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
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.
白大为, 杜炳锐, 方慧, 张鹏辉, 仇根根, 裴发根, 何梅兴. 低频探地雷达探测冻土带天然气水合物正演模拟研究[J]. 物探与化探, 2017, 41(6): 1248-1254.
BAI Da-Wei, DU Bing-Rui, FANG Hui, ZHANG Peng-Hui, QIU Gen-Gen, PEI Fa-Gen, HE Mei-Xing. Forward simulation and feasibility study of applying the low frequency ground penetrating radar to detecting gas hydrate in permafrost area. Geophysical and Geochemical Exploration, 2017, 41(6): 1248-1254.
[1] SLOAN JR E D.Clathrate hydrates of natural gases[M].2 nd ed.New York:Marcel Dekker Inc.,1998. [2] Michael D M.Natural gas hydrate in oceanic and permafrost environments [M].Kluwer Academic Publishers,2000:295-310. [3] Collett T S,Lee M W,Agena W F,et al.Permafrost associated natural gas hydrate occurrences on the Alaska North Slope [J].Marine and Petroleum Geology,2011,28(2):279-294. [4] Craven J A,Roberts B J,Bellefleur G,et al.Recent magnetotelluric measurements at the Mallik gas hydrate production research well site,Northwest Territories[J].Proteomics,2012,12(12):2045-2059. [5] 祝有海,张永勤,文怀军,等.青海祁连山冻土区发现天然气水合物[J].地质学报,2009,83(11):1762-1771. [6] 郭星旺,祝有海.祁连山冻土区DK-1钻孔天然气水合物测井响应特征和评价[J].地质学报,2011,30(12):1869-1873. [7] 卢振权,祝有海,张永勤,等.青海省祁连山冻土区天然气水合物基本地质特征[J].矿床地质,2010,29(1):182-191. [8] 祝有海,张永勤,文怀军,等.祁连山冻土区天然气水合物及其基本特征[J].地球学报,2010,31(1):7-16,130. [9] 王平康,祝有海,卢振权,等.祁连山冻土区天然气水合物岩性和分布特征[J].地质通报,2011,30(12):1839-1850. [10] 卢振权,祝有海,张永勤,等.青海祁连山冻土区天然气水合物的气源条件及其指示意义[J].矿床地质,2013,32(5):1035-1044. [11] 李大心.探地雷达方法与应用[M].北京:地质出版社,1994. [12] 刘澜波,钱荣毅.探地雷达:浅表地球物理科学技术中的重要工具[J].地球物理学报,2015,58(8):2606-2617. [13] 李丽英,张立新,赵少杰.冻土介电常数的实验研究[J].北京师范大学学报:自然科学版,2007,43(3):241-244. [14] 潘语录,田贵发,栾安辉,等.测井方法在青海木里煤田冻土研究中的应用[J].中国煤炭地质, 2008,20(12):7-9. [15] 王通,俞祁浩,游艳辉,等.物探技术在多年冻土探测方面的应用[J].物探与化探,2011,35(5):639-642. [16] 杜二计,赵林,李韧.探地雷达在祁连山多年冻土调查中的应用[J].冰川冻土,2009,31(2):364-371. [17] 罗京,牛富俊,林战举,等.青藏高原北麓河地区典型热融湖塘周边多年冻土特征研究[J].冰川冻土,2012,34(5):1110-1117. [18] 胡俊,俞祁浩,游艳辉,等.探地雷达在多年冻土区正演模型研究及应用[J].物探与化探,2012,36(3):457-461. [19] 何茂兵, 孙波, 杨亚新, 等. 天山乌鲁木齐河源一号冰川探地雷达测厚及其数据分析 [J].东华理工学院学报,2004,27(3):235-239. [20] 王璞玉,李忠勤,吴利华,等.探地雷达在冰川厚度及冰下地形探测中的应用[J].吉林大学学报:地球科学版,2011,41(1):393-400. [21] 崔祥斌,孙波,田钢,等.冰雷达探测研究南极冰盖的进展与展望[J].地球科学进展,2009,24(4):392-402.
