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Multi-Offset Vertical Seismic Profiles: Fracture and Fault Identification for Appalachian Basin Reservoirs--Two Case Examples

Douglas E. Wyatt, Bruce A. Bennett, John J. Walsh

Many Appalachian basin reservoirs occur in older rocks that are commonly fractured and faulted. These fractures and faults very often act as the reservoir trapping mechanism, especially in lithologies with no log-detectable matrix porosity. Traditional logging techniques, although possibly showing fault or fracture presence in the well bore, seldom provide clues to the extent of fracturing or location of nearby faults. Surface seismic data should show faults and perhaps even fracturing, but showing these features is often not possible in rugged terrain or in areas with thick coverings of unconsolidated surface material. Traditional seismic also has resolutions lower than that needed to detect small faults (less than 70 ft).

Two case examples are shown from the northern Appalachian basin. The first example utilizes Schlumberger's slim hole seismic tool in cased holes in an area of thick unconsolidated glacial material along the Bass Island trend of western New York. The second example utilizes Schlumberger's "SAT" tool in an open-hole environment in an area of northwestern Pennsylvania with disturbed surface bedding and poor conventional surface seismic returns.

The slim hole tool provides good data but with only slightly greater resolution than surface Vibroseis data. The SAT tool provides excellent resolution (down to 25 ft) in highly disturbed bedding.

AAPG Search and Discovery Article #91031©1988 AAPG Eastern Section, Charleston, West Virginia, 13-16 September 1988.