Natural Gas Exploration Associated with Alleghenian Thrust Faults in the Greenbrier Formation, Southern West Virginia

Edmonds, Craig¹ and Jaime Toro^2
1 Dominion Exploration and Production, Inc., Jane Lew, WV
² Department of Geology and Geography, West Virginia University, Morgantown, WV

A hydrocarbon play has been identified in southern West Virginia targeting the intersection of thrust faults with specific Mississippian reservoir intervals. Late Paleozoic sandstone and limestone reservoirs are traditional pays of the study area, often yielding economic natural gas production, with initial production rates ranging between 100 to 200 Mcfd per well. In contrast, production rates from fault wells often exceed 500 Mcfd. We believe this prolific production results from secondary fracture porosity and enhanced permeability from fracture zones associated with thrust faults, providing a conduit to the Union Oolite reservoir member of the Greenbrier Limestone. Studies are in progress to test this hypothesis.

Thrust faults and associated folds in southern West Virginia were formed during the Alleghenian Orogeny. Within the study area, several thrust faults are laterally extensive, spanning tens of miles along strike. Vertical displacements ranging up to 240 feet have been observed where thrust faults displace the Mississippian Greenbrier Formation. Detailed fault-plane modeling based on well log correlation, structural mapping, thickness isopachs, seismic, and cross sections demonstrates the relationship between excellent production and proximity with abrupt changes of fault dip. We believe this relationship is due to enhanced fracture density in intervals subjected to high strain.

To the author’s knowledge, little research has been published on drilling targets of this type in the Appalachian Basin. However, due to the abundance of faults near the Allegheny Structural Front, this exploration concept is widely applicable and is likely to result in enhanced gas production from this mature basin.

AAPG Search and Discovery Article #90031©2004 AAPG Eastern Section Meeting, Columbus, Ohio, October 3-5, 2004