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Exploration Concepts and Methodology for Deep Medina Sandstone Reservoirs in Northwestern Pennsylvania

William A. Zagorski

The blanket, deltaic sandstones of the Lower Silurian Medina Group have been commercially exploited in Pennsylvania since 1947. Rapid escalation of gas prices in the late 1970s triggered a drilling boom for the Medina Group sandstones which shows little signs of abating. Prior to this recent escalation, most Medina activity was concentrated in Crawford and Erie Counties, Pennsylvania, where the Medina is relatively shallow, ranging from 3,000 to 4,000 ft in depth. Since the late 1970s, interest in Pennsylvania's deep Medina targets has increased dramatically and several major filed complexes have been established.

Analysis of various log, completion, and production data and comparison of the Medina play of northwestern Pennsylvania to other tight sand basins of North America reveal that these deeper (5,000-6,000 ft) Medina targets are largely diagenetic in origin and thus are controlled by widely dissimilar processes than their shallower counterparts.

Detailed analysis of resistivity logs, production tests, and pressure data indicates a basin-center trapping mechanism for the deeper Medina sandstone reservoirs, similar to the Elmworth field of the Canadian Deep Basin. The local and regional trapping mechanisms of the deeper Medina reservoirs can be identified in the subsurface and closely resemble other major "tight"-sand basins, providing effective exploration models. Failure to identify properly the trapping conditions present in site-specific areas can result in inadequate exploration models with associated poor success ratios and inferior per-well recoveries.

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