Study over the Geo-Signal Properties of Ultra-Deep Electromagnetic Wave Logging While Drilling

In order to understand the characteristics and influencing factors of geo-signals of ultra-deep electromagnetic wave logging while drilling through interfaces, the analytical solution of multi-component electromagnetic wave logging in layered anisotropic media was adopted. On this basis, geo-signals of three structures including the axial transmitting and tilt receiving coil system of PeriScope, the tilt transmitting and tilt receiving coil system of DWPR, and the symmetrical measurement of GeoSphere were numerically simulated under a low frequency and long spacing condition of ultra-deep electromagnetic wave logging while drilling. The response characteristics through interfaces, depth of investigation (DOI), and influence of anisotropy of the geo-signals of the three structures were compared, and their applicabilities in ultra-deep detection were discussed. The study found that the geo-signals of the three structures could indicate stratigraphic interfaces and their orientations, and the non-monotonicity of the responses was apparent under long spacing and high frequency. Specifically, the monotonicity of the geo-signals by dual tilt coil system of DWPR was the strongest. Under a stratigraphic model with a resistivity ratio of 100:1, the geo-signals from GeoSphere had the largest DOI, and those from dual tilt coil system of DWPR took second place. The amplitude ratio geo-signals of the dual tilt coil system of DWPR were not influenced by the anisotropy of strata, while other geo-signals were all affected by the anisotropy of strata. The results showed that the DOI of the geo-signals could be effectively improved by lowering the frequency and enhancing the spacing, which was also beneficial to the monotonicity of the geo-signal responses to the stratigraphic interfaces, with the result that the anisotropy had influences on almost all geo-signals.