A Method for Evaluating the Digital Precision of Induction Logging Tools

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.