Magneto-Electric Antenna and Its Application in Geosteering Tool Design

Using coil antennae as transmitter and receiver to develop a geosteering tool, one has to increase the spacing between the transmitter and receiver to detect formation boundaries far away from a well trajectory. This causes the dimension of some tools to go up to 100 ft. We propose a magneto-electric antenna for the development of geosteering tools to overcome the problem of tool lengthening. We introduced a magneto-electric antenna, which has both functions of coil antenna and electric antenna at the same time. When a conductive wire is bent into a semicircle arc, it can be regarded as a combination of two imagined antennae. One is a coil antenna formed by the semicircle arc and an imagined straight conductive wire connecting between the two ends of the arc. The other is an electrode antenna formed by the imagined straight wire. The semicircle arc antenna can thus be used as a coil antenna and as an electrode antenna; therefore, we named it the ME antenna. We propose a prototype tool that includes a coil antenna as a transmitter and an ME antenna as a receiver, and experimentally verify the definition of the ME antenna and demonstrate that the induced voltage on the ME antenna can be measured, and use numerical simulations to investigate the characteristics of ME antenna. The experiment results prove the correctness of the definition of the electromagnetic antenna and also prove that the induced voltage on the ME antenna can be measured. The simulated results show that: 1. The smaller the spacing between the transmitter and the receiver, the stronger the signal reflected by the boundary will be received by the ME antenna. 2. The signal strength received by the ME antenna is far stronger than that received by a coil antenna used by the existing commercial tools. 3. The signal received by the ME antenna is very sensitive to the boundary position. 4. The average of the signal measured by the ME antenna equals that measured by the imagined coil antenna while the tool was rotated, proving that the ME antenna can be used as a coil antenna. 5. The difference between the measured signal and the average of the signal equals that measured by the imagined electric antenna, proving that the ME antenna can be used as an electrode antenna. When a conductive wire is bent into a semicircle arc, it can be regarded as a combination of two imagined antennae. One is a coil antenna formed by the semicircle arc and an imagined straight conductive wire connecting between the two ends of the arc. The other is an electrode antenna formed by the imagined straight wire. The semicircle arc antenna can thus be used as a coil antenna and an electrode antenna at the same time; therefore, we named it the ME antenna. A prototype tool including one coil antenna as the transmitter and one ME antenna as the receiver was designed to study the characteristics of the ME antenna and test its feasibility.