Analysis of microphone and 3C geophone measurements from a 3C-2D seismic survey
Alejandro David Alcudia León, Robert R. Stewart
A 3C-2D seismic survey was conducted at Pikes Peak oil field, Saskatchewan during March 2000. It consisted of conventional arrays of geophones, single 3-C geophones and microphones, designed and tested at the University of Calgary. The aim of deploying pressure sensors in the field was to record the ambient noise and the airwave generated by the vibroseis source. The reliability of using pressure data to suppress some of the noise coupled into the geophone records remains the main goal of the undergoing research. However, a deep understanding of the wave phenomena associated with energy conversion at the air-ground interface is necessary. Therefore, a general model is derived for the air-ground transfer function which is frequency dependent.
The airwave is primarily produced by the vibrator's baseplate, which is modeled as a circular piston vibrating in an infinite rigid baffle. Analysis of the microphone data in the time, frequency and Gabor domains suggests that the model of the airwave source is a good approximation to the actual physics. The sound radiation pattern of the vibrator's baseplate has a direct effect on the airwave frequency content of the microphone traces. A similar signal analysis of the multicomponent data reveals that the coupling of the airwave is broadband, with stronger energy in the vertical and radial components at frequencies in the range 10-25 Hz. Preliminary analysis suggests that the sound beaming might also affect the frequency content of the coupled airwave. These observations are consistent for five consecutive source points.