resolution of 1% at the depth of 200 meters under certain conditions,and that the GPR signals have obvious strong amplitude and frequency mutation characteristics on the bottom of permafrost and the top and bottom of gas hydrate.The theoretical calculation results show that low frequency ground penetrating radar is suitable for detecting natural gas hydrate in permafrost zone.
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Received: 08 September 2017
Published: 20 December 2017
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