Comparisons between data recorded by several 3-component coil geophones and a MEMS sensor at the Violet Grove monitor seismic survey
Donald C. Lawton, Malcolm B. Bertram, Gary F. Margrave, Eric V. Gallant
During the Violet Grove CO2 injection monitor seismic survey, several different 3-C coil geophones and a micro-electro mechanical system (MEMS) sensor were co-located at 8 adjacent stations along one of the receiver lines. The 3-C geophones were manufactured by Oyogeospace and Input/Output Inc., and the MEMS sensor was made by Sercel. The geophones were all fitted with elements with a natural frequency of 10Hz and 0.7 damping. The receiver line crossed a well lease that was covered with a mixture of gravel and dirt that was frozen at the time of the survey. The geophones and sensor were separated from one another by approximately 1 m within each group and the receiver group interval was 20 m across the well lease. A total of 225 shots were recorded for the experiment with a good distribution of source-receiver azimuths and a maximum offset of nearly 2 km.
Common receiver gathers for the vertical and radial components of the datasets were examined for this study. Geophone gathers were compared against each other and with MEMS sensor gathers both in raw form (MEMS devices provide accelerometer output) and after the latter were integrated so that all datasets represented measurements of particle velocity. Visual comparison of receiver gathers showed a very high degree of similarity. The correlation coefficient between gathers of geophone data exceeded 0.98 for most records and was only slightly less between geophones and MEMS sensors, with differences attributable to the phase distortion of geophone data across the resonant frequency. Amplitude spectra for the geophones and integrated MEMS sensor were also very similar. Data quality was consistent regardless of the style of ground coupling of the geophones or the sensor. Two different recording systems were used for the experiment (Sercel for the MEMS sensor and an ARAM Aries system for the geophone data) and some of the phase characteristics of the raw data are interpreted to be related to the instrument antialias filters implemented by the two systems, as well as phase distortions within the signal band of the recorded geophone data.