Seismic Imaging of Quaternary Channels for Shallow Gas at Rainbow Lake, Northwest Alberta
A high spatial and temporal resolution seismic data set was acquired in March 2004 along a 10 km east-west line in the extreme north-west of Alberta, Canada (~Lat. 58° 35', ~Long. 118° 31') to image shallow Quaternary channel gas. A Mini-Vibe generated the source energy with a frequency of 20-250 Hz, a sweep length of 7 seconds and 7-8 sweeps per shot point spread of 24 meters. Data were collected using a 0.5 ms sampling rate and 40 Hz geophones spaced at 4 meters over a maximum 240 channels connected to ‘Geometrics' Geodes resulting in a record length of about 1.2 seconds and about 40 fold data.. The survey is conducted in conjunction with geological mapping by the Geological Survey of Canada and the Alberta Geological Survey. The objectives of this survey are: 1) to image the surface of the Pre-Cretaceous unconformity, 2) to image the post-Cretaceous unconformity or bedrock surface; 3) to image shallow Quaternary or Tertiary channels within or at the base of the drift; 4) to image direct hydrocarbon indicators such as seismic ‘bright spots”. Preliminary interpretation of the dataset after initial processing up to a brute stack clearly reveals the Pre-Cretaceous unconformity, shows the presence of two stacked Quaternary channel margins and two possible ‘bright spots' at very shallow depths (40m to 300m). The ‘bright spots correspond very well in the depth domain to two offsetting wells with gas production from Quaternary channels. Our next step is to apply refraction tomo-statics to the data set to correct for shallow lateral velocity variations.
AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005