Continuation of Eastern North American Mesozoic, Paleozoic, and Proterozoic Rifts
Published:December 01, 2015
2015. "Continuation of Eastern North American Mesozoic, Paleozoic, and Proterozoic Rifts", Petroleum Systems in “Rift” Basins, Paul J. Post, James Coleman, Jr., Norman C. Rosen, David E. Brown, Tina Roberts-Ashby, Peter Kahn, Mark Rowan
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Two continuous gas assessment units (AU’s) are present in the Late Triassic (Norian) onshore rift basins of North Carolina and south-central Virginia. Continuous AU’s are the USGS classification/nomenclature for the oil and gas rich resource plays industry has been pursuing and exploiting throughout the continental United States. “Continuous gas assessment units” include tight gas sandstone as well as two resource plays—coal-bed methane and shale gas/oil. The USGS assessed the East Coast Mesozoic rift basins as continuous gas AU’s primarily as tight gas AU’s because oil and gas have been found (although not produced) from tight (i.e., low porosity and permeability) sandstones, coal beds, and shale beds/intervals. The source rocks are lacustrine shales that were deposited in freshwater lakes that were near the paleo-equator after the onset of Pangea rifting.
These continuous gasprone AUs each have a single total petroleum system (TPS). The Deep River basin continuous AU has an estimated mean gas content of 1,660 billion cubic feet of gas (BCFG) and an estimated mean of 83 million barrels of natural gas liquids (MMBNGL). Noble gases have been documented from two shut-in wells in the Deep River basin by the North Carolina Geological Survey in a separate study (Reid et al., 2015c). The Dan River-Danville basin continuous AU has an estimated mean gas content 49 BCFG and no natural gas liquids from data available in 2011 assessed by the U.S. Geological Survey (Milici et al., 2012) (Table 1).
The Dan River basin stratigraphy has been clarified by Olsen et al. (2015). A continuous 1,477-foot-deep stratigraphic core hole drilled in 2015 by the North Carolina Geological Survey penetrated a 323-ft-thick unconventional lacustrine shale reservoir containing a 3-ft-thick coal having gas shows in the coal and lower siltstone and then drilled through an underlying siliciclastic formation containing previously unknown thin organic strata, to basement at a depth of 1,451.2 ft below the surface.
The Cumberland-Marlboro ‘basin,’ a large, strike-parallel and seaward negative aeromagnetic anomaly that is buried beneath thin unconsolidated coastal plain sediments, also was drilled and cored (three Rotasonic holes) in 2015 by the North Carolina Geological Survey. Metasedimentary Paleozoic(?) basement rock was recovered; no Triassic strata were present.
Additional information that accompanies this extended abstract is found in Appendices 1–3.