Research on high-power and high-efficiency emission of crosswell electromagnetic logging

Abstract

Crosswell electromagnetic (EM) logging has useful applications in oil, gas, and water monitoring as well as carbon sequestration estimation. Difficulties in the efficient propagation of EM waves through a steel casing inhibit crosswell EM logging at distances greater than 300 m. This study investigates whether high-power transmission and high-efficiency transmitting antennas can resolve the challenges of long-distance crosswell EM logging through steel casings. Theoretical analysis indicates that the emission moment should be at least 12,000 A·m2. By calculating the equivalent relative permeability and selecting the appropriate coil materials and magnetic cores, the maximum emission magnetic moment can create a high-power transmission. Based on series and parallel resonant circuits and the alternating current/direct current cable core multiplexing power supply method, the effective transmission bandwidth is broadened and the transmission efficiency increases by three times. The emission unit is fabricated and tested using single, double, and fiberglass casing. We observe that the crosswell EM technology performs better for nonmetal casing wells than that for metal casing wells. The amplitude and phase curves between two fiberglass casing wells in the range of 425 m are quite smooth. However, the receiving signals in the double-layer steel casing decrease to only a few tenths of the value in the fiberglass casing wells, highlighting the difficulty of long-distance EM wave transmission when using steel casings. Thus, studies on EM transmission through four or more layers of steel casings should be conducted in the future.