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Upper Devonian Sandstone Sequence Stratigraphy Using Well Logs

Cary P. Kuminecz, Seneca Resources Corporation, Williamsville, NY 14221

The Upper Devonian sandstone play in the northern Appalachian Basin subsurface is comprised of numerous, usually tight, sandstones encased in marine shales. Regional correlation and mapping of individual reservoirs has been hampered by lack of a consistent and meaningful stratigraphic framework.

Sequence stratigraphy using well logs provides a process and a model to delineate genetically-related sandstone bodies, correlate them over wide areas, and construct geologically meaningful maps of key reservoir parameters and trends.

Use of well log-based sequence stratigraphy requires the construction of a grid of detailed, regional cross-sections, each extending scores of miles in stratigraphic dip and strike directions. Sequence stratigraphic correlations also require noting the surfaces of discontinuity against which sands and shales onlap or are truncated beneath. Once these surfaces of discontinuity (sequence boundaries) are recognized and correlated regionally, it can be seen that they are common in the Upper Devonian section of the northern Appalachian Basin. They are likely the result of repeated small, relative sea level changes across a very low angle foreland shelf ramp. In this setting lowstand and transgressive tract deposits had a relatively high preservation potential, but highstand deposits were rarely preserved.

Isopach mapping of the sands deposited between subsequent sea level drops will produce maps of sand bodies that are laterally coeval. This increases the accuracy of reservoir mapping and meaningfulness of reservoir trends for exploration or development drilling.

AAPG Search and Discovery Article #90059©2006 AAPG Eastern Section Meeting, Buffalo, New York