Simulation and experimental study on magnetic memory effect of drill string under geomagnetic shielding

Abstract

The existing metal magnetic memory (MMM) theory holds that the geomagnetic field is necessary for the MMM effect. However, when working at the drilling platform, it is found that after the drill string, working in multi-layer casing, which can be regarded as a magnetic shielding environment, is pulled out of the wellhead, there is still a strong MMM at the stress concentration part. This phenomenon contradicts the existing research conclusions. To reveal this abnormal phenomenon, it is necessary to explore the MMM effect under the condition of geomagnetic shielding. In this paper, COMSOL software is used to simulate the surface magnetic signal distribution of a specimen under the action of geomagnetic field and constructed zero magnetic environment. By using self-made magnetic shielding device and taking 35 CrMo specimen made of typical drill string steel, the four tensile tests of the specimens under the conditions of high and extremely low initial initial remanences in the geomagnetic environment, high and extremely low initial remanences in the geomagnetic shielding environment are compared. The comparison between simulation and experimental results shows that the geomagnetic field is not the necessary condition of MMM effect, while both the geomagnetic field and initial remanence are the necessary conditions of MMM effect. Therefore, the conclusion of this paper has certain scientific significance for perfecting the definition of MMM, and has certain engineering significance for guiding the field service of drill string.