HR: 1340h
AN: S23B-0261    [Abstracts]
TI: Seismic and DC resistivity imaging of a buried channel, NW Alberta, Canada
AU: * Ahmad, J
EM: jahmad@phys.ualberta.ca
AF: Univ. of Alberta, Inst. for Geophysical Research, Dept. of Physics, Edmonton, AB T6G 2J1 Canada
AU: Schmitt, D R
EM: schmitt@phys.ualberta.ca
AF: Univ. of Alberta, Inst. for Geophysical Research, Dept. of Physics, Edmonton, AB T6G 2J1 Canada
AU: Rokosh, C D
EM: Dean.Rokosh@gov.ab.ca
AF: Alberta Geological Survey, 4th Floor, Twin Atria Bldg. 4999-98 Ave, Edmonton, AB T6B 2X3 Canada
AU: Pawlowicz, J
EM: john.pawlowicz@gov.ab.ca
AF: Alberta Geological Survey, 4th Floor, Twin Atria Bldg. 4999-98 Ave, Edmonton, AB T6B 2X3 Canada
AU: Plouffe, A
EM: aplouffe@nrcan.gc.ca
AF: Geological Survey of Canada, Natural Resources Canada, 601 Booth Street, Ottawa, ON K1A 0E4 Canada
AB: Buried channels are often filled with a variety of porous and permeable sediments which can act as water and hydrocarbons reservoirs. Shallow methane deposits within these channels (less than 50-m deep) represent a significant drilling hazard in some areas. A joint high resolution seismic reflection and DC resistivity 10 km long profiles were acquired in northwest Alberta to define the position and geological setting of a buried channel. Due to the near surface nature (50-m to 300-m) of the target, a high spatial and temporal resolution seismic profile was collected using a 240 channel semi-distributed seismic acquisition system recording 40 Hz geophones placed at a 4-m spacing. A high-frequency seismic vibrator provided a 20-250 Hz source sweep. Electrical resistivity tomography (ERT) data was acquired using a 15-m electrode spacing. At its deepest point, the channel cuts through more than 300-m of Cretaceous sands and shales through a regional unconformity into higher velocity carbonates. The channel fill materials have generally lower seismic velocities and are more resistive than the flanking undisturbed Cretaceous formations. These contrasts allow the channel to be detected on the basis of both refraction and resistivity analysis, which is in good agreement with geology. The resistivity profile further shows highly resistive zones that may be indicative of shallow gas which correspond to a known producing horizon. These filled incised valley sediments were may have been deposited during different periods of glaciation. Geochemical analyses of shallow gas from wells within the channel indicates a thermogenic origin and suggests that the channel both breeches the source zone and serves as a conduit for escaping methane.
UR: http://www-geo.phys.ualberta.ca
DE: 0925 Magnetic and electrical methods (5109)
DE: 0935 Seismic methods (3025, 7294)
DE: 0994 Instruments and techniques
DE: 5100 PHYSICAL PROPERTIES OF ROCKS
DE: 5102 Acoustic properties
SC: Seismology [S]
MN: Fall Meeting 2005