摘要
海洋可控源电磁(CSEM)方法已广泛应用于地质构造研究以及海底资源探测,但其在各向异性地层中的分辨能力依然不明确.灵敏度分析是一种分析电磁场对探测目标分辨能力的有效方法,传统的地球物理反演方法也需要精确计算电磁场关于地下介质电阻率的灵敏度.在模拟和解释海洋CSEM资料时,地球物理数值模拟常在笛卡尔直角坐标系下进行,且通常假定发射源为理想的水平电偶极源.然而,在实际的海洋可控源电磁勘探作业中,由于海水运动等影响,发射源可能会发生旋转和倾斜等.复杂姿态的电偶极源可通过计算并矢量叠加三个正交方向发射源分量的电磁场以获得总电磁场,因此需三个正交方向电偶源电磁场的计算方法.本文推导了笛卡尔直角坐标系下,电阻率垂直各向异性介质中三个正交方向电偶极源电磁场表达式,并详细导出了电磁场分量关于各向异性电导率的灵敏度解析表达式.通过与各向同性算法对比,验证了本文所提出灵敏度计算方法的正确性;模拟了不同方向电偶源情况下地电模型的灵敏度并分析其特征.计算结果表明,薄层将显著影响地下介质各向异性电阻率的灵敏度分布,垂直电偶源对海底地层各向异性电阻率的分辨能力高于水平电偶源,通过反演各向异性率间接恢复低灵敏度的各向异性电阻率值是一个可行的反演策略.
Marine controlled-source electromagnetic(CSEM)method has been widely used in the study of geological structures and the exploration of seabed resources,but the resolution of this method in anisotropic formations is still unclear.Sensitivity analysis is an effective method to understand the resolution ability of electromagnetic field in geoelectric model to detecting targets.Traditional geophysical inversion methods also need to accurately calculate the sensitivity of electromagnetic field with respect to the resistivity of underground media.When simulating and interpreting marine CSEM data,geophysical numerical simulation is usually carried out in Cartesian coordinate system,and it is usually assumed that the source is an ideal horizontal electric dipole source.However,in the actual Marine CSEM exploration,the source may rotate and tilt due to the influence of sea water movement.The total electromagnetic field of electric dipole source with complex attitude can be obtained by calculating and vector-stowing the electromagnetic fields of three orthogonal emission source components.Therefore,the calculation method of electromagnetic fields of three orthogonal emission sources is needed.In this paper,the expressions of electromagnetic fields in three orthogonal directions of electric dipole sources in vertically anisotropic media with resistivity in Cartesian coordinate system are derived,and the analytical expressions of the sensitivity of electromagnetic field components to the anisotropic conductivity are derived in detail.We simulated the sensitivities of different geoelectric models and analyzed their characteristics.The simulation results show that the surrounding rock has a significant effect on the sensitivity of the controlled source electromagnetic response to the anisotropic resistivity of the thin layer.In the geoelectric model of surrounding rock with different resistivity,the anisotropic resistivity sensitivity characteristics of the high resistivity thin layer and the low resistivity thin layer are dif
作者
罗鸣
裴建新
叶益信
LUO Ming;PEI JianXin;YE YiXin(College of Marine Geosciences,Ocean University of China,Qingdao 266100,China;Key Lab of Submarine Geosciences and Prospecting Techniques of Ministry of Education,Ocean University of China,Qingdao 266100,China;School of Geophysics and Measurement-Control Technology,East China University of Technology,Nanchang 330013,China)
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2022年第8期3139-3156,共18页
Chinese Journal of Geophysics
基金
国家自然科学基金(41904075,41774078)
中央高校基本科研业务费专项(201964015)
江西省自然科学基金青年重点项目(20202ACBL211006)联合资助.
