Comparison of PRBS and Square-wave Transient CSEM Data over Peon Gas Discovery, Norway

We examine the application of the transient CSEM method in shallow water (less than 500 m deep) using towed-streamer EM data obtained in a 2009 survey over the Peon gas field, Norway, and consider the in-line electric field component. We compare the results obtained with two different source signatures: a square wave and a pseudo-random binary sequence (PRBS). We show that the PRBS data after deconvolution have more detailed information in the frequency domain than the square wave data and include the DC component, which is absent in the square wave data. In addition, PRBS data have the advantage that further time-domain processing may be applied, including correlated noise removal, which can increase the signal-to noise ratio by as much as 20 dB, and air wave removal. In addition, using the time of the peak of the earth impulse response function and travel-time to resistivity mapping has the potential to provide a starting model for inversion. These techniques must be applied in the time domain and are therefore not available to square wave data.