Waveform design for electroseismic exploration

Abstract

In earlier work, we described field tests that successfully detected electromagnetic-to-seismic (ES) conversions from gas sands and carbonate reservoirs. ES conversion amplitudes measure the electric properties of permeable rock with near-seismic resolution. This information is a new indicator of hydrocarbons. ES conversions produce small seismic responses. Detecting these signals requires high-power electromagnetic sources and high-sensitivity detectors. Extraction of signal from noise also requires sophisticated signal processing. Here, we describe coded waveforms of binary sequences optimized for the expected signals. These coded waveforms distinguish between linear and nonlinear conversions. We detected both linear and nonlinear conversions in field studies. Novel, high-power signal generators synthesize the required sequences from three-phase power lines. The electroseismic exploration system includes optimized source electrodes and digital accelerometers that are free of electromagnetic interference.