Well log study and seismic survey of a coal-bed methane site: Alder Flats, Alberta
Michael Jason McCrank, Han-xing Lu, Kevin W. Hall, Donald C. Lawton
The seismic reflection characteristics of a coal-bed methane reservoir are studied with synthetic modeling and a seismic field survey. The reservoir consists of two coal seams encountered at depths of 404 m and 414 m below surface. The coals are understood to be saturated with an aqueous phase. A simple rock physics model is assumed in order to investigate the AVO response of the existing wet coals and that of hypothetical "dry" coals. The model results show that the seismic reflectivities of the wet and dry coals are sufficiently distinct that the AVO response should discriminate between the two states of water saturation. In the summer of 2006, two 1C-2D seismic lines were acquired by the University of Calgary at the study site using an ENVI mini-vibe source. Although the source sweep was 10-200 Hz, the reflected energy had lesser bandwidth with a major peak in the amplitude spectrum at ~30 Hz and a lesser peak ~75 Hz. The signal to noise ratio diminishes above 100 Hz. Reflection continuity and frequency content improve by excluding near-offsets from the stack. Radial trace filtering is successfully used to remove linear noise from the shot gathers. Various methods of boosting amplitudes at higher frequencies (spectral whitening, surface-consistent deconvolution, Gabor deconvolution) improve data quality in the 0-100 Hz range. Although the signal bandwidth is limited and the target are thin, closely space beds, the coals are resolved as two distinct events in the migrated seismic section.