Three-dimensional finite element simulation study on abnormal magnetic positioning signals inside perforated casing

Perforating operations induce changes in the physical state of well casings, and the resultant abnormal magnetic positioning signals severely interfere with downhole casing coupling identification and depth positioning. To address this issue, based on the principle of electromagnetic induction, this study constructed a three-dimensional numerical model incorporating casing couplings, perforation holes, perforation burrs and casing deformation using the COMSOL Multiphysics finite element method. Combined with field measurement data from 24-arm caliper imaging, the interference mechanisms and quantitative relationships of various influencing factors on magnetic positioning signals were systematically analyzed. The results show that the signal at an ideal casing coupling position presents a stable “single-peak double-valley” pattern. Within the model parameter ranges defined in this study (perforation diameter ≤ 20 mm, burr height ≤ 2.5 mm), the amplitude of signal disturbance induced by perforation holes and burrs is on the order of 10 − 5 V, approximately two orders of magnitude lower than that of the casing coupling signal (10 − 3 V), and thus its impact on coupling identification and depth positioning is negligible. However, the applicability of this conclusion is constrained by perforation diameter scale and perforation density. In contrast, casing deformation disrupts the uniformity of magnetic field distribution and acts as the key interference source leading to depth misjudgment. Its signal disturbance amplitude can reach the order of 10 − 3 V, and there is a highly linear positive correlation between deformation magnitude and anomaly intensity (R 2 = 0.9808).Field measurement data further verify that the magnetic positioning signal disturbances caused by perforation holes and burrs are characterized by low-amplitude irregular fluctuations, consistent with simulation predictions. The signal anomalies induced by casing deformation are comparable in magnitude to the casing coupling signal. This conclusion is mainly based on numerical simulation and is indirectly supported by field data from partial well sections. This study provides a theoretical basis and discrimination criteria for the interpretation of post-perforation magnetic positioning signals and the evaluation of casing integrity.