Influence of Structure of Modular Electromagnetic Logging While Drilling Instrument on Measurement Signals

Conventional electromagnetic logging while drilling is an important method for evaluating stratigraphic fluids, but it does not have azimuth property. In this paper, a new modular electromagnetic logging while drilling instrument was proposed with good azimuth detection property. In order to accurately understand the influence of modular electromagnetic logging while drilling instrument on the measured voltage signal, a 3D model was established using the finite element method, and the influence laws of various instrument parts were explored. The results show that with the increased resistivity of the drill collar and antenna slot filling material, the received voltage signal has a sudden change, which is closely related to the frequency and geometric size of the instrument. The resistivity of the cover plate material has a great influence on the intensity of the received signal, and the cover plate should be selected with a little lower resistivity than metal. The measurement signal increases with the increasing resistivity of the sensor body, so the non-metallic material should be selected as the sensor body. When the resistivity of the instrument structure such as drill collar and filling material is low, the received voltage signal has obvious attenuation, and its influence can be ignored when the resistivity of the filling material is high. By deducting the instrument response in the air medium, the influence of the instrument structure can be well eliminated. After deducting the influence of the instrument structure, the magnetic flux in the coil decreases, resulting in a smaller instrument signal than before. The research results can provide a theoretical basis for the design and manufacture of actual logging instruments.