| 琼东南盆地天然气水合物及其成藏模式的海洋可控源电磁研究 |
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| 引用本文： | 景建恩,赵庆献,邓明,罗贤虎,陈凯,王猛,涂广红.琼东南盆地天然气水合物及其成藏模式的海洋可控源电磁研究[J].地球物理学报,2018,61(11):4677-4689. |
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| 作者姓名： | 景建恩 赵庆献 邓明 罗贤虎 陈凯 王猛 涂广红 |
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| 作者单位： | 1. 中国地质大学(北京)地球物理与信息技术学院, 北京 100083;2. 广州海洋地质调查局, 广州 510760;3. 地下信息探测技术与仪器教育部重点实验室(中国地质大学, 北京), 北京 100083 |
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| 基金项目： | 国家重点研发计划（2016YFC0303100），国家自然科学基金项目（61531001），中国地质调查局水合物专项（GZH201100307）联合资助. |
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| 摘 要： | 南海琼东南盆地是天然气水合物重要远景区之一.由于盆地大部分地区海底地形平缓、地层近于水平，增加了利用地震反射剖面识别似海底反射（BSR，bottom simulating reflector）的难度，从而影响了对水合物的评价.为了进一步开展琼东南盆地水合物调查研究，本文在研究海域进行了海洋可控源电磁探测试验，将自主研发的10台接收机以500 m的间距，投放至水深约为1360 m的海底，完成了一条4.5 km剖面的电磁数据采集.通过对采集的数据进行处理与二维（2D）反演，获得了研究剖面海底的电阻率断面图.反演结果显示，研究区海底60~330 mbsf（meter bottom of seafloor）的地层中，存在多个横向不连续分布的高阻异常体，电阻率介于2~10 Ωm之间；在海底330 mbsf之下，横向上发育了电阻率为2~4 Ωm的3个高阻体.根据研究区热力学条件，本文估算了生物成因气与热成因天然气的水合物稳定带（GHSZ，gas hydrate stability zone）厚度，结合高阻体的分布特征推断了地震剖面上BSR的位置.在此基础上，对反演的电阻率断面进行解释，推断了研究区水合物的分布及游离气运移通道.研究表明，勘探区具有形成天然气水合物矿藏的地质与地球物理条件，其成藏模式可能属于"断层、裂隙输导的下生上储型"，水合物的气源为生物成因气.
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| 关 键 词： | 南海 琼东南盆地 天然气水合物成藏模式 海洋可控源电磁法 2D反演 |
| 收稿时间： | 2018-03-19 |
A study on natural gas hydrates and their forming model using marine controlled-source electromagnetic survey in the Qiongdongnan Basin |
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| JING JianEn,ZHAO QingXian,DENG Ming,LUO XianHu,CHEN Kai,WANG Meng,TU GuangHong.A study on natural gas hydrates and their forming model using marine controlled-source electromagnetic survey in the Qiongdongnan Basin[J].Chinese Journal of Geophysics,2018,61(11):4677-4689. |
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| Authors: | JING JianEn ZHAO QingXian DENG Ming LUO XianHu CHEN Kai WANG Meng TU GuangHong |
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| Institution: | 1. School of Geophysics and Geoinformation Technology, China University of Geosciences(Beijing), Beijing 100083, China;2. Guangzhou Marine Geological Survey, Guangzhou 510760, China;3. Key Laboratory of Geo-detection(China University of Geosciences, Beijing), Ministry of Education, Beijing 100083, China |
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| Abstract: | The Qiongdongnan Basin is one of important areas for gas hydrate prospecting in the South China Sea. However, because of the gentle terrain and the nearly horizontal seabeds, it is difficult to recognize the BSR (bottom simulating reflector) and to infer gas hydrates. To solve this problem, the first marine controlled-source electromagnetic detection experiment was carried out in this area, with the aim to image the gas hydrates and free gas below the GHSZ (gas hydrate stability zone) in the seabed. In total 10 receivers spacing 500 m were deployed on the seafloor at a depth of about 1360 m below water, and electromagnetic data were acquired along a 4.5 km profile. By processing and two-dimensional (2D) inversion of the collected data, the resistivity profile of the study section of the seabed was obtained. It shows that there are several resistive anomalous bodies with resistivity between 2 Ωm and 10 Ωm characterized by discontinuous transverse distribution above the seabed of 330 mbsf (meter bottom of seafloor). Under the seafloor 330 mbsf, 3 high resistivity bodies with a resistivity of 2~4 Ωm are present laterally. According to the thermodynamic conditions of the study area, the thickness of GHSZ of biogenic gas and thermal genetic gas is estimated, and the location of BSR in the seismic section is deduced from the distribution characteristics of the high impedance bodies. On this basis, the resistivity section is interpreted, and the distribution of hydrates and the migration path of free gas are inferred. The thickness of GHSZ estimated by thermodynamic conditions and the BSR of the seismic profile have a good relationship with the bottom boundary of the high resistivity body. Furthermore the distribution of hydrates and the free gas migration pathway in the study area are explained by the inversion profile. The results show that the hydrate deposits in the study area belong to the type of lower generation and upper storage with natural gas migrating through faults and cracks, and the gas source of hydrates may be biogenic gas. |
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| Keywords: | South China Sea Qiongdongnan Basin Gas hydrate accumulation mode Marine CSEM 2D inversion |
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