STRATIGRAPHIC CORRELATION OF THE POTOMAC AND WASTE GATE FORMATIONS IN DELAWARE, POTENTIAL TARGETS FOR CARBON SEQUESTRATION

In recent years, the Potomac and Waste Gate Formations of the U.S. Atlantic Coastal Plain have drawn interest as potential target for carbon sequestration. The depths, thickness, and hydrologic properties of the aquifer sands in these formations are well suited for CO2 storage. As part of the Midwest Regional Carbon Sequestration Partnership, this study examines these units in Delaware, adding to recently published work by Rutgers University and Maryland Geological Survey geoscientists utilizing deep wells in New Jersey and southern Maryland. Because no deep well data exist in southern Delaware to directly characterize these units, this study attempts to predict their geological characteristics in southern Delaware by projecting the stratigraphy southward from southern New Castle County, Delaware, to deep wells of southern Maryland. We constructed three stratigraphic cross sections using geophysical logs: one north-south, dip-oriented section across Delaware, and two strike-oriented sections from Maryland to New Jersey. Using these cross sections, we then assessed trends in thickness, depth, and percent sand in the Potomac Formation in northern Delaware. Although not deep enough for CO2 sequestration, the northern Delaware section can be compared to southern Maryland and trends projected in intervening areas of Delaware where no deep well data exists.

The thicknesses of this interval increase southward from 675 ft in the northern Delaware wells to 3,575 ft in southern Maryland. Net sand thicknesses total 700 ft in southern Delaware and Maryland, compared to about 175 ft in northern Delaware. The cumulative percent of sand transitions from 26 percent sand in the north to 35 percent sand in the south.

A gradual transition of non-marine lithofacies appears to occur from north to south. In northern Delaware, the Potomac is known to be predominantly fluvial plain muds and paleosols with highly permeable fluvial sands. In southern Maryland, the deeper section (Waste Gate and Lower Potomac) is more sand-rich and the shallower section (Middle to Upper Potomac) more comparable to northern Delaware

Overall, the stratigraphic interpretations permit a first evaluation of the potential for CO2 sequestration in southern Delaware and comparison to other targets in the Middle Atlantic region.