Oil and Gas Research & Publications

Geology of North Carolina Oil and Gas

For most of North Carolina's geologic history, the state's potential for oil and gas has been modest. Much of the Blue Ridge and Piedmont is formed from old, crystalline metamorphic and igneous rocks. While these rocks are important sources of minerals and groundwater, they are largely non-productive for petroleum because of their non-organic structure and they do not contain the  organic-rich sedimentary layers needed to generate oil and gas. The Coastal Plain of North Carolina has been explored and has shown limited promise.

The main exception are geologic features that began to form around 235-200 million years ago, during the Triassic Period, when the supercontinent Pangea was beginning to break apart and the Atlantic Ocean was starting to form. As Earth's crust was stretched, long rift valleys opened along the eastern edge of North America. In what-is-now North Carolina, several rift basins formed, including the Deep River and Dan River Basins. These basins filled with sediment eroded from nearby highlands and some contained lakes, swamps, and low-oxygen environments where plant and algal material could accumulate.

Sanford sub-basin

The most important of the Triassic basins in North Carolina is the Sanford sub-basin of the Deep River Basin in Lee and Chatham counties. Here, the Cumnock Formation contains organic-rich black shale and coal. 

This type of rock can act as a "source rock" as buried organic material that is heated over geologic time can generate oil or natural gas. Researchers' work have found that potential source rocks occur in the Sanford sub-basin and Dan River Basin, and that the rocks are generally more gas-prone than oil-prone, although both oil and gas generation occurred. This same geology also explains why the Deep River area became known first for coal, not natural gas. Coal in the Deep River Basin was recognized very early in North Carolina's history, and mining occurred over several periods, including through the 1800s and the 1920s-1940s. The old coal mines were "gassy" which was an early practical sign that methane was present in the rocks. Later petroleum interest built on that same basic observation - the basin had organic-rich rocks, coal, gas shows, and some oil staining but it had never become a commercial oil or gas field.

Exploration increased in the late twentieth century. In the 1980s, companies drilled several "wildcat" wells in the Sanford sub-basin but many were drilled before the basin was well understood with modern seismic data. Later work showed that the basin is structurally complicated, with faults, tilted rock layers, and diabase igneous intrusions. Those intrusions locally heated the organic-rich rocks and in some places may have helped generate gas, while in others it may have "overcooked" the source rock or complicated interpretation.

Wells drilled in the Sanford sub-basin during the 1980s and 1990s showed that natural gas is present. The shale gas boom on the 2000s and early 2010s renewed interest in North Carolina's potential. The USGS assessed East Coast Mesozoic basins, including the Deep River and Dan River-Danville basin, and estimated a mean undiscovered natural gas resource of 3,860 billion cubic feet across five East Coast Mesozoic basin, not only in North Carolina.

North Carolina Coastal Plain

The Coastal Plain and offshore areas add a separate chapter. The Atlantic Coastal Plain has been explored by drilling but the results have generally been sparse onshore. Offshore, the Atlantic Outer Continental Shelf has long been considered more prospective than much of onshore North Carolina, but the exploration history has not produced active development. The Bureau of Ocean Energy Management (BOEM) notes that the last remaining active federal oil and gas leases offshore North Carolina were relinquished in 2000 and there are now no oil and gas leases in existence off the Atlantic Coast.

For additional information on Oil & Gas research and publications, contact Jim Chapman.

• Mail: Jim Chapman, NC Geological Survey, 1612 Mail Service Center, Raleigh NC 27699-1612
• Phone: 919-707-9231
• Email: james.chapman@deq.nc.gov