Influential factors of the electromagnetic wave instrument while drilling in coal seam horizontal wells and resistivity simulation calculation

In order to figure out the influential factors of the detection by the electromagnetic wave instrument while drilling in coal seam horizontal wells, we studied the impacts of roof and floor surrounding rock resistivity, instrument eccentricity, coal seam borehole collapse and coal seam thickness on the measurement of resistivity through finite element numerical simulation. The resistivity response law of the amplitude ratio and phase difference calculation under the condition of high-resistivity coal rock formation was analyzed. On this basis, a three-layer geological mathematical model was established to simulate the difference between analytical and numerical solutions of the amplitude ratio and phase difference resistivity when the electromagnetic wave instrument while drilling was drilling in the coal seam at different emission frequencies, as well as the influence of formation relative dielectric constant on the amplitude ratio and phase difference calculation. The simulation results show that the analytical and numerical solutions of resistivity calculated by the amplitude ratio and phase difference are in good agreement, but when the resistivity is greater than 100 Ω·m, the amplitude ratio resistivity could not reflect the real resistivity of the coal seam, so it is better to use phase difference resistivity in the actual processing and interpretation. At different emission frequencies of high-resistivity coal seams, the resistivity data are mainly sensitive to the formation resistivity and insensitive to the dielectric constant. Only at ultra-high frequencies, the dielectric constant will have a great impact on the propagation of the electromagnetic wave.