Research on Non-destructive Testing Technology for Downhole Casing Based on Constant False Alarm Rate Processing

The uniform linear multi-coil array (ULMA) has been successfully utilised for non-destructive testing of downhole casing. However, the narrow and complex detection environment underground limits the degrees of freedom of the ULMA system, thereby affecting its detection efficiency. Aiming to enhance the detection performance of ULMA in complex noise environments, this paper proposes a non-destructive testing technology for downhole casing based on constant false alarm rate (CFAR) processing. This technology establishes an array signal model for downhole casing non-destructive testing by analysing the structural characteristics of transient electromagnetic signals in the borehole and employs the linearly constrained minimum-variance (LCMV) algorithm to correct the phase offset of the array signals, enhancing detection reliability. By setting reasonable detection thresholds and combining them with CFAR processing criteria, real-time and accurate detection of casing damage is achieved. In the experiments, we built a downhole transient electromagnetic detection system using ULMA and validated the effectiveness of the proposed method through simulations of non-destructive testing of oil well casings.