可控源电磁法(CSEM)是一种重要的地电磁勘探方法,通过引入人工场源从而大大改善了观测信号质量,使得其具有分辨率高及抗干扰能力强等特点.目前广泛用于石油、天然气、金属矿、地热、水文、环境等勘探领域(Kalscheuer,Kuvshinov et al.20...
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可控源电磁法(CSEM)是一种重要的地电磁勘探方法,通过引入人工场源从而大大改善了观测信号质量,使得其具有分辨率高及抗干扰能力强等特点.目前广泛用于石油、天然气、金属矿、地热、水文、环境等勘探领域(Kalscheuer,Kuvshinov et al.2012).本文从传统积分方程法一般采用近似积分公式、简单矩形网格和近似的奇异性体积分计算技术,制约了体积分方程法处理复杂地下异常体的能力,降低了计算精度等问题出发,推导并计算了基于完全积分公式、四面体非结构化网格和奇异体积分的精确解析解来高精度求解复杂可控源电磁模型的正演响应.首先,从电场积分公式出发,推导了可控源电磁问题满足的积分方程;其次,借助于非结构化四面体网格离散技术,实现了地下复杂异常体的有效模拟.最后,利用散度定理把强奇异值体积分转换为一系列弱奇异性的面积分公式,并通过推导获得了这些弱奇异性的面积分公式的解析解,从而最终实现三维可控源电磁问题的高精度积分求解.以块状低阻体地电模型为测试模型,采用本文提出的积分方程方法获得的数值解与其他公开数值算法解进行对比分析,其对比结果具有高度的吻合性,验证了算法的正确性.
In planning and executing marine controlled-source electromagnetic methods, seafloor electromagnetic receivers must overcome the problems of noise, clock drift, and power consumption. To design a receiver that perform...
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In planning and executing marine controlled-source electromagnetic methods, seafloor electromagnetic receivers must overcome the problems of noise, clock drift, and power consumption. To design a receiver that performs well and overcomes the abovementioned problems, we performed forward modeling of the E-field abnormal response and established the receiver＇s characteristics. We describe the design optimization and the properties of each component, that is, low-noise induction coil sensor, low-noise Ag/AgCI electrode, low-noise chopper amplifier, digital temperature-compensated crystal oscillator module, acoustic telemetry modem, and burn wire system. Finally, we discuss the results of onshore and offshore field tests to show the effectiveness of the developed seafloor electromagnetic receiver and its performance： typical E-field noise of 0.12 nV/m/rt（Hz） at 0.5 Hz, dynamic range higher than 120 dB, clock drift lower than 1 ms/day, and continuous operation of at least 21 days.
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