Bed-Detection Sensitivity Employing 1D Response to an Electric Dipole Source in Multilayer Anisotropic Formations

Abstract

Electric and magnetic field responses originating from a primary electric current source have been analytically derived, explored, and employed to explore and detect electrical anomalies due to the presence of a bed boundary in a two-layer model, using the controlled source electromagnetic method. However, previous works on the subject demand in-depth knowledge of mathematics, which could become an obstacle for the practitioner looking to immerse into the realm of induction logging and who needs a straightforward approach to develop their algorithms. Consequently, we introduce the analytical expressions for electric and magnetic field responses to an electric current dipole source arbitrarily oriented in one-dimension (1D) transversely isotropic media. In addition, we apply these equations to examine both electric and magnetic field responses to a distant resistive anomaly from electric transverse electric dipole transmitters. Our analysis shows that magnetic field responses are significantly more sensitive to the anomaly ahead of the tool for a vertical or a horizontal borehole. While the coplanar electric field measurements with conventional electric resistivity tools are known to be sensitive to the resistivity anomaly around the tool, the axial magnetic field measurement using the transverse electric dipole transmitter and the transverse magnetic field measurement using an axial electric dipole transmitter are significantly more sensitive to the anomaly around the tool than any electric field measurements. This deep-looking capability is achieved with a relatively short source-receiver spacing of 10 m. Based on the increased deep-looking capability, we encourage the use of magnetic components from our generalized geosteering tool based on electric dipole sources because it can potentially flag anomalies at a distance 60% further in comparison to the sensitivity of electric measurements.