层状垂直各向异性介质海洋CSEM发射源及接收站姿态和位置对电磁响应影响研究

众所周知,电阻率各向异性对海洋可控源电磁(CSEM)响应有显著影响.在模拟和解释海洋可控源电磁资料时,通常假设接收站布放于平稳的海底,发射源以理想的水平电偶极源形式按预设路径拖曳前进.然而,在实际海洋作业中,自由下沉的接收站可能沉降在局部倾斜的海底面上,在海底的方位可能是任意取向的.同时,由于洋流等因素的影响,发射源偶极子会发生旋转、倾斜,其位置也会偏离预设的拖曳路径,所以发射源和接收站姿态的变化都将对电磁资料产生影响.本文计算了电阻率各向异性介质中,发射源任意姿态任意位置激发、接收站任意姿态任意位置接收的海洋CSEM响应,分析观测系统引起数据误差的机制,分别在电阻率各向同性、围岩电阻率各向异性和高阻储层电阻率各向异性三种模型中,讨论发射源和接收站的姿态及位置变化对响应的影响.计算结果表明,电磁场振幅误差主要来源于发射源和接收站的倾斜角,而相位的变化为发射源位置和接收站倾斜角、位置共同影响的结果.

Effects of uncertainties in the orientation and position of both the transmitter and receivers on marine CSEM responses in layered vertical anisotropic medium

It is well known that resistivity anisotropy has a significant effect on the marine controlled-sources electromagnetic (CSEM) data. In simulating and interpreting CSEM data, it is common to assume that the receiving station is laid out on smooth seabed and that the source is dragged along the preset path in the form of an ideal horizontal dipole source. However, in the survey, free-sinking receivers may sit on partially sloping seabed surfaces with any orientation. At the same time, due to ocean currents and other factors, the source dipole will rotate, tilt, and its position will deviate from the default drag path. So, the uncertainties in the transmitter and receiver will have an impact on the CSEM data. In this paper, we calculate the CSEM responses excited by dipole sources of arbitrary orientation and received by receivers of arbitrary location in layered anisotropic medium. We analyze the mechanism of the data error caused by the observation system. We discuss the effects of uncertainties in the orientation and position of both the transmitter and receivers on CSEM data in three equivalent models:isotropic model, anisotropic-sediment model and anisotropic-reservoir model. The results show that the amplitude error of electromagnetic field is mainly caused by the dip angle of the transmitter and the receiver, and the change of the phase is the result of the common influence of the position of the transmitter and the receiver.