The Hussar Low-Frequency Experiment

Gary F. Margrave, Lawrence E. Mewhort, Tom Phillips, Mike Hall, Malcolm B. Bertram, Donald C. Lawton, Kristopher A. Innanen, Kevin W. Hall, Kevin L. Bertram

In early September of 2011, CREWES collaborated with sponsors Husky Energy, Geokinetics, and INOVA, to conduct a seismic experiment designed to study the initiation and recording of very low frequency seismic reflections. The motivation is to collect a dataset that will be useful to test inversion methods. The site chosen was a 4.5km line, near Hussar, Alberta, that passes through 3 wells owned by Husky and near two others, all with good logging suites. Both dynamite and Vibroseis sources were tested along with 5 different receiver types. A specially modified low-frequency vibrator, the INOVA AHV-IV (model 364), was brought to the experiment by INOVA and a more conventional Failing (Y2400) was rented. Both vibrators were programmed with specially designed low-dwell sweeps which spend extra time in the low -frequency range. The receiver used were Vectorseis 3C (MEMS) accelerometers, 10Hz SM-7 (ION-Sensor) 3C geophones, 4.5Hz Sunfull 1C geophones, 10 Hz SM-24 high-sensitivity geophones, and Nanometrics Trillium seismometers. The first 3 types were planted densely along the entire line while the last two were only available in limited quantities. A total of 12 P-P and 8 P-S lines were recorded and are presently being processed. Spectral analysis of raw records shows that in large part the various instruments performed as expected. There was significant low frequency energy excited by all four sources with dynamite being the strongest, followed by the INOVA 364 low-dwell, the Failing low-dwell, and the INOVA 364 linear, in order of the strength of low frequency energy. The Vectorseis receivers seem to record strongly down below 1 Hz; however the response is higher than the corresponding geophones. The 10 Hz SM-7 and 4.5 Hz geophones performed well down to their resonant frequencies. After application of the inverse filters for their instrument response, it appears that signal was recovers down to perhaps 1.5 Hz. We qualify these remarks with a cautionary note as these measurements are based on raw data not final processed images.