Energy in the Coastal Plain

Overview

The Southeastern Coastal Plain is best known for its oil and gas deposits in and offshore of Mississippi and Alabama. While the Gulf Coast in the Southeast has not been nearly as productive as the Gulf Coast of Louisiana and Texas to the west, it has similar characteristics as a petroleum producer. Natural gas also drives the Coastal Plain. The harvest of natural gas and the infrastructure to move this energy resource throughout the region are extensive, making natural gas to be one of the most consumed types of energy. The Coastal Plain also supports a variety of alternative energy sources, including solar, biomass, and nuclear power generation.

Oil and gas

Salt domes

As Pangaea broke apart during the Jurassic, the Gulf of Mexico opened and began to take shape. In its early stages, the Gulf experienced periods of restricted marine circulation. During these periods, salt was deposited through evaporation of seawater. This Jurassic salt occurs in flat layers now known as the Louann Salt Formation.

Today, the Louann Salt is covered by over 6000 meters (20,000 feet) of sedimentary rock. Salt has moved upward through the overlying rock layers through time, forming hundreds of salt domes. As these salt domes push through the overlying rock, they can form oil traps, or gaps in the rock where oil and gas can accumulate. Oil and gas can also accumulate under and along salt structures. Salt domes have created prolific oil reservoirs both on- and offshore in the Gulf Coast region.

Conventional oil and gas

The Coastal Plain along southern Mississippi and southwest Alabama was submerged under high sea levels for much of the Late Cretaceous and Paleogene periods. Because of this, thick layers of limestones, shales, and sandstones occur there. Many Late Cretaceous and early Paleogene shales became source rocks for oil, significant quantities of which have migrated into more porous sandstone and limestone, ultimately pooling in reservoirs. Impermeable sedimentary deposits such as gypsum, anhydrite, limestone, and dolomite serve as cap rock that trap the oil and gas.

The underlying Jurassic salt structures that occur in abundance along the Gulf of Mexico explain the geographic distribution of many oil and gas reservoirs from eastern Texas to western Alabama. Locally thick occurrences of salt are found in the Mississippi Interior Salt Basin, which extends from central Louisiana through central Mississippi and southwestern Alabama. Impermeable rocks pushed up by salt domes became caprock where oil could be trapped. This is the case in the South Carlton field in southwestern Alabama, the Norphlet Formation in central and southern Mississippi and Alabama, and dozens of fields in central Mississippi. Oil and gas production takes place mostly in Cretaceous sandstones.

Offshore oil and gas

Today, oil and gas production associated with Coastal Plain sediments has moved mostly offshore, into the Gulf of Mexico. Offshore reservoirs exist where sandy sediments accumulated. Substantial quantities of sediment were eroded from the midcontinent into the Gulf of Mexico through the ancestral Red, Mississippi, and Sabine river systems. These sediments accumulated on the continental shelf and also along deeper submarine fans on the continental slope and even the abyssal plain. Much of this offshore oil and gas formed and trapped in similar ways to that onshore. Many of the offshore reservoirs are thick Paleogene and especially Miocene deposits, with Cretaceous- and Eocene-aged source rocks.

The largest Gulf of Mexico oil field to date was found in 1999, 250 kilometers (155 miles) due south of the Mississippi coastline. Drilling in the deepest parts of the Gulf is extremely challenging due to weather, the harsh environment, and water pressure at depth. This became publicly apparent during the Deepwater Horizon oil spill in 2010, when a seafloor gusher discharged 4.9 million barrels of oil over a period of 87 days before it was capped.

Oil and gas storage

Due to their inherent impermeability, salt domes themselves are often solution-mined to create caverns that have been used to store petroleum, gas, and even chemical waste. In solution mining, water is pumped underground to dissolve the salt. Salt domes in the Coastal Plain are also used to store large quantities of oil and gas. Sempra US Gas & Power's Mississippi Hub Storage is one storage operation, currently holding up to 850 million cubic meters (30 billion cubic feet) of natural gas in four storage caverns below Simpson County, Mississippi. Other salt dome storage facilities include the Bond Salt Dome Storage Field in Jackson County, Mississippi, and the McIntosh storage cavern in Alabama. 

