Dual Transmitter Receiver Electro Magnetic system for lateral boundary detection of subsurface formations

R. Rajesh*  and V.S.Sarma

Electromagnetic methods are popularly known for a wide variety of applications in exploring the internal structure of objects by transmitting the primary electromagnetic field and analyzing the induced secondary field intensities. A new frequency domain electromagnetic system engaging two transmitters and one receiver was designed and tested its efficacy over the existing systems in the laboratory.  Two transmitter coils producing opposite magnetic fields help to generate a magnetic null plane at their geometric center. The receiver coil is placed in the null plane to record the induced secondary field. Our laboratory experiment suggests that the new system can help identifying conducting bodies from greater depths compared to the existing systems. The measure secondary filed is proportional to magnetic permeability/ susceptibility difference of the subsurface medium on either side of the receiver. The schematic diagrams of system, model anomaly over an outcropped embedded formation in homogeneous medium are shown in Figure 1. Figure 2 shows the percentage of anomaly observed over vertical graphite cylinder at different depths. Finally, the study concludes that there is a significant increase in depth of investigation and secondary field strength in the new system over the existing conventional frequency domain systems and also more robust for boundary detection. Further, the field and borehole versions of the system are to be developed for its real time applications and commercialization.

For more details read: http://www.currentscience.ac.in/Volumes/114/08/1747.pdf 

Figure 1: (a) Block diagram and (b) schematic magnetic field diagram of dual transmitter electromagnetic (DuTrEM) system (c) Model anomaly cure over an outcropped embedded formation within homogeneous medium. A : Formation with electromagnetic properties μ₂, σ₂ and  ε₂  embedded within an homogeneous medium with properties μ₁, σ₁ and  ε₁. B1: Mangetic field induced in the formation of length l with properties μ₁, σ₁ and ε₁. B2 : Magnetic field induced in the formation with properties μ₂, σ₂ and  ε₂..  L: Transmitter–receiver separation.

Figure 2: Percentage of anomaly obtained over a vertical graphite cylinder (L=150 mm, r=75mm) for different target depths using Tx-Rx separation 50mm using frequency 50K.Hz. at different depths (d=75mm, 100mm, 125mm)