STRATIGRAPHIC CORRELATIONS IN SOUTHWESTERN VIRGINIA

The Appalachian Plateaus geologic province in Virginia hosts the highly productive Southwest Virginia Coalfield that has yielded over 2.7 billion tons of coal since the late 1740s. The Pennsylvanian-age rocks that host deposits of coal and coal bed methane occur in a sedimentary sequence range from surface to 3,000 feet in depth. Unconventional gas reservoirs that occur in Devonian-age shales and Mississippian-age limestones and sandstones have produced over 3,100 billion cubic feet of natural gas since 1950s. Small quantities of crude oil have also been recovered from several zones within Ordovician-age limestones. An estimated 10,000 gas and oil wells have been drilled in the region, and for most of these, well drilling reports and geophysical logs are available. The most recent stratigraphic correlation charts that show hydrocarbon-bearing strata and coal zones were published by the Virginia Department of Energy in 1983 and 1994. These correlation charts contain no geologic cross sections indicating the thickness and lateral extent of stratigraphic units.

The goal of this study is to develop a comprehensive stratigraphic model for the southwestern part of Virginia. We aim to 1) create a complete digital database of wells and subsurface stratigraphic data, 2) revisit existing stratigraphic interpretations and perform correlation for key subsurface units (formation tops and bases), and 3) prepare a new set of stratigraphic columns and correlation cross sections. To date, all well information has been collected from oil, gas, and coalbed methane wells and loaded into a geological interpretation platform, Petra Software. Stratigraphic correlations will utilize existing geophysical well log data, well drilling records, bedrock geologic maps, and existing publications.

The results of this study will improve our understanding of the geological framework and the petroleum systems in southwestern Virginia, thus benefiting the surface and 3D geological mapping efforts. The revised stratigraphic correlation will also provide insights into future energy resource exploration and geologic storage potentials in the subsurface reservoirs.