A Model for Exploring and Developing Silurian Clastic Reservoirs in the Appalachian Basin: The East Lake Erie Experience

Marianne Molgat and Lynne Davies
Talisman Energy, Calgary, AB

Lower Silurian sandstone reservoirs in the Appalachian Basin have produced almost 11 Tcf equivalent of natural gas over the last 125 years. Ontario's contribution to this is about 400 Bcf, of which 125 Bcf comes from Lake Erie. Presently, offshore sandstone reservoirs account for 45% of Ontario's total gas production, delivering an annual average of 6 Bcf.

Geological mapping of Silurian clastic strata in East Lake Erie suggests there is little correlation between depositional facies, abundance of sandstone, net pay, and cumulative production. Reservoir quality appears to be controlled by other factors. Furthermore, many Whirlpool reservoirs tend to be linear and this linearity can be loosely correlated to deep-seated strike-slip faults. It is hypothesized that fracture networks not only improved local reservoirs by causing fracture porosity, but also allowed diagenetic fluids to dissolve carbonate cements, thus creating secondary porosity. These observations/postulations assisted in devising a new, lower risk geological model that targets down-dropped faulted blocks, or grabens.

Because seismic coverage in Lake Erie is sparse and data quality is generally poor and costly to acquire, conventional seismic data could not assist in clearly outlining fault locations and orientations. To help resolve some of these issues, an economical single channel boomer survey was acquired in 2003. The survey allowed for high resolution mapping of lake bottom (Devonian) bedrock topography by using broadband seismic reflection data. This helped to delineate strike-slip faults trends, identify numerous drilling prospects, and more importantly, increase the chance of success from the historical 33% to over 80%.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005