High-Resolution Seismic Reflection to Delineate a 1200 ft Deep Potential Coalbed Methane Layer Under Fort Yukon, Alaska

By

R.D. Miller (Kansas Geological Survey), J.G. Clough (Alaska Division of Geological and Geophysical Surveys), and J.C. Davis (Kansas Geological Survey)

High-resolution seismic reflection data delineate a sequence of lignite beds with possible methane content beneath Fort Yukon, Alaska. Dominant frequencies in excess of 150 Hz throughout the upper 400 m distinguish coal seams as thin as 4 m. Lateral continuity of the coal-bearing sequence was estimated and mapped with associated confidence established using geostatistical techniques designed to correlate specific layers from one 2-D seismic profile to another. Unconventional data acquisition techniques were used in this permafrost setting to enhance the dominant frequency, signal-to-noise ratio, and imageable depths. Limitations imposed by site access restriction and the necessity of acquiring data through the middle of town required non-explosive methods; transport of all equipment was by air. A specially adapted, buggy-mounted, minivibrator provided the non-destructive seismic energy while receivers were frozen to the ground to optimize coupling. Permafrost depths ranged from 0 m to over 100 m across the site and provided a significant challenge to producing a uniform seismic section. General stratigraphic associations were possible using a single 350 m deep borehole located in the southeastern portion of the survey area. Sediments above the coal-bearing sequence are likely saturated and predominantly Tertiary lacustrine silts and clays covered by Quaternary river deposits. Key characteristics of prospective coalbed methane reserves can at least in part be evaluated from these seven, tied seismic profiles. These seismic data will also be integral to 3-D geologic models designed to fully evaluate the potential of coalbed methane as a municipal resource for the rural village of Fort Yukon.

AAPG Search and Discovery Article #90008©2002 AAPG Pacific Section/SPE Western Region Joint Conference of Geoscientists and Petroleum Engineers, Anchorage, Alaska, May 18–23, 2002.