Florida peninsula

The Florida peninsula has produced small quantities of oil since the mid-1900s from deep—3000–4000 meter (9800–13,100 feet)—Cretaceous-aged rocks. Although the thick sequence of carbonate rocks in Florida is permeable and can act as a reservoir, very few source rocks exist. Therefore, little oil or gas is present to fill the potential reservoirs. Small amounts of oil are still being produced today in a belt of porous Cretaceous limestones from west of Miami to near Fort Myers.

Coal

During the last 100 million years, the seas have advanced and retreated several times, shifting the position of the Coastal Plain's shoreline back and forth. At different times, peat swamps accumulated along the old coastlines and far up the Mississippi River Valley. The largest deposits of coal are Eocene-aged deposits, which are present from Texas east across northern Louisiana and eastern Arkansas, into Mississippi and Alabama, and also north into the Mississippi Embayment. These thinly bedded coals are formed from plants that lived in marshy environments, brackish lagoons, and between streams near the Eocene coastline.

In contrast to the Carboniferous peats of the Inland Basin, which became anthracite and higher-grade bituminous coal, The Coastal Plain's peats were not as deeply buried and were not exposed to the same pressures and temperatures as the Carboniferous peats of the Inland Basin. Therefore, while the Carboniferous peats became anthracite and higher-grade bituminous coal, only lignite and "high volatile" (lower-grade) bituminous coals formed in the Gulf Coastal Plain.

While the Coastal Plain region does not produce much coal, the Lamberts Point coal export facility in coastal Norfolk, Virginia, is the largest and fastest coal transload facility (that is, transferring from one form of transportation to another) in the Northern Hemisphere. It has serviced approximately one-third to one-half of US coal exports since 2000.

Some large deposits of peat that have not yet been compacted occur along the Atlantic Coastal Plain, including Holocene deposits in coastal North Carolina. Here, the peat ranges from 0.3–4.6 meters (1–15 feet) thick and averages 1.4 meters (4.5 feet) thick. The largest deposits are found in the Albemarle-Pamlico peninsula of North Carolina and the Great Dismal Swamp of North Carolina and Virginia.

Renewable energy

Bioethanol and biomass plants

The Coastal Plain is rich in biomass resources. Biomass resources are organic materials that are burned to generate energy. These include oils that come from plants (soybeans and canola), as well as biomass from sugar production (sugarcane, sugar beets, and sorghum), starchy crops (grains like rice and corn), wood and wood products, and certain types of municipal waste. Across the Southeastern states, biomass accounts for 6.3% of energy use. States within the Coastal Plain generate a slightly higher percentage of their energy from biomass. Alabama has the largest share―10.1% in 2013―of the states in the region. Of the 737 public and private-access biodiesel fueling stations nationwide, more than 18% are in North Carolina.

A bioethanol and electric power plant that produces energy from wood, vegetable, and municipal wastes was recently built in Vero Beach, Florida. The fermentation and gasification process in this plant uses municipal and other non-food biomass waste, thus avoiding issues associated with using farm crops for biofuel production. The power plant produces commercial-level amounts of biofuel―300 million liters (80 million gallons) of ethanol―as well as electricity to run the plant and from six to eight MW of energy for area homes and businesses. Many people see this type of plant as one possible solution to reducing municipal waste and the use of fossil fuels.

Solar energy

Between August of 2014 and August of 2015, North Carolina's production of electricity from solar power increased 127%, more than in any other state in the country during that time period. The state’s solar electric power production in 2015 accounted for more than twice the total production for all the other states in the Southeast combined. Nevertheless, California accounts for more than half of the country’s solar electric production, and the total US output of solar power is also dwarfed by other sources.

Nuclear power

Every Southeastern state in the Coastal Plain has at least one nuclear power plant. Of the 18 plants in the Southeastern US, 9 are located in the Coastal Plain region, producing a combined total of 17,029 MW of power. The largest nuclear facility is the Turkey Point Nuclear Generating Station near Miami, Florida, which has a capacity of 3552 MW. There are also several nuclear reactor fuel processing facilities in the Coastal Plain, notably in North and South Carolina.