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.