History and Geology of the Giant Elk-Poca Field, West Virginia, USA

PATCHEN, DOUGLAS G., West Virginia Geological Survey, Morgantown, WV, and KATHERINE R. BRUNER and MILTON T. NOALD, West Virginia University, Morgantown, WV

The 165,000 acre Elk-Poca field was discovered in 1933 when a wildcat well tested the Oriskany Sandstone (Lower Devonian) on the Milliken Anticline in Elk District, Kanawha County. Rapid expansion occurred northward, along the anticline, and westward into Poca District on the Sissonville high. Begun as a structural play, it soon became an exploration program for thick, well-developed clean sandstones. The northward extension of the field into Jackson County followed thickness trends in the Oriskany.

Elk-Poca is a combination stratigraphic and structural trap. In Jackson County, salt water is present downdip, and updip production is limited by a loss of highly permeable beds. To the south, the east-west-trending Sissonville high and the north-south-trending Milliken Anticline are responsible for the wider productive area.

The reservoir was developed in clean, highly permeable sandstones in the upper part of the Oriskany. Reservoir beds are generally light gray to white, fine to medium grained, subrounded to rounded, and friable with intergranular porosity due to incomplete cementation by quartz and carbonate. Carbonate cement is less in the upper, permeable beds, but increases in lower, tighter beds and in the updip area. The average pay section is 30 ft thick, and characterized by high permeabilities, and consistent, but low porosities. High initial flow rates for both natural wells and wells stimulated by shooting correlate with areas of thick sandstone.

Nearly 1200 wells were drilled in the field, and more than 1100 produced gas. Since 1933, nearly 1 tcf of gas have been produced, with the best wells in areas of thick sandstone. Production decline was rapid, due to the high permeability and moderate porosity.

This giant field is in the only area in West Virginia where a certain set of geologic factors coincide. The north-south structural strike is paralleled by an east-west decrease in sandstone thickness, and a west-east increase in thickness of the organic-rich Devonian shales. Deposition of the shales was accompanied by subsidence to the east, which created a dip of 30-40 ft/mi on the Oriskany. Once a critical dip was reached, gas migrated from the shales into the permeable Oriskany before compaction and cementation by carbonate eliminated all porosity and permeability. The presence of gas in open pores may have retarded further cementation.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)