A study of Coalbed Methane (CBM) reservoir boundary detections based on azimuth electromagnetic waves

Abstract

In this research, a coal-gangue-rock geological model based on geological parameters was established by studying the relationships between different dielectric constants, conductivity and attenuation coefficients, and emission frequencies when electromagnetic waves were propagated in a medium. The effects of the electromagnetic wave energy attenuations on coal-rock interfaces under different electrical parameters, and the variations in boundary reflection energy under different lithological interface conditions were examined. Also, the influences of the coal gangue interlayers on the boundary detections, as well as the theoretical conditions and basis for electromagnetic wave detections at coal-rock interfaces were obtained. On the aforementioned basis, the parameters design method of azimuth electromagnetic wave resistivity logging tool while drilling were proposed. Then, the applicability potential of the proposed electromagnetic wave coal-rock interface identification method was examined. This research content included the influences of the measuring response signals on the instrument itself under different source distances, transmitting frequencies, and coil installation angles. Also, an external influence analysis of the instrument's distance to formation boundaries and the formation resistivity contrasts were studied in detail. The boundary response characteristics of the electromagnetic wave signals under different coil structures and instrument parameters were obtained using numerical simulations. Furthermore, under the many constraint conditions, the basis for selecting the parameters of the instruments which were suitable for underground coal mines was put forward.