### 3D Forward Simulation of Marine Natural Gas Hydrate Production Monitoring with the Downhole Controlled-Source Electromagnetic System

LIU Ying1,2, HE Tao1,2,†, ZHANG Yi3

1. 1. Key Laboratory of Orogenic Belts and Crustal Evolution (MOE), School of Earth and Space Sciences, Peking University, Beijing 100871 2. Beijing International Center for Gas Hydrate, Peking University, Beijing 100871 3. Chinese Academy of Geological Sciences, Beijing 100037
• Received:2021-11-13 Revised:2022-02-24 Online:2022-11-20 Published:2022-11-20
• Contact: HE Tao, E-mail: taohe(at)pku.edu.cn

### 海域天然气水合物开采的井中可控源电磁监测三维正演模拟

1. 1. 造山带与地壳演化教育部重点实验室, 北京大学地球与空间科学学院, 北京 100871 2. 北京天然气水合物国际研究中心, 北京 100871 3. 中国地质科学院, 北京 100037
• 通讯作者: 何涛, E-mail: taohe(at)pku.edu.cn
• 基金资助:
国家自然科学基金(42174133, 41676032)和中国地质调查局项目(DD20190234, DD20190218, HD-JJHT-20)资助

Abstract:

In order to know well the range and degree of gas hydrate dissociation during the large-scale exploitation of marine natural gas hydrate, the finite element software COMSOL is used to simulate the electromagnetic monitoring of the natural gas hydrate exploitation through the downhole controlled-source electromagnetic (CSEM) method. By constructing the 3D formation model containing the high-resistivity hydrate reservoir layer, the comparison between the downhole vertical source and the conventional towed horizontal source indicates that the former has advantages on the electric field responses for small source-receiver offsets required for monitoring. Then, the influence of vertical source monitoring system parameters, such as metal casing, vertical source depth, emission frequency, observation errors and noises, on the seafloor electric field responses are analyzed. The simulation results show that the metal casing, vertical source depth and emission frequency have significant influences on the seafloor electric field responses, and especially for the existence of metal casing, the vertical source should be placed below the hydrate reservoir and the low frequency such as 1 Hz of emission electrical current should be considered. The observation errors and noises of the monitoring system would not significantly affect the performance of the monitoring system with metal casing under the condition of small offsets. When the production range of the hydrate reservoir increases, the downhole vertical source monitoring system ensures that seafloor receivers can detect the electric field changes caused by hydrate exploitation and effectively identify the lateral boundary of production area. Hence, it is feasible to use the downhole CSEM method to monitor the dynamic reservoir process during marine hydrate exploitation.