47th Annual AAPG-SPE Eastern Section Joint Meeting

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Petroleum systems of coastal North Carolina: What we know, what we think we know, and the range of uncertainty in the interpretation of geochemical data


As part of a regional analysis of oil and gas occurrences in eastern North Carolina, the North Carolina Geological Survey initiated a comprehensive geochemical project using samples and cores from Esso Hatteras Light #1 (HL#1), and Mobil State of North Carolina #3 (NC#3). These were two of at least 19 exploration wells drilled in coastal North Carolina where oil/gas shows were reported. The study objective was to determine if the shows were in situ or represented migrated hydrocarbons. The wells are located in a local depression on an otherwise elevated regional basement complex extending from the Cape Fear Arch on the south to the Fort Monroe High on the southern flank of the Salisbury Embayment on the north. In the downdip-adjacent U.S. Atlantic OCS, sea-surface hydrocarbon seepage slicks are identified on satellite synthetic aperture radar images and hydrocarbon-related diagenetic zones and “chimneys” interpreted on seismic data indicate vertical hydrocarbon migration. Geochemical sampling and analyses concentrated on intervals where hydrocarbons were reported in the two wells. Biomarkers in aggregated samples appear to originate from marine shale source rocks at immature/early maturity levels of thermal maturity. Oleanane suggests the hydrocarbons are Cretaceous or Jurassic age. Analytical data indicate sampled intervals are too thin, organically lean, and immature to source commercial hydrocarbons in either conventional or resource plays in coastal North Carolina. However, possible occurrences of mobile hydrocarbons were detected in Tertiary strata (~815’) and solid bitumen and migrabitumen were reported from Cretaceous rocks. The sporadic nature of the bitumen, lack of viable source rock and low level of thermal maturity suggested that these bitumen occurrences probably lie on a migration pathway(s) rather than being in situ. Better potential may exist offshore in deep water Assessment Units interpreted by the Bureau of Ocean Energy Management.