感应仪器数字化精度评估方法

A Method for Evaluating the Digital Precision of Induction Logging Tools

感应仪器的电阻率测量动态范围,特别是高电阻率测量范围受仪器的实际精度制约,而感应仪器的数字化精度是仪器实际精度的主控因素之一。为量化评估感应仪器数字化精度,建立了感应仪器“模数转换(Analog to Digital Converter,ADC)电导率分度值”的概念与计算公式。以阵列感应仪器AFIT-A为例,根据该仪器线圈系结构、发射电流频率和幅度、采集电路放大倍数以及ADC设计参数,计算出各子阵列在不同频率下“ADC电导率分度值”。通过分析仪器实测的感应内刻“零”信号等效视电导率与理论计算的仪器“ADC电导率分度值”的一致性,证实了“ADC电导率分度值”概念与计算方法的合理性,从而建立感应仪器的数字化精度评估指标,为阵列感应以及三分量阵列感应仪器的线圈系结构设计、发射电流频率及幅度分配以及采集电路放大倍数等设计提供了依据。

For an induction tool,its digital precision is critical for ultimate accuracy in actual measurements,and it actually determines the dynamic range of the resistivity,especially the high-resistivities.As a way to quantify the digital precision of induction tool,this paper proposed a new concept of"Analog to Digital Converter(ADC)conductivity scale",with its mathematical formulation given.In specific,the"ADC conductivity scales"are evaluated for each subarray at different frequencies,based on the configurations of the array induction tool AFIT-A,i.e.,the coil structure,frequency and amplitude of transmitting current,amplification multiple and design parameters of ADC.Effectiveness of the proposed method is verified by inspecting the consistency between the equivalent apparent conductivity of the"zero"signal and the theoretical outcomes of"ADC conductivity scales".On this basis,a new protocol is established to evaluate the digital precision of induction tools,which can further impact coil system design,frequency/amplification optimization of transmitting currents and acquisitions for both array induction and 3D array induction tools.